Improvement of Time‐Driven Models of Lamina Cocksfoot Digestibility by a Process‐Based Model to Take Account of Plant N Nutrition and Defoliation

Abstract

For management purposes, models of lamina digestibility (DW) that are thermal time driven (Tsum) fail to account for plant nitrogen status (0 < Ni < 1) and defoliation intensity (residual sheath height: Sr). The objective of this paper was to enrich them using a functional processed‐based model, which assumes that the decline in DW over time depends on the metabolic : structural tissue ratio and plant ageing. An experiment combining two N fertilizer rates and two defoliation regimes (differences in Sr) for two spring and two summer regrowth was done to analyse DW of laminae (youngest fully expanded) and tiller (whole green lamina) levels. For laminae, we show that both processes contribute to explain the decline in DW at a rate that depends on Ni but not on Sr. For tillers, consistent results were found justifying the use of a simple model: DW = f(+Ni; −Ni × Tsum; −Sr). Two different databases (from experiment and commercial farms) were used for validation: RMSD varied from 35 to 49 g kg−1. The process‐based model strengthened the empirical model and improved the comprehensiveness of how management practices change DW. We used both models to create applications for reasoning yield in function of herbage mass in complement than in function of time.

Plant trait–digestibility relationships across management and climate gradients in permanent grasslands

“…This could result from multiple effects of fertilization according to phenological stage. At the plant level, fertilization increases digestibility early in the season (due to a reduction in the fraction of vascular tissues), but digestibility decreases more rapidly because fertilization enhances herbage growth (Duru ). These opposite effects of fertilization over time could not be disentangled in this study because plant traits and digestibility were measured only at vegetative peak.…”

“…). A large variability in digestibility can be observed across grasslands, resulting from variations in botanical composition, climate and management regimes, because of their distinct effects on herbage structure (proportion of structural tissues) and on tissue ageing which reduce digestibility (Duru ).…”

“…Together with the amount and the timing of production, dry matter digestibility is a critical component of herbage nutritive value and provides a synthetic measure of the amount of energy available for herbivores in plant constituents (Bruinenberg et al 2002). A large variability in digestibility can be observed across grasslands, resulting from variations in botanical composition, climate and management regimes, because of their distinct effects on herbage structure (proportion of structural tissues) and on tissue ageing which reduce digestibility (Duru 2008).…”

Seasonal dynamics of biomass production and herbage quality of three grasslands with contrasting functional compositions

“…, 1995). When biomass accumulation and reproductive development is faster, as in the plants of the PFT A and B grasslands compared with plants of the PFT C, the decrease in digestibility occurs faster (Duru, 2008; Duru et al. , 2008).…”

Species interactions in a grassland mixture under low nitrogen fertilization and two cutting frequencies. II. Nutritional quality

“…The timing of reproductive development and stem elongation varies among and within species, as does the tendency to produce stems during regrowth after defoliation. As a result of the strong effect of heading, stem development and the age of tissues (Duru, ), nutritional composition is highly influenced by the defoliation regime, with earlier and more frequent defoliation resulting in forage of higher digestibility (Gardarin et al ., ).…”