The effect of phosphate and potash fertilizers on cut and grazed grassland

Abstract

SUMMARYAn experiment was carried out over a 5-year period on a grass/clover sward at North Wyke to compare three methods of experimental management—individually grazed plots, communally grazed plots and cutting with removal of herbage. Responses to phosphate and potash fertilizers under each management were measured.P fertilizer increased grass yields in the first 4 years and decreased clover yields in the last 2. In almost all respects cut and grazed sward responded similarly to P. Fertilizer K had no effect on grass yield but markedly increased clover yield and raised herbage K content. Grazed swards developed a higher herbage K content than cut swards, and K fertilizer increased it more in the fourth and fifth years on the individually grazed than on the communally grazed plots. Thus communal grazing resulted in appreciable transfer of K from plot to plot in animal returns.It is concluded that whilst cutting management may be used for short-term experiments, its use in long-term experiments gives different results from grazing. Communal grazing can lead to the transfer of N and K effects from plot to plot, so that plots must be grazed individually except perhaps where P is the only variable nutrient.

The Effect of Stage of Growth at Defoliation on White Clover in Mixed Swards

“…been a consequence of the absence of the grazing animal for a period, as grazing per se has been shown in this and other North Wyke experiments (4,17,20) to reduce clover. Clover regrowth was observed to be more rapid following cutting than grazing, suggesting that nonselective defoliation by the mowing machine left clover in a stronger position for regrowth than did selective close grazing by sheep.…”

The Simulation of Animal Returns in Grassland Experimentation

“…The apparent low rate of return in the North Wyke experiments was probably a result of differences between the estimate of herbage yield made by the Teagle hedge-trimmer and the amounts actually cut by the Mayfield autoscythe and fed to the caged sheep. Changes in technique have been made to minimize this discrepancy in subsequent experiments (1,2). Table 7 shows that the relationship between the N :P :K ratio in the excreta and in the herbage varied between years.…”

“…Fertilizer treatments invariably affect the chemical composition of the herbage as well as its DM yield, but in this experiment neither natural nor simulated rettim affected the response to the PK treatment. However, in other experiments at North Wyke N rettimed by the grazing animal has enhanced responses to fertilizer N (10) and returned K has modified the effects of fertilizer K (1,2). There is therefore a need to take account of"animal returns in fertilizer experiments whose results are to be applied to grazed swards.…”

“…One simple technique is to graze the whole area after samples have been taken for yield estimation. However, with this method there are risks of nutrient transfer within the experiment that may invalidate its applicability to fertilizer trials (2).…”

Effects of mowing interval, return of clippings, and potassium fertiliser on production and botanical composition of pasture in a mowing trial

“…Another explanation may be that returning 70% of the clippings does not (under a high annual rainfall of 1600 to 3500 mm) provide sufficient nutrients (particularly nitrogen) to sustain the growth of ryegrass. Other nutrients, notably potassium (K), may also have been limiting because the plots in mowing trials have been shown to have a high K requirement (Brockman et al 1970). On the South Island west coast, Morton (1981) recorded pasture responses to applications of up to 350 kg KClIha in a mowing trial on a K-deficient site.…”