Ground cover reduces erosion, helps pasture recovery

New soil formation is as low as 1.4 t/ha a year, but in some environments can be up to 10 t/ha. In contrast, soil loss from storm rains has been recorded at around 100 t/ha per event. Wind erosion over a lengthy blow can be 10s of t/ha.

If erosion is not contained, soil fertility, soil quality and long-term productivity will be severely compromised.

Soil loss of 100 t/ha can result in 100-200 kg/ha loss of total nitrogen. Phosphorus losses can also be as high as 150 kg/ha per 100 t/ha of lost soil. Around 7.5 kilograms of this loss is generally the immediately available form. Less available phosphorus is also important as it is the source of future phosphorus via natural cycling.

Lack of ground cover is clearly the driver of water and wind erosion. Some of the worst affected paddocks have been dual purpose crops over the last two years, totally grazed off in respective springs, leaving no cover for several months.

Research over the last 40 years has repeatedly shown that stubble retention, even as low as 20-30 per cent ground cover in cropping, could reduce water erosion by 80-90 per cent, as well as allow far more efficient capture of rainfall.

Zero or no-till cropping, combined with stubble retention, even where carefully grazed or cut for hay, has been a godsend in protecting soil as well as being critical for higher yields when combined with timely weed kills.

Backing research is the common observation these last two summers of how effective low stubble levels can be. Minimal wind erosion occurred where stubble of dual purpose or grain only crops was retained at only 10cm height and equivalent to 20-30 per cent ground cover. In contrast, bare paddocks eroded badly as a consequence of water or wind.

Cultivation has crept back into farming systems for legitimate reasons, such as for strategic killing of herbicide resistant weeds, pre-emergent herbicide use, and applying fertiliser into deeper layers.

Research suggests little soil structural damage resulting from the odd cultivation. However, my feeling is the "odd" cultivation may be too common and is contributing to greater risk of soil erosion.

Pastures totally grazed out have also been extremely vulnerable to wind and water erosion. It has not been uncommon for storm rains of 30-50mm to fill dams (with water and soil) but with very little water entering the soil to promote pasture growth.

Wind erosion of bare pasture paddocks, blotting out the sun and amounting to tones/ha soil loss, over repeated wind events has been unfortunately common.

Perennial pastures, even heavily grazed, generally provide useful soil protection compared to grazed out annual pastures. Totally grazed out lucerne also provided little soil protection, especially from wind erosion.

Greater retention of root systems of perennials, including lucerne, improves soil protection compared to the faster loss of annual pasture roots.

An aspect to improve soil protection from wind and water erosion is "feed budgeting", not an easy task but one achievable via regular monitoring of available feed (pasture, crop, stored fodder) combined with calculating animal consumption.

A simple example is 200 steers each consuming around 10kg/ha (dry-matter) pasture per day, or 2t/ha for the mob. Assessment made early in the drought may have measured 200 t/ha of available farm feed, but as the drought proceeded consumption commonly drew down the forward feed supply.

Regular feed assessment however does provide early warning of pending feed deficit and allows for sounder decision making (e.g. sell stock, purchase feed, wean early, mini feed lot etc).

Management that preserves sufficient ground cover not only dramatically reduces impact of erosion, but also contributes to faster pasture recovery post rain and higher total production.

Next week: Assessing nitrogen requirements for coming winter crops.