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

The research team, led by Luiz Henrique Quecine Grande and Moacir Tuzzin de Moraes of the University of São Paulo’s Luiz de Queiroz College of Agriculture, set out to fill a persistent gap in crop modelling. Semi-empirical models that link root elongation to soil penetration resistance and water status exist for soybean, wheat and maize, but no equivalent framework had been built for sugarcane. That omission matters because sugarcane is a semi-perennial crop: its root system is renewed after each harvest and must keep functioning across ratoon cycles lasting three to ten years, exposing it to soil physical constraints far longer than annual crops face. If soil structure shapes how roots respond to stress, then any model that ignores structure risks systematically misjudging how deep and fast sugarcane roots will grow, and therefore how much water they can extract during drought.

To isolate the effect of structure, the team designed an elegant three-way comparison. Soil cores with undisturbed structure were collected from a field trial established in 1993, which compares conventional tillage, last disturbed five years before sampling, with a no-tillage system that had gone 31 years without mechanical disturbance apart from furrow opening at planting. A third treatment consisted of repacked soil, sieved and compressed into cylinders at five bulk densities, deliberately destroying any continuous pore network. The soil itself was a clay-rich Rhodic Eutrudox, an Oxisol with roughly 70 percent clay, typical of Brazil’s premier sugarcane region. Sampling at 0 to 20 centimetres captured the topsoil where most early root activity occurs, and 100 undisturbed cores per tillage system ensured the natural field variability in compaction was represented rather than averaged away.

Each structural condition was then subjected to a matrix of five levels of mechanical stress and five levels of hydric stress. The researchers equilibrated the cores at matric potentials ranging from a wet −5 hPa to a dry −8000 hPa, producing degrees of water saturation between roughly 58 and 95 percent. Pre-sprouted sugarcane seedlings, 60 days old, had their existing root systems carefully removed so that only new, uniform first-order roots of 0.5 to 2 centimetres were transplanted into the cores. After about 95 hours in a growth chamber held at 27 degrees Celsius, the roots were extracted, washed and measured. The elongation rate, expressed in centimetres per day, became the response variable for every combination of structure, compaction and moisture, with a maximum observed rate of 3.62 centimetres per day under stress-free control conditions.

The results revealed a striking hierarchy of vulnerability. In the repacked soil, root elongation collapsed by up to 84 percent as compaction increased, falling from 3.04 to just 0.51 centimetres per day under near-saturated conditions. Conventional tillage soil showed intermediate losses, declining from 2.14 to 0.69 centimetres per day across the same compaction range. The 31-year no-tillage soil, by contrast, lost only about 30 percent of its elongation rate across the entire compactness range from 75 to 95 percent. Under the harshest combination tested, a penetration resistance of about 6.2 megapascals at 95 percent water saturation, roots in no-tillage soil grew 8.2 times faster than in repacked soil and 1.8 times faster than in soil under conventional tillage. Mechanical impedance, the team concluded, was the dominant stress, with water stress acting largely by amplifying it.

The mechanism behind this resilience lies in the pore network. As macropore volume, the fraction of pores larger than 50 micrometres, declined from 0.20 to 0.05 cubic metres per cubic metre, root elongation fell by only 38.5 percent in the no-tillage soil, but by 74.4 percent under conventional tillage and 83.1 percent in repacked soil. Remarkably, roots in no-tillage soil at a macropore volume of 0.05 grew as fast as roots in the other treatments at roughly 0.12, meaning the preserved structure effectively compensated for a loss of more than half the macroporosity. Saturated hydraulic conductivity told the same story: at equivalent macropore volumes, water moved through the structured soils up to 3.3 times faster than through the repacked samples, indicating that the remaining pores in undisturbed soil were better connected and more permeable.

From these data the researchers fitted a three-dimensional Gaussian model expressing root elongation rate as a joint function of penetration resistance and degree of water saturation, one model per structural condition. The models performed well, explaining 47 percent of elongation variability in conventional tillage, 71 percent in no-tillage and 78 percent in repacked soil, with determination coefficients above 0.87 and near-zero bias. The shape of the response surfaces carried the key message: the same nominal physical stress produced very different elongation rates depending on structure. The authors argue this means root elongation functions cannot simply be transferred between soils with contrasting structural histories, a caution that applies directly to the agro-hydrological models, such as Canegro and SWAP, which often assume constant root growth rates regardless of what the soil is doing.

To translate the laboratory measurements into architectural consequences, the team integrated their stress functions into RootBox, a three-dimensional functional-structural root model. Simulating 45 days of growth at a moderate water saturation of 81 percent, they found rooting depth reached 31 centimetres in the no-tillage scenario, 20 centimetres under conventional tillage and only 15 centimetres in repacked soil, roughly half the no-tillage depth. Under completely stress-free conditions, simulated roots reached about 65 centimetres, underscoring how much potential depth is forfeited to physical limitation. Deeper rooting is not an aesthetic detail: it determines access to subsoil water during dry spells, and previous field studies have linked no-tillage to greater sugarcane root biomass at depths of 80 to 100 centimetres.

The findings carry practical weight for one of the world’s largest sugar and bioenergy crops. Conventional tillage temporarily loosens compacted layers, but that loosening is short-lived and can leave subsurface plough pans while degrading load-bearing capacity under heavy harvester traffic. The new results suggest that abandoning disturbance, or simply leaving tilled soil undisturbed for five years as in the conventional treatment here, allows a continuous, biologically generated pore network to re-establish, giving roots low-resistance pathways through otherwise hostile ground. These biopores, left behind by decayed roots, also improve gas diffusion, which matters because waterlogged, compacted soil can suffocate the oxygen-hungry meristem at the root tip. The study notes that roots sense compaction partly through restricted ethylene diffusion, a hormonal signal trapped by dense soil, and that preserved pore continuity appears to blunt this stress perception.

The authors are careful about limits. Their models are calibrated for penetration resistances between 1 and 8 megapascals and water saturations between 50 and 95 percent, so drier conditions and full saturation remain outside their predictive range, and the RootBox simulations were illustrative rather than field-validated. The penetration resistance equation, fitted with the Busscher model, is best suited to soils with similar clay content. Even so, the central conclusion stands firmly: soil structure is not a passive backdrop to root growth but an active buffer against mechanical and hydric stress, and it deserves a place inside the soil–plant–atmosphere models that forecast crop water use. For an industry facing more erratic rainfall and heavier machinery, the message from this Brazilian Oxisol is that the cheapest root growth insurance may simply be to stop disturbing the ground.

Subject of Research: The effect of no-tillage soil structure on sugarcane root elongation under mechanical and hydric stresses in a Brazilian Oxisol

Article Title: No-tillage soil structure increases sugarcane root elongation under mechanical and hydric stresses in an Oxisol

Article References: Grande, L. H. Q., Macedo, M. D., dos Santos, J. K., da Silva, L. H. A., de Alencar, A. A., dos Santos Vianna, M., Bolonhezi, D., & de Moraes, M. T. (2026). No-tillage soil structure increases sugarcane root elongation under mechanical and hydric stresses in an Oxisol. Plant and Soil. https://doi.org/10.1007/s11104-026-09113-2

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09113-2

Keywords: sugarcane, no-tillage, soil structure, root elongation, soil compaction, penetration resistance, biopores, macroporosity, Oxisol, soil physics, root growth modelling, hydric stress