Effects of Sulfur‐coated Urea on California Annual Grassland Yield and Chemical Composition1

Abstract

AbstractFall 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.