Tillage influence on soluble salt movement in silt loam soils cropped to paddy rice

Rice (Oryza sativa L.) produced in a dry-seeded, delayed-flood system common to the southern USA is extremely sensitive to excessive accumulation of soluble salts during the seedling growth stage. Recent observations have been made by producers, county agents, and researchers that the use of conservation tillage systems, particularly no-till systems, may increase the level of salinity in the rice root zone in dry-seeded, delayed-flood systems during the 4- to 6-wk period prior to permanent flood establishment. With the use of conservation tillage practices for rice production steadily increasing in the southern USA, it is important to determine if these practices increase potential for accumulation of soluble salts, to determine the mechanisms involved, and to develop management strategies to overcome the problem. A 2-yr study was initiated in the fall of 1994 to monitor salt distribution within the soil profile under different tillage regimes. A conventional system, a para-till operation, a chisel plow operation, and a no-till system were implemented in the fall and Br^- was applied to monitor salt movement. 'Kaybonnet' rice was seeded during 1995 and 1996 and soil samples were collected from each plot at the two- to three-leaf growth stage. Salt accumulation at the rice seedling growth stage near the soil surface was higher in the no-till treatment than in any of the other tillage treatments based on higher electrical conductivity, Cl^- concentration, and NO₃/^- concentration in the top 2.5-cm depth. At this depth, the electrical conductivity was 30 to 40% greater, the Cl^- concentration was 30 to 160% greater, and the NO₃/^- concentration was 10 to 160% greater in the no-till treatment than in the other tillage treatments. Salt distribution within the profile was similar for all treatments beyond the 2.5-cm depth. The data suggest that tillage does tend to reduce the potential for salt accumulation in the root zone.