Effects of date of autumn closing and timing of winter grazing on herbage production in winter and spring

Growth of grass herbage in Ireland is highly seasonal with little or no net growth from November to February. As a result, feed demand exceeds grass supply during late autumn, winter and early spring. At low stocking rates [<= 2 livestock units (LU) ha(-1)], there is potential to defer some of the herbage grown in autumn to support winter grazing. This study examined the effects of four autumn-closing dates and four winter-grazing dates in successive years on the accumulation of herbage mass and on tiller density in winter and subsequent herbage production at two sites in Ireland, one in the south and one in the north-east. Closing swards from grazing in early and mid-September (north-east and south of Ireland respectively) provided swards with > 2 t DM ha(-1) and a proportion of green leaf > 0.65-0.70 of the herbage mass above 4 cm, with a crude protein (CP) concentration of > 230 g kg(-1) DM and dry matter digestibility (DMD) of > 0.700. The effects of autumn-closing date and winter-grazing date on herbage production in the subsequent year varied between the two sites. There was no significant effect of autumn-closing date in the north-eastern site whereas in the south earlier autumn closing reduced the herbage mass in late March by up to 0.34 t DM ha(-1) and delaying winter grazing reduced the herbage mass in late March by up to 0.85 t DM ha(-1). The effects of later grazing dates in winter on herbage mass continued into the summer at the southern site, reducing the herbage mass for the period from late March to July by up to 2 t DM ha(-1). The effects of imposing treatments in successive years did not follow a consistent pattern and year-to-year variation was most likely linked to meteorological conditions.