Researchers affiliated with the Federal Technological University of Paraná, the University of São Paulo, the Federal University of Viçosa, the Federal Rural University of the Semi-Arid, and other Brazilian institutions set out to quantify how maize stover, the shredded residue left on fields under no-till farming, alters the environmental behavior of S-metolachlor. Their work, published in the journal Discover Soil, focused on two chemically contrasting soils collected from the state of Paraná: a clayey Oxisol from Pato Branco and a sandy Ultisol from Paranavaí. These two soil orders dominate much of Brazil’s arable land, and they differ sharply in texture, organic matter, and water retention, making them an ideal natural experiment for testing how residue management interacts with soil type.

The team amended both soils with maize stover at rates ranging from zero to one percent by weight, equivalent to field applications of zero to 20 tonnes per hectare. They then ran a battery of standardized tests. Sorption and desorption were measured using the batch equilibrium method recommended by the Organisation for Economic Co-operation and Development, in which soil samples are shaken with herbicide solutions and the amount of chemical remaining in the liquid phase is quantified. Leaching was assessed in 30-centimeter PVC columns packed with soil and covered with stover, then subjected to 60 millimeters of simulated rainfall over two hours, a scenario based on average January rainfall at the collection sites. In every case, S-metolachlor concentrations were measured by high-performance liquid chromatography, with the analytical methods validated for selectivity, linearity, detection limits, and recovery following Brazilian regulatory guidelines.

The results showed that the stover did far more than sit on the surface. Adding it measurably changed the chemistry of both soils, raising pH, increasing organic carbon, and boosting levels of phosphorus and potassium. In the Oxisol, organic carbon climbed from 2.38 percent in the unamended soil by 16 to 36 percent depending on the stover rate, while potassium rose by as much as 61 percent. The researchers attribute these shifts to the nutrient content of maize residue itself, which is known to contain appreciable amounts of nitrogen, phosphorus, potassium, sulfur, and calcium. The residue also appears to exert a mild liming effect, with its basic cations reacting with exchangeable acidity and nudging pH upward by 11 to 18 percent across the two soils.

Those chemical changes translated directly into stronger herbicide retention. Freundlich sorption coefficients for S-metolachlor ranged from 3.24 to 5.98 in the Oxisol and from 1.48 to 2.61 in the Ultisol, with the highest values generally occurring at the greatest stover rates. At the one percent amendment rate, roughly 64 percent of the applied herbicide was sorbed in the Oxisol and about 37 percent in the Ultisol. The clayey soil consistently outperformed the sandy one, a pattern the authors attribute to its 88 percent clay content and higher organic carbon, both of which provide abundant sorption sites. Desorption, meanwhile, declined as stover rates increased, meaning that once the herbicide bound to the amended soil, it was less inclined to let go. The hysteresis coefficients all exceeded one, indicating negative hysteresis and a degree of reversibility in sorption that the researchers link to the herbicide’s moderately hydrophobic character interacting with nonpolar functional groups in the plant residue.

The leaching experiments revealed an equally striking story. Without any stover, more than 70 percent of the applied S-metolachlor stayed within the top five centimeters of soil in both soils, indicating limited vertical mobility under the tested rainfall. In the Oxisol, adding stover at rates of 5 to 20 tonnes per hectare trapped 9 to 30 percent of the herbicide in the residue layer itself, with the remainder concentrated near the surface; no herbicide was detected in the leachate at all. The sandy Ultisol behaved differently. There, the herbicide appeared in the leachate at stover rates of 5, 10, and 15 tonnes per hectare, with roughly 50 to 63 percent of the applied chemical recovered from the collected drainage water, though it vanished from the leachate at the highest, 20-tonne rate and in the unamended controls.

That soil-dependent behavior is one of the study’s most important takeaways. The authors caution that the simulated rainfall of 30 millimeters per hour represented a high-intensity event that may have promoted rapid water movement and preferential flow, particularly through the sandy Ultisol, so the leaching patterns they observed should be interpreted within that specific scenario. They also note that lipophilic constituents of maize residue can alter sorption-desorption equilibria in ways that sometimes enhance vertical movement, echoing earlier findings that wheat residue increased the mobility of atrazine. In other words, crop residue is not a simple shield; it is an active chemical participant whose effects depend on the soil it covers.

For weed management, the implications cut in a promising direction. Herbicide held in the stover layer and near the soil surface may be released gradually into the soil solution, potentially extending the window of activity against emerging weeds during early crop establishment. The residue itself adds a physical barrier that delays weed emergence, reducing the need for repeat applications. At the same time, stronger sorption and reduced desorption lower the risk that S-metolachlor will migrate into aquifers, addressing a long-standing environmental concern for a compound whose sorption coefficient normalized to organic carbon typically falls between 100 and 200 milliliters per gram and whose soil half-life ranges from 15 to 50 days. The researchers emphasize that soils with higher organic carbon and intrinsic sorption capacity are better equipped to retain the herbicide safely.

The authors are careful to frame their conclusions as laboratory findings that still require validation under field conditions, where factors such as residue decomposition, microbial activity, and variable rainfall will complicate the picture. Even so, the study makes a compelling case that the residue, the herbicide, and the soil must be considered as a single interacting system rather than in isolation. Adjusting stover rates to match soil-specific conditions, they suggest, could simultaneously improve herbicide performance, sustain weed control, and shrink the environmental footprint of one of agriculture’s most indispensable chemicals. In an era when both water quality and herbicide resistance demand smarter solutions, the humble corn stalk may turn out to be one of the cheapest tools available.

Subject of Research: The effect of maize stover amendment on the sorption, desorption, and leaching of S-metolachlor herbicide in Brazilian Oxisol and Ultisol soils

Article Title: Sorption, desorption, and leaching of S-metolachlor in two soils amended with maize stover

Article References: da Silva Borges, M. P., Trezzi, M. M., da Costa Lima, A., Araújo, G. R., Junior, V. B. P., Paiva, A. C. P., Silva, D. V., da Silva Brochado, M. G., & Mendes, K. F. (2026). Sorption, desorption, and leaching of S-metolachlor in two soils amended with maize stover. Discover Soil, 3(1), Article 178. https://doi.org/10.1007/s44378-026-00333-7

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00333-7

Keywords: S-metolachlor, maize stover, herbicide sorption, leaching, Oxisol, Ultisol, soil organic carbon, no-till farming, Freundlich isotherm, water contamination, weed management, soil chemistry

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