Impact of methane fermentation waste fluid application rates on maize yield and fate of N with special reference to soil textures

Efficient nitrogen (N) utilization is crucial for improving fertilizer use efficiency in crop production. Methane fermentation waste fluid (MFW) has emerged as a promising biofertilizer; however, its interaction with soil texture and application rates remains inadequately understood. This study aimed to evaluate the effects of MFW application rates on maize (Zea mays L.) growth and N dynamics under contrasting soil textures – sandy loam (SL) and clayey loam (CL) – and to identify the optimum application rates for balancing crop productivity and environmental impacts. Pot experiments (1/2000a) were conducted over two years with three MFW application rates (375, 750, and 1500 mg N pot−1), a chemical fertilizer (NH4Cl, 750 mg N pot−1), and a control treatment (0N). To track N derived from inorganic fertilizer (Ndfif) across plant uptake, soil retention, and environmental losses, 15NH4Cl (99%) was added as a tracer while keeping the total N content in each treatment. The results indicated that maize SPAD values, biomass, and yield were significantly enhanced in SL soil than in CL soil. Increasing MFW rates improved maize yield in 2021 but showed reduced effectiveness under limited irrigation in 2022. Despite lower Ndfif retention in SL soil, total Ndfif recovery (soil and plant) was significantly higher (73–79%) compared to CL soil (53–76%), which was strongly influenced by MFW rates and water availability. Ndfif losses were more pronounced in CL soil due to NH3 volatilization and NO3-N leaching, especially at higher MFW rates. Although N recovery from MFW was lower than chemical fertilizer at equivalent N levels, MFW provided sufficient N for maize yield. Considering yield and environmental impact, the optimum MFW application rate was estimated at 700–1000 mg N pot−1 for SL soil and 500–776 mg N pot−1 for CL soil. Our findings highlight that while MFW is highly effective in sandy soils, its application in clayey soils requires careful management to mitigate N losses through volatilization and leaching. By tailoring MFW rates to soil texture and water regimes, it is possible to enhance maize productivity and reduce environmental impacts, supporting sustainable nutrient management strategies in agricultural systems.