Soil Nitrogen and Greenhouse Gas Fluxes in Response to Reduced Tillage Practices under Maize-Bean Intercropping in Western Kenya

Abstract

Smallholder farmers in western Kenya produce maize (Zea mays L.) intercropped with common bean (Phaseolus vulgaris L.) using inversion-type deep tillage. Crops are grown twice per year during long rains (LR) and short rains (SR) at low altitude and only once during the LR at high altitude areas. Conservation Tillage or reduced tillage is being promoted in these areas as important alternatives to help enhance soil quality and mitigate increasing climate variability. Information on early agroecosystem responses to farmers’ adoption of reduced tillage strategies is however, limited. The objective of this study was to assess the impact of reduced tillage practices on soil nitrogen (N) mineralization and greenhouse gas (GHG) fluxes at low altitude (Bungoma) and high altitude (Trans-Nzoia) locations during the transition period. Soil and air samples were collected during LR, SR and fallow period (FP) for a period of three years under three tillage practices; conventional (CT), minimum (MT) and no-till (NT) in a maize-common bean intercrop. Experimental design was a complete randomized block design replicated four times. In general, Potential Mineralizable Nitrogen, and greenhouse gas fluxes were higher in Bungoma than Transzoia. Introducing MT and NT reduced Carbon dioxide (CO₂₎ and nitrous oxide (N₂O) fluxes in both locations. These observations indicate early signs of improved retention of soil organic N in less labile N pools, and greater N availability to plants rather than loss to N gas emissions.

Key words:  Reduced tillage, carbon dioxide; methane; nitrous oxide; potentially mineralizable nitrogen