Abstract
Post-defoliation carbohydrate stores, leaf area and the number of active meristems are important factors affecting the subsequent regrowth of grasses. Defoliation height affects the magnitude of all these factors. Timothy (Phleum pratense L.) and meadow fescue (Festuca pratensis Huds.) are the two most common pasture species in Finland, but little is known about their response to defoliation height. In this study the effect of three defoliation heights, 3, 6 and 9 cm, on the regrowth rates of timothy and meadow fescue in both the generative (JuneJuly) and vegetative (August) phases of growth were examined in two one-year experiment in year 2000 and 2001. In addition, the main postdefoliation parameters were measured and their contributions to regrowth were studied. In JuneJuly 2000 the regrowth rates, kg dry matter ha-1 d-1, of both species increased linearly by 19% by increasing the cutting height from 3 to 9 cm. In August 2000 the regrowth rates increased by 27% and the cumulative regrowth dry matter yield increased by 29%. In 2001 the defoliation height had no effect on the regrowth rates but the cumulative regrowth yield increased by 10% by increasing the cutting height. Meadow fescue produced 821% higher cumulative regrowth yields than timothy. In the reproductive phase, the regrowth rate of timothy is dependent on the population density of vegetative tillers but for meadow fescue population density did not have such importance. In vegetative phase there was no single factor essential for regrowth rates of either of the species.;
Highlights
Numerous studies have been undertaken to identify plant responses to defoliation height and frequency as well as to disclose the key factors behind regrowth potential
Of the abovementioned four factors affecting regrowth rate, the residual leaf area, WSC reserves and number of active meristems are of major interest, since the relative N content and total N pools in residual herbage are predominantly determined by nitrogen fertilization, which in turn is largely determined by other, especially environmental reasons
Since there was no interaction between defoliation height and species, it can be concluded that herbage mass (HM) yields during the experiment increased by 10% by increasing the defoliation height from to 9 cm in 2000 but were not affected in year
Summary
Numerous studies have been undertaken to identify plant responses to defoliation height and frequency as well as to disclose the key factors behind regrowth potential. Of the abovementioned four factors affecting regrowth rate, the residual leaf area, WSC reserves and number of active meristems are of major interest, since the relative N content and total N pools in residual herbage are predominantly determined by nitrogen fertilization, which in turn is largely determined by other, especially environmental reasons. Both timothy and meadow fescue are known to accumulate fructans of different degrees of polymerization The degree of polymerization may play an important role for regrowth potential as well. According to Volaire and Gandoin (1996), increased death rates of cocksfoot (Dactylis glomerata L.) under drought have been associated with a low proportion of high degree polymerization fructans
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