The factorial experiment, summarized in the study abstract, tested nitrogen rates of 0, 70, 150 and 250 kg N ha⁻¹ with biochar rates of 0 and 15 t ha⁻¹. Researchers measured nitrate leaching and assessed chlorophyll, relative water content and stomatal characteristics. Rhizome analyses covered phenolics, flavonoids, curcuminoids, oleoresin and antioxidant activity. Nitrogen rate, biochar rate and their interaction significantly influenced physiological traits and nitrate leaching, with the reported analysis giving p < 0.001.

Without biochar, measured nitrate loss rose from 360 mg N pot⁻¹ at the zero-nitrogen treatment to 2,906.67 mg N pot⁻¹ at 250 kg N ha⁻¹. With biochar, nitrate loss was 180–280 mg N pot⁻¹ across the tested nitrogen levels. The N150B15 treatment, combining 150 kg N ha⁻¹ with 15 t ha⁻¹ of biochar, recorded the highest chlorophyll content at 41.99 SPAD and relative water content at 92.61%. It also had the highest measured concentrations of phenolics at 39.65 mg gallic acid equivalents g⁻¹, flavonoids at 16.22 mg catechin equivalents g⁻¹ and curcuminoids at 61.67 mg curcuminoid equivalents g⁻¹. Oleoresin reached 61.89% in that treatment.

Antioxidant measurements were also highest under N150B15: 75.03% 2,2-diphenyl-1-picrylhydrazyl activity and 45.56 mg ascorbic acid equivalents g⁻¹ of ferric reducing antioxidant power. The abstract therefore reports improved measured physiology and rhizome phytochemical quality, together with reduced nitrate leaching, for moderate nitrogen combined with biochar in the tested sandy soil. These results are limited to a greenhouse pot experiment using one type and application rate of coffee husk biochar, one soil context and four nitrogen rates. The authors state that field-scale validation using diverse biochar types and rates is required before broader recommendations can be made; the supplied evidence does not establish field performance or wider applicability.

Subject of Research: Effects of coffee husk biochar and nitrogen rates on nitrate leaching and turmeric physiology and rhizome quality in a sandy-soil pot experiment

Article Title: Biochar and nitrogen effects on nitrate leaching, physiological performance, and rhizome quality of turmeric (Curcuma longa L.) in sandy soil

Article References: Eshetu, T., Dessalegn, E., Belew, D., Gobena, A., & Nigusie, A. (2026). Biochar and nitrogen effects on nitrate leaching, physiological performance, and rhizome quality of turmeric (Curcuma longa L.) in sandy soil. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09940-6

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09940-6

Keywords: turmeric, Curcuma longa, biochar, nitrogen fertilization, nitrate leaching, greenhouse pot experiment, sandy soil, rhizome quality, curcuminoids, chlorophyll, nitrogen, effects

The study was conducted over the 2023 and 2024 growing seasons at the Central Laboratory for Agricultural Climate of the Agricultural Research Center in Giza Governorate, Egypt. Uniform geranium seedlings were planted in plastic pots in sandy soil during the first week of March, thinned to three plants per pot after 45 days and maintained in a greenhouse. Plants were harvested twice in each season, at 90 and 180 days after planting, with the second harvest recording higher values for most growth and yield measures.

Five treatments were evaluated in a completely randomized design with four replicates per treatment. The control received a complete Hoagland nutrient solution, while the other treatments received weekly applications through irrigation water of Azolla extract at 50% or 75%, or Moringa leaf extract at 5% or 10%. Each replicate consisted of eight pots with three plants per pot. Fresh Azolla extract was prepared by boiling washed biomass in distilled water, whereas fresh Moringa extract was produced by blending leaves with distilled water, filtering the mixture and centrifuging it at 8,000 × g for 15 minutes.

Both plant-based extracts significantly enhanced vegetative growth relative to the control, with 10% Moringa producing the highest values. In the second harvest, plants receiving this treatment reached 114.5 cm in the first season and 119.6 cm in the second, compared with fold increases of 2.5 and 2.6. Branch numbers increased by 2.1- to 2.3-fold, fresh biomass by 2.0- to 2.1-fold and dry biomass by 2.0- to 2.1-fold. Treatment and harvest effects on the growth variables were generally significant at P ≤ 0.001, although some treatment-by-harvest interactions were not significant.

