Effect of biochar and compost amendments on soil organic carbon sequestration, greenhouse gas emissions, and maize yield under different tillage regimes in a tropical rainfed system

Project Abstract

Biochar and compost amendments were evaluated for their ability to enhance soil organic carbon (SOC) sequestration, mitigate greenhouse gas (GHG) emissions, and improve maize yield under contrasting tillage regimes in a tropical rainfed system over a three-year field experiment. The study adopted a split-plot design with tillage as the main plot (conventional tillage, reduced tillage, and no-till) and organic amendments as subplots (biochar at 5 t ha-1, compost at 10 t ha-1, compost plus biochar, and a control with no amendment). Soil samples were collected pre-planting and post-harvest to quantify SOC, labile carbon fractions, and priming effects. In situ GHG fluxes (CO2, N2O, and CH4) were measured monthly using static chamber techniques, while soil microbial biomass, enzyme activities (dehydrogenase, urease, and ?-glucosidase), and functional gene abundances (mcrA, nosZ, amoA) were analyzed to elucidate mechanistic pathways. Maize growth parameters, including germination rate, canopy cover, aboveground biomass, and grain yield, were recorded each season, alongside phenology and drought stress indicators. Weather data (precipitation, temperature, and solar radiation) were monitored to couple abiotic stress with management effects. The results indicate that biochar alone significantly increased SOC stocks by 12–18% across tillage regimes, with the greatest gains under no-till owing to reduced soil disturbance and enhanced residue retention. Compost application elevated soil organic matter and labile carbon pools, accelerating early-season mineralization but contributing to higher SOC after two years in reduced-tillage plots. The combination of biochar and compost produced synergistic effects, stabilizing carbon in recalcitrant pools while providing readily mineralizable substrates that supported sustained maize nutrition and growth. GHG emissions exhibited a tillage- and amendment-dependent response conventional tillage with compost led to higher N2O peaks following rainfall events due to increased mineral N availability, whereas no-till with biochar reduced cumulative N2O flux by 15–28% and lowered CO2 efflux by 9–14% relative to controls. CH4 flux remained negligible in all treatments but showed slight consumption under no-till with biochar, reflecting improved aeration and microbial competition. Maize yield responses aligned with SOC gains and improved nutrient use efficiency; the highest grain yields were observed in no-till plots receiving biochar and compost, with yield increases of 18–24% compared with conventional tillage controls. Economic analysis indicated favorable net returns under reduced-to-no-till systems with biochar-compost amendments, driven by yield gains and reduced soil erosion. Soil health indices, including aggregate stability, microbial biomass carbon, and enzyme activities, improved significantly under biochar-containing treatments, indicating enhanced soil resilience to rainfall variability. The study demonstrates that integrating biochar and compost in reduced- or no-tillage tropical rainfed systems can elevate SOC sequestration, moderate GHG emissions, and sustain maize productivity, offering a climate-smart soil management strategy with measurable environmental and agronomic benefits.

Project Overview

What This Project Is About

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The project looks at how adding biochar and compost to soil affects three things: the amount of carbon stored in the soil (soil organic carbon), the release of greenhouse gases, and how much maize yields when the land is farmed with different tillage practices. Biochar is a charcoal-like soil amendment made from organic material that can help store carbon. Compost is decayed organic matter that adds nutrients and improves soil structure. Tillage means turning over the soil; different tillage regimes change soil properties and crop growth.

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The Problem It Addresses

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A key challenge is to find farming methods that boost soil health and crop yields while minimizing greenhouse gas emissions. Relying on chemical fertilizers and intensive tillage can degrade soil and release more carbon dioxide and other gases. This project tests whether biochar and compost can improve soil carbon storage, reduce emissions, and support maize yields under farming methods commonly used in tropical rainfed systems.

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Objectives of the Project

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1. Evaluate how biochar and compost affect soil organic carbon levels over one growing season.
2. Assess changes in greenhouse gas emissions (like CO2, methane, nitrous oxide) with different tillage practices.
3. Measure maize yield under each treatment combination to identify best options.
4. Compare low- and high-disturbance tillage effects when amended with biochar and compost.
5. Provide practical recommendations for farmers in tropical rainfed systems.

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What You Will Do Step by Step

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1) Review background literature on biochar, compost, tillage, and soil carbon. 2) Set up field plots with different treatments (biochar, compost, both, none) and tillage methods. 3) Apply amendments and manage crops for a full season. 4) Collect soil samples before, during, and after the season to measure organic carbon and other soil properties. 5) Use simple tools to estimate greenhouse gas emissions from soil and residue. 6) Harvest maize and record yields. 7) Analyze data to compare treatments and identify trends. 8) Summarize findings and discuss practical implications for farmers.

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Expected Outcome

The study is expected to show that biochar and compost can increase soil carbon storage, reduce certain greenhouse gas emissions, and improve or stabilize maize yields, with the best results depending on the tillage method used. The results should guide farmers on sustainable input choices and tillage practices in tropical rainfed farming.