The research, conducted by Jaynos R. Cortes of North Eastern Mindanao State University in the Philippines and Brett Laudato of VDS N.V. in Belgium, set out to evaluate the effects of a dietary additive blend containing choline chloride, L-carnitine, glycerol monolaurate, and lysophospholipids on growth performance, feed utilization, morphometric condition, growth uniformity, allometric growth, and low-salinity stress tolerance in juvenile P. vannamei. Rather than examining each additive in isolation, the study was designed to assess the overall response to the combined formulation, reflecting how such blends are deployed in commercial feed manufacturing. The team hypothesized that supplementation would primarily enhance nutrient-use efficiency, as reflected by improvements in protein efficiency ratio (PER) and feed conversion metrics, and that these metabolic gains might be associated with favorable changes in growth uniformity, morphometric condition, and tolerance to acute low-salinity stress.

The experimental design was rigorous and controlled. Juvenile shrimp, obtained from White Panther Hatchery in Austria and acclimated in a recirculating aquaculture system at VDS N.V. in Belgium, were stocked at a mean initial body weight of 0.90 grams into 500-liter HDPE tanks, with 80 shrimp per tank. Two dietary treatments were compared over a 42-day feeding trial: a control diet and an additive-supplemented diet, each assigned to four replicate tanks. Both diets were formulated to contain approximately 42 percent crude protein and 7 percent crude fat, ensuring that any observed differences could be attributed to the additive blend rather than to underlying nutritional disparities. The supplemented diet contained choline chloride at 0.30 percent, L-carnitine at 0.05 percent, glycerol monolaurate at 0.07 percent, and lysophospholipids at 0.05 percent. Water-quality parameters, including temperature, salinity, dissolved oxygen, and nitrogenous waste compounds, were monitored throughout the trial and remained comparable between treatments, confirming that environmental conditions did not confound the dietary comparison.

The four additives were selected for their complementary mechanisms of action in lipid digestion, transport, and utilization. Choline chloride functions as a lipotropic factor involved in phospholipid synthesis and lipid transport, facilitating the movement of fats through the body. L-carnitine plays a critical role in mitochondrial physiology, shuttling long-chain fatty acids into the cellular powerhouses where they undergo beta-oxidation to produce energy. Lysophospholipids enhance lipid emulsification and nutrient absorption in the digestive tract, potentially improving intestinal morphology and feed utilization. Glycerol monolaurate has been associated with improved intestinal health and nutrient absorption. Together, these compounds were designed to support the efficiency with which dietary nutrients are digested, absorbed, and converted into growth and maintenance processes, with the potential to reduce reliance on amino acids as energy substrates and thereby exert a protein-sparing effect.

After 42 days, the results painted a nuanced picture. The most striking finding was that dietary supplementation significantly increased the protein efficiency ratio compared with the control treatment, rising from 0.0221 to 0.0237, a statistically significant improvement of approximately 7.2 percent. This was the only significant treatment effect detected among the measured growth and feed-utilization variables. In contrast, survival remained high and comparable between treatments, averaging 93.75 percent in the supplemented group and 92.19 percent in the control. Final biomass, final mean body weight, and final body length were similarly unaffected. The feed conversion ratio was numerically lower in the supplemented group at 1.35 compared with 1.46 in the control, representing an improvement of approximately 7.5 percent, but this difference did not reach statistical significance, likely due to the limited number of tank replicates available for comparison.

Beyond the headline growth metrics, the researchers examined a battery of complementary phenotypic indicators that are often overlooked in conventional aquaculture nutrition studies. Growth uniformity, measured by the coefficient of variation for both weight and length, showed no significant differences between treatments, indicating that the additive blend neither enhanced nor disrupted competitive interactions among shrimp within culture tanks. Morphometric condition, assessed through modified condition factor and allometric growth coefficient, remained unchanged. Length-weight relationships, described by the power function W = aL^b, revealed approximately isometric growth patterns in both treatments, with allometric coefficients of 2.948 for the supplemented group and 3.126 for the control, neither differing significantly from the theoretical isometric value of 3.0. Analysis of covariance detected neither a significant treatment effect nor a significant treatment-by-length interaction, demonstrating that dietary supplementation did not alter the fundamental scaling relationship between body length and body weight.

To probe the physiological resilience of the shrimp, the team subjected ten randomly selected individuals from each tank to an acute low-salinity challenge at the end of the feeding trial. Shrimp were transferred directly into test tanks containing water at 0.35 parts per thousand salinity, a level approaching freshwater conditions that was selected to induce severe osmotic stress and maximize the ability to detect potential treatment-related differences in survival. However, because the challenge water temperature was approximately 14 degrees Celsius lower than the culture temperature maintained during the feeding trial, the shrimp were exposed simultaneously to both osmotic and thermal shock. Kaplan-Meier survival analysis and Cox proportional hazards modeling revealed no significant differences in mortality risk between treatments, with a hazard ratio of 1.34 for the supplemented group whose confidence interval encompassed unity. The authors caution that the combined nature of the stressor means any effects of dietary supplementation on salinity tolerance specifically may have been masked by the concurrent thermal challenge.

Multivariate and exploratory modeling analyses provided converging evidence for the study’s central conclusion. Principal component analysis revealed that the first two principal components explained 75.1 percent of the total variance, with protein efficiency ratio and feed conversion ratio contributing most strongly to the multivariate structure. Tanks receiving the additive-supplemented diet tended to be associated with higher PER values and lower FCR, whereas variation in body condition and growth uniformity contributed to differences among individual tanks regardless of treatment. Standardized path analysis and Random Forest classification, though limited by the availability of only eight tank-level experimental units, consistently identified protein efficiency ratio as the variable most strongly associated with dietary supplementation. These exploratory approaches, while hypothesis-generating rather than confirmatory, reinforce the univariate results and suggest that nutrient-use efficiency may be a more sensitive indicator of dietary additive responses than conventional growth metrics.

The authors acknowledge several important limitations when interpreting their findings. The use of four replicate tanks per treatment, while consistent with many controlled shrimp nutrition trials, limits statistical power to detect small-to-moderate treatment effects. The slight difference in analyzed crude protein content between the experimental diets, 42.06 percent in the control and 42.54 percent in the supplemented diet, cannot be completely excluded as a minor contributor to the observed PER response. Additionally, shrimp used in the survival analysis originated from replicated culture tanks, yet tank identity was not incorporated into the survival models, meaning the stress-tolerance results should be regarded as exploratory. The authors also note that feed intake values represent apparent feed intake derived from cumulative feed allocation rather than direct measurements of consumption, as uneaten feed was not quantitatively recovered.

From a practical perspective, the observed improvement in protein utilization efficiency carries meaningful implications for intensive shrimp production systems. Dietary protein is typically the most expensive component of shrimp feeds, and enhanced protein retention could contribute to reduced nitrogen excretion, lowering the environmental footprint of aquaculture operations. Even modest improvements in nutrient-use efficiency may therefore have both economic and environmental value. However, the absence of significant effects on growth performance, morphometric condition, growth dynamics, and low-salinity stress tolerance indicates that the benefits of supplementation are likely to be subtle and primarily related to nutrient utilization rather than broad enhancements of shrimp performance. The authors call for future studies incorporating longer feeding periods, larger sample sizes, temperature-controlled stress challenges, and factorial or dose-response designs to clarify the mechanisms underlying the observed responses and determine whether improved protein-use efficiency can translate into economically meaningful production benefits under commercial farming conditions.

