Orthophosphate (PO4–P) is important for plant production and as an environmental pollutant. Its partitioning between the solid and solution phases of the soil can be described by the Freundlich equation: X = a Cb, where X is the P sorbed from a soil suspension spiked with P under defined conditions, C is the ‘equilibrium’ concentration in solution, and a and b are coefficients. P that is already sorbed (Q) decreases the sorption of subsequent P additions, which should enable Q to be estimated statistically. Our intensive study of P-sorption on well-characterised acidic soils has enabled the development of an extended statistical approach to better estimate Q, a and b, which is detailed in an accompanying article (Tellinghuisen et al., 2023). The resulting estimates of Q, a and b are statistically superior to those from traditional, non-linear regression modelling. In addition, with increasing P-fertiliser additions, the estimates of Q increase linearly (R2 = 0.908 to 0.998), are linearly related to isotopically exchangeable P (PE, R2 = 0.94), and the estimates of a and b behave more consistently with mechanistic expectations than do their traditionally estimated counterparts. We also report strong linear relations of Q and the P extracted by acidic oxalate (Pox, R2 = 0.94) and suggest that Pox be tested as a surrogate for Q to simplify quantitative P-sorption modelling and improve the management of P for plant production and the environment.

Context Dairy pasture production is reliant on fertiliser to supply nitrogen (N); however, fertiliser N-use efficiency (FNUE) is low and N can be lost to the environment. Aims The aim of this study was to track the fate of N fertiliser applied in a pasture system of ryegrass (Lolium multiflorum, temperate grass) oversown into kikuyu (Pennisetum clandestinum, tropical grass). Methods We used 15N-labelled urea to track the residual plant uptake of a one-off application of 15N over three pasture cuts subsequent to the first cut in the kikuyu growing season from February 2018 to April 2018 (Experiment 1), followed by total soil and plant recoveries of 15N over a 12-month period (Experiment 2). Total N treatment rates were 0, 120, 240 and 480 kg N ha−1 year−1, consisting of application events of 40 kg N ha−1. In Experiment 1, 15N was applied only at the first fertilisation, whereas in Experiment 2, 15N-labelled urea was applied at each fertilisation event. Key results In Experiment 1, uptake of residual 15N fertiliser in the pasture biomass was <6%. In Experiment 2, FNUE was 29–32% and unaccounted 15N fertiliser was 22–142 kg N ha−1, across the 120, 240 and 480 kg N ha−1 year−1 treatments. Conclusions Recovery of 15N residual fertiliser did not increase with N rate and was attributed to the mass increase in soil 15N recovery. FNUE in the pasture did not decrease with N rate. Unaccounted 15N increased with N rate. Implications Existing and alternative N and pasture management strategies such as clover and multi-species pasture need to be implemented and explored to reduce the amount of unaccounted N in dairy pasture production.

In order for land managers and policy makers to manage excessive soil phosphorus (P) concentrations and reduce the risk of this particular source of P from impacting water bodies, models of soil P decline under various scenarios are needed. We modelled the decrease in calcium chloride-extractable P (CaCl2-P), and sodium bicarbonate-extractable P (Olsen-P and Colwell-P) using data from six Australian grazed pasture soils with contrasting P sorption properties, over a period of 4.5 years. Each soil had four initial soil P concentrations (Pinit), each of which received four on-going rates of P fertiliser (Pfert). The model predicts the final P concentration (Pfinal) by taking into account the P concentration previously measured (CaCl2-P, Olsen-P or Colwell-P), Pfert applied since measurement, and time since previous measurement: Final P concentration = (previously measured P concentration + ep x P fertiliser applied) exp (-dp x years since previous P concentration measurement). Where ep is the increase in soil P for each unit of applied P and dp is the decay constant representing how quickly the soil P decreased. The greatest decreases in proportion to Pinit occurred for CaCl2-P, followed by Olsen-P, and then Colwell-P. The model tended to fit the dataset well for Olsen-P and Colwell-P, with mean overestimation (modelled Pfinal concentration greater than actual Pfinal) of the Pfinal concentrations of 6.1 (32%) and 4.3 mg/kg (10%), respectively. Although there was less CaCl2-P data, the model successfully described it, with a mean overestimation of Pfinal CaCl2 of 3.1 mg/kg (26%). The overestimation of Pfinal CaCl2 was possibly due to the high CaCl2-P concentrations of the low P buffering index soils. The model predicted an average of 32 years (ranging from 26 to 49 years) for Olsen-P concentrations of between 55 and 96 mg/kg to decrease to an agronomic optimum of 17 mg/kg. Agronomic optimum was not a reliable indicator of environmental risk as some soils did not exceed the CaCl2-P environmental threshold until Olsen-P concentrations were twice the agronomic optimum, whereas low P sorbing soils tended to exceed the threshold before reaching agronomic optimum. Further work with more soils is required to examine the influence of soil properties – such as P sorption – on decreases in soil P.

