Fertilizing smooth bromegrass pastures in spring can be an excellent way to improve productivity, but producers should first pencil out costs and returns.

With the cost of fertilizer quickly exceeding the potential increase in production realized from most perennial grass pastures, managers should carefully evaluate the point of diminishing returns in these systems.

Older stands of smooth bromegrass may become dense and sod-bound, markedly lowering productivity as a result of low nitrogen cycling. In pastures, smooth bromegrass must be fertilized with nitrogen to avoid becoming sod-bound and improve productivity.

Although smooth bromegrass will respond to nitrogen rates of up to 275 pounds an acre, research by SDSU range scientist Alexander “Sandy” Smart in eastern South Dakota has suggested that applying about 90 pounds an acre likely will produce the highest economic returns. Nitrogen fertilizer applications to smooth bromegrass pastures should be made in early May when the onset of the rapid growth phase occurs.

Nitrogen can come from any number of sources, such as liquid nitrogen solutions, urea, or ammonium nitrate.

If smooth bromegrass pastures are grazed in the spring and fall, split applications of nitrogen fertilizer, putting down 80% in early May and 20% in early September, will produce more desirable results.

Over-fertilization of smooth bromegrass also can cause problems. Excessive nitrogen availability may lead to stem lodging, resulting in poor utilization, especially in wet years.

Rapid accumulation of forage as a result of excessive nitrogen applications also can lead to grass tetany and nitrate nitrogen toxicity to grazing livestock. Soil tests should be conducted every two years in smooth bromegrass pastures to determine phosphorous and potassium needs.

Next Range Science 101 tip:Watch for grass tetany during spring