Abstract:
A series of field experiments was conducted on a black earth of the Darling Downs, in south-eastern Queensland, to examine nitrogen availability to irrigated wheat (Triticum aestivum) after stubble of the previous crop had been either removed, mulched, or incorporated. Three crop sequences were considered: S-W, sorghum (Sorghum bicolor), short (3-month) fallow, wheat; W-W, wheat, normal (7-month) fallow, wheat; LFW, sorghum, long (15-month) fallow, wheat. The effect of stubble management on the availability of nitrogen to the test crop of wheat in each sequence was assessed by the response of the test crop to urea applied at planting (0, 25, 50, 75, 100 and 150 kg N/ha). Soil mineral nitrogen was measured at the beginning and end of the fallow during the experiments. There was a little evidence that stubble management influenced plant growth in any of these cropping sequences. Responses to nitrogen were very large in the S-W sequence, moderate in the W-W and very slight in the LFW sequence. Apart from a slight effect in the S-W sequence, measured soil mineral nitrogen concentrations were unaffected by stubble treatments.