In dairy grazing systems, livestock urine patches are hotspots that contribute to global warming, both directly through nitrous oxide (N2O) emissions, and indirectly, through nitrate leaching. However, under warm-dry temperate environments, N2O emission factors (EFs) have not been thoroughly evaluated, accounting for the influence of urinary nitrogen (N) concentration and urine volume, and emissions measurement approach through different urine application methods. Here we quantified and compared N2O emissions and EFs on a moderately well-drained sandy loam soil from urine patches established in naturally expanding effective area (NEEA), representing urine volumes of 2, 3 and 4 L m-2 (equivalent to urine -N loadings of 141, 211 and 282 kg N ha-1), and using the uniformly wetted area (UWA) with urine applied at 10 L m-2 (709 kg N ha-1), under two different soil moistures (below field capacity, BFC; field capacity, FC). The results showed that cumulative N2O emissions in the NEEA urine patches were 0.36-0.52 kg N2O-N ha-1 over 146 days (early-winter to late-spring). In the UWA urine patches, cumulative N2O emissions were 2.3 times higher at FC (1.96 kg N2O-N ha-1) than BFC (0.87 kg N2O-N ha-1). The EFs were similar between UWA (0.09%) and NEEA (0.07-0.10%) at BFC but were significantly higher (P < 0.05-0.1) in UWA (0.26%) than NEEA (0.09-0.16%) at FC. The EFs in NEEA were not affected by urine-N loadings under BFC and FC, ranging between 0.07 and 0.16%. The relatively high versus low urine-N loadings in NEEA enhanced pasture herbage and N-uptake responses under both soil moistures. However, there were no differences in apparent N-use efficiency (ranging from 27 to 39%) across the treatments. The EFs observed in this study are much lower than the existing Australian cattle urine annual EF of 0.4%, and further examination to determine a more accurate EF for the industry is required.

In intensively grazed pastures, urine patches deposited during livestock grazing are the hotspots for nitrous oxide (N2O) emissions and nitrate leaching. The impacts of spatial and temporal variability in urine N concentration and volume on N2O emissions required to accurately estimate country-specific N2O emission factors (EFs) have not been thoroughly evaluated under variable warmer and drier temperate environments (e.g., Menangle, NSW, Australia). Here we quantify and compare N2O emissions and EFs from a naturally expanding effective area (NEEA), with that from a uniformly wetted area (UWA) of urine application in large versus small chambers, respectively. The results show that over 146 days (early winter to late spring), there was the least cumulative N2O emissions with low urine-N loading (141–282 kg N ha-1) under NEEA, relative to the urine-N loading of 709 kg N ha-1 under UWA. In NEEA, there was no difference in N2O emissions with different urine volume treatments applied at the below field capacity (BFC) soil moisture condition. In contrast, there was a significant difference in N2O emissions at the field capacity (FC), for example, 0.52±0.06 kg N2O-N ha -1 (1.5 L urine) versus 0.36±0.05 kg N2ON ha (1.0 L urine). In UWA, cumulative N2O emissions were 2.3 times higher at FC (1.96 kg N2O-N ha ) than BFC (0.87 kg N2O-N ha ). The EF values in NEEA did not vary significantly with urine-N loading and soil moisture conditions and ranged between 0.07±0.01% to 0.10±0.02% in the BFC, and 0.09±0.02% to 0.16±0.03% in the FC. The EF values in UWA were 0.09±0.02% and 0.26±0.05% in the BFC and FC, respectively. The N2O EF was higher in UWA than NEEA only at the FC soil moisture condition. The results suggest that the cattle urine-derived EFs for N2O emissions (over winter to spring) in the drier temperate environment are lower than the country-specific EFs of 0.4 and 1.0% currently used in the Australian and New Zealand inventories, respectively.

