The research team, led by Leonardo Zamora-Leiva of the Bionostra Chile Research Foundation together with colleagues at Universidad Andrés Bello and the University of Chile, sampled a trial established in 1998 at the Sugar Cane Research Institute in Santiago de Cuba. The experiment spans eleven fertilizer treatments varying nitrogen, phosphorus, and potassium, from plots receiving no nitrogen at all to those receiving very high doses of a single macronutrient. Because the fertilization regimes assigned to each plot have been maintained without interruption since the trial began, the soils sampled in 2022 carry the cumulative legacy of 24 years of continuous nutrient management, making the site an unusually clean natural laboratory for asking how sustained inputs shape the rhizosphere microbiome.

Using high-throughput sequencing of the bacterial 16S rRNA gene and the fungal internal transcribed spacer region, the researchers identified 421 bacterial and 471 fungal genera from 5,741 amplicon sequence variants across the treatments. The dominant bacterial phyla were Actinomycetota, Pseudomonadota, and Acidobacteriota, which together accounted for roughly 60 percent of relative abundance, while fungal communities were overwhelmingly dominated by Ascomycota, which exceeded 69 percent across all plots. These core lineages appeared in similar proportions regardless of whether a plot had been drenched in nitrogen for decades or left without it, and statistical tests for differences in alpha and beta diversity, along with differential abundance analyses using LEfSe and ANCOM-BC2, found no significant treatment effects on community composition.

The physicochemical data help explain why. Soil pH remained nearly constant across the site, ranging from 6.4 to 6.5 in potassium chloride and 7.7 to 7.9 in water, a stability the authors attribute to the massive buffering capacity conferred by consistently high reservoirs of exchangeable calcium and magnesium. Organic matter, available phosphorus, and potassium varied among plots, but those variations did not align with the theoretical fertilizer doses. The team argues that intense tropical rainfall and the leaching-prone clay matrix of sialitic soils, which are classified internationally as inceptisols or Cambisols, rapidly redistribute applied nutrients, homogenizing bulk soil chemistry and decoupling what farmers apply from what microbes actually experience.

Where the study becomes genuinely striking is in its network analysis. Rather than treating the bacterial and fungal datasets separately, the authors merged them into a single trans-domain co-occurrence network of 371 nodes and 747 edges, retaining only robust correlations with a Spearman coefficient above 0.6 and a false-discovery-rate-adjusted p-value below 0.01. The resulting architecture was highly modular, organized into 48 distinct structural modules, and overwhelmingly positive in sign: 99.8 percent of the correlations were cooperative or commensal rather than competitive. Fungal taxa, particularly Ascomycota and Basidiomycota, showed higher connectivity than bacteria, suggesting that fungi form the structural backbone of the rhizosphere interaction web in these soils.

Within that architecture, the vast majority of amplicon sequence variants, about 95 percent, behaved as peripheral nodes, while a small subset of highly connected connectors and module hubs, including taxa related to Pseudomonas, Steroidobacter, Gaiella, and Streptomyces, appeared to stabilize the whole system. A substantial fraction of the interacting taxa remained taxonomically unclassified, a reminder that tropical and Caribbean soil microorganisms are poorly represented in reference databases such as SILVA and UNITE. The authors suggest these unresolved lineages may include endemic or highly specialized microbes that contribute to the unique functioning of nutrient-leached tropical soils, and they call for expanding genomic reference databases to cover such environments.

The most ecologically revealing result came from an overlap analysis of which microbes appear under which fertilization regime. By intersecting presence-absence matrices across treatments, the team identified a universal core of 76 amplicon sequence variants shared across every nitrogen, phosphorus, and potassium gradient, a trans-domain alliance built on bacterial Bacillota and Pseudomonadota and fungal Ascomycota including genera such as Fusarium and Cladophialophora. This core appears to be the stable foundation of the sugarcane rhizosphere, resistant to profound nutritional fluctuations. Beyond it, each macronutrient recruited its own distinct satellite community: nitrogen variation recruited 18 exclusive specialists, predominantly fungal, while phosphorus addition recruited a much larger accessory cohort of 40 unique variants, heavily dominated by fungi including Talaromyces and various Basidiomycota. Potassium produced the most restricted response, with only six strict specialists.

This core-and-satellite assembly strategy has direct agronomic implications. Yield records from the trial show that fertilized plots consistently outperform unfertilized controls, but that yields plateau across a wide range of NPK doses, with the highest nitrogen treatments actually producing the lowest yields among fertilized plants. The new microbial data offer a possible explanation: once the universal core is in place, additional nutrients do not restructure the community but instead selectively recruit specialized accessory taxa to exploit available resources. Fertilization, in other words, may influence soil functioning by modulating specialized ecological niches rather than through broad taxonomic turnover, which is why diversity-based monitoring alone can miss the ecological consequences of management decisions.

The authors argue that trans-domain interaction networks provide crucial insights into how soils respond to long-term fertilization that are not evident from diversity or abundance data alone. In tropical sialitic soils, where leaching and rapid nutrient turnover render bulk chemistry erratic, physically protected rhizosphere microhabitats, formed by roots, fungal hyphae, and bacterial extracellular polymers, appear to act as ecological refuges that preserve microbial organization. Sustainable fertilization strategies, the study concludes, should aim to support these foundational microbial architectures while optimizing nutrient inputs, rather than assuming that more fertilizer simply means more of everything below ground. For sugarcane producers in Cuba and other tropical systems, the message is that the invisible network around the roots may matter as much as the nutrients themselves.

Subject of Research: Effects of long-term NPK fertilization regimes on sugarcane rhizosphere microbial diversity and bacterial-fungal co-occurrence networks in tropical sialitic soils

Article Title: Fertilizer regimes reshape microbial interaction networks without altering sugarcane rhizosphere diversity

Article References: Zamora-Leiva, L., Soto, J., Ramos-Tapia, I., & Paneque, M. (2026). Fertilizer regimes reshape microbial interaction networks without altering sugarcane rhizosphere diversity. SOIL, 12(2), 999-1019. https://doi.org/10.5194/soil-12-999-2026

Image Credits: AI Generated

DOI: 10.5194/soil-12-999-2026

Keywords: sugarcane, rhizosphere, soil microbiome, fertilization, co-occurrence networks, 16S rRNA, ITS sequencing, Ascomycota, nutrient leaching, inceptisols, tropical agriculture, soil ecology

The concept at the heart of the review is called the carbon sink by carbonate weathering coupled with aquatic photosynthesis, or CCW. When rainwater percolates through limestone and other carbonate rocks, it dissolves them, pulling atmospheric carbon dioxide into the water as dissolved inorganic carbon. In karst regions, this process produces dissolved inorganic carbon concentrations that are six to ten times higher than in non-karst watersheds. Aquatic plants, algae, and microorganisms then convert a portion of this dissolved inorganic carbon into autochthonous organic carbon through photosynthesis, a process the researchers term autochthonous production. That organic carbon, once buried in sediments or transported downstream to the ocean, becomes a long-term stable carbon sink rather than a transient one.

What makes the CCW theory particularly compelling as a nature-based solution is its dual benefit. The review details how elevated dissolved carbon dioxide acts as a fertilizer for aquatic photosynthesis, alleviating what the authors identify as a chronic carbon limitation in high-pH karst waters. In these alkaline environments, the carbonate equilibrium system is dominated by bicarbonate and carbonate ions, leaving free carbon dioxide at often less than one percent of the total dissolved inorganic carbon pool. This scarcity constrains photosynthetic organisms that preferentially use carbon dioxide over bicarbonate, which requires energy-intensive carbon concentrating mechanisms to assimilate.

The fertilization effect ripples through the entire aquatic food web in ways that suppress eutrophication rather than exacerbate it. When carbon dioxide is scarce, cyanobacteria—blue-green algae equipped with highly efficient carbon concentrating mechanisms—dominate because they can strip bicarbonate from the water when other organisms cannot. These blooms produce toxins, deplete oxygen, and degrade water quality. But when dissolved carbon dioxide is abundant, species with weaker carbon concentrating mechanisms, such as green algae and diatoms, gain a competitive edge. The review cites field data from Erhai Lake in Yunnan and Caohai Lake in Guizhou showing that cyanobacteria decline relative to other phytoplankton when the carbon-to-nitrogen and carbon-to-phosphorus molar ratios in the water exceed specific thresholds, suggesting that carbon fertilization can tip the ecological balance away from harmful bloom-forming species.

Submerged aquatic plants, the foundation of healthy shallow lake ecosystems, also benefit disproportionately from carbon fertilization. Unlike phytoplankton, these rooted plants have limited capacity to use bicarbonate and typically begin switching to it only when carbon dioxide concentrations exceed 50 micromoles per liter, far above the 10 to 15 micromole threshold for many algae. Their higher carbon-to-nitrogen and carbon-to-phosphorus stoichiometric ratios mean they are better adapted to carbon-rich environments. Dense beds of submerged plants improve water clarity, stabilize sediments, provide habitat for aquatic fauna, and release chemical compounds that inhibit algal growth, creating a self-reinforcing cycle of water quality improvement.