Photosynthetic pigments also increased under extract application. With 10% Moringa at the second harvest, chlorophyll a reached 0.8 and 0.9 mg g−1 fresh weight, chlorophyll b reached 0.4 and 0.5 mg g−1, and carotenoids reached 0.6 mg g−1 in the two seasons. Compared with the control, the treatment was associated with 1.7-fold higher chlorophyll a, 2-fold higher chlorophyll b and 1- to 1.3-fold higher carotenoids. The treatment and harvest effects were significant for chlorophyll a at P ≤ 0.001, for chlorophyll b at P ≤ 0.05 and for carotenoids at P ≤ 0.01, without significant treatment-by-harvest interactions for these pigments.

Essential oil content was higher at the first harvest, but essential oil yield per plant was greater at the second harvest. The highest oil yield under 10% Moringa was 1.4 g per plant in the first season and 1.7 g per plant in the second, representing increases of 1.4- to 2.3-fold relative to the control; oil content rose by 1.1- to 1.4-fold. Gas chromatographic analyses identified citronellol, geraniol and α-gurjunene as major constituents, with oxygenated monoterpenes forming the dominant chemical group. Under 10% Moringa at the second harvest, citronellol reached 774.2 mg per plant, geraniol was associated with a 3.3-fold increase over the control, α-gurjunene increased 2.7-fold and total oxygenated monoterpenes increased 2.3-fold.

Leaf chemical measures generally rose with extract treatment and were higher at the second harvest. At the second harvest with 10% Moringa, total phenolics reached 16.6 and 19.3 mg g−1 dry weight in the two seasons, 1.5- and 1.6-fold above control values. Flavonoids increased by 1.6- to 1.9-fold, while free-radical scavenging inhibition reached 62.34% and 60.2%, representing 1.7- and 1.8-fold increases. Total carbohydrate content was reported as 1.3-fold higher than the control, and crude protein content increased by 1.5-fold in the first season and 1.8-fold in the second.

The treatments also increased plant-tissue concentrations and total uptake of nitrogen, phosphorus and potassium. With 10% Moringa at the second harvest, nitrogen uptake reached 3.6 and 3.7 g per plant in the two seasons, compared with fold increases of 3.1- to 3.6-fold over control. Potassium uptake increased by 2.9- to 3.3-fold, while phosphorus uptake was reported as 5- to 25-fold higher. Because larger nutrient uptake figures reflect both tissue concentrations and total biomass, these values cannot be interpreted independently of the observed increase in plant growth.

The authors proposed that the extracts improved geranium performance through effects on nutrition, photosynthetic activity and secondary metabolism, while successive cutting stimulated regrowth and altered physiological and biochemical processes. They also cautioned that larger-scale field and economic studies are needed to establish commercial feasibility, and that the industrial applicability of the changes in essential oil composition requires further research. The findings therefore come from a greenhouse experiment using potted plants over two seasons, rather than from an open-field trial or commercial production assessment, and the tested extract concentrations should not be assumed to produce the same results under field conditions.

Subject of Research: Effects of Azolla and Moringa extracts on geranium growth, physiology, nutrients and essential oil production in sandy soil

Article Title: Response of geranium to soil applications of Azolla and Moringa extracts: effects on growth, essential oil and physiological parameters

Article References: Abd-Rabbu, H. S., Aboud, F. S., & Khalid, K. A. (2026). Response of geranium to soil applications of Azolla and Moringa extracts: effects on growth, essential oil and physiological parameters. BMC Plant Biology, 26(1), Article 1623. https://doi.org/10.1186/s12870-026-09900-0

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09900-0

Keywords: geranium, Azolla, Moringa, sandy soil, biostimulants, essential oil, plant growth, nutrient uptake, greenhouse study, Response, soil, applications

The research, led by Xiaoxian Duan, Quanjiu Wang, Weiyi Mu and colleagues at Xi’an University of Technology, set out to test whether the two amendments work better together than either alone. Organic fertilizer supplies carbon, nutrients and microbial substrate, while sodium carboxymethyl cellulose, or CMC-Na, is a water-soluble, biodegradable polymer derived from cellulose that can bind soil particles, improve water retention and stabilize aggregates. The team reasoned that the polymer could provide the structural scaffolding that sandy soils lack, while the organic fertilizer would fuel the biological and chemical recovery, and that the combination might unlock synergies neither material could achieve on its own.

