Effect Of Nitrogen Fertilizer Rate And Split Application On Growth And Yield Of Selected Rice Varieties In Mwea Irrigation Scheme

Abstract

Irrigated rice production is the main source of livelihood for a majority of farmers in Mwea Irrigation Scheme and its environs. The rice yields have, however, been declining progressively and this can be partly associated with poor fertilizer management techniques. Thus, a field experiment was conducted at Mwea Irrigation and Agricultural Research (MIAD) center for two seasons (March to July, 2015 and August to December, 2015) with three specific objectives: (1) to document existing soil fertility management practices for rice production; (2) to determine the effect of different nitrogen fertilizer rates on the growth and yield of three rice varieties; and (3) to determine the effect of split nitrogen fertilizer application on the growth and yield of three rice varieties. To achieve the first objective, a survey was carried out in five sections of the irrigation scheme namely, Karaba, Tebere, Thiba, Wamumu and Mwea using a semi-structured questionnaire that was administered to 200 farmers (40 farmers randomly selected from each section). Data collected included; soil fertility maintenance practices, types, sources and rates of organic and inorganic fertilizers used by the farmers, and the status of major weeds and diseases and their control measures. Statistical Package for the Social Sciences (SPSS) program version 20 was used to analyze the data obtained from the survey. In the second and third objectives, a field experiment was conducted in which four nitrogen fertilizer rates (0, 40, 80 and 120 kg/ ha) and split N fertilizer application (Basal + one top-dressing at panicle initiation stage and Basal + two topdressings at tillering and panicle initiation stages) were tested against three rice varieties (IR 05N 221, ITA 310 and BW 196) in a randomized complete block design with a split-split plot arrangement. Data collected included: plant height (cm), number of tillers per plant, panicle length, and days to 50% flowering, 1000 grain weight and grain yield (kg) at 14% moisture content. The data collected were subjected to analysis of variance (ANOVA) using GENSTAT 15th edition and comparison of treatment means tested at p = 0.05 using the least significant xii difference (LSD) test. All the farmers interviewed reported to use fertilizers in rice production with sulphate of ammonia (SA) being the most widely used fertilizer. However, only 2% of those interviewed had their soil tested at least once since they started rice production. More than half of the interviewed farmers bought their fertilizers from either input dealers or commercial farmers. Lack of enough water for irrigation, high input prices, low market prices for the harvested produce, pests and diseases, weeds, poor infrastructure especially the roads, labour expenses and birds’ infestations were cited as the major challenges in rice production by farmers across the five sections. Majority of the farmers (95.8%) did not rotate rice with any other crop in their fields. In all the five sections of the scheme, only (17.98%) of the farmers had received training on soil fertility management which was cited as the leading need to help them improve soil fertility. Azolla was the most common weed and water shortage was cited as the greatest challenge faced by the farmers in rice production. Rice variety ITA 310 had significantly taller plants in both seasons than variety IR 05N 221 and BW 196. Variety IR 05N 221 had significantly more tillers per plant than varieties BW 196 and ITA 310 in both seasons. Variety BW 196 had more panicles per plant in the first season while IR 05N 221 had more panicles per plant in the second season. Variety BW 196 had longer panicles in both seasons of the experiment compared to varieties IR 05N 221 and ITA 310. Variety BW 196 had significantly more net grain yield in both seasons in comparison with varieties IR 05N 221 and ITA 310. Nitrogen application rate of 80kg N/ha had significantly higher number of panicles per plant and net grain yield in both seasons. Split nitrogen application regime of a basal plus top dressing at tillering and panicle initiation stages had more tillers per plant in the first season while that of a basal plus top dressing at tillering stage had more tillers per plant in the second season. The split application regime of a basal plus top dressing at tillering and panicle initiation had taller plants in both seasons. There were significant differences xiii in split application of nitrogen fertilizer. Split application of nitrogen as a basal plus top dressing at tillering recorded more yield than that of a basal plus top dressing at tillering and panicle initiation stages. From the study, it can be concluded that application of nitrogen fertilizer in splits can increase the productivity of rice.