CHICKPEA IN WHEAT-BASED CROPPING SYSTEMS OF NORTHERN NEW-SOUTH-WALES - I - N-2 FIXATION AND INFLUENCE ON SOIL NITRATE AND WATER

Chickpea has potential as a rotation or break crop in the northern gra ins region of New South Wales and Queensland. Definition of that poten tial requires information on chickpea Na fixation and on effects of ch ickpea on maintenance of soil N fertility and delivery of mineral N fo r use by a following cereal crop. Results from 6 experiments in northe rn NSW in which chickpea and wheat in one season were followed by whea t in subsequent seasons indicated variable N-2 fixation by chickpea (m ean 73 kg/ha; range 4-116 kg/ha), associated with variable Pfix (perce ntage of chickpea N derived from N-2 fixation) (mean 57%; range 4-79%) . There were no consistent differences between chickpea and wheat in e ffects on soil water, either pre-harvest or after the summer fallow. C hickpea 'spared' nitrate, relative to wheat (mean 15 kg/ha; range 1-35 kg/ha), and mineralised additional nitrate during the summer fallow ( mean 18 kg/ha; range 5-40 kg/ha). Nitrate-N in the top 1.2 m of the so il profile at sowing of the following wheat crop was on average 89 kg/ ha after chickpea (range 63-113 kg/ha) and 56 kg/ha after wheat (range 33-94 kg/ha). Nitrogen mineralisation rates during the summer fallow at 2 sites of 0.17 and 0.21 kg N/ha.day (after chickpea), although gre ater than the rates after wheat (0.07 and 0.12 kg N/ha.day), were not sufficient to meet the N requirements of a moderate to high yielding c ereal crop. We concluded that chickpea did not fix sufficient Nz or mi neralise sufficient N from residues either to maintain soil N fertilit y or to sustain a productive chickpea-wheat rotation without inputs of additional fertiliser N.