Dry matter yield and response to nitrogen of an Agrostis stolonifera-dominant sward

A small-plot cutting trial was carried out 1983-85 at North Wyke Research Station, Devon to compare the dry matter (DM) production and response to nitrogen (N) of a naturally occurring Agrostis stolonifera-dominant sward, developed under low fertility conditions on a poorly structured soil. and a sward of Lotium perenne cv. Melle, direct-drilled in 1982 at the same site. All plots received standard inputs of P. and graded inputs of K, related to the four annual N treatments (0, 200, 400 and 800 kg ha^?1, in seven equal applications). All plots were cut six times each year, except in 1983; DM yield, herbage digestibility, herbage N concentration, response to applied N, apparent recovery of applied N. and botanical composition of the swards were recorded. On average, A. stolonifera gave 69% of the DM yield of L. perenne. A. stolonifera did not out-yield L. perenne at the low N levels (0 or 200 kg N ha^?1 a^?1), or in mid-season. and yielded significantly (P<0-001) less in drought conditions in 1984 (4-4 t DM ha^?1 and 6-9 t DM ha^?1, s.e.d.±0-22). Average digestibility of A. stolonifera was 3 units of D-value lower (P<0-001) than L. perenne, but N concentrations were higher (3-01% and 2-53%, s.e.d. ±0-074). However, total yields of N from A. stolonifera were lower. Responses in DM production per kg N applied were lower in A. Stolonifera than in L. perenne for all N increments, except the highest, (400-800 kg N ha^?1). Fitted response curves allowed interpolation of the values of DM yield (Y10) and N input (N10) where the response was 10 kg DM (kg N)^?1. Values of Y₁₀ for A. stolonifera and L. perenne averaged 7-1 t DM ha^?1 and 12-9 t DM ha^?1respectively. and values of Mo averaged 460 kg N ha^?1 and 570 kg N ha^?1, which further indicated the lower responsiveness of A. stolonifera to applied N. Apparent recovery of applied N was generally low, with significantly higher values (P<0-001) for L. perenne in 1983 and 1984, but not in 1985. The botanical composition of L. perenne swards with no applied N showed a steady and rapid decline in ground cover by the sown species. AH L. perenne swards showed an abrupt decrease of L. perenne cover in late 1985, with invasion by A. stolonifera at all but the highest N level (800 kg N ha^?1). A. stolonifera treatments receiving 400 or 800 kg N ha^?1 showed initial expansion of their native L. perenne populations; however, these declined after the drought in 1984. Only low levels of L. perenne cover remained in the A. stolonifera swards at the end of the trial; these were unaffected by N level. It was concluded that under the conditions of this trial, A. stolonifera had lower DM productivity and efficiency of N use than L. perenne.