Part of the Plant Sciences Commons, and the Soil Science Commons This document is available at https://uknowledge.uky.edu/igc/22/2-11/28 The XXII International Grassland Congress (Revitalising Grasslands to Sustain Our Communities) took place in Sydney, Australia from September 15 through September 19, 2013. Proceedings Editors: David L. Michalk, Geoffrey D. Millar, Warwick B. Badgery, and Kim M. Broadfoot Publisher: New South Wales Department of Primary Industry, Kite St., Orange New South Wales, Australia

Unnecessary accumulation of phosphorus (P) in agricultural soils continues to degrade water quality and linked ecosystem services. Managing both soil loss and soil P fertility status is therefore crucial for eutrophication control, but the relative environmental benefits of these two mitigation measures, and the timescales over which they occur, remain unclear. To support policies toward reduced P loadings from agricultural soils, we examined the impact of soil conservation and lowering of soil test P (STP) in different regions with intensive farming (Europe, the United States, and Australia). Relationships between STP and soluble reactive P concentrations in land runoff suggested that eutrophication control targets would be more achievable if STP concentrations were kept at or below the current recommended threshold values for fertilizer response. Simulations using the Annual P Loss Estimator (APLE) model in three contrasting catchments predicted total P losses ranging from 0.52 to 0.88 kg ha depending on soil P buffering and erosion vulnerability. Drawing down STP in all catchment soils to the threshold optimum for productivity reduced catchment P loss by between 18 and 40%, but this would take between 30 and 40+ years. In one catchment, STP drawdown was more effective in reducing P loss than erosion control, but combining both strategies was always the most effective and more rapid than erosion control alone. By accounting for both soil P buffering interactions and erosion vulnerability, the APLE model quickly provided reliable information on the magnitude and time frame of P loss reduction that can be realistically expected from soil and STP management. Greater precision in the sampling, analysis, and interpretation of STP, and more technical innovation to lower agronomic optimum STP concentrations on farms, is needed to foster long-term sustainable management of soil P fertility in the future.

Understanding the legacy effect of tillage-based fanning systems on soil organic carbon (SOC) mineralisation and nutrient [nitrogen (N), phosphorus (P) and sulphur (S)] supply after crop residue input is critical to appropriately manage plant available nutrients at the farm scale. To enhance this understanding, crop residues [canola (Brassica napus: delta C-13 124 parts per thousand) or wheat (Triticum aestivtan: delta C-13 461 parts per thousand)] were added to Luvisol and Vertisol from two long-term (16-46 years) field experiments and incubated under a controlled environment for 126 days. The practices in the Luvisol were conventional tillage (CT) and reduced tillage (RT) under mixed crop-pasture rotation, and no-till (NT) under continuous cereal-cover crop rotation. The practices in the Vertisol were CT and NT under wheat-wheat rotation. The residue input significantly stimulated SOC mineralisation via "positive priming", which was greater (p < 0.05) in the CT than RT/NT in the Luvisol only. The SOC mineralised after 126 days was 3.1-4.2 and 1.6-2.5 times higher in the canola and wheat residue-amended soils, respectively, than the unamended soils. Although the CT or RT versus NT had higher net N availability in the Luvisol only, the residue input did not increase plant available N in both soils, possibly due to stronger residue-induced N immobilisation than mineralisation. The results showed a significant release of available P and S in both residueamended soils (canola > wheat) after 26-50% of residue-C was mineralised over 126 days, and the Vertisol had greater net available P than Luvisol. Our results suggest that considerable quantities of available P and S may release from the soil reserves via SOC priming, and possibly via dissolution/desorption reactions in the soils, in addition to their direct release from the residues. In conclusion, crop residue input to historical farming systems enhanced the supply of available P and S, which varied with tillage, crop residue and soil type.

