Improving rice productivity in the coastal saline soils of the Mahanadi Delta of India through integrated nutrient management.

The coastal saline belt of the Mahanadi Delta in Orissa, India, is mostly monocropped with rainfed rice during the wet season (WS). In the dry season (DS), a small area is planted to rice using harvested rainwater. Currently, yields are low; however, integrated nutrient management combined with improved salt-tolerant rice varieties could increase system productivity substantially. On-farm trials were conducted in the Ersama block of Jagatsinghpur district (Orissa) using rice varieties Pankaj (shallow lowland) and Lunishree (intermediate lowland) in the wet season and Annapurna and Canning 7 in the dry season. Selected nutrient management practices were evaluated during 2004-2006 and the most promising options were validated in participatory farmer-managed trials in 2006-2007 conducted at six to eight locations. In the shallow lowlands, Sesbania green manuring (GM)+prilled urea (PU; 20 kg/ha N), Azolla+PU (30 kg/ha N) and Sesbania+Azolla were as effective as PU at 60 kg/ha N, in both the 2004 and 2005 WS, with a yield advantage of 30-40%. In the intermediate lowlands, the grain yields with Sesbania in 2004 and farmyard manure (FYM; 5.0 t/ha)+PU (20 kg/ha N) in 2005 were comparable with the yield achieved with urea supergranules (USG; 45 kg/ha N), which had limited scope because of unavailability and placement problems. The yield advantage of these treatments was 23-68%. During the DS of 2005 and 2006, Azolla+PU (50 kg/ha N) resulted in significantly higher yields (15%) than the application of PU at 80 kg/ha N. In demonstration trials at six on-farm sites in the 2006 WS, Sesbania and Sesbania+Azolla increased rice yields in the shallow lowlands by 12-40% (mean 23%) and 19-77% (mean 41%), respectively. In the same season, the yield advantage due to Sesbania was 8-50% (mean 29%) for eight on-farm sites in intermediate lowlands. In the 2007 DS, Azolla increased rice yield by 16-35% (mean 24%) over a control treatment at eight onfarm sites. These findings suggest that, under both the shallow and intermediate lowlands, Sesbania for the WS and Azolla biofertilizer for the DS are promising organic nutrient sources that can improve soil quality and contribute to enhancing and sustaining crop productivity in coastal areas.