Although liming is the preferred method to treat acid soils, there are other management options that will reduce the level of acidification. However, they will not stop it or reverse it. Liming is still the preferred treatment for soils that have topsoil pH less than 5.5 and subsoil pH less than 4.8.
Management options to reduce acidification
Using less-acidifying rotations
The benefit of less-acidifying rotations is that the process of acidification, which cannot be prevented in agriculture, will be slowed. The downside may be that the options are less profitable or unsuitable to the rotations that best suit the business.
The rate of soil acidification due to agriculture can be reduced but not eliminated — liming will always be needed to prevent the soil from becoming too acidic.
Removal of produce also contributes to soil acidification and some product removal is more acidifying than others because more alkalinity is exported from the paddock. Usually, it is desirable to maintain optimal crop and pasture choice and apply lime to counter soil acidification. However, if soil is already highly acidic, the choice of less acidifying options in conjunction with a recovery liming program may help.
The DAFWA Lime and Nutrient calculator can estimate the acidification and removal of nutrients associated with broadacre rotations. This information can be used to choose less acidifying rotations and to calculate the maintenance levels of lime needed to prevent further acidification. Any system that removes more biomass will lead to increased acidification. For instance, removing hay or silage will lead to more acidification than removing only grain.
Using less-acidifying fertilisers
Consider using non-acidifying or less-acidifying nitrogen fertilisers.However, always assess the cost-effectiveness of non-acidifying options compared with other nitrogen fertilisers used in conjunction with appropriate liming.
Reducing nitrogen leaching
The inefficient use of nitrogen fertiliser is a major contributor to soil acidification in WA. Inputs of nitrogen fertiliser can be managed to reduce nitrogen leaching and this is especially important in high-rainfall areas. Carefully calculate required amounts of nitrogen fertiliser and split applications may be an option.
In practice, the nitrogen fertilisers used are determined more by cost and application technique than by the risk of leaching.
Returning plant material to the paddock
Most plant material is slightly alkaline. Plant roots take up nutrients as either cations, which are positively charged (for example, ammonium, potassium, calcium or magnesium) or as anions, which are negatively charged (for example, nitrate, phosphate or sulphate). Plants absorb more cations than anions and each time a plant absorbs a positively charged cation, a positively charged hydrogen ion must be excreted into the soil to maintain electrical balance. If plant material is removed by grazing or harvest or relocated by the concentration of dung into stock camps, rather than being returned to the soil, there is a net export of alkalinity and residual hydrogen ions remain in the soil. Over time, as this process is repeated, the soil becomes acidic. A translocation of alkalinity can occur in windrows with the soil off the windrow becoming more acidic.
One way to manage this is to return chaff and other material from harvesting back to the originating paddock. This can also be done by feeding hay back onto the harvested paddock. In practice, this is only marginally successful in arresting acidification, as the underlying acidification process continues, and the plant material is rarely fully or evenly returned.
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