Prediction of nitrogen fertiliser requirements of maize in subtropical Queensland

Abstract

Sixteen field experiments were conducted at 9 sites in the South Burnett region of subtropical Queensland, to determine grain yield response of maize to fertiliser nitrogen (N) and to assess soil mineral N levels at sowing for predicting N requirement. At 6 sites, areas were either winter-cropped or bare-allowed, resulting in different cropping histories immediately prior to summer maize. In each experiment, 4 rates of N (0, 38, 76, and 152 kg/ha) were applied, with an additional rate (304 kg/ha) at 3 sites that received supplementary irrigation. Immediately prior to sowing, soil samples for mineral N and moisture were taken from each 10-cm increment to a depth of 120 cm. Soil nitrate-N levels (0-120 cm) before sowing were 16-100 kg N/ha (winter-cropped) and 65-167 kg N/ha (bare-fallowed). Application of N significantly (P<.05) increased grain yield in 14 of the 16 experiments. Maximum grain yields in non-irrigated experiments ranged from 2.08 to 5.61 t/ha and reflected profile available water at sowing and rainfall during the growing season. Maximum yields in irrigated experiments ranged from 4.44 to 6.95 t/ha. The magnitude of the response was greater at winter-cropped sites (relative yields 33-89%) than at fallow sites (82-100%). Relative grain yield was well correlated with nitrate-N in the 0-60 cm profile ( R2 = 0.74). There was also a good relationship between relative grain yield and nitrate-N at 0-10 cm depth ( R2= 0.64).