Weaver D.M.,44 Albany Hwy |
Weaver D.M.,University of Western Australia |
Plant and Soil | Year: 2011
Aims: Fluctuating phosphorus (P) fertiliser costs, water quality issues and on-going debate over global P supply and demand support the need to evaluate and ensure that P is used efficiently in agriculture. Methods: We analysed the P balance of farming systems across southern Australia to south east Queensland in relation to P management and soil properties at farm and sub-farm scales. Phosphorus input, yield of products and soil data were collected from Mediterranean, temperate and sub-tropical farming environments to assess soil chemistry and P Balance Efficiency (PBE; percentage of P inputs harvested as P outputs) of sheep, beef, dairy and cropping systems. Results: The median PBE was 11% for sheep, 19% for beef, 29% for dairy and 48% for cropping. Phosphorus applied in excess of product removal (P balance) ranged from 18. 1 for dairy to 6. 1 kg P ha-1 yr-1 for cropping. The bicarbonate-extractable (Colwell) P concentration of surface soils increased with fertiliser application and this differed in relation to P Buffering Index (PBI), production history and the rate of P input. Soil test values for 63% to 89% of soil samples from pastures and crops exceeded critical values (CV; defined by PBI, bicarbonate-extractable P and land use) when little yield improvement would be achieved by applying additional P. A greater percentage of these soil test values exceeded environmental thresholds for water contamination. Conclusions: A transition to using lower rates of P fertiliser to maintain soil P fertility at near optimal levels (P maintenance) has not occurred in farming systems represented by these soil samples. Over 50% of the samples had indications of more important constraints (soil acidity, potassium and sulphur deficiency) to yield. Alleviating these constraints is likely to improve PBE. For soils that exceed the CV for P, there is a need to adopt P maintenance practices to improve financial and environmental outcomes. © 2011 Springer Science+Business Media B.V.
Brennan R.F.,44 Albany Hwy |
Bell R.W.,Murdoch University |
Raphael C.,Murdoch University |
Eslick H.,Murdoch University
Journal of Plant Nutrition | Year: 2010
Leaching of sulfur (S) on sandy soils may limit the effectiveness of S fertilizers especially when applied at sowing. The effectiveness of S sources for canola (oil seed rape, Brassica napus L.) grown in sandy low S soils of south-western Australia is not known. This study was completed to determine the relative effectiveness of gypsum and a gypsum-based by-product from synthetic rutile processing called Canola Blue for canola grown in low S soils of the region. Canola Blue is a mixture of gypsum and elemental S, and is granulated so its effectiveness may vary from gypsum. We measured the effectiveness of the two S sources in the glasshouse for young seedling growth and for minimizing S leaching. In the four field experiments, the two S sources were evaluated for relative effects on canola seed yield and the concentration of oil in seed. Canola Blue applied at sowing was as effective as gypsum for canola growth in the glasshouse and when applied at 35 days after sowing (DAS) was as effective as gypsum for seed yield in the field. For the glasshouse study, Canola Blue when applied to the soil surface (topdressed) at 35 DAS was as effective as gypsum in achieving a rapid recovery of leaves from S deficiency symptoms and of shoot growth. Where S deficiency appears during the growing season, topdressing with Canola Blue appears to be as effective under the conditions of this experiment as was gypsum. However, the S in Canola Blue was less prone to leaching than that applied as gypsum. © Taylor & Francis Group, LLC.
Weaver D.,44 Albany Hwy |
Summers R.,20 South Western Highway
Environmental Monitoring and Assessment | Year: 2014
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 60 % 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 60 %, and when combined with leachate, 96 to 99 % of P lost from hillslopes was FRP, in contrast with 40 % measured as FRP at the large catchment scale. Measurements of the P retention and release characteristics of catchment soils (<2 mm) compared with stream bank soil (<2 mm) 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 99 % FRP) to large catchments (40 % 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. © 2014 The Author(s).
Powell J.M.,U.S. Department of Agriculture |
Gourley C.J.P.,Australian Department of Primary Industries and Fisheries |
Rotz C.A.,Pennsylvania State University |
Weaver D.M.,44 Albany Hwy
Environmental Science and Policy | Year: 2010
Escalating fertilizer and feed costs, declining product prices, and increasing regulations to reduce environmental pollution have created new pressures to improve nutrient use in agricultural production. This study provides an overview of factors and processes that impact nitrogen use efficiency (NUE) in dairy production, identifies practices that may bridge gaps between actual-NUE obtained on commercial farms and potential-NUE obtained under experimental conditions, and explores the possibility of using NUE as a performance indicator and policy tool for dairy production. Actual feed-NUE varies from 16% to 36% and is impacted by of a range of dairy practices; manure/fertilizer-NUE varies from 16% to 77% and is very site-specific; and whole-farm NUE varies from 8% to 64% and declines as stocking rates increase. Optimal stocking rate and manure nitrogen (N) crediting can enhance NUE, increase farm profits, and reduce N loss from dairy farms. NUE could be used to further engage dairy producers in collaborative assessments of gaps between their actual N use and the biological potential of N use, to develop performance goals for N use in various production components, and to monitor and evaluate the impacts of alternative feed, manure and fertilizer management practices on N use, profitability, and environmental outcomes. © 2010.