Aggregate-size classes may have different microbial accessibility and therefore different decomposability of aggregate-associated soil organic matter (SOM). However, processes and mechanisms of soil organic carbon (SOC) mineralisation and availability of nutrients [nitrogen (N), phosphorus (P) and sulphur (S)] in different aggregate-size classes, and particularly, the interaction of aggregates with tillage intensity and crop residue type in contrasting soils is poorly understood. Soil samples from conventional tillage (CT) and reduced tillage (RT) systems under mixed wheat–pasture farming, and no-till (NT) under continuous cereal–cover cropping in a Luvisol, and from CT and NT under continuous wheat cropping in a Vertisol, were separated into three dry aggregate classes of different sizes [mega-aggregates (>2–6.5 mm), macro-aggregates (0.25–2 mm) and micro-aggregates (<0.25 mm)]. Two residue types (canola and wheat stem; δ13C 124 and 460‰, respectively) were added into each of the three aggregate class samples from Luvisol (δ13C −24.7‰) and Vertisol (δ13C −18.5‰). Total CO2-C, δ13C in CO2-C, microbial biomass C (MBC), and plant available N, P and S were measured periodically during the 126-day incubation. The results showed that crop residue input increased native SOC mineralisation (via positive priming), MBC and microbial metabolic quotient in all three aggregate-size classes from different tillage systems in both soils. Native SOC mineralisation was 1.5–3.7 and 0.6–2.8 times higher in the canola and wheat residue-amended (cf. control, non-amended) aggregates, respectively. Native SOC mineralisatiion and MBC were higher in the macro- and micro- than mega-aggregates in both soils. However, priming of native SOC mineralisation, relative to the control, was similar across the aggregates, except for the CT in the Luvisol where priming was higher in the macro- than micro- and mega-aggregates. Native SOC mineralisation among the aggregate-size classes was 26–114% higher under CT or RT cf. NT in the Luvisol but was similar under CT and NT in the Vertisol. Net available N was significantly higher in the residue-amended than the control aggregates, particularly in the CT and/or RT versus the NT at day 30 only, and mainly in the Luvisol. Further, substantial amounts of available P and S were released from the residue-amended versus the control aggregates at day 126, with Vertisol releasing 2–3 times more available P than Luvisol. In conclusion, our findings showed the importance of returning crop residues to enhance nutrient availability from all aggregate-size classes in different soils and farming systems. In particular, the tillage (versus no-till) and canola (versus wheat) residue induced a greater release of nutrients, generally in the pattern of micro- ≥ macro- > mega-aggregates. Clearly, the input of crop residues enhanced the release of SOM-bound nutrients, possibly via positive priming, and may have mobilised mineral-bound nutrients, such as P and S in each aggregate-size class, with tillage intensity and soil type modulating these processes.