The review also illuminates a second, purely geochemical mechanism by which autochthonous production removes phosphorus, the nutrient most responsible for eutrophication. As aquatic organisms photosynthesize, they raise the pH of the water, shifting the carbonate equilibrium toward carbonate ions and triggering the precipitation of calcium carbonate. This newly formed calcite has an enormous specific surface area and abundant adsorption sites. Dissolved phosphate co-precipitates with the calcite crystals or adsorbs onto their surfaces, converting soluble reactive phosphorus into an insoluble form that settles into the sediment. The authors report that when pH rises above 9.5, more than 74 percent of phosphorus can co-precipitate with calcium carbonate, a self-purification mechanism they call the AOCP-CP removal hypothesis, linking the organic carbon pump to the carbonate pump.

Field evidence for this mechanism comes from multiple sources. In Sicilian reservoirs, managers successfully controlled cyanobacterial outbreaks by spreading lime powder to induce calcium carbonate precipitation and phosphorus removal. Enclosure experiments in nutrient-poor lakes showed that added phosphorus stimulated productivity and calcium carbonate precipitation, but much of the phosphorus was ultimately buried in sediment through co-precipitation, creating a negative feedback on eutrophication. X-ray diffraction analyses of calcium carbonate products exposed to phosphate solutions revealed the formation of hydroxyapatite, the most thermodynamically stable calcium phosphate mineral, confirming the long-term sequestration of phosphorus in these systems.

The scale of the potential carbon sink is substantial. The review estimates that enhanced autochthonous production in inland waters could sequester between 0.38 and 1.8 billion tons of carbon per year, a range that positions these aquatic ecosystems as significant contributors to closing the global carbon budget. Data from the Shawan Karst Test Site in Guizhou Province showed that autochthonous organic carbon fixed in surface waters ranged from 156 to 493 tons of carbon per square kilometer per year, increasing with dissolved inorganic carbon concentration. In the Pearl River, a typical karst river, phytoplankton biomass and total organic carbon both rose with dissolved inorganic carbon, and autochthonous organic carbon accounted for 65 percent of the total organic carbon pool.

The authors acknowledge that significant research gaps remain. Most existing studies have focused on single regions and short time periods, lacking the global coverage and high-frequency monitoring needed to fully quantify carbon fluxes. The role of methane and nitrous oxide emissions from these waters in offsetting carbon gains remains poorly constrained. The mechanisms linking carbon fertilization to community structure shifts and phosphorus removal need further elucidation across different climatic zones, land uses, and lithologies. To address these gaps, the review proposes establishing a global monitoring network for carbon fluxes in karst surface waters, employing hydrological modeling, radioisotopes, stable carbon isotopes, and machine learning to trace carbon sources and quantify lateral transport and vertical burial.

Looking forward, the authors propose coupling enhanced carbonate rock weathering with aquatic photosynthesis as a next-generation carbon removal strategy. By deliberately managing aquatic productivity to convert dissolved inorganic carbon from enhanced weathering into stable organic carbon, the approach could approach near-complete carbon sequestration efficiency. As climate targets slip further out of reach and eutrophication intensifies across the globe, the humble chemistry of limestone and sunlight may prove to be one of the most elegant and scalable nature-based solutions available.

Subject of Research: Carbon fertilization of aquatic photosynthesis in karst surface waters as a nature-based solution for carbon sequestration and eutrophication mitigation

Article Title: Carbon fertilization of autochthonous production in karst surface waters and its role in carbon reduction and eutrophication mitigation—a nature-based solution (NbS)

Article References: Shao, M., Liu, Z., Zeng, S., Sun, H., & He, H. (2025). Carbon fertilization of autochthonous production in karst surface waters and its role in carbon reduction and eutrophication mitigation—a nature-based solution (NbS). Frontiers in Geochemistry, 3, Article 1622714. https://doi.org/10.3389/fgeoc.2025.1622714

Image Credits: AI Generated

DOI: 10.3389/fgeoc.2025.1622714

Keywords: karst, carbon cycle, eutrophication, nature-based solutions, carbonate weathering, aquatic photosynthesis, carbon sink, water quality, Carbon, fertilization, autochthonous, production

The research, published in Frontiers in Soil Science, was carried out at the Regional Research Station in Bhuj, Kutch, one of the hottest arid zones in India. The experimental soil was an alkaline sandy Aridisol with a pH of 8.5, electrical conductivity of 2.78 dS m⁻¹, and organic carbon content of just 0.20 percent. Initial available potassium stood at 210 kg ha⁻¹, while available nitrogen and phosphorus were extremely low at 45 and 8 kg ha⁻¹ respectively. Over the course of a single growing season, from cladode establishment in February 2021 to final harvest in May 2022, the team imposed a factorial randomized block design with four replications, testing four calcium rates (0, 20, 40, and 60 kg ha⁻¹) crossed with four potassium rates (0, 30, 60, and 90 kg ha⁻¹), generating sixteen treatment combinations.

Calcium was supplied as agricultural gypsum, chosen because it delivers readily available calcium without substantially raising soil pH while also contributing sulfur. Potassium was applied as sulphate of potash, a chloride-free source considered more suitable than muriate of potash for moderately saline arid soils. Because both fertilizers contained sulfur, the researchers acknowledged that the individual effect of sulfur could not be separated from those of calcium and potassium, a limitation they factored into their interpretation. Fertilizers were broadcast within the root zone of each plant, incorporated into the upper 10 to 15 cm of soil, and irrigated with normal-quality groundwater at intervals of roughly 10 to 15 days in summer and 20 to 30 days in winter.

The results were striking. Potassium application significantly influenced every morphological characteristic measured, from cladode length and circumference to cladode number, thickness, and plant height. Calcium, meanwhile, significantly affected cladode circumference, cladode number, cladode thickness, and plant height, though it did not significantly alter cladode length or width. The tallest plants, reaching 65.2 cm, were recorded under the combination of 40 kg Ca ha⁻¹ and 60 kg K ha⁻¹, which also produced the highest cladode number at 22.2 per plant and the greatest cladode thickness at 2.5 cm. Notably, no significant calcium-potassium interaction emerged for any morphological trait, suggesting the two nutrients acted largely independently rather than synergistically in driving structural development.

Biomass production told a similar story of complementary roles. Fresh cladode yield, the key measure of forage output, responded significantly only to potassium, with the highest yield of 16.9 t ha⁻¹ recorded under 20 kg Ca ha⁻¹ combined with 90 kg K ha⁻¹. Dry matter yield, however, was significantly affected by both nutrients, peaking at 3.51 t ha⁻¹ under 40 kg Ca ha⁻¹ with 90 kg K ha⁻¹. The researchers attributed these responses to the distinct physiological functions of the two elements: potassium serves as the principal inorganic osmoticum in plant cells, regulating turgor, stomatal movement, enzyme activation, and assimilate transport, all critical under the high evaporative demand of hot arid environments. Calcium, by contrast, strengthens cell walls and plasma membranes through calcium-pectate cross-linking in the middle lamella, providing the structural integrity needed for rapid succulent cladode expansion.

Forage quality improved even more dramatically than yield. Crude protein concentration rose from 4.8 percent in the unfertilized control to 11.2 percent under 40 kg Ca ha⁻¹ with 60 kg K ha⁻¹, a value at the upper end of reported ranges for cactus pear cladodes. Corresponding tissue nitrogen concentration climbed from 0.768 percent to 1.79 percent. Simultaneously, neutral detergent fiber fell from 42.1 percent to 27.2 percent, and acid detergent fiber dropped from 28.3 percent to 18.2 percent, both indicators of improved digestibility. The researchers suggested that better nutrient availability may have favored metabolically active parenchymatous tissues over structural carbohydrates, reducing the proportion of indigestible cell wall constituents. Because neither calcium nor potassium supplied nitrogen, the accumulated nitrogen presumably derived from existing soil pools and mineralization of the uniformly applied farmyard manure, with fertilization potentially enhancing the plant’s capacity to acquire these sources.

Crude protein yield, the product of dry matter and protein concentration, showed an approximately 24-fold increase, from 0.0151 t ha⁻¹ in the control to 0.363 t ha⁻¹ under 40 kg Ca ha⁻¹ with 90 kg K ha⁻¹. This dramatic gain resulted from the combined increase in biomass and the smaller rise in tissue nitrogen concentration. The team emphasized that the fertilizer combination producing the highest crude protein concentration was not necessarily the same as that producing the greatest crude protein yield, underscoring the importance of considering both nutritive value and total protein production when developing nutrient management strategies for livestock feed systems.

Yet the study revealed a critical tension between productivity and efficiency. Partial factor productivity declined consistently with increasing fertilizer rates, indicating diminishing returns as nutrient supply exceeded crop demand. Agronomic efficiency of both calcium and potassium showed no significant response to treatments, suggesting that partial factor productivity was the more sensitive index for detecting treatment effects. The highest partial factor productivity for calcium, 0.845 t kg⁻¹, occurred under 20 kg Ca ha⁻¹ with 90 kg K ha⁻¹, while the maximum for potassium, 0.357 t kg⁻¹, was recorded under 60 kg Ca ha⁻¹ with 30 kg K ha⁻¹. These patterns align with well-established principles of nutrient-use efficiency, where progressively larger inputs produce proportionally smaller yield gains, and may partly reflect a shift from high-affinity to low-affinity potassium transport systems as external concentrations rise.

