Water Productivity of Irrigated Rice under Transplanting, Wet Seeding and Dry Seeding Methods of Cultivation

摘要

Water productivity (WP) of irrigated lowland rice was determined during the 1994 dry (January to May) and wet (August to December) seasons on a heavy clay acid sulphate soil. Treatments consisted of three cultivation methods: transplanted rice, pregerminated seeds broadcasted on puddled soil (wet seeding) and dry seeds broadcasted on unpuddled soil (dry seeding). In wet and dry seeded plots, continuous standing water condition was initiated 17 days after sowing.Total water requirement for rice production was highest in transplanted plots (755 mm in wet season and 1154 mm in dry season) and was lowest in dry seeded plots (505 mm in wet season and 1040 mm in dry season). Dry seeding required no water for land preparation but transplanting and wet seeding methods required 18 - 20 % of total water requirement in dry season and 27 - 29 % in wet season. Total percolation was maximum (99 mm in wet season and 215 mm in dry season) in dry seeding method and was minimum(62 mm in wet season and 94 mm in dry season) in transplanting method. In dry and wet seeding methods, daily percolation gradually decreased with the age of the crop. Total seepage loss did not show any significant difference between the cultivation methods in the two seasons. Grain yield was not affected by the three cultivation methods in both seasons. Water productivity (the ratio between grain yield and total amount of water used in production) was 3.5 - 4.1 kg ha~(-1) mm~(-1), 3.8 - 4.4 kg ha~(-1)mm~(-1) and 4.1 - 5.5 kg ha~(-1) mm~(-1) in transplanted, wet seeded and dry seeded rice, respectively. Labour requirement for land preparation and sowing was maximum in transplanted (219 - 226 man-hours ha~(-1)) followed by wet (104 -112 man-hours ha~(-1)) and dry seeded (94 - 99 man-hours ha~(-1)) methods. However, in wet season extra labour (77 man-hours ha~(-1)) was required for weeding after crop establishment in dry and wet seeding methods. Crop maturity was 20 days earlier in wet and dry seedingmethods compared to transplanting. Dry seeding was considered the best rice cultivation method on heavy clay soils with expanding type of clay minerals to save water and labour cost.