Performance of irrigated lowland rice (Oryza sativa L.) under different nitrogen levels and control measures for stem borer (Chilo suppressalis Wlk., Scirpophaga incertulas Wlk.) and sheath blight (Rhizoctonia solani K.)
1998
Noack, R.
Grain yield increased from 398 g/sq m to 441 g/sq m when nitrogen fertilizer rate was increased from 67.5 kg N/ha to 105 kg N/ha. The application of insecticide against stem borer and its combination with fungicide against sheath blight increase grain yield. The yield increase was, however, 9 percent below the simulated yield potential of 554 g/sq m. Application of fungicide alone was ineffective in increasing grain yield. The number of hills infested with stem borer and sheath blight infected hills was higher in plots fertilized with the higher level of nitrogen. The number of white heads/sq m was correlated negatively with grain yield obtained from area samples at the higher N rate. The nitrogen content on the straw of healthy hills (0.79 percent) was lower than those of hills with dead hearts, white heads and sheath blight with about 1.10 percent, 1.08 percent, and 1.00 percent, respectively. The average of all plant materials showed a higher nitrogen accumulation in the straw at plots with the higher nitrogen level. Samples from healthy hills showed an increase in number of panicles and grain weight at the higher nitrogen rate. No significant yield reduction in hills infested with stem borer was found at high nitrogen levels. Rice plants compensate for dead heart damage by development of new tillers and for white head damage by an increase in number of grains per panicle. The number of white heads and grain weight per hill correlated negatively at the lower nitrogen level. Hills with sheath blight showed a reduction in leaf chlorophyll content; number of panicles and in grain weight at both N levels. The magnitude of yield reduction due to pest infestation was sheath blight alone sheath blight plus stem borer stem borer alone
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