Effect Of Nitrogen Sources On Nitrous Oxide Emission, Maize (Zea Mays L) Yield And Nitrogen Use Efficiency In Western Kenya

ABSTRACT

Nitrogen deficiency is a major limiting factor for maize production in western Kenya, therefore, nitrogen fertilizer inputs are required to increase yields in the region. However, most resource poor farmers use low rates of inorganic fertilizers leading to low maize yields. While high rates of inorganic fertilizer application may increase yields, they are however associated with low nitrogen use efficiency (NUE) and emission of greenhouse gases (GHGs) to the environment. Cattle manure may be used as a mitigation option but it is not available in sufficient quantities to meet N needs of the crop. Combining cattle manure and inorganic N fertilizers can result into increased NUE, higher yield and reduced GHGs emission compared to either of them applied alone, due to synergistic effects and improved synchronization of nutrient release and uptake by crops. Hence, the need to come up with a better approach in managing N fertilizers more efficiently to increase yield while keeping emission of GHGs at lower levels. The main objective of this study was to evaluate the effect of applying inorganic and organic sources of nitrogen fertilizer or their combination on N2O gas emission, maize yield and NUE. The study was conducted in 2014 during the long rainy season at two sites with contrasting soil characteristics; a highland (Kericho West District) and lowland (Nyando District).The experiment consisted of six treatments i.e. a control with no N input, urea applied alone at 30 kg N ha-1 and at 100 kg N ha-1, manure applied alone at 30 kg N ha-1, a combined application of manure and urea each providing 50 kg N ha-1, and NPK fertilizer applied at 100 kg N ha-1. A completely randomized design with three replicates was used in the highland where the soil was homogenous, but in the lowland where the soil was heterogeneous, a randomized complete block design was used. Soil gases were sampled using the general static chamber methodology and the N2O emissions quantified by use of a SRI 8610C gas chromatograph. Maize yield was determined at harvest and the NUE calculated after plant samples analysis. There were significant differences in N2O emissions among treatments with a cumulative seasonal emission range of 0.11 kg N2O-N ha−1 (control) to 0.31 kg N2O-N ha−1 (urea100 kg N ha-1). Sole manure and urea at 30 kg N ha-1 did not significantly increase N2O emission above the control. However, sole urea and NPK at 100 kg N ha-1 produced a significantly higher emission compared to all other treatments. Occurrence of floods and droughts during the season in the lowland resulted into low yields that did not show any treatment effects. However, yields differed significantly in the highland (p < 0.05). The highest grain yield of 3.98 ton ha-1 was realized from combined manure and urea at 100 kg N ha-1 while the control treatment gave the least yield of 1.36 ton ha-1. Sole urea fertilizer at both 30 kg N ha-1 and 100 kg N ha-1 did not show significant difference in maize yield from the control treatment. However, sole manure at 30 kg N ha-1, integration of manure and urea, and NPK at 100 kg N ha-1 increased yield significantly. N-uptake followed a similar trend as grain yield at both sites. Application of urea alone resulted in relatively higher N2O emissions per unit of yield compared to other treatments. Increasing the N rate led to further increase in emission per unit kilogram of yield. Combining urea and manure produced the lowest N2O emissions per unit of yield. The findings of this study show that the efficiency of use of nitrogenous fertilizers and maize yield can be increased, while keeping the emission of GHGs from agricultural productions systems to the environment at lower levels by combining both organic and inorganic N sources.