TIME OF APPLICATION AND SOURCE OF NITROGEN FERTILIZER ON YIELD, QUALITY, NITROGEN RECOVERY, AND NET RETURNS FOR DRYLAND FORAGE GRASSES

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Abstract
Studies were conducted in Saskatchewan for 4 yr at Swift Current (Brown soil zone) and 3 yr at Scott (Dark Brown soil zone) to assess the effect of time of application and source of N fertilizer on grass forage yields and N and P content, fertilizer N recovery and net returns. A single rate of N, 50 kg ha−1 was applied to established forage stands at three dates during the late fall to early winter period and one or two dates during the early spring period. Six grass species were grown at Swift Current and one at Scott. At Swift Current there were significant differences in dry matter yields between grass species but no species × fertilizer interactions. Fertilizer applied in April generally gave the highest forage yields and N concentration, N recovery, and net returns, but sometimes October and/or November applications provided as good or better results. At Swift Current relative yields (averaged over grass species and source of N) for the different application dates were: April, 158; late October, 154; late November, 145; and late December, 137; with the unfertilized control given a value of 100. At Scott, a similar rating of yields gave: mid-April, 225; mid-October, 219; mid-November, 216; mid-December, 213; and mid-March, 192. Nitrogen concentration in forages averaged 2.06% at Swift Current and 1.53% at Scott, and was mainly affected (increased) by the April fertilizer application date. Yields were 11–13% greater when ammonium nitrate was used compared to when urea was used. Because the N was broadcast and yields were small, recoveries of N by the crop were low, variable due to weather, and averaged 21% at both sites. In most years N fertilizer increased yields, but net returns varied depending on the occurrence of early spring precipitation and on whether the forage was sold for hay or fed on the farm. Fertilization was profitable in the wetter years, but in dry years money was lost irrespective of the N source or site. Net returns favored the ammonium nitrate source of N.Key words: Grass species, grass yield, urea, ammonium nitrate, net returns