Abstract
Four permanent pastures which differed greatly in their botanical composition and in their herbage P and K nutritional status were or were not supplied with P-K fertilizers during a four-year period. By the fourth year, the four plots given P-K had similar herbage nutritional status, but differed in their botanical composition, whereas the two plots of a given pasture were similar in their botanical composition but differed in their herbage nutritional status. We exploited this variation to compare the effects of herbage nutritional status and botanical composition on herbage accumulation rate.Dry matter yield, leaf area index and dead material were measured several times from early April to early July. To compare plots, the pattern of herbage growth was divided into three phases. The first period lasted until the attainment of a leaf area index (LAI) of 2.0, when about 70 per cent of the radiation was intercepted. In the second period, we calculated the slope of the herbage accumulation curve with accumulated temperature. We also assessed the moment when the herbage accumulation rate started decreasing as a result of senescence.Compared with the most productive plot, the lower dry matter yields of the other plots (at the heading stage of Dactylis glomerata) were associated with a low rate of increase in LAI rather than a low dry matter accumulation rate, once the leaf area index had reached the value of two. At that stage, the effect of a low P herbage nutritional status was as great as that of a poor botanical composition (lack of good grasses). Afterwards, the main factor affecting herbage accumulation was the herbage nutritional status, except in cases where the main species were leafy. The moment when the dry matter accumulation rate started decreasing depended on the phenology of the species and the amount of standing herbage.
Published Version
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