Ground Cover North : Ground Cover 050 June-July 2004 - North
By TROY CLARKSON Not so long ago, many people felt the role of soil was simply to hold up the crop. Its physical and chemical structure, its own management needs, were rarely considered. Today, however, sustainable healthy soils have become crucial for a productive and ongoing agriculture. The cost of soil degradation is becoming more widely recognised, making soil and soil management one of the most important considerations for most farmers. Understanding the basis of a healthy soil structure becomes the starting point for better soil management. Soil structure comprises solid soil components such as individual sand, silt and clay particles, plus organic matter. The chemical- attraction properties found in clay and organic matter cement all soil material together to form aggregates. The arrangement of aggregates, along with size and shape, varies the structure of soils. Macropores that occur between the soil aggregates allow rapid movement of air and water into and through the soil. Micropores occur within the soil aggregates themselves (the spaces between the sand, silt, clay and organic matter particles). Micropores are what hold water in soil for extraction by roots (see graphic). Soil pits (holes dug in the ground) are excellent tools to assess an area's soil structure. Knowing the soil structure at different depths can help farmers make important management decisions governing land use, fertilisers, and choice of crop. The benefits of well-structured soils include: n provision of oxygen needed by roots to grow, and to move into and through the soils; n increased availability of water and nutrients; n root development down the soil profile, increasing water and nutrient availability; n allowing water to drain freely, preventing waterlogging and at times salinity; n increased water input into the soil profile; n stabilised soil and less erosion; n microbial activity which breaks down organic matter, increasing nutrient availability to plants. Soil structure generally begins to break down if sodium levels are too high. A simple field test to indicate high sodium levels is to drop a dry aggregate into fresh water. After 24 hours, if the aggregate breaks down into individual particles (dispersion) and forms a cloud, it is high in sodium. A soil test at a laboratory can accurately determine how sodic a soil is and how much gypsum needs to be added to rectify the situation. To strengthen soil structure, you need organic matter. This can be increased by including pasture phases into crop rotations, by adding organic matter (such as manure) and, where feasible, by incorporating organic waste (such as stubble) into the soil. Compaction caused by livestock and machinery also breaks down soil structure. This process escalates when soils are too wet. Compaction increases runoff and potential for soils to erode. It also restricts root development, which may significantly decrease crop and pasture production. Compaction can, however, be reduced through good grazing management and controlled traffic. Raised beds are an excellent method for controlling traffic and reducing compaction on high-rainfall cropping country. It is well documented that over-cultivation or cultivation with certain implements can also damage soil structure. For example, disc ploughs are today discouraged because they have the maximum disturbance on soil structure, compared with direct drilling, which has minimal impact. Generally, minimal tillage or no tillage are now recommended to maintain an optimum soil structure. GRDC RESEARCH CODE SFS 00007, program 4 For further information: Troy Clarkson, Department of Primary Industries, Victoria, 03 5226 4604 By KELLIE PENFOLD Greater profitability and sustainability would be the rewards if more accurate and affordable soil testing and mapping were available to Australian farmers, according to a report to the GRDC. 'Rapid Soil Measurement -- a review of potential benefits and opportunities for the Australian grains industry' has revealed Australian agriculture is trailing the world in some aspects of high quality and rapid soil measurement, data and mapping. The report was prepared by a team drawn from CSIRO Land and Water, CSIRO Telecommunications and Industrial Physics and the Australian Wine Research Institute, and with review comments from the Australian Centre for Precision Agriculture at Sydney University. It recommends a "multi-pronged approach to the development of an improved soil information base for Australian agriculture". Program consultant to GRDC's Sustainable Farming Systems program Dr Phil Price, says the report highlights issues of obtaining accurate soil data at the right spacing and timing. "Having soil information at a fine spacing is important in managing paddock variability through Precision Agriculture (PA) methods, while real-time data would help growers to adjust sowing rate and fertiliser application. "However, at present, growers cannot afford to use soil test methods to get the required fine scale, and there is a delay between taking the sample and getting the result." Dr Price says there are many areas in which accurate soil mapping and testing can help farmers make money, such as measuring plant- available water capacity. "If a grower could make the decision to sow based on what water was available and rainfall probability, there is a large potential for more money in the pocket." With a brief established in consultation with growers, Dr Price believes the report will provide a good working base for the GRDC when funding for soil measurement projects becomes available. "In Australia there is a lack of site specific information on soil conditions for most farms, for example, maps of critical soil properties relating to nutrient content, subsoil constraints and plant-available water capacity," the report states. "The advent of precision agriculture and demands for more efficient crop production have highlighted the need for timely information on soil properties, preferably as maps for individual paddocks. "This information is needed to diagnose constraints to production, reduce risks associated with decisions on the quantity and timing of inputs and to manage off-site impacts." After fully assessing all available soil monitoring tools and techniques, the report makes recommendations on six key areas: specimen acquisition and preparation; measurement platforms; sensors and measurement systems; integrated soil and crop measurement; key data sets, and training. It says new technologies for soil measurement are now creating an efficient means for providing farmers with relevant information to support better systems for crop production. However, the report finds some of these are in their infancy, while others are well developed in terms of instrumentation, but have few agreed procedures for data analysis. It says their value in improving crop performance is not yet proven. Unlike the United States, detailed soil survey programs to support crop production have not been undertaken across large parts of Australia's cropping lands. Working on the premise of soil information being of benefit if it can be provided at a reasonable cost through efficient analysis, the review assesses 12 different technologies (see table for recommendations). The report notes that many farmers rely on informal and often vague definitions of soil types on their properties and in their district, such as red loam or black clay. Typical values for key soil properties are generally unavailable and, therefore, it is difficult to accurately determine soil factors limiting crop production. The report says this level of information does not provide a reliable framework for applying extension and research recommendations. GRDC RESEARCH CODE CSO 00027, program 4 For more information: Dr Phil Price, 0419 122 572 email@example.com The full report will be available shortly on the GRDC website www.grdc.com.au FEATURE 23 JUNE 2004 SOIL INFORMATION SOIL STRUCTURE COMPONENTS MICROPORES AGGREGATES MACROPORES Centre for Land Protection Research 2001 More groundwork needed, says report SOME KEY RECOMMENDATIONS n the need for rapid geo-referenced sampling systems and automatic soil sample preparation equipment: rapid coring systems are needed for deeper soil characterisation; n a study of the potential for automatic core scanning using a range of sensors allowing deeper layers to be automatically analysed using a small mobile drill rig; n improved mid-infrared data acquisition: increasing the scanning area of mid-infrared instruments would improve predictions of soil properties; n cheap telemetry systems for opening up new and cost- effective possibilities for monitoring soil water content across the landscape; n remote sensing with repeated scans to identify differences in crop water-use and soil hydraulic properties; and n a basic land resource survey across Australia's farming lands to ensure greater awareness of soil-based limitations to crop production and to provide basic data sets. Growers are getting the message: the answer lies in the soil Getting down and dirty: Troy Clarkson gives growers an in-depth demonstration of their soil structure.
Ground Cover 051 August-September 2004 - North
Ground Cover 049 April-May 2004 - North