Spatial distribution of nitrate in soil as affected by uniformity of sprinkler fertigation

Field experiments were conducted in the growing season of winter wheat to investigate the nitrogen distribution and deep percolation under nonuniform sprinkler fertigation. Three uniformity levels were used in the experiments with the seasonal averaged irrigation Christiansen's uniformity coefficients (CU) varying from 72% to 84% and the seasonal averaged fertigation uniformity coefficients varying from 71% to 85%. Soil water potentials at 70 cm and 90 cm depths were monitored to estimate deep percolation caused by nonuniformly applied sprinkler water. The results showed that the deep percolation was minor for the sprinkler uniformity range tested. A temporal and spatial varied distribution of nitrate in soil was observed with the uniformity coefficient ranging from 23% to 97% and the coefficient of variation from 0.04 to 1.00. The results obtained from the field experiments suggest that the spatial distribution of nitrate in the irrigation season is greatly dependent upon the initial distribution of nitrate and the impact of sprinkler fertigation nonuniformity is insignificant.