Soil organic matter (SOM) has the potential to supply substantial quantities of nutrients [Le nitrogen (N), phosphorus (P) and sulphur (S)] for plant uptake. Yet there is little understanding of the impact of management on the nutrient supply potential in soils (particularly, P and S). To quantify N, P and S availability from SOM, surface soils (0-10 cm) were collected from 14 management practices across three long-term (16-46 years) experimental sites under semi-arid (Luvisol), Mediterranean (Luvisol) and sub-tropical (Vertisol) environments in Australia. The practices comprised conventional (CT) and reduced tillage (RT) with mixed farming, no-till with continuous cropping (NT), and perennial pasture (PP) in the semi-arid Luvisol, while in a Mediterranean direct-drilled continuous cropping system, stubble was either retained (SR) or burnt (SB). Practices on the Vertisol comprised a factorial combination of CT, NT, SR, SB with either 0 (ON) or 90 kg urea-N ha(-1) (90N) in a continuous cropping system. Soils were incubated under controlled soil moisture and temperature, and cumulative organic C mineralised (C-min), and net available N, P and S were measured over 126 days. In the semi-arid Luvisol, CT and/or RT showed significantly higher C-min and net available N, P and S than NT and PP. In the Mediterranean Luvisol, C-min and net available P were not influenced by stubble management. In the Vertisol, CT SR (cf. CT-SB and NT-SR/SB) with or without N fertilisation significantly increased C-min, and CT-SR and/or-SB with N fertilisation (cf. CT-SR/SB without N fertilisation and NT-SR and/or-SB with or without N fertilisation) significantly increased net available N and P. This study found a continuous release of net available N (11-49 kg N ha(-1) over 126 days) across all management practices, whereas, the release of available P and S was evident only during the first 30 days (6-74 kg P ha(-1),-4 to 22 kg 5 ha(-1)), after which microbial immobilisation or clay fixation of P and S predominated, particularly in the Vertisol. In conclusion, the results indicate that SOM is a ready source of plant available P and S (in addition to N), and tillage and stubble retention generally enhanced SOM mineralisation and nutrient release, which varied with soil type.

The loss of nitrogen (N) and phosphorus (P) from dairy-farmed land can impair water quality. Efforts to curtail these losses in Australia and New Zealand (Australasia) have involved a mixture of voluntary and regulatory approaches. In the present paper, we summarise the losses of N and P from Australasian dairy farms, examine the policy drivers used for mitigating losses and evaluate the effectiveness of contrasting approaches to implementing mitigations. Median losses for N and P were 27 and 1.6 kg/ha.year respectively, with a wide range of variation (3–153 kg N/ha.year and 0.3–69 kg P/ha.year) caused by a complex array of climate, soil types, flow paths, nutrient surpluses and land management factors. This complexity, coupled with the variable implementation of measures to mitigate losses, means that many voluntary programs to decrease losses have had uncertain or limited success. Although there is little or no formal regulation in Australia, regulation exists in New Zealand that requires regional authorities to implement the best strategy to improve water quality according to regional-specific characteristics. In testing a generalised approach to mitigation (priority given to those that are easy to implement) in four regions in New Zealand, we found that P could be mitigated quite cheaply, but N reductions required more measures, some of which are costly. Conversely, prioritising on the basis of mitigation cost-effectiveness for a specific nutrient will lead to more rapid reductions in losses of the target nutrient, but with fewer co-benefits for the non-target nutrient or other water pollutants, such as faecal microorganisms and sediment. This information will assist farmers in deciding how to meet a catchment target at least cost.

Diffusive gradients in thin-films (DGT) technology provides an alternative assessment of available phosphorus (P) for a range of crops, suggesting a preliminary examination of the performance of the new DGT-P test, compared to existing bicarbonate extractable Olsen and Colwell P tests, for pastures is justified. This study utilized historic data from the Australian National Reactive Phosphate Rock (NRPR) study (1992-1994) that included 25 experimental sites representing a wide range of soil types and climates used for pasture production. Stored (similar to 19yr) soil samples were analysed for DGT-P, Olsen P and a single point P buffering index (PBI) and re-analysed for Colwell P. Results showed the traditional bicarbonate extractable Colwell (r(2)=0.45, P<0.001) and Olsen P (r(2)=0.27, P<0.001) methods predicted relative pasture P response more accurately, compared to the novel DGT-P test (r(2)=0.09, P=0.03) when all 3yr of data were examined. We hypothesize that the harsher bicarbonate extraction used for the Olsen and Colwell methods more accurately reflects the ability of perennial pasture roots to access less labile forms of P, in contrast to the DGT-P test, which does not change the soil pH or dilute the soil and appears unable to fully account for a plants ability to solubilize P. Further studies are needed to compare the capacity of DGT-P to measure P availability in perennial pasture systems and to better understand the soil chemical differences between pasture and cropping systems.

