Physiological And Morphological Basis Of Yield Difference In Upland Rice Varieties In Response To Low Nitrogen In Kirinyaga County, Kenya.

ABSTRACT

Rice is the third most important cereal grain in Kenya after maize and wheat. It has been grown by smallholder farmers as a commercial food crop under irrigated and rain fed ecologies .Low soil N fertility, prevalent in smallholder farmers’ fields is a major constraint to upland rice production mostly under rain fed ecology. The ever escalating fertilizer prices have made the input to be unaffordable to most smallholder farmers who are resource poor. Efficient use of nitrogen in agricultural practice can increase yields, decrease production costs and reduce the risk of environmental pollution. The response of rice crop to N-fertilizer have been documented, however the effects of low soil N on yield and quality of rice are lacking. The objective of this study was to evaluate growth and yield of upland rice varieties under different nitrogen fertilizer treatments in order to determine the efficiency of nitrogen fertilizer uptake and identify rice varieties adaptable to low soil nitrogen. A field research was carried out at the experimental farm of Kenya Agricultural and Livestock Research Organization (KALRO- Mwea), Kirinyaga County (0°39′S, 37°20′E).The experiment was split-plot in a randomized complete block design (RCBD), replicated three times. The main plot treatments were five upland rice varieties, MWUR1 (M1), MWUR4 ((M4), NERICA4 (N4), NERICA10 (N10) and IRAT 109. Four N rates, 0, 26, 52 and 78 kg N ha-1, were randomly allocated to subplots. Calcium ammonium nitrate (26%N) was top-dressed in two equal splits at 21 and 45 days after sowing, without P and K application. Soil sampling was done before planting for analysis, to establish the soil nutrient status. The growth parameters determined included plant height, tiller numbers, leaf area, leaf chlorophyll content and stomatal conductance. At maturity, grain yield, shoots dry weight, root dry weight, culm length and panicle length were determined. Plant tissue and grain nitrogen content analysis were also determined by Kjeldahl method. Analysis of variance was performed using Statistical Analysis System version 9.00. Mean separation was done using least significance difference at a 5 % level of probability. Associations between variables were determined by polynomial functions in regression analysis. Although results revealed significant variations due to varieties and N treatments, the interaction between varieties and N treatments were not significant (P ≤ 0.05) on grain yield. NERICA 4, MWUR 1 and MWUR 4 recorded higher plant height, higher filled grain ratio and higher yield components hence may be suitable for soils with low nitrogen. Across all varieties and N treatments, grain yield correlated positively ((P ≤ 0.05) with total plant shoot dry weight (R2=0.95). In addition, root dry weight, culm length, number of tillers and panicle length positively correlated with grain yield. There were significant variations ((P ≤ 0.05) in nitrogen partitioning from the soil to the grains under nitrogen rates, unlike in the varieties. The results from this study revealed lack of interactions between varieties and nitrogen rates meaning that the rice varieties did not have synergetic effects on nitrogen uptake and utilization due to incremental nitrogen. Further studies are recommended on nitrogen use efficiency in upland rice under low soil fertility. In addition, cost benefits analysis of low soil nitrogen upland rice production need to be undertaken.