Subject of Research: Effects of a functional feed additive blend on protein efficiency ratio, growth performance, and stress tolerance in juvenile whiteleg shrimp

Article Title: Effects of functional additive blend containing choline chloride, L-carnitine, glycerol monolaurate, and lysophospholipids on protein efficiency ratio, growth performance, and stress tolerance in juvenile Penaeus vannamei

Article References: Cortes, J. R., & Laudato, B. (2026). Effects of functional additive blend containing choline chloride, L-carnitine, glycerol monolaurate, and lysophospholipids on protein efficiency ratio, growth performance, and stress tolerance in juvenile Penaeus vannamei. Frontiers in Aquaculture, 5, Article 1909583. https://doi.org/10.3389/faquc.2026.1909583

Image Credits: AI Generated

DOI: 10.3389/faquc.2026.1909583

Keywords: Penaeus vannamei, whiteleg shrimp, aquaculture, feed additives, choline chloride, L-carnitine, lysophospholipids, glycerol monolaurate, protein efficiency ratio, nutrient-use efficiency, stress tolerance, feed conversion ratio

The research team, led by Nathan Howell and Behnam Askarian, built three identical 250-liter aquaponics systems, each combining koi fish with basil grown in deep water culture rafts. The only variable was the source water, drawn from three supplies relevant to the Texas Panhandle: purified reverse osmosis water, fresh groundwater from the Ogallala aquifer, and brackish groundwater from the deeper Dockum aquifer. Each system ran through three sequential basil crop cycles lasting between 32 and 41 days, giving the researchers something rare in the aquaponics literature: temporal replication across multiple growing periods rather than a single snapshot.

The choice of fish was deliberate. Koi are not food fish, but they command high prices as ornamental animals and ship easily in small quantities, making them a practical entry point for a region with almost no aquaculture tradition. Basil, meanwhile, is a high-value herb with established local demand. Together, the pair offered a test of whether aquaponics could work economically in the southern Great Plains using nothing more than the water already beneath farmers’ feet.

On the water side, the numbers were striking. Evapotranspiration across the systems ranged from 0.86 to 1.6 centimeters per day, and overall water use efficiency reached 361 to 615 grams of wet basil biomass per 1,000 liters of water consumed. Daily volume loss hovered around one percent, almost entirely attributable to plant transpiration rather than open-water evaporation. For a semi-arid region where the Ogallala aquifer is steadily declining, these figures suggest that aquaponics could deliver high-value crops with dramatically lower water demand than open-field production.

The fish themselves were remarkably indifferent to water quality. Across all three sources, koi grew at similar rates, with total mass gains of 394 to 435 grams over the full experiment and feed conversion ratios between 1.68 and 1.99. The brackish Dockum system did show a slight numerical lag in later cycles, but the differences were not statistically significant. This finding matters because it suggests that moderately saline groundwater, which is abundant in the region, may be perfectly acceptable for the aquaculture side of the equation even when it stresses the crops.

The basil told a different story. Statistical analysis using mixed-effects ANOVA revealed significant effects of water source, growth cycle, and their interaction on plant dry mass. By the third cycle, electrical conductivity in the Dockum-fed system had climbed above 3 millisiemens per centimeter, well above the roughly 1.5 millisiemens maintained in the fresher systems. Basil yields in the brackish treatment declined accordingly, and the plants showed visible chlorosis. The researchers traced the salinity buildup primarily to accumulating chloride and sodium ions, which neither the fish, the bacteria, nor the plants removed in meaningful quantities.

One of the more counterintuitive findings involved sodium accumulation in the plants themselves. Basil grown in reverse osmosis water, which contained essentially no sodium, accumulated significantly more leaf sodium than basil grown in Ogallala groundwater, which contained 99 milligrams per liter. The researchers speculate that the high calcium and magnesium content of the hard Ogallala water competitively suppressed sodium uptake at the root level, a mechanism they had not directly measured but which is consistent with known ion antagonism in plant physiology.

Iron presented another puzzle. Despite leaf tissue iron concentrations exceeding recommended ranges in all treatments, the basil showed chlorosis consistent with iron deficiency. The explanation lies in partitioning: iron and manganese accumulated preferentially in root tissue rather than shoots, with root iron concentrations reaching 2,450 to 2,880 milligrams per kilogram compared to just 205 to 336 in the leaves. This pattern is characteristic of hydroponic systems operating at elevated pH, where iron forms insoluble precipitates near the root surface and cannot be effectively loaded into the xylem for transport upward. The finding suggests that total tissue iron is a poor indicator of actual iron nutritional status when pH remains chronically above 7.

The mass balance itself proved humbling. The researchers could close the nutrient budget within plus or minus 25 percent for nitrogen, copper, and magnesium, but struggled with most other elements. Phosphorus and potassium always showed negative residuals, meaning more of these nutrients appeared in sinks than could be accounted for by fish feed inputs alone. Sodium was the worst offender, with residuals exceeding 300 percent. The researchers attribute these discrepancies to measurement uncertainty and to unmonitored processes, particularly the possibility of gaseous nitrogen loss through denitrification in low-oxygen zones within the biofilter and sedimentation tanks.

Nutrient use efficiency told its own story. Plants captured only 2.19 to 9.48 percent of the nitrogen and 2.06 to 9.14 percent of the phosphorus supplied in fish feed, values at or below the low end of what previous studies have reported. Potassium uptake was notably higher, ranging from 10.2 to 47.5 percent, but this came with a caveat: leaf potassium concentrations exceeded recommended ranges in all treatments, producing nitrogen-to-potassium ratios far below the published optimum for basil. The researchers suggest that coupled aquaponics systems may structurally tend toward potassium excess relative to nitrogen, since fish feed delivers potassium without any deliberate balancing against crop demand.

Perhaps the most important practical conclusion is that production-scale coupled aquaponics in brackish water regions will require periodic drain events. Because chloride and sodium accumulate relentlessly in a fully closed loop, the only way to prevent salinity stress on crops is to periodically discard water and replace it with fresh supply. This partially undermines the water-saving narrative, but the researchers note that even with such losses, aquaponics would still use far less water than conventional irrigation. They also point out that blending brackish groundwater with fresher sources, or investing in targeted treatment, could extend the intervals between drains.

The study’s multi-cycle design proved essential. Nutrient use efficiency changed significantly over time as systems matured, with the second cycle often showing the highest values before rising salinity in the brackish treatment depressed performance in the third. A single-cycle experiment would have missed these dynamics entirely and potentially led to overly optimistic conclusions about long-term sustainability. The researchers argue that temporal replication should become standard practice in aquaponics mass balance studies, which have historically relied on single crop cycles in the vast majority of cases.

For the Texas Panhandle specifically, the findings offer a qualified green light. Koi and basil can indeed be produced together using local groundwater, including moderately brackish sources, with water use efficiencies that compare favorably to any field-based alternative. The economic model remains untested at commercial scale, and the researchers acknowledge that larger demonstrations will be needed. But the fundamental chemistry works: fish waste can fertilize herbs, hard water can support nitrification, and the region’s declining aquifers can be stretched further by growing high-value crops in closed loops rather than open fields. The caveats about salinity management and nutrient balancing are real, but they are engineering problems rather than fundamental barriers.

Subject of Research: Nutrient mass balance and water source effects in koi-basil coupled aquaponics systems in the Texas Panhandle

Article Title: Nutrient mass balance of koi–basil aquaponics production systems

Article References: Howell, N., & Askarian, B. (2026). Nutrient mass balance of koi–basil aquaponics production systems. Frontiers in Aquaculture, 5, Article 1914289. https://doi.org/10.3389/faquc.2026.1914289

Image Credits: AI Generated

DOI: 10.3389/faquc.2026.1914289

Keywords: aquaponics, koi, basil, mass balance, nutrient use efficiency, brackish groundwater, Ogallala aquifer, Dockum aquifer, salinity, water use efficiency, Texas Panhandle, sustainable agriculture

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

Soil acidity is one of the most widespread constraints on crop production in tropical highlands, and Ethiopia is no exception. When soils become acidic, aluminum and manganese become soluble and toxic to plant roots, while essential nutrients such as phosphorus are locked into unavailable chemical forms. The molecular basis of this problem is well understood: root growth is inhibited, and the plant’s ability to take up water and nutrients collapses. For wheat, a staple crop that Ethiopia has been striving to produce in sufficient quantities for its growing population, acidic soils translate directly into depressed yields and poor returns on fertilizer investments. Previous work by the same research group has mapped the extent and distribution of surface soil acidity across Ethiopia’s rainfed areas, finding that the problem is extensive and worsening under continuous cultivation.

