Maize yield responses to soil organic carbon under integrated soil fertility management in tropical environments

Abstract To ensure the sustainable management of tropical cropping systems, tracking changes in soil fertility and distinguishing long-term crop yield trends from season-to-season fluctuations are essential. However, a scarcity of long-term datasets for tropical systems has left a gap in understanding how soil organic carbon (SOC, used as a proxy for soil fertility) and yield co-evolve in these systems. Here, we present a unique analysis of maize yield and SOC trends in four long-term experiments in Kenya, conducted under contrasting pedo-climatic conditions. Experimental treatments consisted of yearly applications of organic resources with different C:N ratios (12 to 200) at two quantities (1.2 and 4 t C ha -1 yr -1 ), with and without mineral nitrogen fertilizer (240 kg ha -1 yr -1 ). At sites with adequate rainfall (475-600 mm in-season rainfall), long-term Maintenance of Maize yields and SOC were strongly correlated. Specifically, 74% of the variation in long-term yield trends across sites was explained by the interaction between site and the trend in SOC, increasing to 84% when adding the interaction with the mineral nitrogen fertilizer treatment. In contrast, no significant correlation between yield and SOC trends existed at the driest site (300 mm in-season rainfall). Differences in the strength of the SOC-yield relationships between treatments with and without mineral N fertilizer were significant at only one of the four sites. In addition, seasonal maize yield variability at three of the four sites was strongly influenced by seasonal mean temperature and total rainfall, overriding the effect of site fertility and SOC in any given season. However, the strength of climate effects varied between sites. We conclude that maintaining SOC is important for sustaining maize yields, but this potential can only be fully realized under favorable climatic conditions, particularly sufficient rainfall.