Ammonia Volatilization and Nitrogen Uptake for Conventional and Conservation Tilled Dry-Seeded, Delayed-Flood Rice

Abstract

In the southern U.S. dry-seeded, delayed-flood rice (Oryza sativa L.) culture system, there are two practices that can aggravate NH 3 volatilization losses of urea applied preflood: untimely application of the permanent flood and conservation tillage. The objectives of this study were to determine the influence of tillage practice, N source, and application time on NH 3 volatilization, N uptake, and grain yield of delayed flood rice grown on a clay and silt loam soil. Multisite field studies were conducted in 2000 and 2001 using both stale-seedbed and conventional tillage practices with urea and (NH 4 ) 2 SO 4 applied 14 d preflood and urea 1 d preflood at four N rates. Ammonia volatilization was measured and plant samples were collected for N uptake and grain yield. Ammonia volatilization was the highest (14-32%) and N uptake and grain yield of rice the lowest when urea was applied 14 d preflood. Ammonium sulfate applied 14 d preflood lost little N (1.5-7%) via NH 3 volatilization and resulted in N uptake and grain yields of rice similar to urea applied 1 d preflood. The stale seedbed had no effect on NH 3 volatilization of (NH 4 ) 2 SO 4 and only affected urea in 1 yr on the silt loam soil when weedy residue was greater and the two tillage systems still produced rice with similar N uptakes and grain yields. Ammonia volatilization was more rapid and greater when urea was applied to the silt loam than to the clay. Ammonia volatilization loss of urea was impacted the most from delaying the flood and not from conservation tillage.