Soil nutrient-pest interaction in a sustainable rice production system

A study was conducted at the PhilRice Central Experiment Station in dry season and wet season of 2004 using the hybrid rice variety PSB Rc72H and inbred variety PSB Rc82. The study was laid out in a Randomized Complete Block Design with five treatments each in three replications at 104 sq m per plot. Specifically, the treatments were T1=EM Organic fertilizer at 2.0 tons/ha, T2=Inorganic Fertilizer at 120-40-60, T3=Compost at 5.0 tons/ha, T4=Carbonized Rice Hull (CRH) at 3.0 tons/ha + EM Organic Fertilizer at 300 kg/ha, and T5=Control (no fertilizer application). The objectives were to determine the effects of organic farming and microbial technology on profiles of rice insect pests, natural enemies, diseases and other pests, and to determine the relationship between soil nutrient and pest incidence in a sustainable rice production system. Population counts revealed that green leafhopper (GLH) predominated the insect pests present in both PSB Rc72H and PSB Rc82. Spiders, mirid bugs and lady beetles were the most dominant natural enemies observed in both cropping seasons. During the dry season, the only disease observed was sheath rot with 12.5 percent incidence during the dough stage, whitehead caused by stem borer was recorded at 10 percent but only on the hybrid variety. No disease or insect damage was observed in the inbred variety. Furthermore, bacterial leaf blight (BLB) was not observed even after artificial inoculation of both varieties. The diseases observed during the wet season were blast, bacterial leaf blight and false smut. In the hybrid variety, high incidence of blast (58.11 percent) with a severity rating of 9 was observed in one plot of treatment 2. In one plant of treatment 3, the incidence was higher (72.58 percent) but with a lower severity rating of 3. Blast incidence was also noted in treatment 2 (11 percent) and 3 (5 percent) in the inbred variety. BLB incidence was high in both varieties in inoculated and uninoculated (natural infection) rice plants. Highest BLB rating was recorded in treatment 2 in all growth stages in both varieties. However, even though there were significant differences in disease incidence among the treatments, there was no significant difference obtained in yield of both varieties. Furthermore, courts of whitehead caused by stemborer showed significant differences among treatment means in the hybrid although generally, whitehead count was low in both varieties during the wet season. Whitehead using very minimal in the dry season.