Nitrogen fractions and amino acid content in alfalfa and red clover immediately after cutting and after wilting in the field

Abstract

The aim of this study was to determine the composition of nitrogen fractions in alfalfa and red clover, which differ in proteolytic activity, and to evaluate the effect of wilting on changes in nitrogen fractions in alfalfa and red clover herbage. Total nitrogen was divided into protein and non-protein nitrogen, and the amino acid profile of protein was analyzed. Buffer-soluble nitrogen (BSN), including buffer-soluble protein nitrogen (BSPN) and non-protein buffer-soluble nitrogen (NPBSN), was determined. The NPBSN fraction was further subdivided into peptide nitrogen, amino acid nitrogen, neutral detergent-insoluble nitrogen (NDIN) and acid detergent-insoluble nitrogen (ADIN). Wilting in the field to 40 % dry matter content (the swath was tedded once) did not reduce the total nitrogen content of alfalfa and red clover herbage, although it affected the concentration of the BSNfraction, in particular NPBSN, and free amino acid nitrogen. During alfalfa wilting, the soluble protein content decreased and the concentrations of non-protein nitro-gen compounds increased, mostly due to an increase in free amino acid nitrogen. A reverse trend was observed during red clover wilting – the concentrations of non-protein nitrogen compounds decreased and soluble protein content increased. A decrease was also noted in peptide nitrogen,