Effects of Sulfur-coated Urea on California Annual Grassland Yield and Chemical Composition1
- C. E. Vaughn,
- M. B. Jones and
- J. E. Ruckman2
Fall applications of N fertilizers on California annual grasslands are often accompanied by luxury N uptake, excessive N leaching losses, and N deficiencies the following spring. Sulfur-coated urea (SCU), a slow-release fertilizer, was applied to a grassland soil (Laughlin, fineloamy, mixed mesic, ultic haploxeroll) to determine whether it could supply adequate N and S and eliminate problems encountered with more soluble N fertilizers.
Urea (U), urea with 100-mesh elemental S (U + S), and two formulations of SCU were broadcast on resident annual grassland, dominated by annual bromes (Bromus spp.), wild oat (Avena barbata) broadleaf filaree (Erodium botrys), and clover (Trifolium spp.), in a climate with cool, rainy winters and hot, dry summers. Forage ield and N and S uptake were measured seasonally in the 1st year and annually the following 5 years. Seasonal growth distribution was similar from all fertilizers in the 1st year. However, U + S was significantly more productive and gave greater herbage S uptake than the SCU's and U throughout the first growing season, and greater N uptake in the first winter.
Residual studies suggested the long-term benefit of S fertilization; the U + S and SCU treatments were significantly more productive for the last 5 years. Residual N uptake responses were similar to the yields. Herbage S uptake was similar in the U and check treatments for the entire study. The more heavily coated SCU formulation gave greater S uptake than both U + S treatments in the 4th and 6th years after application.
It was concluded that the SCU's were of no greater benefit than urea combined with fine S in fertilizing California annual grasslands. The slow release of N from SCU did not give any greater apparent residual N response. There was a long-term response to the larger particles of S in SCU, but it is questionable that this would justify the extra cost of the fertilizer.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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