Perhaps the most consequential finding concerned soil potassium dynamics. The change in soil available potassium after harvest was significantly affected by calcium, potassium, and their interaction, with the largest depletion of 173 kg ha⁻¹ recorded under 60 kg Ca ha⁻¹ combined with 90 kg K ha⁻¹. Linear regression revealed a significant positive relationship between fresh cladode yield and the change in soil available potassium, with an R² of 0.77, indicating that treatments producing greater forage yields were also associated with larger reductions in soil potassium. The researchers calculated an apparent potassium removal of 263 kg ha⁻¹ under the highest combined treatment, a figure they cautioned cannot be attributed solely to crop uptake, as it may include leaching, fixation, release from non-exchangeable reserves, and potassium acquisition below the sampled 0 to 15 cm layer. In calcareous arid soils, potassium fixation and release processes can strongly influence extractable potassium following fertilization, complicating interpretation.

The implications extend beyond a single season. Because Opuntia ficus-indica is harvested repeatedly over multiple years, continued reductions in exchangeable soil potassium without adequate replenishment may gradually diminish soil fertility during successive production cycles. The maximum fertilizer rates applied in this study, 60 kg Ca ha⁻¹ and 90 kg K ha⁻¹, remain considerably lower than the seasonal calcium and potassium removal reported for high-yielding cactus pear, which can reach 464.63 kg Ca ha⁻¹ and 421.04 kg K ha⁻¹. The researchers concluded that fertilizer recommendations for this crop should integrate forage productivity with fertilizer-use efficiency and post-harvest soil nutrient dynamics rather than focusing solely on maximizing biomass. They called for long-term field studies incorporating plant nutrient uptake together with measurements of exchangeable and non-exchangeable soil potassium fractions to distinguish crop removal from soil transformations and to determine whether repeated harvesting progressively depletes soil fertility under continuous cactus production in hot arid environments.

Subject of Research: Calcium and potassium fertilization improves productivity and forage quality with implications for soil available potassium in Opuntia ficus-indica under hot arid condition

Article Title: Calcium and potassium fertilization improves productivity and forage quality with implications for soil available potassium in Opuntia ficus-indica under hot arid condition

Article References: Naorem, A., Hassan, S., Louhaichi, M., Dayal, D., Machiwal, D., Dev, R., & Singh, D. (2026). Calcium and potassium fertilization improves productivity and forage quality with implications for soil available potassium in Opuntia ficus-indica under hot arid condition. Frontiers in Soil Science, 6, Article 1950553. https://doi.org/10.3389/fsoil.2026.1950553

Image Credits: AI Generated

DOI: 10.3389/fsoil.2026.1950553

Keywords: Calcium, potassium, fertilization, improves, productivity, forage, quality, implications, soil, available, Opuntia, ficus-indica

The research team, led by Vitaliy Volkogon of the Institute of Agricultural Microbiology and Agro-Industrial Production of the National Academy of Agrarian Sciences of Ukraine, measured nitrous oxide fluxes from a leached light-loam Chernozem soil near Chernihiv over three growing seasons, from 2019 to 2021. The measurements were taken within a four-crop rotation of potato, spring barley, pea, and winter wheat, part of a field experiment established in 2009. By the time emissions monitoring began, the plots had undergone more than a decade of systematic fertilization, meaning the soil biological processes in each treatment had acquired distinct characteristics shaped by the type and combination of fertilizers applied.

The experimental design was ambitious. The team compared an unfertilized control with organic systems — 5 tonnes per hectare of winter wheat straw, post-harvest lupine green manure, or both — and with mineral fertilizers at low, medium, and high rates, from N40P40K40 up to N120P120K120 for potatoes and N30P30K30 to N90P90K90 for the grain crops. Crucially, they also tested mineral fertilizers applied against the background of the organic amendments, tracking both the direct effect in the year of incorporation and the residual effects over the following three years. Each treatment was duplicated in parallel blocks, one without microbial inoculation and one with pre-sowing treatment using plant growth-promoting rhizobacteria, or PGPR: Azospirillum brasilense for potato tubers and barley seeds, Rhizobium leguminosarum for peas, and Paenibacillus polymyxa for winter wheat.

Measuring nitrous oxide from field soil is technically demanding because the gas is produced by two microbial processes — aerobic nitrification, in which ammonia is oxidized, and anaerobic denitrification, in which nitrate serves as the terminal electron acceptor under low-oxygen conditions. The team used closed static chambers inserted 5 centimeters into the soil, sealed with a water lock, and exposed for three hours. To capture the full extent of nitrogen losses, they employed the acetylene inhibition technique: cups of water containing calcium carbide released acetylene inside the chambers, which blocks the reduction of nitrous oxide to benign dinitrogen. This forces any nitrous oxide that would otherwise have been further reduced to accumulate, allowing the researchers to quantify total emissions from both nitrification and denitrification. Gas samples were then analyzed by gas chromatography with an electron capture detector, and fluxes were extrapolated to a per-hectare, per-day basis.

The results confirmed what many studies have shown before: mineral fertilizers alone increased nitrous oxide emissions, and the losses rose proportionally with nitrogen rates. Under potato cultivation, applying 40 kilograms of nitrogen per hectare increased N-N2O losses by 72 to 98 percent relative to the control, depending on the growth stage; at 80 kilograms the increase reached 102 to 127 percent, and at the highest rate of 120 kilograms it climbed to 125 to 163 percent. But when the same fertilizer rates were applied over the background of straw and lupine green manure, the picture changed dramatically. Emission intensity dropped by 7 to 12 percent under potatoes, with similar reductions at the medium and high fertilizer rates.

The residual effects of the organic amendments proved equally important. In the first year after incorporation, when spring barley followed the potato crop, nitrous oxide losses under mineral fertilization combined with the residual organic background fell by 6 to 13 percent compared to mineral fertilizers alone. In the second year of residual action, under peas, the reduction widened to 10 to 18 percent across developmental stages. By the third year, under winter wheat, however, the mitigating capacity of the straw and green manure had largely faded — differences compared to mineral-only treatments were either statistically non-significant or marginal. The organic carbon, in other words, buys roughly two years of emission relief before its effect dissipates.

The PGPR inoculation added a persistent layer of mitigation on top of the organic carbon effect. Across all four crops and all fertilization backgrounds, pre-sowing inoculation lowered nitrous oxide emissions, with the largest reductions occurring when mineral fertilizers, organic matter, and bacteria were combined. Under peas, the integrated system of the lowest fertilizer rate plus residual straw, green manure, and Rhizobium inoculation cut emissions by 23 to 29 percent across growth stages compared to the same fertilizer rate applied alone. Under barley, the highest fertilizer rate combined with organic residues and Azospirillum reduced losses by up to 28 percent at germination compared to mineral fertilization alone.

What makes these results particularly compelling is the mechanism the researchers propose. The straw, with its wide carbon-to-nitrogen ratio of 77:1, and the lupine biomass, with a narrower ratio of about 16:1, together supplied roughly 3,600 kilograms of carbon per hectare. This carbon drives microbial immobilization of the mineral nitrogen that crops fail to assimilate — a fraction that can be substantial, given that nitrogen use efficiency from fertilizers typically ranges between 35 and 65 percent. Rather than leaving that surplus nitrogen available to nitrifiers and denitrifiers, the added carbon channels it into microbial biomass and organic pools, where it is temporarily locked away and can later mineralize as a slow-release nitrogen source for subsequent crops.

The bacterial strains appear to work through two complementary routes. Azospirillum brasilense and Rhizobium leguminosarum possess functional denitrification capabilities, meaning they can enzymatically reduce nitrous oxide to benign dinitrogen. But even Paenibacillus polymyxa, which lacks denitrifying capacity, still significantly reduced emissions under winter wheat. This strongly supports the hypothesis that inoculation-enhanced plant nitrogen uptake depletes the soil mineral nitrogen pool accessible to native nitrifiers and denitrifiers. Phytohormone production by the bacteria stimulates root system expansion, accelerating nutrient flux from the bulk soil — and crucially, this root growth stimulation occurs independently of soil nitrogen levels, unlike root nodulation in legumes.

Perhaps the most surprising finding was the yield data. Contrary to the conventional agronomic dogma that straw incorporation requires supplemental mineral nitrogen — typically at least 10 kilograms per tonne of straw — to avoid transient nitrogen immobilization that impairs crop nutrition, the experiment revealed consistent yield increases when straw and green manure were combined with mineral fertilizers. Under potatoes, the medium fertilizer rate plus organic residues produced 38.46 tonnes per hectare compared to 36.35 under mineral fertilization alone, a statistically significant gain. Under peas, all fertilizer doses applied over the second-year residual organic background produced significant yield increases. Pre-sowing PGPR inoculation added further productivity gains across the rotation, with the highest potato yield of 45.25 tonnes per hectare achieved under the fully integrated system of high fertilizer rates, organic residues, and inoculation — a 152 percent increment over the unfertilized control.

