Robert Summers

Effect of application of bauxite residue (red mud) to very sandy soils on subterranean clover yield and P response

Bauxite residue (red mud) is the byproduct from treatment of crushed bauxite with caustic soda to produce alumina. When dried the residue is alkaline and has a high capacity to retain phosphorus (P). The residue is added to pastures on acidic sandy soils to increase the capacity of the soils to retain P so as to reduce leaching of P into waterways and so reduce eutrophication of the waterways. This paper examines how red mud influences the effectiveness of P from single superphosphate for producing subterranean clover (Trifolium subterraneum) dry herbage, in the year of application and in the years after application (residual value). Red mud was applied at 0, 2, 5, 10, 20, and 40 t/ha and the P was applied at 0, 5, 10, 20, 40, 80, and 160 kg P/ha. In the year of application and the year after application of red mud, dry matter yields were doubled on the soil treated with 20 t/ha of red mud compared with the untreated control. Improvements in production were initially greater in the red mud treatments than in the lime treatment (2 t lime/ha). Red mud increased the maximum yield plateau for P applied in current and previous years. When P was applied to freshly applied red mud, more P needed to be applied to produce the same yield as the amount of red mud applied increased. Red mud increased soil pH, and the increases in yield are attributed to removing low soil pH as a constraint to pasture production. This initial need for higher amounts of fertiliser P when increasing amounts of red mud were applied may be due to increased P sorption caused by increased precipitation of applied P when the fertiliser was in close contact with the freshly alkaline red mud. When P was freshly applied to red mud that had been applied to the soil 12 months ago, yield response and P content increased. This was attributed to the reduction in sorption of P due to red mud being neutralised by the soil and because sorption of P already present in the soil reduced the capacity of the red mud to sorb freshly applied fertiliser P. Residues of P in the soil and pH were also increased with application of red mud. In the years after application of red mud and lime, relative to P applied to nil red mud and nil lime treatment, the effectiveness of fertiliser P applied to the red mud and lime treatments increased. This was so as determined using plant yield, P concentration in plant tissue, and soil P test.

Western Australian fly ash on sandy soils for clover production

Abstract An experiment was conducted to determine the value of fly ash collected from flue gases of the Kwinana coal fired power station in Western Australia, as an amendment for sandy soils and as a replacement for phosphorus or potassium fertilizers. The results showed large increases in clover dry matter production (49% to 278%), attributed to improvements in nutrient and water retention from the fly ash. The fly ash provided a substantial amount of the phosphorus needed by the clover, although application of phosphorus fertilizer further increased dry matter production in the presence of fly ash. No evidence was obtained from plant growth or tissue analysis that the fly ash provided potassium to the pasture. The maximum yield was achieved when 501 ha‐1 of fly ash was applied to the soil. However, only 10 to 401 ha‐1 was required to achieve 75 to 90% of the maximum production. Although a statistically significant increase in cadmium and mercury concentration could be attributed to fly ash, the increase...

Guiding BMP adoption to improve water quality in various estuarine ecosystems in Western Australia

The Australian Governments Coastal Catchment Initiative (CCI) seeks to achieve targeted reductions in nutrient pollution to key coastal water quality hotspots, reducing algal blooms and fish kills. Under the CCI a Water Quality Improvement Plan (WQIP) is being prepared for targeted estuaries (Swan-Canning, near Perth, and the Vasse-Geographe, 140 km south of Perth) to address nutrient pollution issues. A range of projects are developing, testing and implementing agricultural Best Management Practices (BMPs) to reduce excessive loads of nutrients reaching the receiving waters. This work builds on progress-to-date achieved in a similar project in the Peel-Harvey Catchment (70 km south of Perth). It deals with the necessary steps of identifying the applicability of BMPs for nutrient attenuation, developing and promoting BMPs in the context of nutrient use and attenuation on farm and through catchments and estimating the degree to which BMP implementation can protect receiving waters. With a range of BMPs available with varying costs and effectiveness, a Decision Support System (DSS) to guide development of the WQIP and implementation of BMPs to protect receiving waters, is under development. As new information becomes available the DSS will be updated to ensure relevance and accuracy for decision-making and planning purposes. The DSS, calibrated for application in the catchments, will play a critical role in adaptive implementation of the WQIP by assessing the effect of land use change and management interventions on pollutant load generation and by providing a tool to guide priority setting and investment planning to achieve agreed WQIP load targets.

