Measurement of Ammonia Volatilization from Sesbania and Farmyard Manure Applied in Flooded Soils Varying in pH and Cation Exchange Capacity

Significant amounts of ammonia may be lost from agroecosystems. While NH₃ volatilization from fertilizers has been well-documented, corresponding losses from crop residues, particularly legume green manure (GM) and farmyard manure (FYM) under waterlogged soil systems have not been adequately quantified. Ammonia losses from decomposing Sesbania and FYM were measured under controlled conditions by applying the above two to soils left inside sealed conical flasks, establishing air flow and periodically measuring accumulated NH₃ loss using acid traps. An incubation experiment was also conducted to study the kinetics of soil pH and net NH₄⁺-N mineralised at regular time interval. The results of the experiments showed that the NH₃ volatilization loss demonstrated the following pattern: an initial lag followed by a rapid flush of NH₃ volatilization, apparently from the ammonification of labile N. The highest loss of NH₃ occurred between 12 to 15 days of manure application. The quantity of NH₃ lost from GM (8.06–11.4%) was greater than that from FYM (3.24–6.02%). Kinetics of soil pH and mineralised NH₄⁺-N was well associated with the kinetics of NH₃ volatilization loss. Soil cation exchange capacity (CEC) was more effective in reducing NH₃ volatilization loss than soil pH as lower amount of NH₃ was lost from Vertisol than from Alfisol. The volatile loss of labile N from decomposing GM and FYM may appreciably diminish its fertility benefit and represent an important contribution to atmospheric N concentration.