The authors argue that this challenges a long-standing assumption. Under modern, high-input fertilizer regimes, a fraction of applied mineral nitrogen routinely remains unassimilated by the crop. Rather than compensating with supplemental nitrogen when straw is incorporated, they suggest, that residual pool should be biologically immobilized into organic forms. Straw and related crop residues should serve as an exogenously supplied carbon source to drive microbial assimilation of surplus fertilizer nitrogen, simultaneously advancing soil carbon sequestration. The combined organic inputs also balanced each other’s mineralization rates — the straw releasing carbon slowly, the lupine biomass more rapidly — optimizing the timing of microbial carbon availability.

The findings arrive at a moment when alternative mitigation technologies face mounting scrutiny. Enhanced-efficiency fertilizers, nitrification inhibitors, and urease inhibitors can improve nitrogen use efficiency, but chemical inhibitors raise production costs and pose non-target environmental risks. Nitrapyrin, a widely used nitrification inhibitor, has been detected in stream water, indicating off-site transport, while residues of dicyandiamide have been found in cow milk in New Zealand, prompting regulatory bans on its use in pasture systems. Biological approaches based on PGPR strains avoid these pitfalls, and recent work with Stutzerimonas stutzeri has shown similar potential for mitigating soil nitrous oxide emissions through microbial community shifts.

The study is not without limitations. The acetylene inhibition technique, while cost-effective and feasible for large-scale field evaluations, is less sensitive than nitrogen-15 isotope tracing, and the researchers acknowledge specific methodological constraints. The literature on crop residue effects also remains conflicting: some studies report straw mulching reducing emissions by 23 to 34 percent, while others document increased fluxes when straw is co-applied with mineral fertilizers, attributed to enhanced carbon and nitrogen substrate availability promoting microbial activity. A meta-analysis of cover crops found increased nitrous oxide emissions in 60 percent of evaluated studies, regardless of species. The Ukrainian team hypothesizes that these discrepancies derive from differences in residue carbon-to-nitrogen ratios, cropping system architecture, and agronomic management practices.

Nevertheless, the overall message is clear and operationally actionable. Integrating mineral nitrogen fertilizers with straw, intercropped green manures, and pre-sowing microbial inoculation provides an effective management strategy to suppress gaseous nitrogen losses and improve yields within crop rotations. These practices align directly with the principles of sustainable agricultural intensification: achieving higher yields from existing arable land while minimizing environmental externalities and enhancing ecological services. For a world grappling with both food security and climate change, a strategy that cuts a potent greenhouse gas by up to 29 percent while boosting potato yields by half again over the control is the kind of trade-off agriculture has been searching for.

Subject of Research: Soil N2O emission intensity under different crop fertilization systems and the use of PGPR

Article Title: Soil N2O emission intensity under different crop fertilization systems and the use of PGPR

Article References: Volkogon, V., Volkogon, K., & Sydorenko, V. (2026). Soil N2O emission intensity under different crop fertilization systems and the use of PGPR. Frontiers in Agronomy, 8, Article 1959485. https://doi.org/10.3389/fagro.2026.1959485

Image Credits: AI Generated

DOI: 10.3389/fagro.2026.1959485

Keywords: Soil, emission, intensity, under, different, crop, fertilization, systems, PGPR, scientific research

The research team, led by Weina Zhang of Huanghuai University and China Agricultural University, turned to the Agricultural Production Systems Simulator, or APSIM, a widely used crop-soil modeling platform, to run a long-term virtual experiment. Calibrating the model against field trial data from Quzhou County in Hebei Province — where the soil is a calcareous fluvo-aquic type with a pH of 8.7 — the researchers simulated eleven years of maize cultivation from 2007 to 2017 under eight phosphorus application rates ranging from zero to 300 kilograms of P₂O₅ per hectare. They then extended the simulations 22 years beyond the fertilization period to see what would happen once the P inputs ceased.

The results revealed a clear optimum. A phosphorus application rate of 71 kilograms of P₂O₅ per hectare maximized maize productivity, producing mean aboveground biomass of 17.5 tonnes per hectare and grain yields of 9.3 tonnes per hectare. Beyond this threshold, the marginal returns on each additional kilogram of fertilizer dropped sharply: the biomass increment per kilogram of applied P₂O₅ fell from 92 kilograms at moderate rates to just 25 kilograms at the highest rate, while the yield increment declined from 52 to 15 kilograms. Phosphorus use efficiency, meanwhile, sank from 17 percent at 75 kilograms per hectare to a mere 10 percent at 300 kilograms — meaning nine-tenths of the applied nutrient was never taken up by the crop in the year it was applied.

What happens to the unused phosphorus is the crux of the environmental concern. In the calcareous soils of the North China Plain, phosphate ions tend to precipitate onto calcium carbonate surfaces rather than remaining in soil solution, gradually building up both labile P — the plant-available fraction — and large stable inorganic P pools. Over the eleven simulated years, labile P under the 75-kilogram treatment climbed from 20.0 to 28.1 milligrams per kilogram, while the 100-kilogram treatment pushed it from 22.2 to 35.2 milligrams per kilogram. The 300-kilogram treatment sent labile P soaring to 121 milligrams per kilogram. Critically, established environmental thresholds for calcareous soils sit at 39.9 milligrams per kilogram — and the P100 treatment crossed that line by 2017, reaching 40.8 milligrams per kilogram, signaling elevated risks of P leaching into groundwater.

The most remarkable result emerged from the post-cessation simulations. After eleven years of applying 75 kilograms of P₂O₅ per hectare annually, the model showed that legacy phosphorus stored in the soil could sustain maize yields at 8 to 10 tonnes per hectare for 12 to 13 years without any further P inputs. During this period, labile P declined from 32.3 to 15.8 milligrams per kilogram — yet the crops kept drawing on the residual reserves. Even the large stable inorganic P pools, which had accumulated to 447 milligrams per kilogram under the P75 treatment, gradually released P back into available forms, buffering the decline. This hysteresis effect — where historical inputs continue to govern soil P dynamics long after they stop — underscores how nonlinear the relationship is between fertilization intensity and environmental legacy duration.

The study is not the first to observe that crops can exploit residual soil P, but it is among the first to quantify the phenomenon with a process-based model in the calcareous soils of the North China Plain. Evidence from around the world supports the pattern: Japan maintained stable crop yields from 1985 to 2005 while progressively reducing both mineral and organic P fertilizer inputs, and European Union nations saw agricultural productivity stabilize or even improve after the 1980s alongside declining total P use, attributed to efficient mobilization of legacy P reserves. In high P-fixing red soils, a single high-dose application has sustained crop production for 7 to 9 years under subsequent withdrawal regimes.

Yet the modeling exercise also exposed a significant limitation in APSIM’s current phosphorus module. The module calculates labile P primarily through adsorption-desorption mechanisms — the process by which phosphate ions bind to and release from soil particle surfaces. But in neutral and calcareous soils like those at Quzhou, the dominant chemistry is precipitation-dissolution: phosphate precipitating onto calcium carbonate surfaces and dissolving back into solution as pH shifts. By neglecting this pathway, the model may misestimate labile P dynamics in exactly the soil types where precipitation-dissolution equilibria prevail. The researchers note that enhancing the module’s performance across pedologically diverse systems will require new experimental data quantifying P fractionation and transformation kinetics across different soil types.

The implications for the North China Plain — a major maize production region facing P overuse under intensive farming — are substantial. China’s current phosphate reserves are insufficient to meet economic development demands, and global phosphate resources are projected to be depleted in the near future, making P a non-renewable resource with peak production expected within decades. Meanwhile, P loss from agricultural soils remains a key contributor to water eutrophication, with leaching risks threatening groundwater quality across the region. The study’s scenario-based approach provides a theoretical foundation for P reduction strategies that could ease both pressures simultaneously.

The practical message is a phased strategy: apply around 71 to 75 kilograms of P₂O₅ per hectare annually for roughly a decade, then discontinue fertilization for 12 to 13 years while the legacy P pool is drawn down, before resuming applications. This cycle would allow farmers to maintain grain yields at 8 to 10 tonnes per hectare while conserving phosphate rock resources and mitigating pollution risks. As the researchers conclude, the approach achieves the dual objectives of P resource conservation and environmental protection without compromising crop productivity — a rare alignment of agronomic, economic, and ecological interests in one of the world’s most demanding farming systems.

