Effect of fallow history on cane and sugar yield of a following plant cane crop

An experiment was condueted at the Yield Decline Joint Venture sub-station at Feluga, near Tully, into the effects of various fallow. treatments in the 1994/95 summer on sugarcane planted in September 1995. Superimposed on the fallow treatments were either 0 or 140 kglha nitrogen. Fallows included bare, farmer fallow (cowpea broadcast), continual cane, and mungbean, cowpea, peanuts and soybeans grown on ridges and sprayed with pre-emergent herbicide. Following soybeans, which contributed the most nitrogen (over 300 kglha) to the soil of all the fallows, the cane and sugar yield was as good with no added fertiliser nitrogen as it was with 140 kglha N. All other fallows responded to applied nitrogen but the magnitude of the response was inversely related to the amount of nitrogen returned to the soil from the previous fallow. The largest responses to fertiliser N were recorded following bare fallow and farmer fallow. The results indicate that following a well grown fallow crop of soybeans, there is no need to apply nitrogen fertiliser to plant cane, thus saving considerable produetion costs. The effects on the first ratoon are currently being followed. The results are discussed in terms of crop management, the potential for utilising fallow legumes as a nitrogen source and the implications for sugarcane yield decline.