Burying Straw Twice a Year Supercharges Maize Yields in Problematic Black Soil

Every harvest season, farmers around the world face a deceptively simple question: what should be done with the mountains of leftover stalks and straw? Burning them pollutes the air, removing them strips fields of organic matter, and yet the practice of ploughing crop residues back into the ground has remained surprisingly difficult to optimize. A new long-term study from China now offers some of the clearest evidence yet that the answer, at least for one notoriously difficult soil type, is to incorporate straw in both growing seasons rather than just one. The research, published in BMC Plant Biology, tracked maize performance across experimental plots that have been managed continuously since 2008, and found that returning both wheat and maize straw to the soil each year produced the strongest gains in soil fertility, leaf photosynthesis, and ultimately grain yield.

The setting for the study is lime concretion black soil, a distinctive and problematic soil class found in parts of the Huang-Huai-Hai plain of eastern China. These soils are characterized by shallow topsoil, poor water-holding capacity, and a hard, compacted layer rich in lime concretions that restricts root penetration. Farmers working such land have long struggled with low and unstable yields, and the region has become a priority target for soil amelioration programs. Straw incorporation has been promoted as a residue management strategy that improves soil structure and supports sustainable agriculture, but the authors of the new work note that its long-term effects on the nutrient balance of these soils, and on the subsequent development of maize crops, had remained insufficiently explored.

To fill that gap, the research team, led by Jingyao Huang of Anhui Agricultural University together with colleagues at the Anhui Academy of Agricultural Sciences and the Jiangsu Collaborative Innovation Centre for Modern Crop Production, drew on a field experiment established in 2008. Over more than fifteen years, the plots had been managed under four contrasting residue regimes: a control with no straw incorporation at all, a treatment in which full maize straw was returned in a single season, a treatment with full wheat straw returned in a single season, and a double-season regime in which both wheat and maize straw were fully incorporated every year. During the 2024 and 2025 growing seasons, the researchers measured soil nutrients, maize growth, leaf photosynthesis, and final yield, giving them an unusually robust window into how decades of residue management translate into crop performance today.

The soil chemistry results were unambiguous. Across all growth stages, straw incorporation significantly increased the contents of soil nitrogen, phosphorus, potassium, and organic matter compared with the untreated control. The team also computed a soil nutrient balance index, a composite measure of how well the soil’s nutrient economy is functioning, and found that straw treatments raised this index by between 12.50 and 24.44 percent at the R6 stage, the point at which maize kernels reach physiological maturity. In practical terms, the fields that had received residues for years were holding and cycling substantially more of the elements that crops need, and the double-season treatment delivered the largest enrichment, consistent with the idea that more frequent organic inputs compound over time rather than simply replacing one another.

Those below-ground changes rippled upward into the crop itself. At the R1 stage, when maize silks emerge and the plant is setting the potential size of its harvest, the double-season treatment had accumulated 13.06 to 14.18 percent more dry matter than the control, and its functional leaf area was larger by 24.71 to 24.76 percent. Functional leaves, particularly the ear leaf and the canopy around it, are the photosynthetic engines that fill the grain, so a quarter more of that productive surface represents a meaningful shift in the plant’s capacity to capture sunlight. The authors describe this as an optimization of source-sink dynamics: the source, meaning the photosynthesizing leaves, expanded in step with the sink, the developing ears, so that neither limited the other.

The physiological machinery inside those leaves also ran more efficiently in the straw-amended plots. The researchers measured SPAD values, a proxy for chlorophyll content, along with the activities of two enzymes central to maize photosynthesis: Rubisco, which fixes carbon dioxide in the Calvin cycle, and PEPC, phosphoenolpyruvate carboxylase, which performs the initial carbon capture that makes maize such an efficient C4 crop. They also recorded photosynthetic gas-exchange parameters, including the net photosynthetic rate, intercellular carbon dioxide concentration, and stomatal conductance. Together, these measurements showed that straw incorporation significantly increased the maximum photosynthetic rate at the R1 and R3 stages by 10.91 to 18.87 percent, and enhanced the accumulation of assimilates after silking, the critical period during which most of the grain’s final mass is assembled.

To move beyond simple correlations, the team applied partial least squares structural equation modeling, a statistical framework that can test whether observed data support hypothesized chains of cause and effect among many variables. The modeling indicated that both the soil nutrient balance index and soil organic matter content were closely related to leaf physiological characteristics, with organic matter showing a particularly strong association. Photosynthetic performance, in turn, emerged as jointly driven by soil water content and the physiological status of the leaves. In other words, the data support a pathway in which long-term residue inputs rebuild soil organic matter and nutrient reserves, which sustains better water conditions and healthier leaf biochemistry, which then powers higher rates of carbon fixation and, ultimately, heavier grain harvests.

The implications extend well beyond the experimental plots. Straw is often treated as a waste-disposal problem, and open burning of residues remains a major source of seasonal air pollution in intensive grain-producing regions. The new findings strengthen the case that residues are instead a valuable on-farm resource: a slow-release fertilizer, a soil conditioner, and a water-management tool rolled into one. Because the experiment began in 2008, the results also speak to a question that short-term trials struggle to answer, namely whether the benefits of straw incorporation accumulate, plateau, or reverse over decades. The persistence of significant nutrient and yield advantages after more than fifteen years suggests that the practice delivers durable, compounding returns rather than a transient flush of fertility.

For the lime concretion black soil region specifically, the study provides what the authors describe as new insights and a theoretical basis for soil amelioration and stable maize production. The double-season full incorporation regime, labeled W1M1 in the experiment, exhibited the most pronounced effects of all the treatments tested, outperforming both single-season alternatives. That detail matters for farmers and extension services designing residue management calendars, because it suggests that returning wheat straw after the winter harvest as well as maize straw after the summer harvest is worth the additional field operations. It also matters for policymakers weighing subsidies for residue return against the costs of enforcement for straw burning bans, since the agronomic case for incorporation now rests on quantified gains in nutrient balance, photosynthetic capacity, and yield.

There are, of course, caveats and open questions. The study was conducted in a single soil type, and the magnitude of the benefits may differ in soils with different textures, climates, and cropping systems. Mechanized incorporation also carries fuel and labor costs that vary by farm. Yet the core message is difficult to ignore: a practice as old as agriculture itself, returning the harvest’s leftovers to the earth, measurably rebuilt the chemistry, biology, and water relations of a degraded soil and converted those gains into more photosynthesis and more grain. As pressures on food systems and soils intensify worldwide, the humble straw barge ploughed into a Chinese field may prove to be one of the simplest climate-smart tools available, provided farmers commit to it season after season, year after year.

Subject of Research: Long-term effects of double-season straw incorporation on soil nutrients and maize yield in lime concretion black soil

Article Title: Double-season full straw incorporation enhances maize yield by regulating soil nutrients and promoting above-ground growth in lime concretion black soil

Article References: Huang, J., Cai, H., Huang, W., Wang, Y., Jin, D., Yang, N., Zheng, B., Chen, X., Zhang, Y., Tian, L., & Li, J. (2026). Double-season full straw incorporation enhances maize yield by regulating soil nutrients and promoting above-ground growth in lime concretion black soil. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10062-2

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10062-2

Keywords: straw incorporation, maize, lime concretion black soil, soil nutrients, soil organic matter, photosynthesis, nutrient balance, crop residue management, grain yield, soil amelioration, PLS-SEM, sustainable agriculture