A Model of Lamina Digestibility of Orchardgrass as Influenced by Nitrogen and Defoliation

Abstract

The morphogenesis of grass-sward regrowth drives the relationship between sward management effects and herbage digestibility. Our objective was to create a model of herbage digestibility for a range of N fertilizer levels and defoliation practices on the basis of changes in vegetative grass tiller structure rather than on dates of cutting or grazing. An experiment was conducted for two spring and two summer regrowths to examine the digestibility of orchardgrass (Dactylis glomerata L.) whole laminae (Lw) and youngest fully expanded laminae (Ly) for two N rates, and two defoliation patterns differing in the initial cutting date. Data were collected for lamina digestibility, dates at which a new leaf and its ligule were visible, and lamina and sheath lengths at least three times during each regrowth. There was a significant effect of N and cutting date on Ly and Lw digestibility, both variables being correlated significantly. At the ligule stage, Ly digestibility decreased between two successive leaves on a tiller, but this decrease was least when the N rate was low. For each regrowth, a single significant relationship was found between Ly digestibility and the growth duration of the lamina outside the sheath. As lamina growth duration depends both on sheath length and herbage N status, Ly digestibility was expressed according to these two easily measurable sward states. The model used to predict the green lamina digestibility at the whole canopy level could also explain the faster decline of herbage digestibility when the N rate was higher or when daily temperatures increased. In both cases, sheath length increased faster from one insertion level to the next, leading to a longer lamina growth duration.

Do plant functional types based on leaf dry matter content allow characterizing native grass species and grasslands for herbage growth pattern?

“…Similar differences could be due to nutrients which lengthen the LLS in case of N deficiency (Duru and Ducrocq 2002). Nevertheless the observed differences are of great importance from an agronomic point of view (Lemaire 1999), and consistent with the differences in LLS observed between a A-and a C-PFT.…”

Influence of management regime and harvest date on the forage quality of rangelands plants: the importance of dry matter content

“…Fertilization combined with more intense grazing induced higher DMD. This increase is explained by an increase in NC ( Pontes et al 2007 ; Carrère et al 2010 ) and a decrease in fibre content ( Duru and Ducrocq 2002 ; Carrère et al 2010 ) and DMC ( Pontes et al 2007 ). Wilson et al (1999) reported that the lower digestibility of species that prefer low-nutrient habitats is the consequence of their chemical composition and tissue anatomy, which is due to their high proportion of non-veinal sclerenchyma cells ( Van Arendonk and Poorter 1994 ).…”

Field indicators of leaf nutritive value for perennial ryegrass and tall fescue pastures under different growing and management conditions

“…The residual post‐grazing height (i.e. height to which swards are defoliated) can affect the nutritive value of the subsequent forage regrowth (Duru & Ducrocq, ) by changes in leaf morphology (Insua et al, ). In the present study, which examined changes at the leaf level, NDFD was increased with reductions in residual sward heights, except for perennial ryegrass regrowth in spring (Table ).…”

“…One critical variable in grazing management is defoliation intensity (either expressed in units of height or herbage mass) because this variable defines the residual (post‐grazing) leaf area to support subsequent regrowth (Parsons & Chapman, ). Likewise, the defoliation intensity also affects the residual length of sheath tubes and both the subsequent length and digestibility of newly formed leaves (Duru & Ducrocq, ). Leaf length is a “plastic” trait that is determined by the interaction between plant morphogenesis, growing conditions (mainly temperature, mineral nutrition and water status) and defoliation management (Lemaire & Chapman, ).…”

“…Therefore, our research question is whether prevailing growing conditions and defoliation management decisions such as residual sward heights, which are known to influence pasture growth (Chapman et al, ; Insua, Utsumi, & Basso, ), leaf length (Duru & Ducrocq, ; Skinner & Nelson, ) and digestibility (Insua et al, ) of perennial ryegrass and tall fescue, affect the rates of nutritive value decline with the herbage mass accumulation and leaf stages of regrowth. This study examined whether or not observed changes of leaf nutritive value can be predicted from changes in plant structure traits such as herbage mass or leaf stage of regrowth.…”