Root growth ofLolium perennel.

Abstract

ABSTRACIThe responses of roots of Lolium perenne plants subjected to various levels of defoliation and shading were examined.A single defoliation caused a rapid drop in root elongation followed by a more gradual recovery, the most severe defoliation having the greatest effect. Shoot and root weights were reduced, but when root elongation had recovered to the control level the shoot/root ratios did not differ from the controls.Repeated defoliation caused a prolonged depression of root elongation, but some recovery occurred. The most severe treatment resulted in considerable root death.Root elongation of shaded plants at first decreased steadily and then increased.Both defoliation and shading caused increases in the length per unit dry weight of roots.

Primary productivity in patches of heterogeneous swards after 12 years of low‐intensity cattle grazing

“…Besides soil nutrients, water may be another resource that is less available in short than in tall patches. Due to a comparatively low sward leaf area index and larger proportions of bare ground, evaporation in short patches is increased (Veldhuis et al, 2014), while at the same time frequent defoliation quickly reduces the root growth rates (Evans, 1971) and leads to decreased rooting depth (Schuster, 1964). Moreover, the leaf area index may decrease to a level at which sward photosynthetic capacity is decreased.…”

Will current rotational grazing management recommendations suit future intensive pastoral systems?

“…In the longer term (over a 5-month period), repeated lax defoliation (to 160 mm height) reduced photosynthesis, through a loss in leaf area index due to pseudostem development (which doubled from 84.9 to 170.7 g/m 2 as cutting height increased from 20 to 160 mm), and through reduced photosynthesis per unit leaf area, possibly as a result of a higher proportion of older leaves, or a metabolic compensation with more severe defoliation pressure (Hernández . Conversely, repeated close defoliation (20 to 25 mm) reduces DM yield (Leafe & Parsons 1983;Hernández Garay et al 2000;Lee et al 2008a), root growth (Evans 1971(Evans , 1973Hernández Garay et al 2000;Lee et al 2008a) and tiller density (Hernández Lee et al 2008a), and increases the period of reliance on plant energy reserves (Davidson & Milthorpe 1965;Fulkerson & Donaghy 2001), putting plants at greater risk of death during adverse climatic conditions and also necessitating a longer subsequent rotation for plants to recover (Chapman 2016;Roche et al 2017b). To illustrate this last point, Chapman (2016) reported data from pasture defoliated to 1500 kg DM/ha (representing 'target' post-grazing residual) and 1150 kg DM/ha (representing 'overgrazing').…”

Nodulation and biological nitrogen fixation (BNF) in forage peanut (Arachis pintoi) cv. Belmonte subjected to grazing regimes

“…Photosynthesis is immediately reduced after defoliation. Consequently, defoliation regimes that cause the removal of large proportions of sward leaf area, herbage mass and/or pre-grazing height (Da Silva et al, 2014) may result in reduction or even cessation of root growth (Evans, 1971(Evans, , 1973Fownes and Anderson, 1991;Hodgkinson and Becking, 1978;Schuster, 1964) as a means of ensuring enough energy to restore leaf area. Root respiration and nutrients uptake from the soil are also reduced after defoliation but, according to Briske and Richards (1995), such reduction is smaller than the reduction in root growth.…”