Yield and protein content of barley as affected by release rate of coated urea and rate of nitrogen application

Coated urea consists of a urea core and a polymer coating. It meters out ur ea over a period of time. In the market place, price is favorable for high protein content feed barley. The objectives of this study were to determine release rate of urea from coated urea products and relative effectiveness of urea, coated urea or a mixture of coated urea products with different re lease rates in increasing yield and protein content of barley. Release rate of coated urea Mini I (quick release) and Mini II (slow release) in water was determined at 23 degrees C by recovering ten pre-weighed granules from 500 mL water at 6 h, 2, 4, 6, 8, 10, and 12 days. The recovered granules we re dried and then weighed. Barley (Hordium vulgare L. cv. Duke) was grown i n potted soil (2 L) at 15 degrees C for 90 days in a growth chamber with tr eatments of Nil, non-coated urea, Mini I, Mini II, Mixture I (1/3 urea+1/3 Mini I+1/3 Mini II) and Mixture II (1/5 urea+2/5 Mini I+2/5 Mini II). The n itrogen (N) application rates were 100, 200 and 300 kg N ha(-1). Above-grou nd plant samples were taken at 22, 44, 66, and 90 (maturity) days after see ding, and dry matter mass per pot and N content of the plant samples were d etermined. The release of urea from Mini I and Mini II followed a lognomial pattern. Increasing N application rate increased dry matter yield of barle y. Dry matter yield from urea tended to be higher than other treatments at each rate of N application, but that did not couple with high grain protein content. At 100 kg N ha(-1), there was no post anthesis N assimilation (PA NA) for urea and Mini I, but there were 4, 14, and 13% PANA for Mini II, Mi xture I, and Mixture II, respectively. However, when N application rate was increased to 200 and 300 kg N ha(-1), there was PANA even for urea treatme nt. Protein content of barley grain was higher with coated urea or mixture treatments than with urea at each rate of N application. The potential N lo ss (i.e., difference between percent N released from fertilizers and percen t fertilizer N recovered by barley) was Mini II<Mini I<Mixture II<Mixture I for the same N application rate, and was 100<200<300 kg N ha(-1) for the s ame fertilizer treatment. In conclusion, at a limited N application rate, c oated urea with a slow release rate or a combination of two coated urea pro ducts (quick and slow release) with urea increased grain protein content of barley. The potential N loss was less with coated urea applied alone than with a mixture of coated urea and urea.