Ammonia volatilization from fertilizers applied to irrigated wheat soils

Abstract

A series of experiments using flow chambers was undertaken in the field to investigate the effects of stubble and fertilizer management, soil moisture and precipitation on ammonia volatilization following nitrogen application on chromic luvisols. In the first factorial experiment, urea at 100 kg N ha⁻¹ was applied to the soil surface one, three and six days following irrigation; there were four rice stubble management systems comprising stubble burnt, stubble burnt then rotary hoed, stubble rotary hoed into the soil and stubble retained on the surface. Cultivation almost halved ammonia loss. The higher loss from uncultivated plots was ascribed to an alkaline ash bed on burnt plots, and to higher soil moisture and some retention of urea prills in the crop residue above the soil surface of the stubble retention plots. Average volatilization over a 12 day period following urea application from plots fertilizer one, three or six days after irrigation was 16, 15 and 4 kg N ha⁻¹, respectively. Daily application of up to 1.7 mm of water did not reduce volatilization and 35 kg N ha⁻¹ was lost within five days of fertilization. Daily precipitation of 6.8 mm reduced loss to 14 kg N ha⁻¹. This quantity of rain is uncommon in the region and it was concluded that showery conditions are unlikely to reduce volatilization. The third experiment demonstrated that the quantity of stubble on the soil surface had no effect on volatilization, and all plots lost 25% of applied nitrogen. In the fourth experiment, 100 kg N ha⁻¹ as urea or ammonium nitrate was either broadcast onto the surface or stubble retention plots, or placed, and partly covered to simulate topdressing with a disc implement. Partial burial of urea reduced ammonia volatilization from 36 to 7 kg N ha⁻¹, while partial burial of ammonium nitrate reduced loss from 4 to 0 kg N ha⁻¹.