Subject of Research: Modeling Long-Term Impacts of Phosphorus Fertilization Strategies on Maize Productivity and Soil P Dynamics in Calcareous Soils of North China Plain

Article Title: Modeling Long-Term Impacts of Phosphorus Fertilization Strategies on Maize Productivity and Soil P Dynamics in Calcareous Soils of North China Plain

Article References: Zhang, W., Xu, D., Wang, H., Jiang, B., Liang, C., Huang, M., Chen, Z., Zhang, X., Su, D., Yu, M., & Liu, J. (2025). Modeling Long-Term Impacts of Phosphorus Fertilization Strategies on Maize Productivity and Soil P Dynamics in Calcareous Soils of North China Plain. Spanish Journal of Soil Science, 15, Article 14718. https://doi.org/10.3389/sjss.2025.14718

Image Credits: AI Generated

DOI: 10.3389/sjss.2025.14718

Keywords: Modeling, Long-Term, Impacts, Phosphorus, Fertilization, Strategies, Maize, Productivity, Soil, Dynamics, Calcareous, Soils

The research team focused on foxtail millet, a hardy cereal crop well suited to semi-arid conditions, grown in soil collected from farmland near Huairen City. The soil in this basin is classified as soda-type saline-alkali soil, characterized by high concentrations of carbonate and bicarbonate ions that severely restrict food production. Rather than relying on expensive hydraulic engineering, chemical amendments like gypsum, or early-stage halophyte planting, the researchers turned to a physical intervention: blending sand into the surface 20 centimeters of soil at five different volume ratios, ranging from zero to twenty percent.

To understand how sand mixing alters water and nutrient movement, the team conducted one-dimensional vertical ponded-infiltration experiments in laboratory soil columns. Each column, eighty centimeters tall with a ten-centimeter inner diameter, was packed with forty-five centimeters of untreated soil beneath a twenty-centimeter layer of soil-sand mixture. A Mariotte bottle system maintained a constant two-centimeter water head at the surface, while sampling ports at five-centimeter intervals allowed researchers to track moisture, salt, and nutrient distributions at ten depths. Three infiltration-water treatments were tested: deionized water, a low-concentration NPK solution containing five grams per liter of ammonium nitrate and 2.5 grams per liter of potassium dihydrogen phosphate, and a high-concentration version with double those amounts.

The results revealed a striking acceleration of water movement. When the wetting front reached fifty centimeters—the benchmark depth—untreated soil took approximately 650 minutes under deionized water. With twenty percent sand mixed in, that time dropped by twenty-six percent. Fertilizer solutions accelerated infiltration even further: the high-concentration NPK treatment shortened infiltration time by roughly forty percent compared to deionized water alone, and combining that with twenty percent sand mixing reduced the total time by forty-four percent. The mechanism, the researchers explain, involves ionic strength. As strong electrolytes, the fertilizer solutions compress the electrical double layer around soil particles, diminishing electrostatic repulsion and promoting flocculation of fine particles. This improves soil porosity and stabilizes structure, allowing water to move more freely through the profile.

Sand mixing also reshaped the vertical moisture distribution in unexpected ways. Within the top twenty centimeters—the mixed layer itself—soil water content decreased as the sand ratio increased, reflecting the coarse particles’ limited water-holding capacity. But below twenty centimeters, the opposite occurred: sand-mixed treatments consistently retained more moisture than the untreated control, with ten to fifteen percent ratios proving most effective. The underlying soil, with its higher clay content and greater specific surface area, adsorbs and holds water more strongly once it percolates down from the faster-draining surface layer. Meanwhile, higher nutrient concentrations in the infiltration water increased soil water content across all layers, likely because ammonium and potassium ions promote clay flocculation and aggregate formation more effectively than sodium ions native to the soil.

Salt dynamics told an equally compelling story. Under deionized water infiltration, all sand-mixing treatments achieved higher desalination rates than the control in the zero-to-forty-centimeter layer, with improvements ranging from ten percent at five percent sand to forty-three percent at twenty percent sand. However, the researchers observed a critical caveat: salts migrated downward and accumulated sharply in the forty-to-fifty-centimeter layer, forming what they describe as a subsurface salt reservoir. In regions with shallow, highly mineralized groundwater—like the Datong Basin—this stored salt could be remobilized through capillary rise and return to the root zone, causing secondary salinization. The team recommends long-term monitoring of the forty-to-sixty-centimeter layer combined with drip irrigation and plastic mulching to prevent this risk.

Nutrient transport patterns varied considerably depending on the interplay between sand ratio and fertilizer concentration. Ammonium nitrogen declined with increasing sand-mixing ratio in the surface layer, while higher fertilizer concentrations enhanced its vertical mobility, pushing it deeper into the profile. Nitrate nitrogen, a non-adsorbable anion, moved in close synchrony with the wetting front and accumulated at greater depths under higher sand ratios. Available phosphorus and available potassium showed inverse relationships with sand mixing in the top layers but responded positively to fertilizer concentration. Correlation analysis revealed that the relationship between available phosphorus and available potassium strengthened as nutrient concentration increased, suggesting that at high inputs, both ions persist in soil solution as free or weakly bound species co-transported with infiltrating water.

To quantify these complex interactions, the researchers deployed four machine-learning algorithms: multiple linear regression, random forest, XGBoost, and LightGBM. Using sand-mixing ratio, infiltration-water treatment, and soil depth as input features, the models predicted six target variables—water content, salt content, ammonium nitrogen, nitrate nitrogen, available phosphorus, and available potassium. XGBoost emerged as the clear winner, achieving coefficients of determination above 0.93 for water content, salt content, and all nutrient indicators, with the lowest or near-lowest root mean square and mean absolute errors. Linear regression performed worst, confirming that the relationships governing water-salt-nutrient transport are fundamentally nonlinear. The team notes that XGBoost’s regularization terms and efficient split-finding algorithm give it an edge in capturing high-dimensional interactions.

The field experiment, conducted from May to October 2024 in Huairen City, translated these laboratory findings into agronomic reality. Forty-five plots, each two by five meters, combined the same five sand ratios with three compound fertilizer rates: 1,050, 1,500, and 1,950 kilograms per hectare. At maturity, both sand ratio and fertilization rate significantly affected plant height and stem diameter, with highly significant effects on panicle weight—the core indicator of yield potential. Plant height generally increased with fertilization, while moderate sand mixing of ten percent produced the tallest plants and thickest stems under high fertilization. Excessive sand mixing at twenty percent consistently reduced plant height, even under high fertilizer inputs, suggesting a threshold beyond which the benefits of improved permeability are offset by diminished water retention.

Panicle weight told the most nuanced story. Under low and medium fertilization, panicle weight rose and then fell with increasing sand ratio, peaking at ten percent mixing—significantly higher than all other treatments. Under high fertilization, differences among sand ratios diminished, indicating that abundant nutrients can partially compensate for soil texture variations. The optimal combination emerged clearly: ten percent sand mixing paired with 1,500 kilograms per hectare of compound fertilizer produced the greatest panicle weight overall. The researchers conclude that a sand-mixing ratio of ten to fifteen percent, combined with appropriate water and fertilizer management, offers the best balance of surface desalination, deep-layer water storage, and crop productivity for moderately saline-alkali soils in northern Shanxi—turning locally abundant river sand from an underused resource into a practical tool for food security.

Subject of Research: Effects of sand mixing and nutrient management on water, salt, and nutrient transport and foxtail millet growth in moderately saline-alkali soil

Article Title: Impact of sand-mixing and nutrient treatments on the growth of foxtail millet in moderately saline-alkali soil

Article References: Wang, W., Qiu, S., Yang, S., Duan, X., Liu, Z., & Cui, Q. (2026). Impact of sand-mixing and nutrient treatments on the growth of foxtail millet in moderately saline-alkali soil. Frontiers in Agronomy, 8, Article 1850435. https://doi.org/10.3389/fagro.2026.1850435

Image Credits: AI Generated

DOI: 10.3389/fagro.2026.1850435

Keywords: saline-alkali soil, foxtail millet, sand mixing, soil infiltration, nutrient transport, XGBoost, soil salinity, fertilization, Datong Basin, soil water content, machine learning, crop yield

A new four-year field experiment conducted by researchers at the Indian Council of Agricultural Research-Central Citrus Research Institute in Nagpur, Maharashtra, together with collaborators from institutions in India, China, and Iran, offers a compelling alternative. Published in Frontiers in Horticulture, the study demonstrates that dividing an orchard into management zones based on tree canopy volume, and then tailoring irrigation and fertilization to each zone, can dramatically improve both water use efficiency and nutrient use efficiency without sacrificing yield or fruit quality. The work was carried out on Typic Ustochrept soil, an Inceptisol characteristic of the hot subhumid tropical climate of central India, in a four-year-old Nagpur mandarin orchard with trees of Citrus reticulata Blanco budded on rough lemon rootstock, Citrus jambhiri Lush.

The experimental plot consisted of 144 Nagpur mandarin plants spaced 6 meters apart in both directions, representing a planting density of 277 plants per hectare. The clay-textured soil had a pH of 7.4, an electrical conductivity of 0.24 dS per meter, and an organic carbon content of 0.67 percent. All 144 plants were treated as georeferenced points for soil fertility evaluation, with initial plant available nutrients varying considerably across the site. KMnO4-extractable nitrogen ranged from 109.3 to 134.6 milligrams per kilogram, Olsen-P from 7.1 to 11.8, and NH4OAc-extractable potassium from 118.4 to 176.3, while DTPA-extractable micronutrients including iron, manganese, copper, and zinc also displayed notable spatial variation.

