The Highs and Lows of the 2006 Grass Growing Season

The 2006 grass growing season is nearing an end, and what a season it has been! The AgriSearch and DARD funded GrassCheck project has monitored grass growth throughout the year, and Figure 1 summarises growth from the current season. The difficulties experienced by all grassland managers are clearly illustrated by the extremes in grass growth highlighted in the graph, with the challenges beginning before many cows were even turned out.

Figure 1. Grass growth throughout 2006 compared to the 6-year average (1999-2005)

Although a small number of herds were able to graze with relative ease throughout February in County Down, a prolonged period of cold and wet weather during March and early April delayed turnout and early season growth. By the third week in April growth was actually over 60 percent below average, with growth this spring being one of the slowest since 1999. The combination of wet ground conditions and poor grass growth, resulted in limited opportunities for grazing during this period, with many farms only grazing for a few hours through the day in late April.

Despite wet conditions continuing into late April and May, there was a rapid improvement in temperatures from mid-April, with the average air temperature recorded at Crossnacreevy being 2.5^oC higher during the second half of the month compared to the first half. This rise in temperature resulted in a dramatic improvement in grass growth, with growth up to average levels by late April. Grazing conditions remained variable throughout May, with the unsettled weather delaying full turnout on many farms. By mid-May grass growth had increased to one of the highest peaks recorded since 1999, with this peak being over 30 percent higher than average. This very high growth and delayed turnout on many farms combined to give grassland managers a real headache by late May. Not only was it difficult to graze paddocks cleanly due to the weather, but grazing paddocks were accumulating herbage cover very quickly and becoming too mature for optimal grazing. The grazing rotation therefore was very erratic in early season. Farmers who removed paddocks for silage had relatively short rotation lengths, compared to those who preferred to graze the herbage, who had a relatively long first rotation, due to the quantity of grass in front of the cows. By late May grass growth had returned to around average, and a settled period of weather into early June improved grazing conditions, and allowed the majority of first cut silage to be taken.

Following the difficulties of April and May, the weather during June and July provided a completely different challenge. The change to drier weather was welcomed by all, and provided an ideal platform for some excellent grazing conditions. However, during this 60 day period there were almost 40 completely dry days measured at Crossnacreevy, with only 4.3 inches of rainfall recorded over this period. The site at Crossnacreevy is susceptible to moisture deficit, and growth actually dropped to a low of 33 KGDM/ha/day in mid-July, were it remained until mid-August. This effect was observed on many farms, particularly those on free-draining soils, resulting in shortages of feed within the grazing area. Growth was actually 37 percent below average around mid-July, and many farmers had to feed silage and lengthen the grazing rotation during this period to compensate for the poor grass growth. A return to showery weather improved growth through August on many farms, but those worst affected by the dry weather continued to struggle.

The scarcity of grass through July and August was quickly reduced in early September, as the well publicised mild temperatures throughout September kept grass growth well above average. Growth remained above average from mid-August until early October, with growth being 40-50 percent higher than average at times during this period. This created a large bank or wedge of grass on many farms. However, the utilisation of this grass has been made very difficult due to poor ground conditions at various times during the autumn. However, the occasional settled periods of weather during the autumn has allowed the majority of heavy covers to be removed during the final grazing rotation, with a few farmers also removing some fields as silage during late September and October.

Despite the major fluctuations in grass growth throughout the season, total average herbage production for 2006 of 11.5 tDM/ha was just above the six-year average of 11.3 tDM/ha. Given the current financial pressures in the beef and dairy sectors, maximising the use of forage, and in particular grazed grass, is essential to reduce production costs. GrassCheck provides a valuable service to farmers by highlighting the major fluctuations in grass growth through the season. This enables timely and informed decision making to avoid either wastage of grass during periods of rapid growth, or grass shortages during periods of poor growth as in early spring and mid-summer this year.