the Symposium on Wheats for More Tropical Environments - cimmyt

277Rice-Wheat Cropping Systemsin South and Sou<strong>the</strong>ast AsiaV.R. Carangal, International Rice Research Institute, Manila,PhilippinesAbstractRice-wheat rotation is practiced in South Asia in India, Pakistan, Nepal, Bhutan,Bangladesh, Burma and China. In Sou<strong>the</strong>ast Asia, wheat is not yet acommercial crop, but national programs are intensifying <strong>the</strong>ir research becauseof increasing demand and heavy importation. IRRI and CIMMYT arecollaborating with 13 countries involved in <strong>the</strong> Asian Rice Farming SystemsNetwork to identify suitable varietal combinationsfor rice-wheat croppingsystems and to evaluate performance of rice-wheat systems in different riceenvironments in Asia. In South Asia, rice-wheat is <strong>the</strong> most predominantcropping pattern; in some countries, it is rice-wheat-upland crop. Most croppingpatternevaluations indicate that three-crop systems give higher production andnet returns than do two crops. The Philippines, Indonesia, Thailand. Burma andSri Lanka are especially interested in increasing wheat production. Varietytrials in nor<strong>the</strong>rn Thailand and high elevation areas have given yields of up to3.5 t/ha. Thefirst International Rice-Wheat Integrated Trials in <strong>the</strong> Philippines,Burma and Thailand showed low yield levels; agronomic management studiesat IRRI reported only up to 2.5 t/ha. There is a need to develop better varietiesfor <strong>the</strong> tropics and better agronomic management in ricefields.Rice and wheat are <strong>the</strong> most importantcereal crops in <strong>the</strong> world. About 90% of<strong>the</strong> world's rice is grown in Asia, withIndia and China accounting for about60%. Rice is grown in temperate,subtropical and tropical countries,under both rainfed conditions (upland,lowland and deepwater) and irrigation(including partial irrigation). Wheat ismainly cultivated in <strong>the</strong> subtropical aridtemperate countries in Asia, usuallywith irrigation under lowlandconditions. In some rainfed lowland anddeepwater areas, wheat is also grown,especially in areas with good moisturelasting into <strong>the</strong> dry season.Rice-wheat rotation is practiced intemperate and subtropical Asia. In <strong>the</strong>last 15 years, <strong>the</strong> rice-wheat rotationhas rapidly expanded to nontraditionalrice-wheat areas, mainly due to <strong>the</strong>development of photo-insensitive, earlymaturing,nonlodging. high-yielding,disease and pest-reSistant varieties ofrice and wheat, but also to <strong>the</strong>development of better agronomicpractices and <strong>the</strong> expanSion ofirrigation. In irrigated areas, rice-wheat,rice-rice-wheat, rice-wheat-upland cropand rice-upland crop-wheat are <strong>the</strong>common cropping patterns. Rice-wheatrotations are mainly practiced in Indiaand Pakistan, and have recentlybecome important rotations in Nepal.Bhutan and Bangladesh.In tropical countries where wheat is nota commercial crop, attention is nowbeing given by national programs to <strong>the</strong>production of wheat because of heavyimportation for local consumption.Research is now in progress in <strong>the</strong>Philippines, Indonesia, Thailand,Burma and Sri Lanka to developappropriate wheat productiontechnology. With <strong>the</strong> development ofearly-matUring rice varieties (100 to120 days), wheat can now be grownunder irrigation and partial irrigationon light to medium-textured soilsdUring <strong>the</strong> dry season, usually <strong>the</strong>cooler months of <strong>the</strong> year. It can also be