Evaluation Of Nutrient Management For Improved Nitrogen Use And Agronomic Efficiencies In Rice (Oryza Sativa L.) In Kisumu, Busia And Kirinyaga Counties, Kenya

ABSTRACT

Nitrogen is a major mineral nutrient limiting growth, development and production of crops in Kenya. The cost of production is way beyond the purchasing power of smallholder farmers, coupled with the low availability of nitrogen in the soil has significantly contributed to the reduction in rice productivity in Kenya. In rice growing regions, including Busia, Kisumu and Kirinyaga counties, there is evidence of pollution due to high losses of N experienced from agricultural fields. Reduction of the losses through proper N management is critical to ensure increased yield and reduced pollution rates of through promotion of good agricultural practices. Therefore, the objectives of this study were to:-(1) analyze farmer’s practices that contribute to nitrogen losses in rice farming fields, (2) evaluate growth and yield of irrigated rice in response to methods of N applications, forms and levels, (3) determine nitrogen partitioning and nitrogen uptake as affected by levels of nitrogen sources and methods of application and (4) determine nitrogen use efficiency (NUE), nitrogen agronomic efficiency (NAE) and nitrogen harvest index (NHI) of irrigated rice under different levels of N sources. The studies were conducted through survey and field experimentations. The surveys were conducted in Kisumu and Busia counties, where 100 farmers were interviewed. The field experiments were conducted at Ahero irrigation scheme in Kisumu county and KALRO Mwea in Kirinyaga county. Field experiments were laid out in Randomized Complete Block Design (RCBD) in factorial arrangements. The treatments included two sources of N as ammonium sulphate [(NH4)2SO4] and urea at three levels (0, 25, and 50kgha-1) applied in two methods (full dose and split). Survey data was subjected to SPSS software while the field data were subjected to ANOVA using SAS software and statistical differences were separated using Fischer’s LSD at 5% level of probability. The survey revealed that (NH4)2SO4 was most commonly used form of fertilizer in both Kisumu and Busia (61% and 48% respectively). Burning and feeding to livestock were the leading N loss pathways farmers were aware of, with 32%, 34% stating that they burned the straws in Kisumu and Busia respectively while 39% and 40% fed to livestock in Kisumu and Busia respectively. N sources and levels led to increased days to 50 % flowering that significantly varied across the treatments, with the unfertilized plot taking the shortest duration (64 and 97 days in Ahero and Mwea respectively). Ammonium sulphate (50kgha-1) led to highest yields in Kisumu and kirinyaga (11.2 t ha-1 and 7.90 t ha-1 respectively) while the control had the lowest. Significant differences were observed on uptake during different growth stages ( p≤0.05), with a higher N uptake being observed during reproductive and harvesting stages in both study sites. In all treatments, highest N was partitioned to the grain. The (NH4)2SO4 (25, kg ha-1) revealed balanced NUE in both study sites recording 73.15 and 90.10 in Kisumu and Kirinyaga counties. In Ahero, (NH4)2SO4 at 50 kgha-1 and Urea at 50 kgha-1 exceeded 100% of the normal NUE, recording 120.6 and 146.5 respectively. This was an indication of excessive soil mining by the plants at this particular stage. In regard to NAE (NH4)2SO4 at 25kgha-1 and urea 25kgha-1 at Ahero and Mwea resulted in higher value of 21.53 and 12.90 respectively. In conclusion, farmer’s straw management practices was thought to contribute N losses in farming systems. (NH4)2SO4 at 50kgha-1 led to highest yield in both study sites. Further studies, need be carried out on nitrogen forms on NUE and NAE on long-term conditions.