the Symposium on Wheats for More Tropical Environments - cimmyt

Wheat in Rice...BasedCropping Systems in ThailandK. Rerkasem and B. Rerkasem. Multiple Cropping Project. ChiangMai University. Chiang Mai. ThailandAbstract265Rice-based multiple cropping in Thailand is currently restricted by <strong>the</strong> lowtemperatures of<strong>the</strong> season after rice harvest; this limits <strong>the</strong> growing of tropicaland subtropical crop species, such as rice or soybeans. The shortage ofirrigationwater after December is also a restriction. A rice-wheat system, with wheat'sadaptability to a cool season and its relative tolerance to water stress, offers amore efficient use oflimited resources. The requirementfor early rice harvestcan easily be met by choosingfrom a wide range ofearly rice varieties,traditional ones as well as <strong>the</strong> new IRRI types. In terms ofmanagement, landpreparation may be a major problem as well as micro-nutrient deflciences.Seasonal and spatial distribution ofirrigation water must be considered indetermining <strong>the</strong> potential area of rice-wheat cropping in nor<strong>the</strong>rn Thailand.The Potential of Wheat inRice-Based Cropping SystemsIn nor<strong>the</strong>rn Thailand, where wheatappears to have some potential, <strong>the</strong>reare about 0.5 million hectares ofirrigated rice land; this is <strong>the</strong> possiblearea for a rice-wheat cropping system.A typical regime of rainfall andtemperature for nor<strong>the</strong>rn Thailand isshown in Figure 1. The rains end quitesuddenly in October, so that any dryseasoncropping after rice must rely onirrigation. The period from November toFebruary has sufficiently lowtemperature for temperate crops suchas wheat to be grown, but <strong>the</strong> low nighttemperatures may limit tropical crops.The planting of soybeans, <strong>the</strong> majorcrop grown after rice, must wait until<strong>the</strong> end of December, because of lownight temperatures; <strong>the</strong>re is an evenlonger delay for dry-season rice.Because of this, <strong>the</strong> current growingseason for a rice-based cropping systemmust extend to April or even later.Wheat, on <strong>the</strong> o<strong>the</strong>r hand, has beensuccessfully planted in October andNovember, with an averageexperimental yield of 3.6 Uha and abest yield of 5 tJha with INIA 66. Thelower evaporative demand fromNovember to February also can lead tomuch better water-use efficiency. O<strong>the</strong>rcrops which currently utilize <strong>the</strong> coolseason are garlic. vegetables andtobacco. Their total area is relativelylimited, due to restricted demand. Ricewheatoffers an improvement in landand water-use efficiency. with itsshorter growing season and betteradaptation to cool wea<strong>the</strong>r (Figure 2).However, <strong>the</strong>re are several agronomicconsiderations that may haveimplications on large-scale adoption of<strong>the</strong> rice-wheat system in nor<strong>the</strong>rnThailand.Management Problemsof Wheat after RicePlanting dateThe growing season for wheat innor<strong>the</strong>rn Thailand is relatively short(Figure 1). It is essential that <strong>the</strong> cropbe planted as early as possible. beforetemperatures begin to rise again.Results from planting-date studies varyconsiderably from year to year. possiblydue to slight variations in <strong>the</strong> length of<strong>the</strong> cool season. The latest date that <strong>the</strong>currently available varieties. such asINIA 66 and CMU26. can be plantedwithout drastic yield reduction rangesfrom <strong>the</strong> end of November to mid­December (2).