No-till seeded winter wheat: influence of date of nitrogen application on the seasonal pattern of crop growth and water use
An experiment was carried out to determine the influence of fertilizer N timing on the early season crop development and water use (ET) of no-till seeded winter wheat (Triticum aestivum L.). Ammonium nitrate N was surface broadcast either as early as possible (early), split between 2/3 early and 1/3 at the beginning of stem elongation (split), and 3 weeks after early (late), at rates of 0, 67, 134, and 202 kg N ha-1. Early and split-N application increased the early season plant development over Iate-N as recorded by tiller number and leaf area production. The development and maintenance of a larger leaf area with N fertilization in 1987 resulted in increased grain yields. However, high evaporative demand prior to anthesis in 1988 resulted in the 'collapse' of early season leaf and tiller responses. A positive correlation (r=0.82*) was recorded between leaf stomatal conductance (gl) and leaf relative water content, illustrating the importance of tissue water content in maintaining high photosynthetic activity. While added N increased pre-anthesis gl over the unfertilized check, the opposite response was recorded during the post-anthesis grain filling period. Increasing fertilizer N rate increased seasonal ET at 2 of the 8 trials by increasing post-anthesis ET over the unfertilized check. High pre-anthesis evaporative demand reduced season long ET to 159 mm in 1988, 59 % of the 218 mm recorded in 1987. Soil water contributed 16 % of total ET in 1987 and 30 % in 1988. The bulk of this soil water was taken up pre-anthesis, with 98 % of post-anthesis ET coming from rainfall.
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