A Critique of Combining Tillage Practices and Nitrogen for Enhanced Maize Production on a Humic Nitisol in Kenya

Abstract

A study was carried out in the short rainy season of 2012/2013 and the long rainy season of 2013 to compare the effects of a combination of two tillage practices and three fertilizer levels on maize production in a warm and wet environment of Kabete in Kenya. This was part of a larger experiment to test water use efficiency and viability of various climate adaptation strategies in east and southern Africa. The trial consisted of a split-plot design experiment of conventional tillage (CT) and tied ridges (TR) as main plots and three fertilizer levels of 0, 20 and 40 kg nitrogen (N) ha−1 as sub-plots. Air-dried grain harvested at physiological maturity was separated from the cob and comparative analysis done of the grain yields under the various fertility rates, tillage categories and their combinations. In the short rains of 2012–2013, TR had higher grain yield compared to CT across all the N levels, while in the long rains of 2013 the reverse was found. In 2012–2013, increasing fertilizer from 0 to 20 kg N ha−1 increased the yields by 20.9%, but increasing from 20 to 40 kg N ha−1 decreased yields by 4.9% across both the tillage categories. In the long rains of 2013, the reductions of the yields were 0.09% and 10.3% for the respective fertilizer increments. Under CT, increasing fertilizer from 0 to 20 kg N ha−1 increased the yields by 56.2%, but increasing from 20 to 40 kg N ha−1 reduced it by 8.0% in 2012–2013, while in the long rains of 2013 the yields were reduced by 8.2% and by 2.7% for the respective fertilizer increments. Under TR, increasing fertilizer from 0 to 20 kg N ha−1 increased yields by 0.08% and by 0.03% for 20 to 40 kg N ha−1 in 2012–2013, while in 2013 the increment was by 15.1% for the first fertilizer increment but a reduction by 23.6% for the second fertilizer treatment. Neither of the two tested tillage practices, fertilizer levels, nor their interactions, however, gave any significant grain yield difference at p < 0.05 for both seasons. Since TR is more labor intensive than CT, the later would be preferable and convenient for farmers in the agro-climatic conditions similar to those at the experimental site, whereas fertilizer application should be based on better understanding of the initial soil fertility.