To test this, the researchers ran a continuous three-year field experiment in southern Xinjiang, comparing plots treated with organic fertilizer alone, CMC-Na alone, and the two applied together, against untreated control plots. They systematically evaluated soil physical properties, enzyme activities, organic carbon content and the availability of nitrogen, phosphorus and potassium throughout the top 40 centimeters of the soil profile. The most striking improvements appeared in the 0 to 20 centimeter topsoil layer, the zone where cotton roots are most active and where drip irrigation and fertilization concentrate their effects.

The numbers from the optimal combined treatment, labeled O2C2, are substantial. Compared with the control, soil bulk density, a measure of how tightly packed and compacted the soil is, decreased by 7.00 to 8.54 percent. Lower bulk density means looser soil, easier root penetration and more space for air and water. At the same time, total porosity rose by 9.33 to 11.93 percent, and the content of water-stable aggregates larger than 0.25 millimeters, the small clumps of soil that resist being washed apart and that underpin healthy soil structure, increased by 13.86 to 15.08 percent. Available water content, the reservoir of moisture plants can actually draw on, climbed by 13.50 to 14.52 percent.

The chemical and biological changes were equally dramatic. Soil organic carbon, the backbone of soil fertility and a key indicator of long-term soil health, surged by 72.76 to 90.35 percent under the combined treatment, while alkali-hydrolyzable nitrogen, a measure of the nitrogen readily available to plants, rose by 23.15 to 28.83 percent. The researchers also tracked soil enzyme activities, which reflect the intensity of microbial processes that cycle nutrients through the soil, and found that the combined treatment maximized the overall soil quality index, a composite score integrating physical, chemical and biological indicators.

Crucially, the soil improvements were not merely cosmetic. Cotton plants growing in the amended soils showed markedly better root vigor, a measure of the physiological activity and health of the root system, which increased by 14.36 to 25.79 percent relative to the control. Vigorous roots are the engine of crop productivity in arid environments, because they determine how effectively a plant can capture water and nutrients from a finite and often hostile soil volume. The enhanced root performance translated into a 13.01 to 16.79 percent increase in seed cotton yield, the raw harvested product before ginning.

To understand which changes mattered most, the team applied partial least squares path modeling, a statistical technique that can trace how different sets of variables influence one another along hypothesized causal chains. The analysis revealed that the improvement of topsoil physical properties was the primary driver of the overall soil quality enhancement, with a path coefficient of 0.776, indicating a very strong influence. In other words, the structural repair of the sandy soil, its loosened density, increased porosity and stabilized aggregates, was the foundation on which the chemical and biological gains were built.

The path modeling also identified the core mechanism linking soil treatment to harvest: a sequential pathway running from soil quality index to root vigor and finally to yield. Better soil structure and fertility create a more favorable habitat for roots; healthier, more active roots capture more water and nutrients; and better-supplied plants produce more cotton. This chain, the authors conclude, is the mechanism by which co-application of organic fertilizer and CMC-Na sustains stable, high cotton yields in sandy agroecosystems, by optimizing physical structures and simultaneously activating the nutrient and biological dynamics of the soil.

The findings carry weight well beyond a single experimental field. Southern Xinjiang’s cotton belt relies heavily on mulched drip irrigation, a system that delivers water and fertilizer precisely but that depends on the soil being able to retain and redistribute what it receives. In coarse sandy soils, that retention is the weak link, and previous studies by overlapping research groups have explored related strategies, including combining carboxymethyl cellulose with biochar to improve water retention and aggregate stability in desert soils, and applying the polymer in coastal saline-alkali croplands. The new work extends this line of research by quantifying, over three consecutive seasons, how the polymer performs when paired with organic fertilizer and by formally modeling the causal chain from soil physics to crop yield.

