Field evaluation of crop yield as affected by nonuniformity of sprinkler-applied water and fertilizers

The determination of target uniformity for sprinkler irrigation system should consider the impacts of nonuniformity of water and fertilizers on crop yield. Field experiments were therefore conducted in north China plains to address the impacts of nonuniformly applied water and fertilizers on winter wheat yield. Irrigation water and fertilizers were applied through a solid set sprinkler system. Three experimental plots were used with seasonal Christiansen uniformity coefficients (arithmetic mean of individual CUs) ranging from 62 to 82%. Each plot was divided into 3 m x 3 m grids. Sprinkler water depth and concentration of fertilizer solution for each grid was measured both below and above the canopy for each individual irrigation event. The spatial distribution of soil moisture for each experimental plot was also measured periodically to determine irrigation times and amounts. On harvest, grain yield and total nitrogen content of plant stems were measured for each grid. The experimental results showed that the uniformity of fertilizer applied increased with sprinkler water uniformity. The distributions of both fertilizers and water applied through sprinkler system can be represented by a normal distribution function. Field experiments also demonstrated that the uniformity of sprinkler-applied water and fertilizers has insignificant effect on winter wheat yield for the studied uniformity range. The current standard for sprinkler uniformity (for example, the target CU is equal to or higher than 75% in China) is high enough for obtaining a reasonable crop yield in dry sub-humid regions. (C) 2002 Elsevier Science B.V. All rights reserved.