To untangle the interactions between acidity correction and nutrient supply, the researchers designed a split-plot factorial experiment. Two levels of agricultural lime occupied the main plots, while five nitrogen rates crossed with four phosphorus rates formed the sub-plots. This design allowed the team to measure not only the individual effects of each input but also the interactions among them, across two full growing seasons. They measured soil chemical properties, wheat grain and straw yields, nutrient uptake, nutrient recovery efficiency, and the concentration of zinc in the harvested grain. Zinc was a critical variable because wheat is a major dietary source of this micronutrient in Ethiopia, and zinc deficiency in human populations remains a serious public health concern according to the World Health Organization’s global reporting on micronutrient status.

The headline finding is that nitrogen, not phosphorus or lime, is the dominant yield-limiting nutrient on these acidic soils. Across the experiment, the median yield gain attributable to nitrogen application was 3.5 tonnes per hectare, substantially larger than the 2.0 tonnes per hectare gained from phosphorus and the 1.1 tonnes per hectare gained from liming. In practical terms, this means that a farmer who applies nitrogen fertilizer alone will see the largest single jump in productivity, but the full benefit of that nitrogen can only be captured when soil acidity is corrected and phosphorus supply is adequate. Lime worked largely by improving the soil chemical environment: neutralizing exchangeable acidity, reducing aluminum toxicity, and thereby enhancing the crop’s ability to take up and recover both nitrogen and phosphorus from the soil.

Yields responded strongly at first but showed clear diminishing returns as fertilizer rates climbed. The maximum observed yield in the first season was 4.8 tonnes per hectare, achieved with 150 kilograms of nitrogen and 40 kilograms of phosphorus per hectare. In the second season, the maximum rose to 5.6 tonnes per hectare, but notably this was reached at a lower nitrogen rate of 100 kilograms per hectare with 20 to 40 kilograms of phosphorus. This pattern illustrates a core principle of agronomy: as one constraint is relieved, the efficiency of additional inputs declines, and the economically optimal rate may be well below the agronomic maximum. For resource-poor smallholders, the difference between the last few kilograms of fertilizer and the yield they deliver can determine whether an input package pays for itself at all.

The most provocative result, however, concerns grain zinc concentration. The researchers uncovered a trade-off between wheat yield and grain nutritional quality that was independent of lime and nitrogen management: as phosphorus application increased, yields rose but grain zinc concentrations fell. Across the experiment, grain zinc rarely exceeded 35 milligrams per kilogram, a threshold relevant to biofortification targets for human nutrition. Lime, by contrast, increased grain zinc concentration, while excessive nitrogen and incremental increases in phosphorus rates both reduced it. This dilution effect, in which larger grain harvests spread a finite pool of micronutrients across more biomass, is a recognized phenomenon in crop physiology, but seeing it play out so clearly against a background of soil acidity correction is a warning for breeding and fertilizer programs alike.

The implications for policy are twofold. First, the study supports the integration of lime with balanced fertilization as the backbone of sustainable intensification in the Ethiopian highlands. Liming is expensive and logistically challenging, and recent analyses in Nature Food have argued that soil acidity remediation across sub-Saharan Africa requires targeted rather than blanket investments. This experiment provides the field-level evidence for such targeting: lime pays off most where it unlocks the response to nitrogen and phosphorus, and its benefits extend beyond yield to include improved nutrient recovery efficiency, meaning less fertilizer is wasted and less is lost to the environment. Second, the yield-versus-zinc trade-off means that cautious phosphorus management is needed, and complementary zinc supplementation, whether through foliar zinc sprays, zinc-enriched fertilizers, or zinc-biofortified wheat varieties, will be required to keep grain quality on track.

The research also speaks to a broader debate about how Africa achieves wheat self-sufficiency. Ethiopia’s national strategy has pursued yield gap closure, land expansion and irrigation, but the yield gap studies led by co-author João Vasco Silva have shown that soil fertility constraints, including acidity, are among the chief culprits keeping actual yields far below potential. By quantifying the marginal productivity of each input and their interactions, this experiment gives Ethiopian extension services and fertilizer blending programs an empirical basis for recommending site-specific packages. The finding that the second year’s maximum yield came at lower nitrogen rates than the first also hints at residual effects of lime and possibly carryover phosphorus, a reminder that soil fertility management is a multi-year enterprise rather than a season-by-season calculation.

Methodologically, the study is notable for its use of nutrient recovery efficiency as a diagnostic, following frameworks established by Dobermann and by the QUEFTS model for quantitative evaluation of tropical soil fertility. Recovery efficiency measures the fraction of applied nutrient that actually ends up in the aboveground crop, and it is a sensitive indicator of whether the soil environment is allowing roots to function. The observation that lime enhanced both uptake and recovery of nitrogen and phosphorus confirms the mechanistic chain: acidity correction improves root health, which improves capture of applied nutrients, which improves yield. The statistical analysis relied on linear mixed-effects models and quantile regression, tools that let the researchers characterize responses across the full distribution of plot-level outcomes rather than only at the mean.

For the farmers of the Upper Blue Nile Basin, the practical message is a recipe: correct the acidity first, supply nitrogen as the primary driver of yield, apply phosphorus judiciously rather than maximally, and plan for zinc. For scientists and breeders, the message is that productivity and nutrition goals must be evaluated together, because a fertilizer recommendation that maximizes tonnes per hectare may quietly erode the micronutrient content of the food that same hectare produces. As Ethiopia and its neighbors invest heavily in soil health and fertilizer value chains, this study demonstrates that the cheapest route to both more food and better food runs through the chemistry of the soil itself, and that ignoring the trade-offs hidden in that chemistry would be a costly mistake.

Subject of Research: Effects of lime, nitrogen and phosphorus management on wheat yield, nutrient use efficiency and grain zinc concentration in acidic soils of the Upper Blue Nile Basin, Ethiopia

Article Title: Nutrient management strategies to balance wheat productivity, grain quality and fertilizer use efficiency on acidic soils in the Upper Blue Nile Basin, Ethiopia

Article References: Lulie, B., Adgo, E., Desalegn, T., Sida, T. S., & Silva, J. V. (2026). Nutrient management strategies to balance wheat productivity, grain quality and fertilizer use efficiency on acidic soils in the Upper Blue Nile Basin, Ethiopia. Plant and Soil. https://doi.org/10.1007/s11104-026-09064-8

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09064-8

Keywords: wheat, soil acidity, liming, nitrogen, phosphorus, zinc, nutrient use efficiency, Ethiopia, Upper Blue Nile Basin, grain quality, sustainable intensification, soil fertility

The research team, led by Aman Dhindsa of the University of Waterloo together with colleagues at Memorial University of Newfoundland, set out to answer a deceptively simple question: can farmers growing crops on freshly cleared boreal soil skip the years of near-barren production that normally follow land conversion? Converting forest to farmland disturbs natural soil horizon development and strips away the organic-rich surface layers, leaving behind mineral soil with poor nutrient retention, low cation exchange capacity, and concentrations of soluble aluminum and iron that suppress root growth and lock up phosphorus. The team hypothesized that pairing nutrient sources with organic matter inputs and liming agents would rapidly relieve these constraints.

To test this, the researchers established a randomized complete block design with 36 treatment combinations replicated across three blocks. Three nutrient sources were compared: a conventional mineral fertilizer blend of 20:10:5 N:P:K supplemented with potash, herring fish meal as a regionally relevant organic alternative, and an unfertilized control. These were crossed with four organic matter and liming treatments: hardwood biochar applied at 20.8 tonnes of carbon per hectare, sphagnum peat at 25.1 tonnes of carbon per hectare, peat combined with limestone at 5,400 kilograms per hectare, and no amendment. Each combination was grown under three cropping systems: monocrop oat, monocrop pea, and an oat-pea intercrop seeded in a 60:40 ratio.

