Integrated Soil Fertility Management Has Altering Effects on Soil Health and Crop Productivity across Sites in Kenya.

Crop productivity in Sub-Saharan Africa (SSA) is largely constrained by poor soil health and limited access to mineral fertilizer. Integrated soil fertility management in Kenya has been promoted to boost crop production while simultaneously improving soil health for long-term sustainability. A common practice is to incorporate organic residues with inorganic fertilizer for increased yields and soil carbon (C). This study was conducted at four identical long-term randomized complete block design trials located in central and western Kenya. The sites differed by soil fertility including, a high and low fertility site in each region. We examined maize yield, labile soil C, and nitrogen (N) responses to organic residue incorporation in the presence (160 kg N/ha) and absence (0 kg N/ha) of fertilizer at each site. The applied organic residues varied in quality and consisted of Tithonia diversifolia (Hemsl.) A. Gray, (high quality; >2.5 % N) and Maize stover (low quality; <2.5% N). Soils were collected from 0-15 cm in the spring of 2015. Overall, grain yield was influenced by fertilizer (<0.0001) and residue quality (<0.05). In addition, there was a significant residue by site interaction (<0.05), as tithonia significantly increased grain yield at three out of the four sites. Mineralizable C and soil protein were strongly influenced by residue quality (<0.05), furthermore, noteworthy differences emerged at high versus low fertility sites. Tithonia resulted in greater mineralizable C and soil protein at low fertility sites, while there were no differences between tithonia and maize stover at either high fertility site. This suggests that incorporating high quality residues can significantly increase yields and nutrient mineralization at low fertility sites but the advantages of applying high quality residues on more fertile soils are less apparent.