Abstract
Rice production in Tanzania, with 67% of its territory considered semi-dry and having average annual rainfall of 300 mm, must be increased to feed an ever-growing population. Water for irrigation and low soil fertility are among the main challenges. One way to decrease water consumption in paddy fields is to change the irrigation regime for rice production, replacing continuous flooding with alternate wetting and drying. In order to assess the impact of different irrigation regimes and nitrogen fertilizer applications on growth, yield, and water productivity of rice, a greenhouse pot experiment with soil from lowland rice ecology was conducted at Sokoine University of Agriculture, Tanzania during the 2019 cropping season. The experiment was split-plot based on randomized complete block design with 12 treatments and 3 replications. Water regimes were the main factors comparing continuous flooding (CF) and alternate wetting and drying (AWD) with nitrogen fertilizer levels as the subfactor, comparing absolute control (no fertilizer) with 0 (P and K fertilizers), 60, 90, 120, and 150 kg Nha−1. Alternate wetting and drying (AWD) significantly improved water productivity by 8.3% over CF (p < 0.05). Water productivity (WP) ranged from 0.6 to 1.5 kg of rice per m3 of water. Average water use ranged from 36 to 82 L per season, and water saving was up to 34.3%. Alternate wetting and drying significantly improved yields (p < 0.05) by 13.3%, and the yield ranged from 21.8 to 118.2 g pot−1. The combination of AWD water management and 60 kg N ha−1 nitrogen fertilization application was found to be the optimal management, however there was no significant difference between 60 and 90 kg N ha−1, in which case 60 kg N ha−1 is recommended because it lowers costs and raises net income. Nitrogen levels significantly affected water productivity, water use, and number of irrigations. Nitrogen levels had significant effect (p < 0.05) on plant height, number of tillers, flag leaf area, chlorophyll content, total tillers, number of productive tillers, panicle weight, panicle length, 1000-grain weight, straw yield, grain yield, and grain harvest index. The results showed that less water can be used to produce more crops under alternative wetting and drying irrigation practices. The results are important for water-scarce areas, providing useful information to policy makers, farmers, agricultural departments, and water management boards in devising future climate-smart adaptation and mitigation strategies.
Highlights
Rice (Oryza sativa L.) is one of the most important grain crops for more than 50% of the world’s population, providing approximately 20% of total energy intake for humans [1].Rice is a substantial part of the protein intake for about 520 million people living in poverty in Asia
Water management under AWD improved water productivity by 8.3% over continuous flooding (CF)
It can be concluded that nitrogen was a limiting factor for rice productivity. wetting and drying improved yield significantly (p < 0.05) by 13.3%. ranged from 21.8 to 118.2 g pot−1 in which AWD ×150 recorded higher grains yield (118.2 g), followed by AWD × 120 (108.6 g), and lowest yield was recorded under absolute control (21.8 g)
Summary
Rice is a substantial part of the protein intake for about 520 million people living in poverty in Asia. In Asia, more than 2000 million people obtain 70% of their calories from rice and its products [2]. In sub-Saharan Africa, rice consumption among urban dwellers in Tanzania has steadily grown, with a per capita consumption that has doubled since 1970 [1]. According to FAO [3], 59 million tons of additional milled rice will be needed by 2020 above the 2007 consumption of 422 million tons. Since there is limited capacity to increase the area of rice cultivation due to urbanization and severe water constraints, additional production must come from less land, less water, and less production costs
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