January 15, 2013
Sandy ground is generally considered unproductive and can be forgotten about. But with land at a premium, many farmers in sandy areas in Victoria, South Australia and Western Australia are turning to clay spreading and clay topping to transform previously low value farmland into productive cropping ground. Tim Dunstan, Dunstan Ag, specialises in paddock renovation, and says clay spreading can be a cost-effective way of improving farmland. Mr Dunstan, who is based in Victor Harbour, SA, said all soil types could be improved, including even non-wetting sands. He said the most cost-effective improvements came in soils where there were sands over a clay base and the clay could be brought up to the surface with a delver, although importing clay from elsewhere can also be done if there is clay available within an economically manageable freight range. “It’s dearer than clay delving, but it can work,” Mr Dunstan said. In terms of delving, Mr Dunstan said clay could be brought up from as deep as a metre below the surface. Not only does the process add some ‘guts’ to sandy top soils, he said the delving could also help break-up clay hard pans in the subsoil. Mr Dunstan said clay topping sandy soils was a good way of boosting fertility. “Right from the start of the season, when there is a more even weed germination, due to the better soil structure, allowing a more effective knockdown, to better water holding capacity and improved soil fertility, it is something that can really improve soils in the right area,” he said. While many farmers clay-top entire paddocks, some choose just to improve a non-productive pocket, which is particularly sandy. Mr Dunstan said the incorporation process was critical. “Most problems experienced after claying arise from poor incorporation,” he said. He said specialist equipment did a better job than traditional cultivation tools. When done properly, a spader machine blends the sand and clay in one pass to a depth of 30 centimetres, which is much more effective than several passes of standard cultivators and the resulting compaction. “It’s worth doing well, because if the clay is sodic, and it is not incorporated correctly, you can get surface crusting, which causes waterlogging and poor rainfall penetration as the water pools on the surface,” Mr Dunstan said. He said it was important to know the specifications of clay before it was spread, in terms of pH and sodicity, and recommended checking crops in the years after clay delving to see if there had been changes in terms of nutrient uptake due to pH change. In terms of application, he said rates could vary from as much of 200t/ha of clay on non-wetting sands, which is why freight becomes an important cost if the clay needs to be brought in. “The rates will be determined by the annual rainfall, the drier the country, the less clay is needed,” he said. “Less clay is needed if the issue is with non-wetting topsoils, more is required to improve fertility in the profile.” In terms of timing, Mr Dunstan said some high rainfall systems used spring delving, but generally a lot of work goes on in the autumn.