The Journal of Soil Science and Plant Nutrition recently published a study by Nozibusiso Mbava, Rebecca Zengeni, and Pardon Muchaonyerwa that challenges common assumptions about agricultural waste management. The researchers discovered that the specific variety, or cultivar, of a crop matters more than the species itself when it comes to how much carbon dioxide is released into the atmosphere or how many nutrients are returned to the soil. By comparing raw residues and biochar from two different maize and two different sorghum cultivars, the team found that the chemical makeup of each specific plant variety dictates its environmental footprint. This means that farmers and scientists cannot simply group all maize or sorghum waste together but must instead look at the unique traits of each cultivar to maximize soil benefits and minimize climate impact.

Carbon dioxide emissions are a major concern when agricultural waste is left to decompose on the soil surface. The study showed that raw feedstocks, which are just the dried and chopped remains of the plants, cause a rapid spike in emissions as soil microbes quickly break down the easy-to-digest carbon. One sorghum variety in particular, known as PAN8816, caused a massive 205 percent increase in emissions compared to soil that had no waste added to it. In contrast, when these same plant remains were converted into biochar—a charcoal-like substance created by heating the material in a low-oxygen environment—the emissions were drastically lower. This is because the process of creating biochar turns the plant’s carbon into a more stable form that soil bacteria find difficult to eat, keeping the carbon locked in the ground rather than letting it escape as gas.

The temperature at which biochar is made also plays a critical role in its performance. The research compared biochar made at 350 degrees Celsius and 650 degrees Celsius, finding that the higher temperature produced a much more stable product. Biochar created at the higher heat level consistently resulted in the lowest carbon dioxide emissions across all plant varieties tested. Furthermore, the high-heat biochar acted as a more effective tool for neutralizing acidic soils. While raw plant waste can actually make the soil more acidic in the short term as it rots, high-temperature biochar has a liming effect that raises the soil pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More. This is particularly important for farmers working with degraded or naturally acidic lands where high acidity can prevent crops from growing properly.

Beyond carbon storage, the study looked at how these materials affect nitrogen and phosphorus, which are the primary nutrients plants need to thrive. The results were varied, showing that while some varieties helped release nitrogen, others actually caused it to be temporarily locked away by soil microbes. For example, one maize variety processed into biochar at high heat increased soil nitrate by 17 percent compared to the control. Meanwhile, phosphorus availabilityPhosphorus is another essential nutrient for plant growth, but it can sometimes be locked up in the soil and unavailable to plants. Biochar can help release phosphorus from the soil and make it more accessible to plants, reducing the need for chemical fertilizers.   More was improved by all types of biochar used in the study. The researchers found that the phosphorus naturally found in the plant waste becomes more concentrated and easier for new plants to access after the material is turned into biochar. This suggests that biochar is not just a way to store carbon, but also a slow-release fertilizer that can help maintain soil fertility over time.

Ultimately, the study proves that effective residue management requires a high degree of precision. The choice of cultivar and the specific heat used during pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More can change the outcome from a net loss of soil carbon to a stable, nutrient-rich environment for future crops. High-temperature biochar appears to be the most promising option for long-term carbon sequestration and soil stability, as it resists microbial breakdown while providing a steady supply of nutrients and buffering the soil against acidity. These findings provide a new roadmap for sustainable agriculture, suggesting that by selecting the right plant varieties and processing them correctly, we can turn vast amounts of agricultural waste into a powerful tool for fighting climate change and improving food security.

Source: Mbava, N., Zengeni, R., & Muchaonyerwa, P. (2026). Residue and biochar-based amendments from maize and sorghum cultivars regulate CO2 emissions and nutrient mineralization. Journal of Soil Science and Plant Nutrition.