Modern dairy farming in Australia relies on substantial inputs of fertiliser nitrogen (N) to underpin economic production. However, N lost from dairy systems represents an opportunity cost and can pose several environmental risks. N-cycle inhibitors can be co-applied with N fertilisers to slow the conversion of urea to ammonium to reduce losses via volatilisation, and slow the conversion of ammonium to nitrate to minimise leaching of nitrate and gaseous losses via nitrification and denitrification. In a field campaign in a high input ryegrass–kikuyu pasture system we compared the soil N pools, losses and pasture production between (a) urea coated with the nitrification inhibitor 3,4-dimethyl pyrazole phosphate (b) urea coated with the urease inhibitor N-(n-butyl) thiophosphoric triamide and (c) standard urea. There was no treatment effect (P>0.05) on soil mineral N, pasture yield, nitrous oxide flux or leaching of nitrate compared to standard urea. We hypothesise that at our site, because gaseous losses were highly episodic (rainfall was erratic and displayed no seasonal rainfall nor soil wetting pattern) that there was a lack of coincidence of N application and conditions conducive to gaseous losses, thus the effectiveness of the inhibitor products was minimal and did not result in an increase in pasture yield. There remains a paucity of knowledge on N-cycle inhibitors in relation to their effective use in field system to increase N use efficiency. Further research is required to define under what field conditions inhibitor products are effective in order to be able to provide accurate advice to managers of N in production systems.

Efficient nutrient management is a critical component of profitable and sustainable milk production on modern dairy farms. While the impact of intensification on nutrient surpluses at the farm scale is well recognised, there are few studies that have quantified the corresponding soil nutrient concentrations within dairy farms at a national scale. In this study, we examine soil phosphorus (P), potassium (K), and sulphur (S) concentrations on 2092 grazed dairy paddocks and animal containment areas within 43 contrasting dairy farms from all dairy producing regions of Australia. More than three quarters of the routinely grazed paddocks sampled had available P, K and S concentrations above agronomic requirements, while 20% of paddocks were at least 3 times above agronomic requirements. An exception to these generally high levels were paddocks sampled on organic or biodynamic dairy farms, which had lower soil P and S concentrations. Within farm nutrient heterogeneity was substantial, irrespective of the characteristics of the dairy farm or the regional location. Animal holding areas often had excessively high soil nutrient concentrations. Overall, there were significant relationships (P < 0.01) between soil P, K and S concentrations and farm management and paddock characteristics including distance from milking parlour, application frequency of mechanically applied effluent, frequency of grazing herd visits, frequency of feeding of conserved forage and frequency of mechanical pasture harvesting. These results highlight generic management practises that exacerbate elevated soil nutrient concentration within grazed dairy farms and have direct implications to farmers and advisors. There are clear opportunities to strategically apply, and more often reduce, P, K and S fertiliser inputs on dairy farms without a loss of production. A greater understanding of farm nutrient fluxes and expected patterns of within-farm nutrient distribution, complemented by comprehensive soil testing, will help guide profitable and environmentally beneficial nutrient management decisions. (C) 2014 Elsevier B.V. All rights reserved.

