AMINO ACID AND PROTEIN CONTENT OF Poa pratensis AS RELATED TO NITROGEN APPLICATION AND COLOR

Abstract

Kentucky bluegrass (Poa pratensis L.) plots receiving 2.5, 2.0, 1.7, 1.2, or 0.8 kg N∙100 m−2 each season in three equal amounts on approximately 15 May, 1 July, and 15 Aug. were analyzed for protein and amino acid content, as well as for the proportions of alcohol-soluble and salt-soluble proteins. Aspartic acid content of protein was the only amino acid that showed a positive regression with both the amount of nitrogen applied and turfgrass color, while the proline content of the dormant grass was highly dependent upon the amount of nitrogen applied during the summer. Total protein was highly dependent upon the nitrogen applied throughout the season and may, in part, explain the greener spring and fall color but, more probably, the high levels of salt-soluble protein in spring and fall mediated the spring and fall greening effects observed. At least 1.7 kg N∙100 m−2 season was required to ensure early greening the following spring.Key words: Kentucky bluegrass, Poa pratensis, nitrogen, amino acids, protein fractions, color