the Symposium on Wheats for More Tropical Environments - cimmyt

268directly into <strong>the</strong> rice stubble, as iscommonly done with soybeans.Preliminary studies have shown that<strong>the</strong> growth of wheat in rice stubble isbetter than in tilled soll (Table 1). Themethod of sowing wheat into stubbledeserves fur<strong>the</strong>r attention. Thepopulation density of wheat needs to be16 to 20 hills per square meter, higherthan <strong>the</strong> original spacing of <strong>the</strong> old ricecrowns.Yield decUneIn <strong>the</strong> last twenty years, <strong>the</strong>re has beena remarkably rapid expansion ofmultiple cropping in nor<strong>the</strong>rn Thailand.Table 1. A comparison of wheat yields from stubble-sown and conventional tillage, ThailandConventional tillageStubble-sown(plantslm2)Density effects (50 plantslm2) 150 45 112Yield h/ha)Grain 1.84 2.18 0.30 1.00Straw 1.83 2.20 0.70 0.80Total dry matter 3.67 4.38 1.00 1.80Yield (g!plant)Grain 3.68 1.45 0.67 0.89Straw 3.66 1.47 1.56 0.71Total dry matter 7.34 2.92 2.22 1.60Source: Jongkaewwatana, S., and K; Rerkasem. 1982. A study of yield~ensityrelationshipon wheat in a rice-wheat system (in Thai). In Proceedings of <strong>the</strong> Third NationalWinter Grain Workshop, Nor<strong>the</strong>rn Agricultural Development Centre, Bangkok,Thailand.Table 2. Responses to boron application on upland crops grown in rice-based systems,Chiang Mai, ThailandBorax application(kg/ha) .Grain yield(g/m2)Sunflower~/Mungbean Jl!0 74.68 169.46.7 298.476.7 +Zn 277.3110 428.90 311.4Sunflower Soybeans Peanut Wheat0 188.49 197.98 144.66 219.2910 314.88 207.48 157.37 219.1220 295.38 207.45 130.90 215.8140 311.11 160.26 141.86 189.56~/ Grown in sunflower-mungbeal1-rice system9,/ Dry matter yield