GREENHOUSE GAS EMISSIONS, SOIL PHYSICOCHEMICAL PROPERTIES, AND NUTRIENT USE EFFICIENCY UNDER INORGANIC-ORGANIC FERTILIZER SUBSTITUTIONS IN MAIZE AND DESMODIUM CROPPING SYSTEMS

Abstract

Climate change continues to threaten ecosystem functions, and agriculture remains one of the major sources of greenhouse gas (GHGs) emissions responsible for global warming. However, little is known about the quantities and intensities of GHGs from major cropping systems in Kenya and, by extension, in Sub-Saharan Africa. This study was aimed to quantify GHG emissions - carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes from soil. It also assessed the optimal organic-inorganic fertilizer substitution in maize (Zea mays) and desmodium (Desmodium uncinatum) cropping systems that enhance crop yields and lead to reductions in GHG emissions. The static chamber method was used from April to November 2024. The experiment consisted of six fertilizer substitution ratios (0 0, 25 75, 50 50, 75 25, 100 0, and 0 100% FYM-inorganic N equivalence) arranged in a randomized complete block design with four replications. Soil chemical parameters (NH4+, NO3−, pH, N, P, and C), plant nutrient uptake, and agronomic and recovery efficiencies were assessed. Results showed that desmodium yield responded positively to increasing Farmyard manure substitution levels (p < 0.0001), with biomass rising under higher organic inputs. Despite these, N2O emission factors and yield-scaled emissions remained consistently low across fertilizer treatments, indicating efficient nitrogen utilization and minimal gaseous losses. The net global warming potential did not vary significantly among treatments. Greenhouse gas intensity declined sharply from the control to the 75,25 fertilizer treatment, representing approximately a 70% reduction. Maize grain yield was highest under the 50,50 (50% FYM, 50% inorganic fertilizer), indicating a strong synergistic effect between organic and mineral nutrient sources. Emission factors increased by nearly 20% relative to the control. Net global warming potential also increased progressively with higher Farmyard manure substitution, showing an approximately 40.7% increase. Despite these increases, the 50,50 treatment achieved the most favorable balance between productivity and emissions, producing the highest maize yield with comparatively lower EF and greenhouse gas intensity (GHGI). Combined FYM–inorganic treatments, particularly 25,75 and 75,25, significantly improved soil nutrient status, enhanced N and P

uptake, and increased maize and desmodium yields compared to sole applications. FYM- rich combinations improved moisture retention and microbial activity, sustaining nutrient

release, while inorganic fertilizers ensured rapid early growth. Intercropping enhanced biological nitrogen fixation and nutrient recovery, leading to higher agronomic efficiency and resilience under moisture-limited conditions.