The chemistry behind the two winning amendments tells much of the story. Hardwood biochar, produced by pyrolysis of biomass, carries alkaline ash fractions along with carboxylic, hydroxyl, and phenolic surface functional groups that neutralize acidity and adsorb cations. The biochar used in the trial had a measured calcium carbonate equivalence of 16.1 percent, contributing roughly 3,458 kilograms of CaCO3 equivalent per hectare. The peat-plus-limestone treatment delivered even more neutralizing power, about 4,806 kilograms of CaCO3 equivalent per hectare, dissolving to release calcium and magnesium that displace hydrogen and aluminum ions from exchange sites. Both amendments pushed soil pH from deeply acidic starting values toward the 5.9 to 6.4 range, while plots receiving peat alone or nothing at all languished between 5.27 and 5.63.

Those pH shifts cascaded through the entire soil-plant system. Biochar-amended and peat-with-limestone plots recorded the highest cation exchange capacity, the largest extractable potassium, calcium, and magnesium concentrations, and, critically, the greatest aboveground biomass, nitrogen, phosphorus, and potassium uptake in all three cropping systems, with differences statistically significant at p < 0.05. In oat plots, the best-performing biochar and fish meal combination out-yielded the worst unamended control treatment by more than fivefold. Biochar treatments alone pushed extractable soil potassium to 67.38 milligrams per kilogram in pea plots, while the intercrop system recorded the highest absolute potassium uptake of any cropping arrangement.

Not every expected response materialized. Despite raising pH, neither liming amendment produced a measurable increase in extractable soil phosphorus, a result the authors attribute to the overwhelming dominance of aluminum in these soils. Phosphorus sorption capacity in Podzols is tightly linked to Mehlich-3 extractable aluminum, which was by far the most abundant mineral measured at the site, so phosphate fixation persisted even as acidity eased. Soil organic matter content, meanwhile, remained stubbornly low at 1.01 to 1.87 percent across all plots after one season, confirming that a single growing season is far too short for microbial turnover and humification to build meaningful carbon stocks, even with massive carbon-rich inputs.

The nutrient source comparison delivered a surprise with practical consequences for remote northern farms. Herring fish meal, a dried fisheries byproduct with a carbon-to-nitrogen ratio of roughly 3.9, matched or nominally exceeded mineral fertilizer across most yield and uptake measurements, though the authors caution that statistical separation was limited. The explanation lies in mineralization dynamics: fish meal’s low C:N ratio supports rapid microbial conversion of organic nitrogen into plant-available mineral forms within a single season, whereas the ammonium and nitrate in mineral fertilizer are prone to leaching from coarse, low-CEC sandy soil before roots can capture them. Fish meal may also have fed the soil’s starved microbial community with additional carbon, improving nutrient cycling beyond nitrogen alone.

Nutrient use efficiency indices reinforced the amendment story. Nitrogen and phosphorus agronomic efficiencies and partial factor productivity consistently formed their top statistical groupings under biochar or peat with limestone, regardless of nutrient source. Recovery efficiency of nitrogen was highest under fish meal in every cropping system, reaching 1.20 kilograms of nitrogen taken up per kilogram applied in oat plots with peat and lime. Potassium recovery efficiency under biochar with fish meal ranged from 12.2 in pea to a striking 28.1 in the intercrop, reflecting biochar’s dual role as both a potassium source through its residual ash and a retention medium that keeps monovalent cations from being displaced by hydrogen and aluminum ions on exchange sites.

One agronomic detail stands out for anyone planning northern legume production: pea crops underperformed in nitrogen use efficiency relative to oat and the intercrop, likely because rhizobial nodulation is pH-sensitive and many plots remained below the optimal range for the nitrogen-fixing symbiosis, particularly where peat alone or no amendment was applied. This underscores that liming is not merely a yield booster but a prerequisite for the biological nitrogen fixation that makes legume intercrops attractive in low-input northern systems. The intercrop’s exceptional potassium uptake, combined with its more moderate yield swings between best and worst treatments, suggests mixed cropping adds resilience on newly converted land.

The authors are careful to frame their results as a first-season, single-site demonstration of chemical alleviation rather than long-term soil transformation, and they flag real-world caveats. The hardwood biochar was trucked in from Quebec, and at 20.8 tonnes of carbon per hectare its cost likely exceeds that of conventional limestone or locally harvested peat, though farmers in the Happy Valley–Goose Bay region are now exploring low-cost trench-pyrolysis methods to produce biochar locally. Peat with limestone matched biochar’s performance across many combinations while being cheaper and more available, but peat extraction is environmentally unsustainable over the long term because peatlands regenerate slowly and store regional carbon. What the trial proves, unambiguously, is that the acute fertility crisis of year one on converted boreal Podzol is solvable: with biochar or peat and lime, oat yields above five tonnes per hectare and pea yields above three tonnes per hectare became possible before any long-term organic matter accumulation had even begun. Multi-year, multi-site trials will now be needed to determine whether these rapid chemical gains persist and compound into durable northern farmland.

Subject of Research: Soil amendment effects on nutrient availability and forage crop uptake in recently converted boreal Podzolic soil

Article Title: Amendment-driven changes in nutrient availability and forage uptake in a recently converted boreal soil

Article References: Dhindsa, A., Unc, A., Kedir, A. J., & Oelbermann, M. (2026). Amendment-driven changes in nutrient availability and forage uptake in a recently converted boreal soil. Discover Soil, 3(1), Article 179. https://doi.org/10.1007/s44378-026-00318-6

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00318-6

Keywords: biochar, Podzol, boreal agriculture, soil pH, liming, peat, fish meal, nutrient use efficiency, forage crops, oat-pea intercrop, Labrador, soil fertility

The research, led by Krishna Murthy Rangaiah of the All India Coordinated Research Project on Soil Test Crop Response at the University of Agricultural Sciences, Bengaluru, was conducted between 2023 and 2025 under the Soil Test Crop Response, or STCR, framework. This approach, long championed by the Indian Council of Agricultural Research, rests on a simple but powerful idea: the amount of fertilizer a crop needs is not a fixed number but a function of the yield the farmer wants and the nutrients the soil can already supply. By quantifying how much of each nutrient comes from the soil, from fertilizer, and from organic amendments such as farmyard manure, the method converts a routine soil test into a tailored fertilizer prescription.

Field bean, Lablab purpureus, is a multipurpose legume of enormous importance in the Eastern Dry Zone, valued for grain, fodder and green manure, and prized for its tolerance of the region’s erratic rainfall. Yet its productivity has remained stubbornly sub-optimal, in part because existing recommendations ignore the wide variation in soil fertility from farm to farm. The Alfisols that dominate the zone are inherently variable, weathered soils whose nutrient-supplying capacity can differ dramatically even between adjacent fields, making them an ideal test case for site-specific nutrient management.

The study unfolded in three carefully sequenced phases. First, the team established a fertility gradient experiment using fodder maize as an exhaustive crop. By applying differential doses of nutrients and organic matter across a single field, they created three distinct fertility strips: low, medium and high, each with measurably different levels of available nitrogen, phosphorus and potassium. This artificial gradient is the statistical engine of the STCR method, because it generates the wide range of soil-test values and crop responses needed to fit reliable equations on a manageable plot of land.

With the gradient in place, the researchers moved to the second phase: a main calibration experiment with field bean. Across the three fertility strips, they applied a factorial combination of fertilizer levels and farmyard manure, then measured both seed yield and the total uptake of nitrogen, phosphorus and potassium in the harvested crop. From these paired observations they derived the core parameters of the targeted-yield equations: the nutrient requirement, expressed in kilograms of nutrient per quintal of grain; the contribution of soil nutrients to yield; the contribution of applied fertilizer; and, in the integrated treatment, the additional contribution of farmyard manure. Separate equations were fitted for the NPK-only system and for the NPK plus farmyard manure system, allowing the organic amendment to be priced into the prescription.

