THE VALUE OF LEGUME BREAKS TO THE SUGARCANE CROPPING SYSTEM-CUMULATIVE YIELDS FOR THE NEXT CYCLE, POTENTIAL CASH RETURNS FROM THE LEGUME, AND DURATION OF THE BREAK EFFECT

IN ROTATION experiments conducted in Australia over the past decade, it has been demonstrated that breaking the sugarcane monoculture between cycles with another species improves sugarcane yields by 20-30% in the plant crop due largely to improvement in soil health. However, to break the sugarcane monoculture, it is necessary to forego at least one cane harvest and many growers are concerned that will jeopardise economic viability. To test this, several of the rotation experiments were carried through to second and third ratoons and the cumulative cane and sugar yields were measured over the crop cycle. The response to breaks in the ratoons was similar to those measured in the plant crop and there were clear indications that over a crop cycle the inclusion of a short-term (6-9 month) legume break would be economically viable. In general, the persistence of yield benefits into the ratoons resulted in cumulative sugar yields over a plant and four ratoons covering the loss of the one cane harvest when the break was included. In two other experiments, sugarcane that had been planted after breaks was removed, following a plant crop in one instance and a plant and two ratoons in the other, and plots were immediately replanted to sugarcane. The yields of the subsequent plant crop were no better than those with long-term sugarcane monoculture, indicating that the break effect per se was short-lived. Thus the longevity of the yield response into later ratoons appears to be largely associated with very positive effects of the break on the immediate plant crop. These findings strongly support the regular inclusion of rotation breaks in the sugarcane cropping system, a strategy that is especially attractive when there are suitable break species like soybeans and peanuts that can be harvested as cash crops. Harvesting these break crops does not detract from the break effect while further improving overall grower profitability.