Recent progress in cassava agronomy research in Thailand

Abstract

Cassava agronomy research in Thailand during 1994-1996 emphasized mainly erosion control, soil fertility maintenance and weed control. Regarding soil erosion control, the planting of cassava in April, at the start of the rainy season, and harvesting in March resulted in the highest soil loss compared with other planting dates. Planting at the start of the dry season in Dec and harvesting in Nov produced by far the highest cassava yield, while soil loss due to erosion was relatively low. Intercropping cassava with either peanut or pumpkin were found to be the best cropping systems to reduce erosion while also giving high gross incomes. Cassava planted on contour ridges at closer spacing (1.0x0.6 m) and with fertilizer application was the most promising package of cultural practices for reducing erosion and increasing yields. Soil fertility maintenance through the use of legumes grown for in-situ production of mulch was studied at Rayong Research Center. The highest yield of cassava, 46.17 t/ha, was obtained when Crotalaria juncea was planted as a green manure and mulched, followed by planting cassava, which was then harvested after 18 months. When Canavalia ensiformis was intercropped with cassava, cut at 2 months and left as a mulch, the yield of cassava, harvested at 12 months, was as high as that obtained with a high rate of chemical fertilizers. The sequential planting of fertilized Rayong 60 after unfertilized peanut, produced the highest yield at Kalasin in the Northeast. The cultivar Rayong 5 planted in either Sattahip or Banbung soils in the East produced a relatively high yield with application of 312 kg/ha of 15-15- 15 together with 100 kg of urea and 78 of KCl/ha. In the Northeast the application of 25-25-25 kg/ha of N, P2Os and K2O produced a significantly higher yield of Kasetsart 50, Rayong 5, Rayong 60 and Rayong 90 than without fertilizer application. Research on the long-term effect of soil management on cassava planted continuously for 15 years in Khon Kaen in the Northeast, showed that when cassava was rotated yearly with sequentially planted peanut and pigeonpea, this could maintain a relative cassava yield of 87 % of that obtained in the first year. Similarly, the application of soil amendments (lime, rock phosphates and compost), as well as that of soil amendments with chemical fertilizers, could reduce the rate of yield decrease over time. However, after 15 years of continuous cropping the cassava yields in all treatments were lower than those obtained in the first year. Research on the optimum period of weed control for Rayong 60 and Rayong 90, planted in both the early and late rainy seasons in the Northeast, indicate that both cultivars need to be free of weeds at least three months after planting in order to produce high yields