Soil acidification affects at least 4 million hectares of agricultural land in Victoria, Australia. Low soil pH can inhibit plant growth through increased soluble aluminum (Al) concentrations and decreased available phosphorus (P). The addition of organic amendments may increase P availability through competition for P binding sites, solubilization of poorly soluble P pools, and increased solution pH. The effect of two organic amendments (lignite and compost) on P solubility in an acid soil was determined through controlled environment (incubation) studies. Three days after the addition of lignite and compost, both treatments increased orthophosphate and total P measured in soil solution, with the compost treatments having the greatest positive effect. Increased incubation time (26 days) increased soil solution P concentrations in both untreated and amended soils, with the greatest effect seen in total P concentrations. The measured differences in solution P concentrations between the lignite-and compost-amended treatments were likely caused by differences in solution chemistry, predominantly solution pH and cation dynamics. Soil amendment with lignite or compost also increased microbial activity in the incubation systems, as measured by carbon dioxide respiration. Based on the results presented, it is proposed that the measured increase in soil solution P with amendment addition was likely caused by both chemical and biological processes, including biotic and abiotic P solubilization reactions, and the formation of soluble organic-metal complexes. (Soil Science 2008;173:267-276)

Abstract. Available soil information and unpublished data from soil survey indicate that high clay contents and high bulk density are the major subsoil constraints to crop growth in the high rainfall zone (HRZ) of south-eastern Australia. Seven high rainfall agroecological zones are proposed as sub-divisions of the region to focus future research and development. The HRZ is dominated by texture-contrast soils (69.9%) and soils with clay subsoil (89.4%) and high bulk density (mean 1.6 t/m 3 ). Sodicity and acidity are also significant constraints to crop production in the HRZ. The physical limitations to root growth in the HRZ subsoils are best appreciated through the least-limiting water range concept and growth-limiting bulk densities. Management options and results of past research and intervention in soil loosening, drainage, raised beds, liming, and gypsum are reviewed. Climatic uncertainty raises questions about the future relevance of waterlogging as a constraint in the HRZ and confounds the development of reliable recommendations for engineering intervention.

Policy frameworks supporting sustainable agriculture development are critical in the delivery of the food and fibre needs of a burgeoning global population. A sustainable and resilient Australian agriculture sector is considered essential if it is to capitalise on the world's growing food and fibre needs. However, an increasingly dynamic climate, changing demographics of regional Australia, and economic factors in a global market constrain sustainable development of the agriculture sector. Although current policy supports investment in research and development and infrastructure, action to increase market access and competitiveness, as well as a suite of agricultural welfare options, it is flawed in its failure to contemplate the relative readiness of individuals and businesses to act on the interventions of government. This paper proposes the adoption of the capability approach to refocus the policy framework to prioritise delivery of outcomes that are valued by individuals and businesses. It proposes a conceptual model that provides a scalable, continuous improvement structure against which policy action can be implemented, monitored, evaluated, and adapted enabling design of more holistic agriculture policy settings that support the sustainable development of the sector and ensure that it can capture the opportunities of future global food and fibre demand.

The effect of 2 organic amendments (lignite and compost) on wheat growth and phosphate fertiliser efficiency (triple superphosphate, TSP; di-ammonium phosphate, DAP) in an acid soil was investigated in a glasshouse experiment. Organic amendments were incorporated into the top 40 mm of soil at rates resulting in a 1% and 2.5% increase in soil C, and fertilisers were banded within the seed row at rates equivalent to 5, 10, and 25 kg P/ha. When no P was applied, addition of both organic amendments increased shoot height, with greatest growth recorded in the compost-amended treatments. Addition of organic amendments and P fertiliser resulted in additive effects, with increased shoot height, tiller number, and shoot dry matter (DM) in both the lignite- and compost-amended soils with fertiliser addition. The addition of 1% C resulted in plant growth equal to that measured at a higher rate of addition (2.5% C), resulting in a higher relative efficiency of application. Tissue P uptake was significantly increased when soil amendment was combined with 25 kg P/ha DAP addition. Significant differences in nutrient uptake were also measured for other important plant nutrients. As the addition of organic amendments resulted in increased DM compared with untreated soil per unit of P fertiliser applied, it is feasible that this growth response may translate into increased yield. However, further study is required to define the agronomic and economic feasibility of broad-scale application of such amendments for production gains.

Soil acidity is a widespread problem in Victoria, Australia, affecting at least 4 million ha of agricultural land. Soil amendments such as lime and organic materials may ameliorate acid soils, resulting in raised soil pH and increased availability of plant nutrients such as phosphorus (P). The addition of lime, lignite, and compost significantly modified P sorption in an acid soil, with the degree of change highly dependent upon the source of P applied. The application of 2.5 t/ha of lime increased P sorption for all P sources, while P sorption was decreased in the lignite and compost treatments when di-ammonium phosphate (DAP) was applied. Lime and compost addition increased the solution pH, with no change in pH in the lignite treatment. Addition of TSP decreased the pH in all treatments, while DAP addition only increased solution pH in the untreated soil and the lignite treatment. The addition of soil amendments had a significant effect on solution cation concentrations, due to both the influx of cations, and the resultant changes in solution pH. The source of P applied (KH2PO4, TSP (triple superphosphate), DAP) also had a significant effect due to both the counter-ions present and the pH of each P source (e.g. TSP pH 2.7; DAP pH 7.4). The lignite treatment decreased total P sorption relative to the other amendments. The combination of lignite and DAP resulted in both the greatest decrease in P sorption, and the formation of soluble Al–organic complexes. Therefore, a combination of lignite and DAP may be of use in decreasing P sorption in acid soils.