The mathematics behind these equations is straightforward once the parameters are known. For a chosen yield target, the required fertilizer dose equals the nutrient requirement multiplied by the target, minus the product of the soil test value and the soil contribution coefficient, minus the manure contribution where applicable. In practice, this means a farmer with a phosphorus-rich soil test value receives a smaller phosphorus recommendation than a neighbor with depleted soils, even when both aim for the same harvest. It is a level of precision that blanket recommendations, by design, cannot achieve.

The third phase put the equations to the test in validation trials at two locations, where STCR-based prescriptions were compared head-to-head with the general recommended dose of fertilizer and with the soil fertility-rating approach, a coarser method that adjusts recommendations only by broad fertility classes. The results were striking. Treatments targeting a yield of 12 quintals per hectare under the integrated NPK plus farmyard manure system delivered the highest seed yields of the entire study, reaching 13.42 and 13.21 quintals per hectare at the two validation sites. That performance exceeded the general recommended dose by 20.2 to 23.7 percent and the soil fertility-rating approach by 35.1 to 38.8 percent.

There is an honest caveat in the data that the authors themselves flag. Observed yields under the four STCR treatments overshot their specified targets by 7.8 to 17.6 percent, indicating positive prediction errors rather than the uniform agreement within plus or minus ten percent that a perfectly calibrated model would show. In other words, the equations lean generous, prescribing slightly more nutrients than strictly necessary to hit a target. For farmers, this bias is arguably the safer direction, since under-fertilizing a legume crop risks forfeiting yield, but the overshoot suggests the equations may warrant refinement as more validation data accumulate.

One of the study’s most economically significant findings concerns farmyard manure, a resource many smallholders in the region already possess. Integrating FYM into the nutrient budget reduced the calculated fertilizer requirements for nitrogen, phosphorus pentoxide and potassium oxide by roughly 8 to 15 percent at comparable soil-test levels. The organic amendment did more than substitute for purchased fertilizer; it also improved the efficiency with which the crop used applied nutrients. Apparent recovery of potassium, a measure of how much of the applied nutrient ends up in the harvested plant, climbed to 2.74 to 2.81 kilograms per kilogram under the integrated system, compared with 1.82 to 1.89 kilograms per kilogram under fertilizer alone. Agronomic efficiency followed the same pattern, reinforcing the case for combining organic and inorganic sources rather than treating them as substitutes.

The implications extend well beyond a single crop or district. India’s fertilizer subsidy bill is enormous, and nutrients applied without reference to soil status are simultaneously a fiscal drain and an environmental hazard, contributing to nitrate leaching and phosphorus runoff. Equations of the kind validated here, which are crop-specific and soil-specific by construction, offer a pathway to site-specific nutrient management that a soil testing laboratory can operationalize with routine analyses. For the Eastern Dry Zone, where Alfisols are marginal and rainfall unreliable, squeezing an extra fifth of the harvest from the same fertilizer investment could meaningfully change the economics of legume farming. The study, funded by the Indian Council of Agricultural Research under grant CRP-18 and conducted with collaborators from the ICAR-Indian Institute of Soil Science in Bhopal and the ICAR-Agricultural Technology Application Research Institute in Kolkata, establishes a replicable template: build a fertility gradient, calibrate against yield and uptake, validate in farmers’ conditions, and hand the resulting equations to the soil testing laboratories that serve the fields. If similar calibrations are extended to the region’s other crops, the era of the blanket recommendation may finally be drawing to a close.

Subject of Research: Soil test crop response-based targeted yield fertilizer prescription for field bean on Alfisols in Karnataka

Article Title: Development and validation of STCR-based fertilizer prescription equations for field bean under Alfisol conditions of the Eastern Dry Zone of Karnataka

Article References: Rangaiah, K. M., Nagendrachari, A. N., Nanjundappa, S. M., Kasturappa, G., Nagaraju, B., Krishna, P., Srivastava, S., Haokip, I. C., & Dey, P. (2026). Development and validation of STCR-based fertilizer prescription equations for field bean under Alfisol conditions of the Eastern Dry Zone of Karnataka. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09986-6

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09986-6

Keywords: field bean, STCR, targeted yield, fertilizer prescription, Alfisols, Eastern Dry Zone, Karnataka, soil fertility, integrated nutrient management, farmyard manure, nutrient use efficiency, site-specific nutrient management

The study, published in the journal Discover Soil, examined surface soils from an ongoing long-term experiment established in 2015 under a soybean-wheat cropping system. The researchers compared five nutrient management treatments: an unfertilized control, soil test crop response-based fertilizer application (STCR), integrated nutrient management combining 75 percent recommended fertilizer with 25 percent farmyard manure, fully organic nutrient management, and conservation agriculture with recommended NPK plus 90 percent crop residue retention. The experimental soil was a classic Vertisol, a fine clayey, montmorillonitic Typic Haplustert containing 52 percent clay, slightly alkaline at pH 7.8, and initially very low in available phosphorus at just 5.74 kilograms per hectare by Olsen’s method.

What makes Vertisols so difficult for phosphorus management is their mineralogy and chemistry. These soils are dominated by smectitic clays that swell and shrink with moisture, and they carry appreciable calcium carbonate along with abundant exchangeable calcium. In alkaline, calcareous conditions, phosphate ions are adsorbed onto clay surfaces and precipitated as relatively insoluble calcium-phosphate minerals. The result is that only a small fraction of applied fertilizer phosphorus remains available for crop uptake during the growing season, making phosphorus deficiency a major constraint on productivity across tropical and subtropical agriculture.

To quantify how a decade of different management had altered this behavior, the team equilibrated soil samples with a series of potassium dihydrogen phosphate solutions ranging from 0 to 100 milligrams of phosphorus per kilogram, prepared in 0.01 molar calcium chloride at a 1:10 soil-to-solution ratio. After six days of equilibration, the amount of phosphorus retained by each soil was fitted to the Langmuir adsorption isotherm, a model that yields two key parameters: the sorption maximum, which describes how much phosphorus the soil can hold, and the bonding energy constant, which describes how tightly that phosphorus is gripped. The model performed superbly, with coefficients of determination of 0.99 across all treatments, confirming its suitability for characterizing phosphorus retention in these soils.

The differences between treatments were striking. The phosphorus adsorption maximum ranged from 394 to 527 micrograms per gram. The highest values appeared under the STCR treatment and the control, both at 527 micrograms per gram, with conservation agriculture close behind at 526. The lowest value by far was recorded under fully organic management at 394 micrograms per gram, followed by integrated nutrient management at 457. The bonding energy constant told an even sharper story, falling from 0.55 milliliters per microgram under STCR to just 0.10 under organic management. In other words, the organic soil not only held less phosphorus overall but held what remained far more loosely, leaving a larger share free to move into soil solution where roots can access it.

Derived quantities reinforced the pattern. The maximum phosphorus buffering capacity, which measures a soil’s ability to resist changes in solution phosphorus concentration, ranged from 278.13 liters per kilogram under STCR down to 40.57 under organic management. The standard phosphorus requirement, defined as the amount of phosphorus that must be sorbed to maintain a solution concentration of 0.2 milligrams per liter, the threshold generally considered adequate for most crops, followed the same trend: 57.39 milligrams per kilogram under STCR against only 7.33 under organic management. Practically, this means the organic soil needed roughly one-eighth as much phosphorus input to keep solution levels adequate, a dramatic improvement in potential fertilizer-use efficiency.