For farmers and soil managers in arid regions, the study suggests that amending sandy soils is most effective when structural and biological interventions are combined rather than applied in isolation. The cellulose-based additive addresses the physical fragility that makes sandy soils leak water and nutrients, while the organic fertilizer rebuilds the carbon reserves and microbial activity that sustain nutrient supply over time. Because CMC-Na is biodegradable and organic fertilizers can be produced from agricultural and animal waste, the approach also aligns with broader goals of sustainable agriculture, turning a waste-derived polymer and recycled nutrients into a durable upgrade of one of the world’s most challenging farming environments. As cotton remains a cornerstone of the regional economy, the demonstration that a 13 to 17 percent yield gain can be achieved by repairing the soil itself offers a practical blueprint for sustaining production on fragile desert farmland.

Subject of Research: Co-application of organic fertilizer and sodium carboxymethyl cellulose to improve sandy soil quality and cotton yield in southern Xinjiang

Article Title: Co-application of organic fertilizer and sodium carboxymethyl cellulose improves soil quality and root vigor to sustain cotton yield in sandy fields of southern Xinjiang

Article References: Duan, X., Wang, Q., Mu, W., Ma, C., Sun, Y., & Su, L. (2026). Co-application of organic fertilizer and sodium carboxymethyl cellulose improves soil quality and root vigor to sustain cotton yield in sandy fields of southern Xinjiang. Plant and Soil. https://doi.org/10.1007/s11104-026-09141-y

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09141-y

Keywords: soil quality, organic fertilizer, sodium carboxymethyl cellulose, cotton yield, sandy soil, soil aggregates, root vigor, soil organic carbon, soil bulk density, path modeling, Xinjiang, sustainable agriculture

The study, conducted at the Wiregrass Research and Extension Center in Headland, Alabama, was set up on a Dothan sandy loam in the Coastal Plain region, where more than 85 percent of the soil is sand and organic matter levels are low. The team, led by Ranveer Singh and Jasmeet Lamba of Auburn’s Department of Biosystems Engineering, together with crop scientist Charles Y. Chen and Sushil Adhikari, spread biochar produced by pyrolysis at roughly 980 degrees Celsius at rates of 0, 7.5, 15 and 30 megagrams per hectare, equivalent to 0, 1.1, 2.2 and 4.4 percent by weight of the top soil layer. The biochar was incorporated into the top 50 millimeters of soil after peanut emergence in May 2024, and undisturbed soil cores were collected just before harvest in October 2024.

The centerpiece of the investigation was the X-ray CT scanning, performed with a GE EVO Revolution 128-slice medical scanner at Auburn’s College of Veterinary Medicine. Operating at 140 kilovolts and 210 milliamperes, the scanner produced three-dimensional image stacks of the top 100 millimeters of soil at a resolution of about 0.195 millimeters. The raw grayscale data were then processed in ImageJ, where a local thresholding algorithm was carefully calibrated using artificial pores of known diameter embedded in the soil columns, ensuring that the segmentation of soil matrix and pore space was accurate to within 1.5 percent. From these images the researchers extracted macroporosity, macropore number density and pore circularity, the geometric fingerprints of the soil’s plumbing system.

The results were striking in their subtlety. In the top 50 millimeters, where the biochar had been incorporated, macroporosity showed no significant change at any application rate. But in the layer just below, between 50 and 100 millimeters, the macropore number density dropped dramatically: by 57 percent at the 15-megagram rate and 64 percent at the 30-megagram rate compared with untreated control plots. Pore circularity, a measure of how close pores are to a perfect circle, fell by about 5 percent at the moderate 15-megagram rate in the surface layer, indicating that biochar particles had disrupted the geometry of existing pores, merging them into elongated, irregular cavities rather than leaving them untouched.