Scanlan C.A.,University of Western Australia |
Bell R.W.,Murdoch University |
Brennan R.F.,44 Albany Hwy
Field Crops Research | Year: 2015
Subsurface potassium (K) supply can make a significant contribution to total K uptake in wheat (Triticum aestivum L.) although its influence on grain yield response to K fertiliser is unresolved. Previous work has shown that the inclusion of subsurface (>10cm depth) soil extractable K (SEK) did not improve the prediction of relative yield (RY) compared to a prediction based on SEK in the 0-10cm soil layer only. Our understanding of the influence of subsurface SEK is constrained by the incomplete nature of the interactions between season × surface SEK × subsurface SEK directly measured in field experiments. To understand these interactions, we simulated wheat growth for two locations in a rain fed environment in south-west Western Australia (SWWA) and two soil types using the crop growth simulation model APSIM, which has been calibrated for the sandy-surfaced soils of SWWA. Sensitivity analysis of the effect of subsurface SEK on grain yield showed that the effectiveness of subsurface SEK relative to surface SEK declined exponentially as the depth of the K-enriched subsurface layer increased. We implemented a Monte Carlo simulation for a deep sand and a sand over clay soil profile for a range of surface SEK levels, subsurface SEK depths, subsurface SEK levels, locations, years, subsurface root constraint and rates of K fertiliser applied. Global sensitivity analysis showed that SEK in the 0-10cm depth was the most important factor for RY in the deep sand and sand over clay profiles followed by SEK 10-20cm and location. We used the results from the Monte Carlo simulation to develop a K fertiliser recommendation model based on SEK 0-10cm only and a recommendation model based on SEK 0-10cm together with subsurface SEK, root constraint and stored soil water at sowing. A net economic benefit (change in income exceeds extra costs) only occurred in a limited number of scenarios where SEK 0-10cm was between 40 and 60mgkg-1 for the deep sand and where SEK 0-10cm was less than 40mgkg-1 for the sand over clay. The greatest potential for improvement in profit from K fertiliser recommendation systems for soils in SWWA is for sand over clay soils where SEK 0 to 10cm is less 40mgkg-1. © 2015 Elsevier B.V.
Paul K.I.,CSIRO |
Roxburgh S.H.,CSIRO |
England J.R.,CSIRO |
Brooksbank K.,44 Albany Hwy |
And 14 more authors.
Forest Ecology and Management | Year: 2014
Root biomass may to contribute a substantial proportion of the carbon sequestered in new tree plantings, particularly in regions where rainfall and/or site quality is relatively low as this may result in relatively high allocation of plant biomass below-ground to source required water or nutrients. However, root biomass is often overlooked because of difficulty with measurement. In Australia, most carbon plantings are currently mixed-species environmental or mallee eucalypt plantings on agricultural land in regions with rainfall of 250-850mmyear-1. Here, we collated new and existing root biomass data from ca. 900 individual trees or shrubs to develop and test allometric equations for predicting root biomass based on stem diameter (of unharvested trees or shrubs) or height (of coppice harvested trees) in these plantings. Equations developed showed significant differences between groupings of species with differing growth habits or from different genera. Grouping species into categories of: (i) non-eucalypts, (ii) tree-form eucalypts, (iii) unharvested mallee eucalypts, and (iv) coppiced mallee eucalypts, provided equations with model efficiencies of 0.64-0.90. In the process of collating data across different studies, corrections were required for data consistency. Uncertainty analysis showed that although these corrections resulted in some uncertainty in the equations developed, measurement errors, particularly of stem diameter, were also important contributors to this uncertainty. We tested equations developed using data from 11 environmental and mallee planting sites where direct measurements of root biomass were made through whole-plot excavation. Site-level predictions of root biomass from individual tree allometry were effective, with an efficiency of prediction of 0.98. These results indicate that the generic allometric equations developed can be confidently applied across the Australian agricultural region with 250-850mmyear-1 rainfall to obtain accurate regional estimates of root biomass in the currently relatively young (<20year old) environmental and mallee plantings. © 2014.