Sequential fractionation, following the classic Chang and Jackson scheme, revealed where the phosphorus actually resided. Calcium-bound phosphorus dominated every treatment, reflecting the inherent calcareous nature of Vertisols, but its share varied enormously. Under the control it accounted for 92.3 percent of the total phosphorus pool, whereas under organic farming it dropped to about 70.7 percent. Meanwhile, aluminum-bound phosphorus rose from roughly 3 to 4 percent under control and STCR to about 14.2 percent under organic management, and iron-bound phosphorus climbed from 2 to 4 percent to between 8.5 and 10 percent under organic and conservation systems. The combined pool of relatively labile fractions, including soluble, aluminum-bound, iron-bound, and available phosphorus, increased from about 7.7 percent in the control to 29.3 percent under organic farming, nearly a fourfold shift toward plant-accessible forms.

The mechanism behind this transformation lies in soil organic matter chemistry. As farmyard manure and crop residues decompose, they release low-molecular-weight organic acids and dissolved organic carbon that compete with phosphate ions for adsorption sites on clay and mineral surfaces. These compounds also chelate calcium and iron ions in solution, reducing the precipitation reactions that convert soluble phosphorus into insoluble calcium phosphates. Organic inputs simultaneously stimulate microbial communities and phosphatase enzymes that mineralize organic phosphorus into plant-available inorganic forms. The chemical data mirrored these processes: organic carbon reached 1.21 percent under organic management and 1.15 percent under conservation agriculture, compared with 0.64 percent in the control, while available phosphorus under organic treatment soared to 80.0 kilograms per hectare against 9.53 in the control. Soil pH also dipped slightly under organic and integrated management, from 8.09 in the control to around 7.87, consistent with organic acid release during decomposition.

The implications extend well beyond a single research farm. Because phosphorus is a finite, mined resource with rising costs and significant environmental risks when it accumulates excessively and runs off into waterways, any management system that reduces fixation losses carries both economic and ecological weight. The authors suggest that standard phosphorus requirement measurements could be used to tailor fertilizer recommendations to a soil’s actual buffering characteristics, avoiding over-application in lightly buffering soils and under-application in strongly fixing ones. Integrated nutrient management and conservation agriculture, by building organic carbon and moderating phosphorus retention, offer sustainable pathways for the Vertisol-based cereal and pulse systems that feed much of Central India.

The researchers caution that their findings come from a single long-term experiment at one Vertisol location, and that validation across diverse Vertisol regions, cropping systems, and climates would strengthen the conclusions. Even so, the message is compelling: a decade of patient organic inputs and residue retention measurably rewired the phosphorus chemistry of some of the world’s most phosphorus-hungry soils, converting locked-up reserves into forms that crops can actually use. For farmers wrestling with the twin burdens of fertilizer cost and declining soil fertility, the black soils of Bhopal suggest that the cheapest phosphorus may be the kind already in the ground, waiting to be released.

Subject of Research: Long-term effects of nutrient management on phosphorus sorption and fractionation in calcareous Vertisols

Article Title: Long-term nutrient management influences phosphorus sorption, buffering capacity, and fractionation in Vertisols of Central India

Article References: Davel, P., Gurav, P. P., Vinaykumar, L. N., Meena, B. P., Biswas, A. K., Shirale, A. O., Jain, R. C., Srivastava, S., Vishwakarma, A. K., Das, H., Shinogi, K. C., Yadav, D. K., & Shibin, M. (2026). Long-term nutrient management influences phosphorus sorption, buffering capacity, and fractionation in Vertisols of Central India. Discover Soil, 3(1), Article 174. https://doi.org/10.1007/s44378-026-00325-7

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00325-7

Keywords: phosphorus sorption, Vertisols, Langmuir isotherm, phosphorus fractionation, organic farming, conservation agriculture, integrated nutrient management, soil fertility, buffering capacity, Central India, soil organic carbon, nutrient use efficiency

The research, published in the Journal of Agriculture and Food Research, grew the semi-dwarf Basmati variety PB 1692 during the kharif seasons of 2022 and 2023 in a split-plot experiment. Five nitrogen regimes were tested against four zinc fertilization strategies, from conventional prilled urea at the full recommended dose of 130 kilograms of nitrogen per hectare to reduced doses supplemented with foliar sprays of liquid nano-urea, nano-zinc oxide, and even a cyanobacterial formulation based on Anabaena torulosa. From 300 plot-level observations, the team compiled 22 variables spanning plant height, tiller density, dry matter production, panicle characteristics, and nitrogen and zinc concentrations and uptake in straw, hull, bran, and white rice kernels.

Those variables became the training ground for five machine learning algorithms: multiple linear regression, support vector regression, k-nearest neighbors, gradient boosting, and random forest. The researchers applied recursive feature elimination with 10-fold cross-validation to select the most informative predictors and used exhaustive grid-search optimization to tune the random forest’s hyperparameters, fixing the number of trees at 500 after confirming error convergence. A strict bias-variance criterion, requiring the difference in R-squared between training and cross-validation to stay below 10 percent, guarded against overfitting, and final performance was confirmed on a held-out test set using Lin’s concordance correlation coefficient.

The random forest emerged as the clear champion. It achieved R-squared values of 0.97 in 2022 and 0.96 in 2023, with root mean square errors of just 0.08 tonnes per hectare and mean absolute errors of 0.063, outperforming support vector regression, which averaged an R-squared of 0.92, and leaving k-nearest neighbors, the weakest performer at R-squared values between 0.73 and 0.80, far behind. Taylor diagrams, which simultaneously display correlation, standard deviation, and error, visually confirmed the random forest’s dominance in both training and prediction stages across both seasons.

More revealing than raw accuracy was what the model considered important. Using two feature-importance metrics, the percentage increase in mean squared error and the increase in node purity, the random forest ranked total nitrogen uptake, grain nitrogen concentration, dry matter production, and total zinc uptake as the dominant drivers of yield. Plant height and tiller counts, traits farmers and agronomists often watch closely, carried relatively little predictive weight. The message is biologically coherent: fertilizer application alone guarantees nothing unless the crop actually captures, assimilates, and remobilizes nitrogen into grain, processes that depend on root architecture, photosynthetic capacity, and source-sink coordination during grain filling.

The field results reinforced that insight. The full recommended dose of 130 kilograms of nitrogen per hectare produced the highest grain yields, 4.79 and 4.52 tonnes per hectare in 2022 and 2023, gains of 25.4 and 28.0 percent over the unfertilized control, along with nitrogen uptake of roughly 120 kilograms per hectare and zinc uptake about 35 percent higher than in unfertilized plots. But the treatment combining 97.5 kilograms of soil nitrogen with two foliar sprays of nano-urea produced statistically equivalent yields, demonstrating that a 25 percent reduction in mineral nitrogen input could maintain productivity when paired with the nanoscale foliar supplement.

Zinc fertilization delivered its own measurable benefits. Foliar sprays of 0.1 percent nano-zinc oxide produced the strongest yield attributes, raising panicle weight by 9.6 percent and grains per panicle by 4.1 percent on a two-year mean basis compared with no zinc, and adding roughly 0.2 tonnes of grain per hectare. Zinc uptake reached nearly 600 grams per hectare under the nano-zinc treatment, a 10.7 percent increase over the control. Because zinc deficiency remains a widespread human nutritional problem, agronomic biofortification of rice grain through such foliar strategies carries significance well beyond the yield column.

The climate accounting added a compelling twist. Using the CCAFS Mitigation Option Tool, the researchers estimated greenhouse gas emissions in carbon dioxide equivalents, incorporating both fertilizer production and field-induced emissions. The 97.5-kilogram nitrogen plus nano-urea treatment cut absolute emissions by 188.9 kilograms of carbon dioxide equivalent per hectare, a 6.55 percent reduction, and lowered emission intensity by 3.22 to 4.62 percent relative to the full recommended dose, all without a yield penalty. Deeper cuts to 65 kilograms of nitrogen, whether with nano-urea or conventional urea, saved more emissions, 377.2 and 323.5 kilograms per hectare respectively, but at a significant cost in grain, defining the agronomic boundary of an acceptable trade-off. Strikingly, the unfertilized control had the worst emission intensity per kilogram of grain, showing that yield and climate goals are inseparable in irrigated rice.

