Volatilisation of ammonia from urea and ammonium sulfate applied to sugarcane trash in north Queensland

Trash retention following green cane harvesting is gaining acceptance as a crop management practice in northern Queensland because of its many benefits which include weed control, moisture conservation and increased soil organic matter. However, the presence of crop residues on the soil surface poses a problem for the management and efficient use of urea fertiliser, the preferred nitrogen source for sugar cane, because of the high urease activity of the cane residues. This paper reports the results of experiments conducted with the explicit aim of determining the factors controlling ammonia loss and the extent of loss following the application of urea to green cane trash in four climatic zones of tropical Queensland. It also reports a similar, parallel investigation into the use of ammonium sulfate as an alternative source of nitrogen for cane grown with trash conservation.