Rather than relying on soil properties alone, the researchers used tree canopy volume as the decision support metric for delineating management zones. Using GPS and QGIS Version 3.5 combined tools, they developed a canopy-based variogram with canopy volumes ranging from 1.30 to 9.64 cubic meters and a coefficient of variation of 22.3 to 34.8 percent. The median canopy volume of 4.2 cubic meters served as a stable metric for mapping spatial variability, and three contrastingly different management zones were delineated as a manageable spatial grid. The high production management zone included trees with canopy volume greater than 5 cubic meters, the medium production management zone covered trees between 3 and 5 cubic meters, and the low production management zone included trees below 3 cubic meters.

Based on these zones, three treatment modules were fixed. The high production management zone received 60 percent of the recommended dose of fertilizer combined with 80 percent of the irrigation requirement, the medium production management zone received 80 percent of the recommended fertilizer dose with 90 percent of the irrigation requirement, and the low production management zone received the full 100 percent of both. The recommended fertilizer dose for mature Nagpur mandarin trees was previously established as 600 grams of nitrogen, 200 grams of P2O5, and 300 grams of K2O per tree per year. Irrigation was scheduled through a drip system with 8 liters per hour drippers, three per plant, and fertigation was administered using a venturi-based liquid fertilizer injector. Uniform foliar sprays of 0.50 percent FeSO4, 0.50 percent MnSO4, and 0.50 percent ZnSO4 were applied thrice during each season, beginning at fruit set and repeated at 45-day intervals during fruit development.

The irrigation requirement was computed daily using the Penman-Monteith method for reference crop evapotranspiration, combined with phenological stage-wise crop coefficients derived from the shaded area technique and a wetted area factor representing the proportion of the effective root zone. Over the four-year study, the average reference crop evapotranspiration was 1,925.90 millimeters, with daily values ranging from 2.89 to 9.40 millimeters and peaking in May. During that peak summer month, the irrigation requirement reached 165 liters per day per tree. The total quantities of irrigation applied under the high, medium, and low production zones, each based on 48 plants, were computed as 73.38, 82.55, and 91.72 thousand liters per day respectively, with the crop evapotranspiration varying between 2.53 and 5.59 millimeters per day during the corresponding period.

The results following four annual cycles of treatment were striking. Tree canopy volume reached 8.08, 6.28, and 5.88 cubic meters in the high, medium, and low production management zones respectively, with corresponding fruit yields of 35.53, 28.15, and 24.26 kilograms per tree. Expressed per unit of canopy, these yields translated to 4.39, 4.08, and 4.12 kilograms per cubic meter of canopy, with coefficients of variation of 12.6 to 15.5 percent within zones and 11.8 to 13.1 percent across zones. Most remarkably, water use efficiency in the high production management zone, which received only 80 percent of the irrigation requirement, was 1.83-fold higher than in the low production management zone receiving the full irrigation dose. Nutrient use efficiency was even more dramatic, reaching 2.44-fold higher in the high production zone at 592.14 kilograms per kilogram compared with 242.59 kilograms per kilogram in the low production zone, despite the latter receiving 40 percent more fertilizer.

These efficiency gains did not come at the expense of fruit quality. Juice content varied from 41.2 to 44.8 percent, total soluble solids ranged from 9.3 to 10.5 degrees Brix, and juice acidity spanned 0.57 to 0.85 percent, with coefficients of variation of 10.2 to 14.3 percent. The low production zone showed marginally higher juice content and acidity than the high production zone, while total soluble solids showed no discernible changes between zones, indicating more or less uniform fruit quality development despite the differential input regimes. Fruit size distribution, a critical determinant of market returns for Nagpur mandarin sold as fresh fruit, showed a clear gradient across zones, with the high production management zone registering the maximum proportion of A-grade fruits exceeding 75 millimeters, followed by the medium and low production zones in decreasing order.

Soil fertility responses corroborated the agronomic outcomes. Plant available nitrogen, phosphorus, and potassium in the soil varied from 119.4 to 212.4, 9.5 to 16.2, and 138.7 to 207.5 milligrams per kilogram respectively, with the high production management zone continuing to record significantly higher available macronutrients than the other two zones even after four years of continuous variable treatments. Pearson correlation analysis revealed that plant available nutrients within the high production management zone were highly correlated with fruit yield, with correlation coefficients reaching 0.99 for available nitrogen, 0.94 for available phosphorus, and 0.94 for available potassium, compared with weaker or non-significant relationships within the medium and low production zones. These coefficients of variation for soil nutrients ranged from 10.0 to 17.1 percent, and the gradual decline in variation with each fruiting season suggested that the orchard was progressively transforming into a more homogeneous production grid.

The study provides a conceptual basis for rationalizing input use in citriculture by exploiting spatial variability in soil properties rather than applying blanket recommendations across an entire orchard. By delineating management zones through canopy volume-based variograms and treating each zone as a statistically homogeneous production unit, the researchers demonstrated that variable rate application of irrigation and fertilizers can squeeze field spatial variability to the advantage of orchard productivity. The findings arrive at a moment when climate variability, regulatory nutrient management, water conservation policies, and declining water availability compound the challenges facing irrigated crop production worldwide. For citrus growers, the message is clear: over-optimization of irrigation and fertilizer inputs is not only wasteful but counterproductive, and precision zoning offers a practical pathway toward more sustainable and economical citrus production.

Subject of Research: Variable-rate irrigation and fertilization across canopy-based management zones in a Nagpur mandarin orchard on Indian Inceptisol

Article Title: Rationale behind the integrated use of irrigation and fertilization in optimizing citrus production on Indian Inceptisol

Article References: Srivastava, A. K., Shigure, P. S., Meshram, D. T., Huchche, A. D., Utkhede, A., Priyamvada, M., Wu, Q.-S., Mousavi, S. M., Rymbai, H., Baishya, L. K., & Jagannadham, P. T. K. (2026). Rationale behind the integrated use of irrigation and fertilization in optimizing citrus production on Indian Inceptisol. Frontiers in Horticulture, 5, Article 1941837. https://doi.org/10.3389/fhort.2026.1941837

Image Credits: AI Generated

DOI: 10.3389/fhort.2026.1941837

Keywords: citrus, Nagpur mandarin, irrigation, fertilization, management zones, water use efficiency, nutrient use efficiency, precision agriculture, Inceptisol, drip fertigation, canopy volume, fruit quality

The study, led by Shikma Zaarur of the Hebrew University of Jerusalem together with colleagues at the Agricultural Research Organization’s Volcani Institute, the Geological Survey of Israel and Ben-Gurion University of the Negev, was designed to simulate the relentless potassium drain of intensive agriculture. The team filled ten-liter pots with three contrasting alkaline soils from Israel: a clayey soil from the coastal plains, a loess sandy loam from the western Negev, and a red sandy soil from Rehovot. Peruvian alfalfa, one of agriculture’s most potassium-hungry crops, was sown in April 2024 and harvested sixteen times over roughly thirteen and a half months, with each cut removing potassium from the system. All essential nutrients except potassium were supplied through drip irrigation, so potassium was the only element expected to become limiting in the unfertilized treatments. A parallel set of pots received potassium chloride fertilizer, split into two applications.

Soil potassium exists in a hierarchy of reservoirs that differ enormously in size and accessibility. The smallest, potassium dissolved in the soil solution, represents only about 0.1 to 0.2 percent of total soil potassium, but it is the only pool plants can absorb directly. The exchangeable pool, one to two percent of the total, consists of potassium adsorbed onto clay surfaces and some interlayer sites, and it is what the standard ammonium acetate extraction measures. Below that sits interlayer potassium, locked between the sheets of 2:1 clay minerals such as illite and illite-smectite, which can account for up to ten percent of total soil potassium. Finally, structural potassium, hosted in micas and potassium feldspar, makes up 90 to 98 percent of the total and is considered almost inert. Fertilizer recommendations worldwide treat the exchangeable pool as the soil’s capacity to feed a crop, effectively ignoring everything beneath it.

The mass-balance results shattered that assumption. In the unfertilized pots, cumulative potassium uptake reached about 7.3 grams per pot in both the clayey and loess soils and 4.4 grams in the red sandy soil, while the initial exchangeable potassium plus the small background input from irrigation water could account for only a fraction of those amounts. Total uptake was 2.0 to 3.9 times greater than the estimated supply from exchangeable potassium and natural inputs. Non-exchangeable pools supplied 67 percent of uptake in the clayey soil, 50 percent in the loess, and a striking 74 percent in the red sandy soil. Direct measurements of total soil potassium at the end of the trial confirmed the depletion: total potassium fell from 88 to 75 grams per pot in the clayey soil, from 75 to 65 in the loess, and from 31 to 28 in the red sandy soil, with the rhizosphere cores showing even greater losses than the mass balance predicted.

