Changes in the uptake function of the rice root to nitrogen, phosphorus and potassium under brown planthopper, Nilaparvata lugens (Stal) (Homoptera: Delphacidae) and pesticide stresses, and effect of pesticides on rice-grain filling in field

Effects of different BPH densities and pesticide applications on the uptake of nitrogen (N), phosphorus (P) and potassium (K), by the root system were investigated using a hydroponics culture. Infestations of 30 BPH had a significant effect on the uptake function of the rice root. A high dose (225 g.a.i. ha(-1)) of jingganmycin reduced the uptake of P and K significantly, but there was little effect on the uptake of N. At a low dose (15 g.a.i. ha(-1)) of imidacloprid the uptake of P and K was promoted significantly. There was also a significant interaction effect between BPH density and pesticide treatments. Field experiment during rice-grain filling showed that both low and high doses of imidacloprid reduced active growth stage (Deltat) and maximum (K) of grain growth of superior grains significantly and a high dose reduced K and growth rate of inferior grains significantly. All doses of imidacloprid and jingganmycin significantly reduced accumulative grain weight during Deltat. A high dose of imidacloprid reduced the growth rate of inferior grains significantly. (C) 2004 Elsevier Ltd. All rights reserved.