The use of herbage nitrogen status to optimize herbage composition and intake and to minimize nitrogen excretion: an assessment of grazing management flexibility for dairy cows

Abstract

A framework for managing rotationally grazed pastures for dairy cattle which enables the cows’ energy and protein requirements to be met while simultaneously limiting the amount of N excreted in order to reduce N losses is described. The first objective is achieved by ensuring that lamina mass and the N concentration of herbage do not limit herbage intake or feeding value. The second objective is achieved by limiting N fertilizer supply or increasing the interval between defoliations to reduce the N concentration of herbage. Lower and upper thresholds for the N concentration of herbage and lamina mass were estimated from published data. The method is illustrated using two vegetative regrowths (beginning and end of spring) in a cutting experiment with two fertilizer treatments, 0 or 120 kg N ha−1 (−N and +N), and early or late cutting. Decreasing N supply led to a reduction in grazing management flexibility, i.e. the defoliation interval ranges which were compatible with the required sward characteristics (minimum lamina mass and N concentration of lamina) for herbage intake and to meet the protein requirements of dairy cows. Aiming for the upper threshold N concentration of herbage increased the minimum interval between defoliations only for the +N treatments. Nevertheless, grazing management flexibility remained the highest for the +N treatments.

Influence of harvest season, cutting frequency and nitrogen fertilization of mountain meadows on yield, floristic composition and protein content of herbage

“…All these factors could explain the decrease in legume proportion and, consequently, in CP content of the herbage collected in the regrowths associated to the application of a higher amount of N fertilizer (Tables 2 and 3). These results are in agreement with Duru & Delaby (2003) who observed a trend towards a decrease in the N index of regrowths of grazing pastures in response to the N fertilization. Also, this change in floristic composition may be markedly affected by cutting or grazing, as frequent cutting is more favourable for short-than for tall-growing species (Frame et al, 1998).…”

“…In agreement with the results described herein (June in Table 2 and spring in Table 3), McCarrick and Wilson (1966) observed an increase in CP content in the first cut herbage when applying high rates of N fertilizer on a permanent pasture (mixture of grasses and white clover), despite of promoting a decrease in the clover content. Increases in N content as a consequence of N fertilization were also detected by other authors in herbage harvested in the first cut after the spring growing cycle (Delagarde et al, 1997;Keady & O´Kiely, 1998;McCaughey & Simons, 1998;Madakadze et al, 1999;Duru, 2003;Duru & Delaby, 2003;Elliott & Abbott, 2003a). This could be due, at least in part, to higher contents of non-protein nitrogen (NPN).…”

“…Nevertheless this may be an expensive alternative which increases the risk of environmental damage and counteracts grassland biodiversity. To attain a sustainable system of utilization of mountain hay meadows, an increase in productivity through fertilization and management practices is desirable, providing it is compatible with important environmental issues such as the biodiversity in species-rich meadows or the risk of pollution of groundwater (Peyraud & Astigarraga, 1998;Duru & Delaby, 2003;Topp & McGechan, 2003).…”

“…However, much less is known about N fertilization of montane-alpine grasslands, where the effects of N fertilization need to be studied under different harvest systems determining the cutting frequency and the cutting date for each harvest season, factors with a significant influence on the plant maturity stage at harvest (Keady & O´Kiely, 1998;Duru & Delaby, 2003). Thus, the aim of the present study was to evaluate the influence of the harvest season, cutting frequency and N fertilization rate on yield and chemical or floristic composition of the herbage harvested from permanent mountain meadows.…”

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

“…The main experiment (expt. 1) consisted of treatments combining N fertilizer supply and defoliation regimes for studying lamina digestibility for laminae (Duru et al, 1999) and tillers (Duru and Delaby 2003). It was conducted at Auzeville, near Toulouse, SW France (latitude 48°70′, longitude 1.2°, altitude 200 m above sea level) on pure grass cocksfoot ( Dactylis glomerata L.) stand ( cv Lude).…”