The effects of autumn closing date on sward leaf area index and herbage mass during the winter period
2010
Ryan, W. | Hennessy, D. | Murphy, J.J. | Boland, T.M.
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 - 29 September, 13 October, 27 October, 10 November, 24 November. Herbage mass, tiller density and LAI were measured every 3 weeks from 28 November 2007 to 20 February 2008; additionally, herbage mass was measured prior to initial spring grazing and tiller density was measured intermittently until September 2008. Delaying CD until November significantly (P < 0·05) reduced herbage mass (by approximately 500 kg DM ha⁻¹) and LAI (by approximately 0·86 units) in mid-February. On average, 35% of herbage mass present on swards on 20 February was grown between 28 November and 30 January. LAI was positively correlated with herbage mass (R² = 0·78). Herbage mass increased by approximately 1000 kg DM ha⁻¹ as spring grazing was delayed from February to April. Tiller density increased from November to February, although it did fluctuate, and it was greatest in April (9930 m⁻²). This experiment concludes that in the south of Ireland adequate herbage mass for grazing in early spring can be achieved by delaying closing to early mid-October; swards required for grazing after mid-March can be closed during November.
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