CHICKPEA IN WHEAT-BASED CROPPING SYSTEMS OF NORTHERN NEW-SOUTH-WALES - II - INFLUENCE ON BIOMASS, GRAIN-YIELD, AND CROWN ROT IN THE FOLLOWING WHEAT CROP

Rotational effects of chickpea, an important Nz-fixing pulse legume of the northern grains region, on subsequent wheat require quantificatio n of the contribution of the legume to soil N and the N status of the wheat, and of suppression of soil and stubble-borne pathogens, such as crown rot (Fusarium graminearum. Schwabe Group 1). Results from selec ted treatments of 10 experiments in northern New South Wales in which chickpea and wheat in one season were followed by wheat in following s easons indicated generally higher dry matter (DM) and grain yields of wheat after chickpea than after wheat. Responses to chickpea were -0.8 to 3.3 t/ha (shoot DM) and -3 to 39 kg N/ha (shoot N). Responses in w heat grain yields were -0.1 to 1.7 t/ha (mean 0.85 t/ha); grain N resp onses were -2 to 33 kg/ha (mean 19 kg/ha). Grain protein responses wer e small (0.6%) and variable. Although these productivity responses cou ld be explained largely in terms of additional nitrate-N following chi ckpea, we measured reduced incidences of crown rot in wheat after chic kpea (range 1-36%, mean of 12%), compared with wheat after wheat (rang e 5-52%, mean 30%). Modelling the incidence of crown rot indicated hig hly significant interactions between prior crop and total water (pre-p lant soil water plus in-crop rainfall). When wheat followed chickpea, incidence of the disease declined sharply with increasing water. When wheat followed wheat, there was a marginal decline in disease incidenc e with increasing water. Our results support the strategy of using leg umes in rotation with wheat in the northern grains region for enhanced soil-N supply and disease-break effects.