The researchers interpret these patterns through two competing mechanisms they call the occupying effect and the expansion effect. Under the occupying effect, biochar particles physically fill existing soil pores, reducing the volume of large, freely draining channels. Under the expansion effect, the biochar’s own inherited internal porosity adds new pore space to the bulk soil. The data suggest that at rates up to about 15 megagrams per hectare, the occupying effect dominates in this sandy soil, while at 30 megagrams per hectare the pore indices began converging back toward control values, hinting that beyond that threshold the expansion effect may take over. The response, the authors argue, is likely a function of the soil-to-biochar ratio.

Perhaps the most intriguing finding concerns where the biochar actually went. Differences in pore indices in the 50-to-100-millimeter layer, below the incorporation depth, point to the preferential downward movement of biochar particles through the coarse pores of the sandy soil. This migration may explain why the amendment failed to deliver the expected benefits: the particles simply did not stay put. Previous studies have documented vertical transport of biochar in coarse-textured soils, and the Auburn team speculates that if biochar particles remained immobile at their depth of incorporation, improvements in bulk density and total porosity might have materialized, as they have in controlled pot experiments where such losses are negligible.

The hydro-physical measurements told a similarly sobering story. Soil water retention curves, generated by combining high-resolution evaporation-method data from HYPROP2 tensiometers in the wet range with WP4C dewpoint measurements extending to oven dryness, showed no significant effect of biochar at any rate or depth. Bulk density, total porosity, wet aggregate stability and plant-available water were all statistically unchanged four months after application. Even the highest dose of 30 megagrams per hectare, a substantial and costly amount, left the soil’s capacity to hold water against gravity and to supply it to plants essentially untouched.

Why did biochar fail here when it has succeeded elsewhere? The authors point to the soil itself. Clay particles, with their high surface area and reactive surfaces, provide the binding sites where organic matter and biochar can knit stable aggregates; sandy soils with low clay and low organic matter offer few such opportunities. Pyrolysis temperature matters too: biochar produced at high temperatures, as in this study, can be hydrophobic, repelling water rather than absorbing it, at least until environmental exposure gradually wears that hydrophobicity down. Other researchers have found that water retention in sandy soils improves only at much higher application rates, in the range of 40 to 65 megagrams per hectare, doses that would be economically prohibitive for most farms.

The implications reach beyond agronomy into environmental policy. Biochar’s ability to reduce nutrient leaching and greenhouse gas emissions depends in part on how it reshapes the soil’s pore network. If biochar occupies large pores and shifts flow from rapid preferential channels to slower matrix flow, solutes spend more time in contact with biochar surfaces and can be adsorbed. But if the expansion effect creates abundant new preferential pathways, contaminants could bypass the amendment entirely. Knowing which regime prevails, at which dose, in which soil, is therefore essential for anyone counting on biochar to deliver its promised environmental services.

The Auburn team is candid that their hypothesis, that biochar would improve the hydro-physical properties of a poorly structured sandy soil within a single growing season, was rejected by the data. They argue that the field needs more refined prescriptions: biochar types and rates matched to specific soil textures, targeted application methods such as banding near the root zone or subsurface placement to reduce runoff losses, and longer observation windows to capture slow structural changes. They also call for micro-CT imaging at micrometer resolution to resolve the pores inside biochar particles themselves, which current medical scanners cannot detect. For now, the message for farmers on sandy ground is one of tempered expectations: biochar remains a promising tool for carbon sequestration, but transforming it into a reliable water-management strategy will require far more precision than simply spreading charcoal and hoping for the best.

Subject of Research: Short-term effects of pine biochar application rates on soil pore networks and hydro-physical properties in sandy soil

Article Title: Elucidating short-term impact of biochar addition on soil pore networks using X-ray computed tomography and soil water retention characteristics

Article References: Singh, R., Lamba, J., Chen, C. Y., & Adhikari, S. (2026). Elucidating short-term impact of biochar addition on soil pore networks using X-ray computed tomography and soil water retention characteristics. Discover Soil, 3(1), Article 102. https://doi.org/10.1007/s44378-026-00252-7

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00252-7

Keywords: biochar, soil pore networks, X-ray computed tomography, macroporosity, soil water retention, sandy soil, pyrolysis, soil physics, peanut production, soil amendment, hydro-physical properties, pore circularity