Weed management in dry seeded rice in the northeast Thailand

Summary onl

Lowland rice improvement in northern and northeast Thailand 1. Effects of fertiliser application and irrigation

Yield of rainfed lowland rice is commonly low because of frequent drought and low fertiliser input. Seven experiments were conducted in Thailand in the period 1993-1995 where effects of various fertiliser regimes: nil, farmyard manure, chemical fertiliser with different rates of N were examined under irrigated and rainfed conditions. The objective of these experiments was to quantify irrigation, fertiliser and their combined effects on crop growth and grain yield of lowland rice. While there was not always standing water in the rainfed paddy, no severe water stress developed in any experiment. The yield, however, was lower by up to 65% under rain fed conditions compared to that obtained under irrigated conditions, and the reduction in yield was greater when no fertiliser was applied. Fertiliser application improved yield under both rainfed and lowland conditions in all experiments, and was particularly effective under rainfed conditions. The mean yield increase due to the farmyard manure application was 850 kg ha, while that of chemical fertiliser was 1000 kg ha. Farmyard manure was as effective as chemical fertiliser, provided the manure contained high nutrient content. Increased N rate at an adequate level of P and K supply increased grain yield by about 10 kg kg (applied N) in treatments with adequate water. The positive effect of fertiliser and irrigation was mostly through greater total dry matter production and panicle number with little effect on harvest index. It is concluded that without severe water stress, grain yield of rainfed lowland rice can be increased with increased nutrient availability. This can be achieved by maintaining standing water for longer or by applying an appropriate fertiliser

Lowland rice improvement in northern and northeast Thailand 2. Cultivar differences

Seven rice experiments were conducted each with 4-6 cultivars to determine if cultivars differed in response to fertiliser and irrigation application in lowland conditions in Thailand. Severe drought did not develop in any of the experiments, but irrigation and fertiliser application increased the yield in most experiments. There were significant cultivar differences in each experiment and cultivar ranking was consistent across experiments. Thus IR57514-PMI-5-B-1-2 out-yielded traditional cultivars KDML105 and NSG19 in most environments, except in very unfavourable conditions where mean yield was below 1000 kg ha. Quick maturing cultivars yielded least because they produced less total dry matter than later maturing cultivars in most environments. Recently developed cultivars had higher harvest index compared to traditional cultivars. In some experiments there were significant cultivar-by-fertiliser or cultivar-by-irrigation interactions. In one experiment, IR20 was more sensitive to soil water deficit than other cultivars whereas response to fertiliser was greatest in IR57514-PMI-5-B-1-2. Overall, however, experimental conditions were favourable and under these conditions these interactions were small. It is, therefore, concluded that cultivars selected under high fertiliser and irrigated conditions are likely to perform better in all but most unfavourable growing conditions

Growth and grain yield of contrasting rice cultivars grown under different conditions of water availability

Rice crops are susceptible to drought, which causes large yield losses in many Asian countries. The development of drought-resistant cultivars may be assisted if mechanisms of drought resistance are known. This work was carried out to elucidate how some rice cultivars achieve higher yield than others under water-limiting conditions. A total of 11 experiments were conducted in northeast Thailand, and four contrasting cultivars were compared in each experiment for phenological development, dry matter growth, leaf death, grain yield and yield components. High-yielding cultivars were generally short statured and had high harvest index, and they tended to perform better than others in all conditions of water availability. When drought developed during late growth stages, early flowering to escape water stress was an important character. During late drought some cultivars were able to retain green leaves longer than others and increased dry matter when others stopped growing. It is thus concluded that cultivars suitable for rainfed conditions are those with high yield potential resulting from high harvest index under favourable growing conditions, appropriate flowering time to escape severe water stress that commonly develops after the end of the rainy season, and an ability to maintain growth during drought so that yield determining processes can be completed with minimum disturbance