Increasing Water Productivity of Irrigated Rice Through Varying Nitrogen And Water Management Methods

ABSTRACT

Globally, rice (Oryza sativa L.) is the third largest cultivated cereal crop with about 79 million hectares of irrigated lowlands providing 75% of the world’s rice production. Its productivity depends on many factors including Nitrogen (N) fertilizer and water management. This study was conducted to determine the effect of water management and N fertilizer on growth and yield of rice. The study also sought to evaluate the cost effectiveness of water use under various water management methods. To achieve the set objectives, pot and field experiments were conducted at Soil and Irrigation Research Centre (SIREC), Kpong between July, 2015 and January, 2016. The pot experiment was designed as randomized complete block (RCBD) in factorial arrangement of three water management treatments namely; continuous submergence (submerged), alternate wet and dry (AWD) and moist soil condition (moist) and three nitrogen fertilizer rates; no N fertilizer (N0), 60 kg N/ha (N1) and 90 kg N/ha (N2). In the field experiment, a split plot design with water management treatments as main plot and the three Nfertilizer treatments as subplots was used. Data including tiller numbers, leaf area index, above biomass accumulation, leaf chlorophyll content, days to 50% flowering, grains/panicles, panicles/m2 , 1000 grain weight, grain yield and harvest index were collected. In addition, data on water use, water productivity, nitrogen uptake, nitrogen use efficiency, cost and benefit analysis were also recorded. Results obtained from both experiments revealed that, plant growth, yield and yield parameters were significantly influenced by water management and N fertilizer and their interaction except 1000 grain weight and days to 50% flowering. Analysis of variance further revealed that plant growth and yields were at par in AWD and submerged but yields were lower (3.4 t/ha) in moist treatment. N fertilizer had positive effect on rice growth and yields with higher yields (5.8 t/ha) observed when plants were treated with 90 N kg/ha. The interaction effect vi of submerged with 90 kg/ha N gave the highest grain yield (6.5 t/ha). For both pot and field experiments, N fertilizer effect on N uptake, water use and water productivity was ranked as N2 > N1 > N0. N uptake was found to be higher in AWD than moist but was at par with submerged treatment. Water management effect on water use and water productivity was ranked in this order: Submerged > AWD > Moist and Moist > AWD > Submerged respectively. AWD treatment had the highest net profit (9341.7 GH₵/ha) and thus making it most cost effective water management method for irrigated rice farming.