Growth of white clover in eight grass species and the effects of propyzamide, a grass‐suppressing herbicide

Abstract Seedlings of white clover (cv. Grasslands Huia) were introduced as spaced plants into 3‐year‐old monoculture plots of eight grass species (Agrostis capillaris, Agrostis stolonifera, Dactylis glomerata, Festuca rubra, Holcus lanatus, Lolium perenne, Phleum pratense and Poa pratensis) during June 1984. In mid‐April 1985 plots were split for application of propyzamide at the following concentrations: 0, 0·2, 0·4, 0·6 kg a.i. ha‐1. During 1984 differences between clover seedling growth in the different grass species became apparent within 2 weeks; growth was greatest in F. rubra, P. pratensis and H. lanatus and smallest in D. glomerata, L. perenne and P. pratense. During 1985, when more N fertilizer was given, H. lanatus and D. glomerata, were equally competitive and clover contributed only 16–18% of the total herbage yield of 10·4 t ha‐1 in them, compared with 33–50% of yields ranging from 9·6 to 119 t ha‐1 in the other six species. Propyzamide decreased grass growth in mid‐season by more than 50% but there was little overall persistent benefit to clover yield, except for A. stolonifera and P. pratense with 0·4 and 0·6 kg ha‐1 treatments. Dactylis glomerata and perenne were least and H. lanatus, F. rubra and P. pratensis most suppressed by the herbicide. Possible reasons for the overall large clover contribution from a very sparse seedling population and the relatively small effects of propyzamide are discussed as well as future work required to improve the predictability of effects of grass suppression.