North-West graziers are in the box seat to repair much-needed pasture ground cover following widespread rainfall that replenished soil moisture profiles for the summer growing season.

NSW Department of Primary Industries research shows ground cover plays an important role in reducing runoff, soil loss and evaporation.

Summer rainfall is often delivered as one big fall with little follow-up, so the need for increasing ground cover is a message that can not be ignored, according to DPI Manilla-based district agronomist, Lester McCormick.

“Only those who are managing ground cover in excess of 70 per cent can make use of the one-off large deluge because their pastures are harvesting the water, with the result that runoff and evaporation is reduced.

The importance of ground cover was highlighted during a storm at the property `Springmount’ Upper Manilla in December 2000, which delivered 36 millimeters in 36 minutes. The peak rainfall intensity of this storm was measured at 115 mm per hour.

Standing cover is preferable to short cover as it intercepts the rain drops before they hit the soil surface, slowing the aggregation of the water droplets and eventual runoff.

“Continuously grazed treatments with 56 per cent ground cover lost 71 per cent of the rainfall or 25.7 millimeters,” Mr McCormick said.

“Meanwhile, fertilized treatments with 97 percent ground cover and the rotationally grazed treatment with 98 percent ground cover lost only 2.5 mm and 3.4 mm respectively.”

The research also highlighted just how important litter was in reducing evaporation, which is estimated to account for 50 per cent of rainfall in the North-West.

Following the December 2000 storm, potential evaporation from the low ground cover plots, without further rain, was 35 mm in the first week. However, where adequate litter was available, evaporation was reduced by 20 per cent.

Mr McCormick said the ground cover situation in the North-West had deteriorated due to a run of poor summer rainfall, dropping paddock rotations, or trying to get a little extra out of each paddock.

“Dropping rotational grazing to allow more selective grazing of the green pick can help animal production, provided we have got the pasture quantity or herbage mass to match the animal’s requirements.

“However, if there is insufficient quantity there is poor animal performance, overgrazing occurs and ground cover is reduced.

“Maintaining the grazing rotation during periods of inadequate rainfall assists graziers’ to better manage ground cover and pastures make better use of smaller falls of rain.”

Again, this was demonstrated at “Springmount” where sheep grazing rotationally were left on the plots and the continuously grazed plots had to be destocked.

Mr McCormick said paddocks identified with minimal ground cover should be targeted this summer, to accumulate as much herbage mass as possible, to contribute to ground cover.

Paddocks closed up now to improve ground cover may grow an attractive quantity of annual grass and clover, but leaving this will provide high quality litter for soil microbes. Their activity will contribute to an improvement in the structure of the soil surface, once again improving water infiltration.

This story appears in the September edition of Agriculture Today.

Further information: Lester McCormick 02 6785 1790 or 0427 401 542

This story appears in Agriculture Today.