Effects of spring defoliation and fertilizer nitrogen on the growth of white clover in ryegrass/clover swards

Abstract

An examination was made of the effects of different spring treatments on the growth of white clover in a ryegrass/white clover sward. Plots were either cut once (in February, March or April) or twice (in February and April) or left uncut. Nitrogen was applied to half of the plots in each instance. The clover was sampled at intervals of approximately 3 weeks from February to June to determine numbers of leaves and growing points and weights of plant parts. Rates of leaf appearance were also observed and estimates were made of total herbage mass from ground-level cuts.Percentages of white clover in the herbage were higher in unfertilized than in fertilized plots and in defoliated than in undefoliated plots. The percentage increases that followed defoliation were usually maintained into later regrowth, showing that clover content was not automatically reduced as herbage mass increased. Increases in growing points were recorded after the beginning of April in defoliated unfertilized plots but not in undefoliated fertilized plots or in plots fertilized and defoliated twice during the spring period, in which numbers fell substantially.Inverse relationships were found between rates of leaf appearance, or the number of green leaves retained per stolon, and herbage mass, whereas heights of clover and grass leaves and Correspondence: Alison Davies. [nstilule of Grassland and Environmenlal Research, Welsh Plant Breeding Station, Aberystwyth, Dyfed SY23 3EB, UK.the percentage of dry matter allocated to petiole rather than leaf in the clover increased with increasing herbage mass.We suggest that the observed differences between spring treatments in clover percentage result primarily from their differential effects on the formation and death of tillers and growing points in the early stages of regrowth.

Effect of high rates of nitrogen fertiliser on white clover growth, morphology, and nitrogen fixation activity in grazed dairy pasture in northern New Zealand

“…Consequently, there was a much smaller effect on clover content. Davies & Evans (1990) found that white clover in mixed pasture under cutting is able to adapt to increasing sward height and mass by producing leaves with longer petioles. Woledge ( 1988) also reported that clover was not overtopped by ryegrass in irrigated swards receiving N during spring and in fact had a greater proportion of its leaf lamina in the upper, well lit layers of the canopy than did ryegrass.…”

A Novel Approach to Grass–Legume Management

“…Since more grass leaf than clover leaf is present in the upper layers of the sward in the spring, it is not surprising to find that spring defoliation can be beneficial in terms of clover composition (Davies and Evans, 1990). Rochon et al (2004) suggested that the timing of the first harvest cut or grazing is also crucial for determining the competitiveness of white clover and sustaining it.…”

Pasture research in the UK: Present knowledge and future prospects

“…During periods of herbage accumulation in the main part of the growing season there is a good relationship between grass height and petiole length (regardless of treatment) which accounts for 96.3% of the variability (Davies and Evans 1990). Clover petiole lengths decrease in autumn, but in ryegrass (unless it is cut or grazed) similar responses in leaf length are constrained by the long sheaths through which they must emerge (Davies and Simons 1979).…”

“…This can result in shading by the grass component and poor clover survival (Davies 1996). Cutting in spring is also beneficial to clover, at least in the absence of applied nitrogen (Davies and Evans 1990). Woledge et al (1992) showed that although the location of clover laminae in the sward during May-September resulted in the removal by cutting of a greater percentage of leaf area from clover than from grass, this shortfall was amply compensated for by the higher relative growth rate (and particularly the greater specific leaf area) of the clover.…”

“…The application of even as little as 50 kg N ha -1 in spring is sufficient to arrest increases in numbers of growing points (Davies and Evans 1990). Split box experiments (D. R. Jones, unpublished data) reveal that the effect is one of reducing light transmission through the nitrogen fertilised grass and that fertiliser nitrogen is not damaging to clover growing on its own.…”