Assessing the Impact of Irrigation and Crop Type on Soil Respiration in Agricultural Soils

Identifying the main drivers of soil CO₂ emissions in tropical agroecosystems is essential for balancing productivity and climate mitigation. This study evaluated the effects of crop type, irrigation, phenological stage, and fertilization on soil respiration in a humid marshland system in Rwanda using a two-season field experiment. Five crops (maize, soybean, common bean, Irish potato, and Brachiaria) were grown under irrigated and rainfed conditions, and soil CO₂ emissions were measured across 19 sampling campaigns in both crop-covered and adjacent bare soil conditions in all plots. Crop type and growth stage were the dominant drivers of soil CO₂ emissions (p < 0.001), while irrigation had no significant direct effect despite increasing yields (p < 0.001). As a result, irrigation reduced yield-scaled CO₂ emissions for several crops (p < 0.05–0.01). Brachiaria showed higher emissions, particularly during the development stage, but its high bio-mass led to lower emissions per unit yield. Fertilization significantly increased soil respiration (p < 0.001), and emissions were higher under crop-covered soils than bare soils (p < 0.001). These findings indicate that crop traits and nutrient inputs primarily control soil respiration under moisture-sufficient tropical conditions.