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 N2-fixing pulse legume of the northern grains region, on subsequent wheat require quantification 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 selected treatments of 10 experiments in northern New South Wales in which chickpea and wheat in one season were followed by wheat in following seasons 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 wheat grain yields were -0·1 to 1·7 t/ha (mean 0·85 t/ha); grain N responses were -2 to 33 kg/ha (mean 19 kg/ha). Grain protein responses were small (0·6%) and variable. Although these productivity responses could be explained largely in terms of additional nitrate-N following chickpea, we measured reduced incidences of crown rot in wheat after chickpea (range 1-36%, mean of 12%), compared with wheat after wheat (range 5-52%, mean 30%). Modelling the incidence of crown rot indicated highly significant interactions between prior crop and total water (pre-plant 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 incidence with increasing water. Our results support the strategy of using legumes in rotation with wheat in the northern grains region for enhanced soil-N supply and disease-break effects.