Relationships between rice intensification, plant nutrition, and diseases in the Red River Delta [Viet Nam]
1995
Ha Minh Trung | Ngo Vinh Vien | Dinh Thi Thanh | Nguyen Thanh Thuy | Ha Minh Thanh | Cassman, K.G. | Mew, T.W. | Teng, P.S. | Cu, R.M.
Average rice yield in the Red River Delta increased from 2.7 t/ha in 1985 to 3.7 t/ha in 1992. This increase was associated with intensification of input use, particularly nitrogen (N) fertilizer and pesticides. Despite an increase in fungicide use, however, disease pressure has also increased so that sheath blight, blast, and more recently a yellow-leaf disorder now causes yield losses of 20 percent or more on nearly 200,000 ha each year. In on-farm experiments in Ha Tay Province in the 1993 spring and summer rice-cropping seasons, the N and potassium (K) concentration in the uppermost leaves after the flowering stage indicated a deficiency for these nutrients with the farmers' level of nutrient management. Increased rates of NPK fertilizer (P, phosphorus) increased yields by 14-19 percent; however, they were still limited by disease. Preventive fungicide applications, (PFA, in addition to the farmers' fungicide application) increased yields by 24-54 percent and the combined effects of PFA and, increased NPK gave yield increases of 30-66 percent above farmers' normal practices. Although normal farmers' practices with fungicide had no effect on disease incidence or yield, PFA reduced disease incidence by 80-90 percent. In both seasons, yield loss from disease resulted mostly from a reduction in spikelet fertility. The potential roles of K deficiency, other nutrient imbalances, and other factors in predisposing the rice plant to disease infection need further elucidation. It is also clear that significant and large yield increases are possible from improved nutrient and disease management
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