Optimizing tillage schedule for maintaining activity of the arbuscular mycorrhizal fungal population in a rainfed upland rice (Oryza sativa L.) agro-ecosystem.

Rainfed uplands in India are predominantly mono-cropped with rice (Oryza sativa L.) in the wet season (June/July to September/October) and grown under aerobic soil conditions. The remaining fallow period (winter followed by summer) of about 8-9 months leads to natural crash in the population of native arbuscular mycorrhizal fungi (AMF) in the soil. Attempts have been made to minimize this population crash by reducing soil disturbance-induced deleterious effects on native AMF activity of improperly scheduled off-season tillage, an agronomic recommendation for weed and disease (soil-borne) management, practiced by the upland farmers. On-farm (farmers' field) evaluation of effects of all suitable off-season tillage schedule combinations on rice during wet seasons of 2004, 2005, and 2006 revealed that a maximum of two off-season tillage schedules with a minimum gap of 13 weeks between them minimized the population crash of native AMF with a concomitant increase in phosphorus (P) uptake and grain yield of upland rice (variety "Vandana").