Comparison of single superphosphate and superphosphate coated with bauxite residue for subterranean clover production on phosphorus-leaching soils

Bauxite residue from alumina refining was used to coat granules of single superphosphate to reduce the leaching of phosphorus in coarse, sandy soils for pastures in high rainfall areas of south-western Australia (>800 mm annual average). The impact of coating the superphosphate on the leaching of phosphorus was measured in a glasshouse experiment and the effectiveness of the fertiliser using dry herbage yield of subterranean clover (Trifolium subterraneum) was measured in a field experiment. The glasshouse experiment measured the effect of coating the superphosphate with bauxite residue at 0, 5, 10, 15, 20, 25, 30, 35, and 40% by weight. A coating of 25% (by weight) was chosen for the field experiment. In the glasshouse experiment, the coated granules were applied to columns of soil, where subterranean clover was grown under leaching conditions. A coating of 30%, by weight, reduced leaching of single superphosphate by about half. Increasing the coating of bauxite residue also increased the phosphorus uptake and increased the plant growth. In the field trial, the effectiveness of single superphosphate with a bauxite residue coating of 25% by weight was increased on average by 100% in Year 1, 303% in Year 2, and 158% in Year 3, relative to freshly applied single superphosphate. The bauxite residue coating also increased the phosphorus content of the herbage in a similar manner to the increases in yield. Limited soil phosphorus tests showed only minor increases in the residues of phosphorus where the superphosphate had been coated with bauxite residue.

Fit-for-purpose phosphorus management: do riparian buffers qualify in catchments with sandy soils?

Hillslope runoff and leaching studies, catchment-scale water quality measurements and P retention and release characteristics of stream bank and catchment soils were used to better understand reasons behind the reported ineffectiveness of riparian buffers for phosphorus (P) management in catchments with sandy soils from south-west Western Australia (WA). Catchment-scale water quality measurements of 60xa0% particulate P (PP) suggest that riparian buffers should improve water quality; however, runoff and leaching studies show 20 times more water and 2 to 3 orders of magnitude more P are transported through leaching than runoff processes. The ratio of filterable reactive P (FRP) to total P (TP) in surface runoff from the plots was 60xa0%, and when combined with leachate, 96 to 99xa0% of P lost from hillslopes was FRP, in contrast with 40xa0% measured as FRP at the large catchment scale. Measurements of the P retention and release characteristics of catchment soils (<2xa0mm) compared with stream bank soil (<2xa0mm) and the <75-μm fraction of stream bank soils suggest that catchment soils contain more P, are more P saturated and are significantly more likely to deliver FRP and TP in excess of water quality targets than stream bank soils. Stream bank soils are much more likely to retain P than contribute P to streams, and the in-stream mixing of FRP from the landscape with particulates from stream banks or stream beds is a potential mechanism to explain the change in P form from hillslopes (96 to 99xa0% FRP) to large catchments (40xa0% FRP). When considered in the context of previous work reporting that riparian buffers were ineffective for P management in this environment, these studies reinforce the notion that (1) riparian buffers are unlikely to provide fit-for-purpose P management in catchments with sandy soils, (2) most P delivered to streams in sandy soil catchments is FRP and travels via subsurface and leaching pathways and (3) large catchment-scale water quality measurements are not good indicators of hillslope P mobilisation and transport processes.

A slowly soluble, sulfur fertiliser from a by-product of mineral sands processing

The effectiveness of a pelletised by-product from mineral sands processing as a sulfur fertiliser was measured on high rainfall sandy soils of Western Australia. The by-product was a lime-neutralised, low-grade, sulfuric acid effluent which produces a precipitate of gypsum containing iron and manganese. The pelletised product has been given the name Ironman gypsum, reflecting its major constituents. Ironman gypsum was compared with ordinary single superphosphate and naturally occurring gypsum from Wyalkatchem (fine) and Jurien Bay (coarse) as a sulfur fertiliser in 2 field experiments. When comparing the relative rates of sulfur release as indicated by plant yield and nitrogen:sulfur ratio, the order of effectiveness was: superphosphate = Ironman gypsum pellets >> coarse gypsum ≥xa0 unpelletised by-product >>Wyalkatchem gypsum. Laboratory leaching studies showed the Ironman pellets to leach more slowly than superphosphate, which in turn leached more slowly than coarse rock gypsum. The soil sulfur tests were of limited value in predicting yield even though they were accurate in predicting the amount of sulfur previously applied. Compared with an unfertilised control, Ironman gypsum did not result in a significant increase in the uptake of heavy metals by plants. Most of the elements of concern, mercury, cadmium, and uranium, actually showed a significant reduction in concentration in the plant matter. This was probably due to the increased growth caused by the improved sulfur nutrition resulting in dilution of these elements. There was a slight but statistically significant increase in the nickel concentration that could be attributed to Ironman gypsum, but the level was still low.