To trace where the missing potassium came from, the researchers exploited a geochemical fingerprint. Rubidium substitutes for potassium in mineral structures because the two ions carry the same charge and nearly the same radius, but different minerals incorporate rubidium in different proportions, giving each mineral source a characteristic potassium-to-rubidium ratio. As plants depleted the exchangeable pool, its potassium-to-rubidium ratio shifted dramatically toward the signature of the fine clay fraction in all three soils. In the loess soil the ratio plunged from 3664 at the start to 284 by the eighth harvest; in the red sandy soil it fell from 547 to 154 within the same period. The exchangeable pool was converging on the composition of the clay minerals themselves, indicating that illite and illite-smectite interlayers, not potassium feldspar, were the dominant suppliers.

The mineralogy of each soil also governed how much the crop responded to added fertilizer. In the clay-rich soil, where abundant mixed-layer illite-smectite buffers the soil solution, fertilization produced only a marginal and statistically insignificant biomass gain of 5.3 percent across sixteen harvests. The loess soil responded with a significant 5.5 percent increase, but only from the eleventh harvest onward, once the plants had drained the readily available potassium. The potassium-poor red sandy soil responded earliest and most strongly, with fertilization boosting cumulative biomass by 13.5 percent, significant at most harvests from the third cut onward. This pattern mirrors decades of puzzling field observations in which crops on alkaline soils showed little or no yield response to potassium fertilizer despite soil tests suggesting deficiency.

Perhaps the most provocative finding concerns the speed of mineral weathering. Using a first-order approximation, the team calculated the illite dissolution rate needed to sustain the observed potassium release. If all the non-exchangeable potassium had come from illite, between roughly 17 and 34 grams of the mineral would have had to weather in each pot over a single year. That translates to dissolution rates of about 10 to the minus 11 to 10 to the minus 12 moles per square meter per second, depending on assumed grain size, which is two to three orders of magnitude faster than natural illite weathering rates and far above laboratory rates measured at neutral pH. The implication is that intensive cropping creates a biological sink that pulls mineral dissolution forward, accelerating weathering of potassium-bearing clays to rates relevant to a single growing season, a phenomenon usually assumed to require millennia.

The mechanism likely lies in the rhizosphere. Alfalfa, with its enormous biomass and repeated cutting schedule, can remove around 200 kilograms of potassium per hectare annually. As roots strip potassium from the soil solution, chemical equilibria shift, and the researchers suggest that root exudation of organic acids may further enhance potassium release from interlayer sites. Consistent with this, recent work has shown that alfalfa roots can trigger significant potassium release from micaceous interlayers within just four months. The exchangeable pool in the study soils did not simply drain to zero; instead it stabilized at a dynamic minimum, a steady state where the rate of mineral release matched the rate of plant removal. That minimum differed for each soil and was controlled by mineral composition and plant demand, meaning the exchangeable test captures only a snapshot of a moving target.

The practical consequences are substantial. If exchangeable potassium tests underestimate plant-available potassium by a factor of two to four in these alkaline Mediterranean soils, then fertilization recommendations built on those tests risk both unnecessary applications on clay-rich soils, where the mineral buffer is strong, and potentially misleading deficiency diagnoses elsewhere. The authors note that the degree of underestimation is likely governed by the abundance of potassium-bearing clay phases, particularly illite and illite-smectite, which are common in eastern Mediterranean soils partly because of mineral-rich dust inputs. Long-term field experiments in Israel, spanning roughly thirty years, have similarly reported little response to potassium fertilization in cotton and wheat grown on soils with comparable clay mineralogy, lending field-scale support to the greenhouse findings.

The study does not mean potassium fertilization can be abandoned. Plants in the unfertilized pots eventually developed classic deficiency symptoms, including chlorosis, necrotic leaf margins and stunted growth, and tissue potassium concentrations fell below the roughly 1.1 percent sufficiency threshold for alfalfa by the end of the trial in all soils. Rather, the message is that the exchangeable test reflects only one slice of a dynamic system in which clay minerals act as both sink and source, fixing potassium when supply is abundant and releasing it when demand is high. Accurate potassium management, the researchers argue, requires methods that account for the mineralogical buffering capacity of soils, ensuring that potassium is applied where it is genuinely needed and conserved where the ground itself can keep feeding the crop.

Subject of Research: Non-exchangeable potassium release from clay minerals sustaining plant potassium uptake in alkaline Mediterranean agricultural soils

Article Title: Non-exchangeable K sustains plant K uptake in alkaline Mediterranean soils

Article References: Zaarur, S., Erel, R., Bier, A. K., Rivlin, A., Nahari, I., Morag, N., Yeshno, E., & Naon, L. (2026). Non-exchangeable K sustains plant K uptake in alkaline Mediterranean soils. Plant and Soil. https://doi.org/10.1007/s11104-026-09118-x

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09118-x

Keywords: potassium, soil fertility, clay minerals, illite, illite-smectite, mineral weathering, alfalfa, fertilization, Mediterranean soils, exchangeable potassium, K/Rb ratio, plant nutrition

The stakes are considerable. Wheat is the backbone of the Egyptian diet, and peri-urban farms like the one studied here sit close to dense urban populations, meaning their grain feeds millions with little delay between harvest and consumption. Heavy metals are a particular concern in such systems because they are persistent, they accumulate in topsoil over years of cultivation, and they can be transferred from soil into grain through the plant’s own nutrient uptake machinery. Cadmium is the most notorious of the group: it has no biological function in humans, it accumulates in the kidneys over decades, and it is classified as a human carcinogen. Lead, nickel, and chromium each carry their own toxicological burdens, while copper and zinc are essential nutrients that become harmful only at elevated doses.

On the productivity side, the trial produced a clear winner. Integrated nutrient management, the hybrid strategy that combines synthetic fertilizers with organic amendments, delivered the highest grain yield of the four treatments, reaching 8.12 tonnes per hectare. This outcome aligns with a growing body of international evidence that mixed nutrient strategies outperform either pure approach, because mineral fertilizers supply immediately available nutrients while organic matter improves soil structure, water retention, and microbial activity. For a country like Egypt, where wheat self-sufficiency is a matter of national strategy and import bills are enormous, a fertilization regime that boosts yield without aggravating contamination is exactly the kind of tool agronomists have been searching for.

Grain quality told a complementary story. Organic fertilization produced the highest grain protein content, at 13.15 percent, a reminder that the nutritional profile of cereals is not fixed but responds to how the soil is fed. The relationship between yield and protein in cereal grain has long been recognized as a trade-off, and the Egyptian results suggest that farmers and millers may face a genuine choice: the integrated approach maximizes tonnage, while the organic route maximizes protein concentration. Neither strategy dominated on every metric, which is precisely why the study’s contamination data matter so much—the yield and quality gains would mean little if they came bundled with a hidden toxicological cost.

That cost, encouragingly, appears to have been modest over the three-year window. Soil concentrations of the six metals did differ significantly among the fertilization treatments, but the researchers emphasize that the quantitative differences were small, indicating limited treatment-induced accumulation during the experimental period. This is an important nuance. Long-term fertilizer experiments elsewhere, including a 25-year trial in China and decades-long studies in Germany, have shown that continuous application of certain fertilizers—particularly phosphate products, which naturally carry cadmium impurities—can gradually raise soil metal loads. Three seasons may simply be too short for such signals to emerge, so the Egyptian team’s finding should be read as a baseline rather than a final verdict on the long-term safety of any given strategy.

The contamination indices used by the researchers add context to the soil numbers. Enrichment factors and the pollution load index, or PLI, compare measured concentrations against a reference baseline—in this case, values for the upper continental crust drawn from standard geochemical references. The recalculated PLI values ranged from 1.107 to 1.127, a modest exceedance of the threshold of 1 that signals enrichment above natural background. Contamination factors identified cadmium and zinc as the principal contributors to the overall soil metal load. In other words, the field is not pristine, but neither is it heavily degraded; the slight enrichment likely reflects a combination of background geology, atmospheric deposition, and the accumulated history of agricultural inputs rather than any single fertilizer treatment.

Inside the grain itself, the metals arranged themselves in a consistent hierarchy: zinc was most abundant, followed by copper, then nickel, chromium, lead, and finally cadmium at the lowest concentrations. This ordering reflects both the natural abundance of these elements in soils and the differing degrees to which wheat roots absorb and translocate them. Zinc and copper are actively regulated as micronutrients, so plants take them up readily, whereas cadmium, despite being far more dangerous to humans, is typically present at much lower concentrations. The treatment effect was nonetheless visible: organic fertilization resulted in slightly higher cadmium and nickel concentrations in the grain than the other strategies, indicating greater transfer of these two metals from soil to grain. This finding echoes a recurring theme in the literature—organic manures can either immobilize metals by binding them to organic matter or, depending on composition and dose, introduce additional metal loads, particularly cadmium from animal-derived inputs.

