Effects of different fertilization practices on the incidence of rice pests and diseases: A three-year case study in Shanghai, in subtropical southeastern China

To implement organic rice farming around a drinking water source in the western suburbs of Shanghai, pioneering field experiments on the relationships between fertilizer applications and occurrences of rice pests and diseases were performed without the use of pesticides and fungicides from 2012 to 2014. The rice plants treated with chemical fertilizers (CF) accumulated higher content of available nitrogen (NH4+ + NO3−) and grew higher and more luxuriantly, but they were more susceptible to pests and diseases. Comparatively, the plants treated with organic manure demonstrated higher resistance to rice pests and diseases and grew more healthily. However, excessive application of organic manure also increased the risks of pests and diseases. The unfertilized plants were highly deficient in nutrients, but they maintained the lowest rates of pests and diseases. This suggests that rice pests and diseases were easily triggered by a high content of N-related nutrients in plant tissues and inhibited by nutrient deficiency. Annual climatic conditions also deeply affected the occurrences of rice pests and diseases. Long-term warm and humid weather in the growing areas favored the development of herbivorous pests and fungal diseases. The incidence of migratory pests in Shanghai is also linked to violent summer storms. Frequent rain storms in southern or southwestern China increased the chance of infestations of migratory pests in Shanghai. Rice yield was primarily determined by the infestations of pests and diseases. In the pest-infested year of 2012, the grain yield for the different fertilizers was only 40%-44% of that under conventional farming practices, and the yield in CF was even significantly lower than that in the unfertilized CK. In 2013, with lower infestation rates, the grain yield of the different fertilizers was more than 80% of the conventional yield. The application of a lower amount of organic manure, 2100 kg ha−1 of cake manure, was recommended for the implementation of organic rice farming in the water source areas in Shanghai.