Effect of nitrogen fertiliser rates and defoliation regimes on the vertical structure and composition (crude protein content and digestibility) of a grass sward

Abstract

The vertical sward structure (proportions of lamina and sheath) and sward composition (crude protein and digestibility) have an effect on animal behaviour and performance, but their variation through management is not well known. We studied the effect of defoliation regime and nitrogen supply on these sward characteristics. There were six treatments, two nitrogen fertiliser rates combined with three defoliation regimes. Two of the latter mimicked a long growth duration (up to 7 weeks) and one mimicked a short period of regrowth (2 weeks). The swards were cut 7 cm from ground level. We found that there was a single relationship between sheath length and sward height, regardless of treatment and sampling date. For the treatments which mimicked a long growth duration, crude protein and digestibility decreased linearly from the top to the base of the sward when these decreases were expressed per unit of herbage mass. Conversely, for the treatments which mimicked a short growth duration, crude protein and digestibility fell quickly between the upper layers and those close to the ground. This discontinuity was the result of a smaller number of laminae per tiller than for the other treatments, whereas the composition of the sheath was the same. For resting periods longer than 20 days a model was proposed to simulate the effect of sward defoliation depth on the chemical composition of the diet selected by grazing animals according to available herbage mass before and during grazing. From a practical point of view the sward height alone could not be used to predict the sward composition from the top to the base of the sward and its effect on diet selection by grazers. The length of the resting period needs to be known in addition to the residual sward height.

The variation in morphology of perennial ryegrass cultivars throughout the grazing season and effects on organic matter digestibility

“…Wilson () found that OMD was highest in the leaf component and lowest in the dead component, following the order leaf > pseudostem > true stem > dead, agreeing with the present study. This suggests that digestibility decreases from the top of the sward to the base, which is also found in cocksfoot (Duru, ), although the individual plant components of perennial ryegrass are more digestible than in cocksfoot and timothy (Terry and Tilley, ). Other studies have also shown that differences exist in digestibility between the pseudostem and true stem (Terry and Tilley, ; Buxton and Redfearn, ), indicating that the pseudostem should be separated from the true stem, especially during the reproductive stage when the true stem is at its highest proportion.…”

Sward and tiller growth dynamics of Lolium perenne L. as affected by defoliation frequency during autumn

“…It has been well established that when N fertilisation is increased, sward herbage production increases (Hopkins et al 1990;Schils 1997), as does the N content [and, therefore, the crude protein (CP)] of the harvested material (Belanger and McQueen 1998;Duru 2003). However, N has very little or no effect on the digestibility of the forage (Duru 2003).…”

Effect of structure of a tropical pasture on ingestive behaviour, digestibility of diet and daily intake by grazing cattle

“…However, it has been reported that in vitro digestibility of vertical layers of the sward decreased linearly from the top to the base of the sward (Wilkinson et al, 1970;Delagarde et al, 2000). This is due to a continuum in chemical composition from the top to the base of a leaf, and also between lamina and sheath components (Duru, 2003). In this study, the taller and leafy the sward was the more large herbivores had the opportunity to remove the leaves in the upper layers of the sward.…”

“…, 2000). This is due to a continuum in chemical composition from the top to the base of a leaf, and also between lamina and sheath components (Duru, 2003). In this study, the taller and leafy the sward was the more large herbivores had the opportunity to remove the leaves in the upper layers of the sward.…”