Implications of nitrogen fertilizer applications and extended grazing for the N economy of grassland

The provision of grass for early spring grazing in Ireland is critical for spring calving grass-based milk production systems. This experiment investigated the effect of a range of autumn closing dates (CD), on herbage mass (kg DM ha )1 ), leaf area index (LAI) and tiller density (m )2 ) during winter and early spring. Thirty-six grazing paddocks, closed from 23 September to 1 December 2007, were grouped to create five mean CD treatments -

Section: Discussionmentioning

confidence: 63%

“…High LAI results in increased herbage mass which eventually restricts the quantity of light reaching the lower leaves of tillers and the tiller buds, resulting in reduced tiller production and increased senescence (Davies, 1972; Hunt, 1978). Laidlaw et al. (2000) and Hennessy et al.…”

Section: Discussionmentioning

confidence: 99%

The effects of autumn closing date on sward leaf area index and herbage mass during the winter period

Ryan

Hennessy

Murphy

et al. 2010

“…(1961a), Wilkinson (1985) and Skinner and Allen (1991) for N applied specifically to produce herbage for late autumn/winter utilization. However, recent work by Laidlaw et al . (2000) has shown that, when N fertilizer is applied after late September, the response is poor and the probability for loss of N by leaching is increased.…”

Section: Discussionmentioning

confidence: 99%

The effects of rate and timing of application of fertilizer nitrogen in late summer on herbage mass and chemical composition of perennial ryegrass swards over the winter period in Northern Ireland

Binnie¹,

Mayne²,

Laidlaw³

2001

A small‐plot experiment was carried out in Northern Ireland on a predominantly perennial ryegrass sward over the period July 1993 to March 1994 to investigate the effect of timing and rate of fertilizer nitrogen (N) application on herbage mass and its chemical composition over the winter period. Eighty treatment combinations, involving four N fertilizer application dates (28 July, 9 and 30 August and 20 September 1993), four rates of N fertilizer (0, 30, 60 and 90 kg N ha−1) and five harvest dates (1 October, 1 November, 1 December 1993, 1 February and 1 March 1994), were replicated three times in a randomized block design experiment. N application increased herbage mass at each of the harvest dates, but in general there was a decrease in response to N with increasing rate of N and delay in time of application. Mean responses to N applications were 13·0, 11·5 and 9·5 kg DM kg−1 N at 30, 60 and 90 kg N ha−1 respectively. Delaying N application, which also reduced the length of the period of growth, reduced the mean response to N fertilizer from 14·3 to 7·4 kg DM kg−1 N for N applied on 28 July and 20 September respectively. Increasing rate of N application increased the N concentration and reduced the dry‐matter (DM) content and water‐soluble carbohydrate (WSC) concentration of the herbage but had little effect on the acid‐detergent fibre (ADF) concentration. Delaying N application increased N concentration and reduced DM content of the herbage. The effect of date of N application on WSC concentration varied between harvests. A decrease in herbage mass occurred from November onwards which was associated with a decrease in the proportion of live leaf and stem material and an increase in the proportion of dead material in the sward. It is concluded that there is considerable potential to increase the herbage mass available for autumn/early winter grazing by applying up to 60 kg N ha−1 in early September.

“…However, in their study, the uncut sward had a very high herbage mass entering the winter, almost 4 t DM ha –1 being removed from the cut sward in December when cut to 5 cm. This dense canopy may have resulted in a severe reduction in tiller density, adversely affecting spring growth ( Laidlaw et al ., 2000 ). Damaging effects of the grazing animal due to treading and poaching may have also contributed to the negative effects on spring herbage mass in the studies by Roche et al .…”

Section: Discussionmentioning

confidence: 99%

Setting management limits for the production and utilization of herbage for out‐of‐season grazing

Laidlaw¹,

Mayne²

2000

Three experiments were carried out on perennial ryegrass‐dominant swards to provide a basis for recommendations for the limits to (a) building up and timing of utilization of a herbage ‘bank’ for out‐of‐season grazing and (b) duration and intensity of early spring grazing in the United Kingdom and Ireland. In experiment 1, the effect of regrowth interval (from 7 September, 20 October, 17 November or 15 December) in autumn on herbage accumulation, leaf turnover and on subsequent spring growth was investigated. Swards regrown from early September reached maximum herbage mass (about 3 t ha–1 DM) and leaf lamina content in mid‐November, by which time senescence rate exceeded rate of production of new leaves. New leaf production and senescence rates were greater in swards remaining uncut until December than in those cut in October or November. Time of defoliation up to December had no effect on spring herbage mass in the subsequent spring. Defoliating in March reduced herbage mass in late May by less than 20%. Experiment 2 investigated the progress in herbage growth and senescence in swards regrowing from different times in late summer and autumn to produce herbage for utilization beyond the normal grazing season. Treatments in a randomized block design with three replicates were regrowths from 19 July, 8 August, 30 August and 20 September. Based on a lower ceiling of leaf and total herbage mass being reached with progressively later regrowths, beyond which leaf senescence generally exceeded leaf production and herbage mass declined, it was concluded that currently recommended rotation lengths for this period should extend from 3 weeks in late July to 8 weeks for swards previously grazed in mid‐September. In both experiments, leaf senescence commenced earlier (by one leaf‐age category) than previously published estimates and so brought forward the time at which senescence rates balanced leaf growth rates. In experiment 3, designed to evaluate the effect of daily grazing period and intensity in early spring on herbage regrowth, dairy cows grazed successive plots (replicates) for 2 or 4 h each day at two intensities (target residual heights of 5 or 7 cm) in March to mid‐April. Regrowth rate was similar in all treatments including the ungrazed control, despite soil moisture content being relatively high on occasions. Tiller density was significantly reduced in May by grazing plots in early or mid‐April. It is concluded that in autumn there are limits to which rotation lengths should be extended to produce herbage for out‐of‐season grazing owing to attainment of ceiling yields. Although utilization in early spring may reduce herbage availability in spring, out‐of‐season utilization need not reduce herbage growth rates in early spring.