Ground Cover Supplement : GC Supplement - Soil constraints
20 Soil acidity ADDRESSING BARRIERS TO LIME USE By Brian Hughes SURVEYS BETWEEN 2005 and 2014 of growers in South Australia with acid soils indicate 40 to 50 per cent believe liming to be too expensive -- due to lime sources being too far away and expensive to transport -- especially in years and areas of low productivity. While most growers believe that lime benefits the productivity of acid soils, barriers to lime use are restricting its application. Of particular concern is the lack of information available from lime suppliers on the quality of lime sources and therefore their effectiveness in lifting soil pH. Other concerns limiting lime use in SA include: the availability of machinery to spread lime; the potential impact of lime application on the introduction of, or increase in, pests; and nutritional deficiencies or imbalances. A new GRDC-funded project running until 2018 will develop a soil acidity strategy for SA with the goals of doubling lime sales in SA agricultural areas by 2018 and lifting grower and adviser capacity in identifying and treating critical soil pH levels in the surface and subsurface. The project is extending local pH and trial data and helping growers and advisers determine the economics of treating soil acidity through comparing lime sources and products, trialling precision pH testing and developing tools for calculating lime rates. □ GRDC Research Code RSS00010 More information: Brian Hughes, Rural Solutions SA, 08 8568 6411, firstname.lastname@example.org LIME LAGGING BEHIND ACIDITY IN VICTORIA By Lisa Miller SOUTHERN FARMING SYSTEMS researchers are working with the Victorian Corangamite Catchment Management Authority (CMA) on three GRDC-funded soil acidity projects to lift liming use across the region: ¢ soil acidity monitoring within the Corangamite CMA to demonstrate the soil acidity issue; ¢ trials to measure crop responses to liming in south-west Victoria so that simple lime-response calculators can be created to help growers make better liming decisions; and ¢ trials to measure pasture responses to liming and biological amendments within the Corangamite catchment. The projects will determine the amount of lime needed in different soil types to remove production constraints and return soil pH to optimal levels. This will enable growers to calculate how often to reapply lime and how much a liming program will cost relative to the production returns of maintaining a good soil pH profile. Soil acidity monitoring across the Corangamite catchment indicates there is an issue with surface soil (0 to 10 centimetres) acidity, with 59 per cent of soil samples returning pH values below the optimum of 5.0. Thirty-three per cent of sites had a soil pH lower at 10 to 20cm depth than in the topsoil and strongly acidic layers (10 to 20cm) existed in 16 per cent of sites in sedimentary, alluvial and granite soils. In 17 per cent of the paddocks tested soil acidity issues extended into the subsoil (20 to 30cm). The soils found to be acidic at depth were mainly formed on sedimentary, alluvial, granite or marl-based soils and located in high-rainfall areas (600 millimetres plus). Soils formed on basalt were not acidic at 20 to 30cm as these soils naturally increased in pH with depth due to their high calcium oxide and magnesium oxide content. □ GRDC Research Code SFS00026 More information: Lisa Miller, Southern Farming Systems, 03 5265 1666, 0488 600 226, email@example.com SOURCE: DAFWA Note: 1.7t/ha of lime with a neutralising value (NV) of 60 per cent is required to achieve the same pH change as 1.1t/ha of 90-per-cent NV lime. FIGURE 1 Amount of lime of varying neutralising values required to achieve the same pH change. 60708090100 Percent neutralising value of lime Equivalent rates (t/ha) 1.8 1.6 1.4 1.2 1.0 0.8 SOURCE: DAFWA Note: Coarse and fine limes with the same neutralising value will treat the same amount of acidity but the finer lime will do it more quickly. FIGURE 2 Impact of particle size on pH change for lime applied at 2.5t/ha. 0.25 0.50 0.75 1.00 Particle diameter (mm) Relative efficiency (%) 100 80 60 40 20 0 NEUTRALISING VALUE AND PARTICLE SIZE Neutralising value and particle size are the key indicators of lime quality. Limes with a higher neutralising value will treat more acidity, while limes with a greater proportion of fine particles will increase soil pH more quickly (Figures 1 and 2). With high neutralising limes, less lime needs to be applied to achieve the same pH change. The Lime Comparison Calculator (www.soilquality.org.au/calculators) calculates and compares the cost-effectiveness of lime sources. Simply copy and enter the product specifications of a lime source (neutralising value and particle size distribution) into the calculator, along with transport and application costs and the cost of the lime itself. Information about neutralising value and particle size distribution of different agricultural limes are available for Western Australia from accredited lime suppliers via The Lime WA Inc (www.limewa.com.au).
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