The study’s authors are candid about limitations. Weather variables were excluded because the two experimental seasons were climatically stable, yet weather remains a major determinant of crop performance, and future models should incorporate it. The work spanned only two years and a single rice variety, and several of the most powerful predictors, including total nutrient uptake and biomass, require destructive sampling and laboratory analysis that are impractical for routine farm use. The researchers argue that the next step is to build simplified, transferable frameworks using readily available inputs such as weather, soil data, fertilizer records, and remotely sensed vegetation indices, potentially augmented by drone observations and process-based crop models.

Even with those caveats, the study marks a meaningful advance in precision agriculture. Most machine learning yield studies lean on satellite or meteorological data; this one integrated field-measured agronomic, physiological, and nutrient variables within a single interpretable framework, and the model’s importance rankings aligned with established crop physiology rather than statistical artifacts. For a crop on which billions of people depend, the combination of a random forest that explains 96 to 97 percent of yield variability and a fertilizer strategy that trims nitrogen and emissions without sacrificing harvest offers a rare, quantified win for both food security and the climate.

Subject of Research: Machine learning prediction of rice grain yield and yield-emission trade-offs under nitrogen and zinc fertilization in a two-year field experiment

Article Title: Rice yield prediction using machine learning models and yield-emission trade-offs from field experiment

Article References: Reddy, K. S., Shivay, Y. S., Prasanna, R., Kumar, D., Peramaiyan, P., Mandi, S., Nayak, S., Baral, K., Alekhya, G., Reddy, K. S., & Borate, R. B. (2026). Rice yield prediction using machine learning models and yield-emission trade-offs from field experiment. Journal of Agriculture and Food Research, 31, Article 103309. https://doi.org/10.1016/j.jafr.2026.103309

Image Credits: AI Generated

DOI: 10.1016/j.jafr.2026.103309

Keywords: rice, machine learning, random forest, nitrogen uptake, nano-urea, zinc biofortification, greenhouse gas emissions, yield prediction, precision agriculture, nutrient use efficiency, Basmati rice, sustainable farming

The research, led by Adebayo Jonathan Adeyemo of the Federal University of Technology, Akure, together with collaborators from institutions in Nigeria, Brazil and Belgium, was designed to test whether locally sourced soil amendments could shift the fundamental chemistry of a tropical Alfisol quickly enough to matter for the growing season that follows. The stakes are considerable. Soil acidity and weak cation-holding capacity reduce nutrient-use efficiency in highly weathered tropical soils, undermining progress toward the United Nations Sustainable Development Goals on zero hunger, responsible consumption and terrestrial ecosystem health. When a soil cannot hold onto the nutrients it receives, every kilogram of fertilizer applied is a partial loss to leaching and fixation.

The experimental design was deliberately practical. The team laid out a 3 × 3 split-plot field trial with three replications, a structure that allows the independent and combined effects of two classes of amendment to be separated statistically. Main plots received one of three fertilizer designations: no mineral input, locally sourced potassium-bearing rock dust, or plots designated for later application of conventional NPK 15-15-15 fertilizer. Within each main plot, subplots received one of three organic treatments: no organic amendment, field-stabilized poultry manure, or fresh Tithonia diversifolia biomass, a plant widely known among West African farmers as a green manure because of its unusually high nutrient content. Baseline soil samples were taken before anything was applied, and okra was sown at the time of amendment incorporation.

Crucially, the researchers took their soil measurements at two weeks after amendment, before any NPK fertilizer had been applied to the plots designated for it. That sequencing decision matters for interpretation: the NPK-designated plots are reported as NPK-pre and cannot be read as evidence of NPK effects. This careful phrasing reflects a discipline that field trials often lack, and it protects the study’s central claims from being overstated. Everything reported in the paper describes the short-term chemical response of the soil to rock dust and organic materials alone.

The headline result concerns potassium, the nutrient whose shortage most clearly defines these soils. At two weeks after amendment, plots treated with potassium-bearing rock dust recorded an average exchangeable potassium concentration of 1.67 centimoles of charge per kilogram of soil, compared with just 0.49 in untreated control plots. That is more than a threefold increase in the pool of potassium held on soil exchange sites, the fraction most immediately available for root uptake. The operational cation-exchange capacity, a measure of the soil’s total ability to hold positively charged nutrients, rose to 8.54 cmolc per kilogram under rock dust, against 4.63 in the controls, nearly doubling the soil’s buffering and storage capacity.

The organic amendments produced their own distinctive signature, particularly on acidity. Poultry manure reduced the baseline-referenced hydrogen ion ratio from 1.07 under no organic amendment to 0.45, a substantial tempering of soil acidity, while lifting the operational cation-exchange capacity to 7.48 cmolc per kilogram. This dual action is chemically coherent: manure supplies basic cations and decomposable organic matter whose charged breakdown products add exchange sites, simultaneously neutralizing acid cations and increasing the soil’s capacity to retain the nutrients that replace them. Fresh Tithonia biomass, though valued as a green manure, behaved differently in combination with rock dust, a nuance that emerges most clearly in the interaction analysis.

Statistically, the most striking finding was the significant interaction between fertilizer designation and organic amendment for exchangeable potassium, with a P value of 0.027. Within rock-dust plots, poultry manure produced the highest exchangeable potassium of any combination, 1.90 cmolc per kilogram, exceeding both rock dust alone at 1.54 and rock dust combined with Tithonia at 1.57. In other words, the best result came not from any single input but from the synergy between mineral and organic sources. The authors suggest a plausible mechanism: the organic matter may enhance the dissolution of potassium-bearing minerals in the dust while adding its own organic-associated potassium pools, and its decomposing residues help the soil retain the released potassium against leaching.

Not every measured property responded to the combined treatments. The interactions were not statistically significant for operational cation-exchange capacity, which showed a P value of 0.145, or for effective cation-exchange capacity, at 0.085. Exchangeable acidity, by contrast, responded in an interactive fashion with high significance, at P below 0.001, indicating that the amendment combinations modified the acid cation fractions of the soil in ways that depended on which mineral and organic inputs were paired. Electrical conductivity, a proxy indicator for soluble salt accumulation, remained between 0.03 and 0.04 decisiemens per meter throughout, an extremely low range that rules out any short-term salinity build-up from the amendments, a concern sometimes raised with repeated manure application.

The authors are careful about what their findings do not establish. The study captures a fourteen-day chemical snapshot; it does not demonstrate long-term potassium retention, crop uptake of the released nutrients, or yield benefits, all of which would require seasons of monitoring. Dissolution of rock dust in tropical soils is generally a slow process, and whether the early gains in exchangeable potassium persist, deepen, or wash away depends on rainfall patterns, continued mineral weathering, and crop removal over time. The team frames its contribution accordingly: as evidence of short-term modification of acidity and exchangeable-cation status without evidence of salinity problems, a foundation on which longer-term agronomic studies can now build.

Even with those caveats, the implications for smallholder agriculture in the region are hard to ignore. Nigeria imports the bulk of its potash fertilizer at considerable foreign-exchange cost, while quarries and mining operations in the country generate potassium-bearing rock waste that is largely unused. If further research confirms that such rock dust, combined with manure that farmers already produce, can durably rebuild the cation-exchange machinery of degraded Alfisols, the result would be a circular soil-fertility strategy built entirely from local materials. For the moment, the study stands as a carefully documented proof of concept: in a weathered Nigerian Alfisol, ground potassium rock and poultry manure measurably and significantly enriched the soil’s potassium and cation-holding capacity within two weeks, pointing the way toward more self-reliant and sustainable soil management across the humid tropics.