The health risk assessment is where the study becomes most directly relevant to consumers. The team calculated the estimated daily intake of each metal from wheat consumption, then applied the target hazard quotient model to gauge non-carcinogenic risk, combined those quotients into a hazard index, and estimated carcinogenic risk using standard United States Environmental Protection Agency frameworks. Two headline findings emerged. First, dietary exposure was greater for children than for adults, a consequence of children’s lower body weight relative to their food consumption—a pattern seen in virtually every dietary metal exposure study and one that makes food safety standards for children disproportionately important. Second, the metals responsible for risk were not the same for the two endpoints: copper and zinc, the two essential elements, were the principal contributors to non-carcinogenic risk, while cadmium dominated the carcinogenic risk estimate, followed by nickel.

That cadmium, present at the lowest grain concentrations of the six metals, drives the cancer risk estimate is a textbook illustration of how toxicology and abundance diverge. Reference doses for non-carcinogenic effects are relatively generous for copper and zinc, but the slope factors and tolerable intakes for cadmium are stringent because the metal accumulates irreversibly in the renal cortex over a human lifetime. The result means that even small reductions in cadmium transfer from soil to grain could yield disproportionate public health benefits. It also reframes the fertilizer debate: if organic manures slightly increase grain cadmium and nickel, while integrated management limits metal transfer to grain, then the hybrid strategy earns its recommendation on safety grounds as well as on yield. The authors explicitly highlight integrated nutrient management as a promising approach for enhancing wheat productivity while limiting heavy metal transfer in peri-urban systems.

Several caveats temper the conclusions, and the researchers are candid about them. Three growing seasons cannot capture the slow accumulation dynamics that govern metal burdens over decades of cultivation, and the health risk models rest on assumptions about consumption rates and metal bioavailability that may vary across populations. The modest PLI exceedance also underscores that the starting condition of the soil, not just the fertilizer bag, shapes the contamination picture. Still, the study offers something rare: a controlled, multi-season, head-to-head comparison of fertilization philosophies measured not only in tonnes of grain but in milligrams of toxic metal and quantified human risk. As Egypt and other wheat-dependent nations grapple with intensifying agriculture on limited, increasingly urban-adjacent land, the message from Giza is that the smartest fertilizer strategy may be the one that refuses to choose between feeding people and protecting them.

Subject of Research: Trace metal accumulation in soil and wheat grain under contrasting fertilization strategies and associated human health risks

Article Title: Soil and wheat grain trace metals under contrasting fertilization strategies: implications for food safety and human health risk

Article References: Hamed, L. M. M., Al-Saeed, A. M., Darrag, H. M., & Emara, E. I. R. (2026). Soil and wheat grain trace metals under contrasting fertilization strategies: implications for food safety and human health risk. Environmental Geochemistry and Health, 48(14), Article 579. https://doi.org/10.1007/s10653-026-03485-1

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03485-1

Keywords: wheat, heavy metals, cadmium, fertilization, integrated nutrient management, soil contamination, food safety, health risk assessment, peri-urban agriculture, Egypt, pollution load index, grain yield

The experiment, conducted during the 2023–2024 growing season, was designed as a completely randomized block study with three replications, a standard arrangement that helps researchers separate genuine treatment effects from the natural variability among trees. The team, led by Amir Ghorbani together with Mousa Mousavi and Esmaeil Khaleghi, compared four fertilization programs: an unfertilized control, the conventional fertilization method commonly used across Khuzestan province, and two regimes built around KHAZRA Advanced Nano-chelate fertilizer, one applied by deep banding with irrigation and another combining deep banding with foliar spraying. The choice of delivery method matters. Chelated nutrients are bound to organic carrier molecules that keep micronutrients soluble and available in alkaline soils, where iron, zinc, and manganese otherwise lock into insoluble forms that roots cannot absorb.

The results were striking in their consistency. Palms receiving the advanced chelate through deep banding and irrigation maintained the highest proportion of active green leaves relative to total leaves per tree, reaching 56.15 percent, a 27 percent increase over the control. That figure is more than a cosmetic improvement. In a palm, the canopy of healthy fronds is the photosynthetic engine that powers fruit filling, and heat stress typically accelerates leaf senescence, browning and killing fronds precisely when developing fruit demand the most carbohydrate. Keeping more leaves functionally green under extreme heat means the tree can sustain photosynthesis longer, translating directly into heavier, better-fed fruit clusters.

Yield told the same story. The deep-banding-plus-irrigation treatment produced the highest fruit yield at 56.1 kilograms per palm, a 30 percent gain over unfertilized trees. For a commercial date operation, where revenue scales with kilograms of marketable fruit per hectare, a difference of that magnitude across an entire orchard represents the margin between a marginal season and a profitable one. The authors note that fruit yield is the paramount objective in date production, and their data suggest that simply improving nutrient availability, rather than altering irrigation or planting density, can unlock a substantial share of the cultivar’s latent productivity even under the region’s characteristic heat stress.

Quality metrics moved in parallel with quantity. Antioxidant capacity in the fruit reached 1.39 millimoles of Fe(II) per 100 grams of fresh weight under the best treatment, a 7 percent increase over the control, indicating a denser concentration of the protective phenolic and related compounds that consumers and nutrition researchers prize in dates. Leaf morphology responded as well: the longest leaflets measured 30.67 centimeters, an 11 percent gain relative to the control, and the most favorable flesh-to-kernel ratio, 8.30, a 25 percent enhancement, was recorded under the conventional Khuzestan fertilization program. A higher flesh-to-kernel ratio means more edible pulp per fruit, a trait that packers and buyers scrutinize closely, since a fruit dominated by its woody seed commands a lower price.

Perhaps the most intriguing layer of the study sits at the molecular scale. The researchers tracked the expression of heat shock protein genes, the cellular emergency responders that fold and stabilize proteins when high temperatures would otherwise cause them to unravel. The pattern they observed was gene-specific and treatment-dependent. Trees receiving the second treatment showed the highest expression of PdHSP17.6 and PdHSP22, while the third treatment produced the strongest PdHSP26.5 expression. Intriguingly, the unfertilized palms mounted the strongest induction of PdHSP23.6, but this apparent molecular alarm came bundled with the highest levels of proline and malondialdehyde, and the lowest fruit yield of any group.

That combination is diagnostic. Proline accumulates in plant tissues as an osmoprotectant when cells are under stress, and malondialdehyde is a canonical marker of lipid peroxidation, the oxidative damage that membranes suffer when heat overwhelms their protective systems. In other words, the unfertilized trees were not thriving; they were struggling, burning molecular resources on stress signaling and damage repair instead of fruit production. The fertilized palms, by contrast, appeared to buffer heat stress through better nutrition, maintaining growth and yield while their stress-marker chemistry stayed comparatively restrained. Well-nourished plants simply have more physiological slack to absorb environmental punishment.

The findings arrive at a moment when heat stress is tightening its grip on agriculture far beyond Khuzestan. Date palms are famously adapted to arid zones, yet even this desert veteran has thresholds, and climate projections for the Middle East and North Africa point toward hotter, more erratic seasons. Breeding programs for heat-tolerant cultivars take decades. Nutritional interventions like the one tested here offer a faster lever, one that growers can pull within a single season using existing orchards. The study also carries a practical message about application technique: the deep-banding-plus-irrigation route outperformed the foliar-spray combination on the headline yield metric, suggesting that placing chelated nutrients into the root zone, where irrigation water can carry them steadily into the soil profile, beats relying on leaf surfaces that scorch under intense sun.

Cautions are warranted before declaring a universal solution. The study covers a single cultivar, Estemaran, in a single location over one growing season, and the published version remains subject to final editorial revisions. Fertilizer responses are notoriously context-dependent, shaped by soil chemistry, water quality, and the baseline fertility of an orchard. Still, the internal coherence of the data, spanning canopy health, yield, fruit chemistry, and gene expression, gives the results unusual weight. When four independent lines of evidence all point in the same direction, the underlying mechanism, improved nutrient availability buffering heat stress, becomes difficult to dismiss.

For the growers of Khuzestan, the takeaway is immediate and actionable. The authors conclude that cultivating Estemaran under Ahvaz’s typical heat-stress conditions while applying advanced chelate fertilization through deep banding and irrigation is likely to deliver fruit yields acceptable for commercial production. For the broader scientific community, the study adds a compelling data point to a growing literature on how targeted nutrition can modulate plant stress responses, down to the level of heat shock protein genes. As heat waves intensify across the world’s fruit belts, the humble date palm, fed a smarter diet, may be showing agriculture one way to keep producing under a warming sky.

Subject of Research: Effects of chelate fertilizer programs on date palm fruit yield and quality under heat stress

Article Title: Evaluation of the effect of chelate fertilizer application-based fertilization programs on improving the quantity and quality of date palm fruit of the Estemaran cultivar (Phoenix dactylifera L.) under natural heat stress conditions

Article References: Ghorbani, A., Mousavi, M., & Khaleghi, E. (2026). Evaluation of the effect of chelate fertilizer application-based fertilization programs on improving the quantity and quality of date palm fruit of the Estemaran cultivar (Phoenix dactylifera L.) under natural heat stress conditions. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10036-4

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10036-4

Keywords: date palm, chelated fertilizer, nano-chelate, heat stress, Phoenix dactylifera, fruit yield, fruit quality, antioxidant capacity, heat shock proteins, Khuzestan, fertilization, plant physiology