肥水管理对稻田主要害虫种群及产量的影响

试验结果表明,在自然情况下,杂交中稻田害虫及天敌的种群密度,随着施氮量的增加而增加,其幅度因年度而异,中等发生年大于大发生年。在同一施氮量下,田水深浅对害虫的效应,因害虫种类而不同,白背飞虱和褐稻虱明显,稻纵卷叶螟和稻蓟马没有差异。杂交中稻在不防治害虫的情况下,因受害虫为害而造成的损失,与施氮量呈正相关。多施氮肥区比药剂保护区减产5成以上;一般施氮水平减产3成;少施氮肥的减产2成左右。

INFLUENCE OF N FERTILIZER LEVEL AND IRRIGATION ON POPULATION DYNAMICS OF THE MAJOR INSECT PESTS IN PADDY FIELDS AND CONSEQUENT RICE YIELD

Experiments were carried out to investigate the variation of population size of the major insect pests and their natural enemies in paddy fields at different N fertilizer levels and irrigation conditions as well as the loss of rice yields caused by the insect pests. The results showed that the population densities of the pests on midseason hybrid rice:and their natural enemies increased with increase of N fertilizer applied. The range of variation in years of moderate injury was wider than that in years of .heavy injury. At a definite level, of N fertilizer applied the influence of, water depth on the population densities differed with different pest species as compared, with 'the fields without N fertilizer application and with only light N fertilizer application (5 kilograms of N per mu). Population densities of Sogatella furifera (Plorvath) and Nilapar-vata lug ens (Stal) in fields with deep waier were much higher than those in fields with shallow water but the difference became insignificant when high level of N fertilizer was applied (20 kilograms of N per mu). On the other hand, Cnaphalowocis medinalis (Guenee) and Stenchaetotlirips biformis (Bagnall) did not show such variation in population densities at different water depths. The results also showed that the yield loss of the midseason hybrid rice due to pest injury as a whole was positively correlated with the level of N fertilizer applied. Plots of high. N fertilizer .level lost more than 50% of the rice yield as compared with the plots with the same fertilizer level but under p'esticide treatment, while plots of medium N fertilizer level (10 kilograms N per mu) lost 30%. Plots of low N fertilizer level gave yield only 20% less. Therefore, in rice areas of high production, more damage is likely to be caused by insect pests due to the high level of N fertilizer and chemical control beeomes more important.