Subject of Research: Short-term effects of potassium-bearing rock dust and organic amendments on soil acidity and cation retention in a tropical Alfisol

Article Title: Soil acidity, cation balance, exchangeable potassium status and cation retention capacity under K-bearing rock dust–organic amendment systems in a tropical Alfisol of southwestern Nigeria

Article References: Adeyemo, A. J., Akinnagbe, A. E., Adeoye, M. O., Adesida, P. A., Agele, S. O., Adejoro, S. A., Oluwagbemi, I. A., Ewulo, B. S., de Freitas, D. A. F., Shittu, O. S., Awodun, M. A., Oyun, M. B., & Oliveira, D. M. D. S. (2026). Soil acidity, cation balance, exchangeable potassium status and cation retention capacity under K-bearing rock dust–organic amendment systems in a tropical Alfisol of southwestern Nigeria. Discover Sustainability. https://doi.org/10.1007/s43621-026-04688-3

Image Credits: AI Generated

DOI: 10.1007/s43621-026-04688-3

Keywords: rock dust, poultry manure, Tithonia diversifolia, soil acidity, exchangeable potassium, cation-exchange capacity, tropical Alfisol, soil fertility, Nigeria, sustainable soil management, nutrient-use efficiency, Soil

The study’s central challenge was to determine whether automated, data-driven scheduling of irrigation and fertigation could actually perform under genuine field conditions, not just in laboratory prototypes. Farmers in Bangladesh typically apply fertilizers and pesticides without knowing whether they are necessary, and more than 80 percent of the country’s irrigation pumps run on costly diesel. Eggplant, a year-round crop grown on roughly 51,165 hectares and a key income source for rural households, suffers an estimated 30 percent yield loss each year to pests and diseases, making it an ideal test case for a system that promises to deliver precisely measured inputs at precisely the right moments.

The system the researchers built combined a sensor node, fitted with soil and meteorological instruments, with an automation node that controlled drip irrigation lines and fertigation pumps. Soil moisture probes, electrical conductivity sensors, and weather stations streamed data wirelessly to the cloud, where a decision-making algorithm determined when to irrigate and when to inject nutrients. A mobile application gave operators remote access to real-time field information, allowing the entire crop to be monitored and controlled from anywhere. The logic was straightforward but finely tuned: irrigation began when soil moisture fell to 13.3 percent, corresponding to the management allowable depletion level, and stopped once moisture reached 26.6 percent, the soil’s field capacity.

Fertigation followed an equally disciplined schedule. On predetermined days after planting, specifically days 20, 40, 60, and 80, the system checked the soil’s electrical conductivity before acting. If conductivity exceeded 0.5 decisiemens per meter, considered unfavorable for plant growth in non-saline soils, fertigation was skipped entirely. Otherwise, separate pumps drew urea and potash solutions into a mixing tank, each motor calibrated to a flow rate of 16.6 milliliters per second so that exactly 20 liters of solution reached the field per event. These doses corresponded to 60 percent of the recommended nitrogen and 70 percent of the recommended potassium, a deliberate reduction designed to test whether precision placement could compensate for smaller quantities.

To evaluate the technology, the team laid out a randomized complete block design with four treatments, each replicated twice. The IoT-based system was compared against BARI-recommended eggplant production practices, a drip fertigation system using pan evaporation-based scheduling, and traditional farmer practices that had been documented through focus group discussions and interviews in the Narshingdi, Jamalpur, and Tangail districts. Traditional plots received surface flooding irrigation at 15 to 20 day intervals, full or excessive fertilizer doses, and frequent pesticide applications. Soil water content was tracked gravimetrically throughout the season at depths from 0 to 30 centimeters, and seasonal actual water use was calculated from irrigation, effective rainfall, and changes in stored soil water.

The yield results were striking in their evenness. The IoT-managed plots produced 30.99 tonnes of marketable fruit per hectare, statistically similar to the 31.73 tonnes achieved by drip fertigation and marginally above the 30.08 tonnes from traditional practice, a gain of roughly 3 percent. The advantage came through better fruit length, diameter, and unit weight, driven by the steady, adequate water supply that sensor-driven scheduling maintained. Traditional plots, by contrast, suffered from inadequate and poorly timed irrigation. The finding aligns with earlier studies showing that smart drip irrigation boosted banana yields by 15 percent and sweet corn yields by 12.8 percent, and with a Chinese meta-analysis finding that drip fertigation raised crop yields by 6 to 40 percent compared with flood irrigation and broadcast fertilization.

Water savings were the headline figure. The IoT system used 63 percent less irrigation water than traditional practices while improving water use efficiency by 172.7 percent, and irrigation water use efficiency rose in proportion. Total seasonal water use in the IoT and drip fertigation plots was nearly identical, and both were far below the furrow-irrigated BARI plots and the flood-irrigated traditional plots. The pattern echoes results from other crops: IoT-based drip systems cut water use by 65 percent in sweet potato, 50 percent in a pear orchard, and 30 percent in field tomatoes. Soil moisture data also revealed that the sensor-managed plots held less water than traditional ones, yet crops thrived, indicating that eggplants, which are moderately deep-rooted, could extract moisture from the 10 to 30 centimeter layer while the system avoided the waste of overwatering.

Nutrient efficiency improved just as dramatically. By delivering urea and potash directly to the root zone in water-soluble form, the IoT system saved 50 percent of urea and 53 percent of potassium relative to traditional practice, while nitrogen use efficiency rose 106.9 percent and potassium use efficiency rose 118 percent. The gain comes from basic physics and plant physiology: conventional flood irrigation washes nitrogen and potassium away in surface runoff, whereas drip fertigation places the right nutrient at the right place at the right time, maximizing uptake and minimizing loss. Pesticide costs also fell by 53 percent, and labor demand dropped by 33 percent, since irrigation and fertigation ran automatically without field visits.

Economics told a more nuanced story. When all gross costs were counted, including the substantial initial investment in sensors, automation hardware, software, and drip accessories, the IoT system’s benefit-cost ratio was initially lower than traditional farming during the first crop cycle. But measured against variable costs alone, the IoT system was clearly superior, with total variable costs about 18 percent lower than conventional production thanks to savings on labor, irrigation, fertilizer, and pesticides. At an 8.5 percent discount rate, the system’s benefit-cost ratio was 1.17, its internal rate of return exceeded the discount rate, and the researchers project that the initial investment would be recovered after roughly five crop cycles, assuming two cycles per year. A sensitivity analysis confirmed that the system remains profitable even when costs rise or returns fall.

The authors are candid about the obstacles to scaling. IoT sensors are scarce in the local market, import tariffs inflate prices, and repeated sensor calibration adds expense and complexity. For smallholder farmers facing high upfront costs, adoption will be difficult without policy support, and the researchers recommend removing taxes on IoT devices, offering incentives, and conducting public field demonstrations across different locations. They also suggest that Long Range Wide Area Network technology, which transmits over long distances with low power, could overcome connectivity gaps in remote areas lacking Wi-Fi or 4G coverage. The study covered a single season at a single site, so the team recommends multi-season, multi-location trials to confirm scalability. Still, the demonstration stands: a sensor-driven irrigation network, working unattended under South Asian field conditions, delivered eggplant yields on par with intensive conventional practice while saving nearly two-thirds of the water and half the fertilizer, a combination that could reshape how resource-constrained farming systems feed a growing population.

Subject of Research: IoT-enabled sensor-based automated drip irrigation and fertigation for water- and nutrient-efficient eggplant production in Bangladesh

Article Title: Field evaluation of sensor-driven drip irrigation systems for eggplant production

Article References: Sarker, K. K., Karim, N. N., Islam, A. T., Ahmed, I., Uddin, M. N., Hasan, S., Hoque, M. R., Ali, M. T., Kabir, M. S., Biswas, S. K., Hossain, M. A., & Mahboob, M. G. (2026). Field evaluation of sensor-driven drip irrigation systems for eggplant production. BMC Agriculture, 2(1), Article 7. https://doi.org/10.1186/s44399-026-00031-3

Image Credits: AI Generated

DOI: 10.1186/s44399-026-00031-3

Keywords: IoT, precision agriculture, drip irrigation, fertigation, eggplant, water use efficiency, nutrient use efficiency, smart farming, Bangladesh, soil moisture sensors, benefit-cost ratio, sustainable agriculture