The influence of nitrogen fertilization and legume species on the productivity of multi-species swards in four production years.

The aim of current research was to investigate forage yield and crude protein content of legume-grass mixtures during four years of sward use, applying three nitrogen (N) fertilisation rates: N0, N60, and N120. Three perennial legume species - red clover Trifolium pratense (Tp), lucerne Medicago sativa (Ms) and fodder galega Galega orientalis (Go) were tested in mixtures with grasses (G). Mixtures were composed of 50% of legumes and 50% of grasses. Lucerne and fodder galega are introduced forage legume species in Latvia, and are raising an ever-growing interest in Latvia. The studies of persistency, quality and yielding ability of these legume species in Latvian agroclimatic condition in comparison with traditionally used red clover are actual. Significant differences in dry matter (DM) yields were found between successive production years, mixtures, and N fertilization rates. The highest average DM yield was found for the mixture with lucerne (Ms+G). The decline in productivity between the first and fourth production years was more expressed for red clover mixture, but a more stable productivity was demonstrated by swards with galega (Go+G). The N rate increase contributed to a significant DM yield increase for all mixtures. The positive effect of the increased N rates on DM yield increase was better expressed for red clover mixture (Tp+G). Red clover mixture (Tp+G) had the lowest average crude protein (CP) content. Mixture with galega had a higher CP content in the third and fourth production years. The CP content of red clover mixtures increased by nitrogen rate. [ABSTRACT FROM AUTHOR]