The level of soil organic carbon (SOC) that is attained under agriculture largely depends upon rates of carbon input and its decomposition under various agronomic practises such as stubble (crop residue) management and fertiliser application. In this study, we used the APSIM-Wheat and APSIM-Agpasture models to simulate changes in SOC in a range of crop and pasture management systems across nine locations in eastern Australia. We explored the extent to which various crop and pasture management options affect changes in SOC from a sub-tropical to a temperate environment. Specifically, we examined how nitrogen fertilisation, stubble management and stocking rate affect SOC and what strategies might be employed by farmers to increase SOC sequestration across eastern Australia. We modelled a continuous cropping regime, a continuously grazed pasture and a mixed cropping and pasture rotation. Under continuous cropping higher nitrogen application and higher amounts of stubble incorporation increased the SOC levels at all locations. At Roma, the northern-most site, there was little additional gain in SOC from increasing N above 70kgNha−1 whereas most other sites showed benefits above 70kgNha−1. The biggest factor in boosting SOC under cropping was the level of stubble incorporation. At all but one site, continuously grazed pasture generally resulted in SOC increases over the 60years. However, increasing stocking rate decreased the rates of SOC changes at all sites. Crop-pasture rotations show that the impacts of even 4years of pasture is likely to be significant in reducing declining SOC at low nitrogen application during cropping phases. N fertilisation and stubble incorporation reduced the impact of stocking rate by reducing the decline in SOC. The difference in SOC changes between nine sites across eastern Australia was largely described by mean temperature and rainfall but high temperature strongly interacted with management practises (stocking rate, N application and residue incorporation) to reduce the sequestration of C despite favourable rainfall. Our results indicate that a mean annual temperature higher than about 20°C can switch a soil from net sink into a net source of atmospheric CO2 if other factors affecting soil carbon changes such as stubble incorporation, stocking rate and site rainfall are constant.

Soil is a valuable natural resource. In the state of New South Wales, Australia, the governance of soil has evolved since Federation in 1901. Following rapid agricultural development, and in the face of widespread soil degradation, the establishment of the Soil Conservation Service marked a turning point in the management of soil. Throughout the 20th century, advances in knowledge were translated into evolving governance frameworks that were largely reactionary but saw progressive reforms such as water pollution legislation and case studies of catchment-scale land and vegetation management. In the 21st century, significant reforms have embedded sustainable use of agricultural soils within catchment- and landscape-scale legislative and institutional frameworks. What is clear, however, is that a multitude of governance strategies and models are utilised in NSW. No single governance model is applicable to all situations because it is necessary to combine elements of several different mechanisms or instruments to achieve the most desired outcomes. Where an industry, such as the sugar industry, has taken ownership of an issue such as acid sulfate soil management, self-regulation has proven to be extremely effective. In the case of co-managing agricultural soils with other landuses, such as mining, petroleum exploration and urban development, regulation, compliance and enforcement mechanisms have been preferred. Institutional arrangements in the form of independent commissioners have also played a role. At the landscape or total catchment level, it is clear that a mix of mechanisms is required. Fundamental, however, to the successful evolution of soil governance is strategic investment in soil research and development that informs the ongoing productive use of agricultural landscapes while preventing land degradation or adverse environmental effects.

Soils managed for field vegetable production often receive high nutrient inputs and are frequently cultivated. This can result in agronomically excessive soil P and soil structural degradation. In combination, these can lead to large losses of nutrients in runoff that can impact on aquatic environments. We investigated the effect of compost application at 62.5 and 125 t ha(-1) in both 2005 and 2008 on soil nutrient and physical properties and runoff and nutrient export using simulated rainfall/runoff. The use of compost reduced (p < 0.01) the accumulation of available P in soils compared to conventional fertilizers but still resulted in excessively high soil P levels. The application of compost increased water stable aggregates, increased infiltration rates, and reduced the volume of runoff (all p < 0.01). Compost at either rate reduced runoff volumes by similar to 50% compared to conventionally managed soils. As a consequence of reduced nutrient inputs/accumulation and improved soil physical properties, the use of compost at 62.5 t ha(-1) resulted in a similar to 50% reduction in N and P export in surface runoff, with no added benefit of using the higher compost rate. The rainfall simulations we reported only represent a 'snap-shot' of compost effects on runoff properties, and longer term monitoring of runoff would add further understanding of treatment effects. Nevertheless, we suggest that the use of compost may have environmental benefits although nutrient supply and status in the soil needs to be managed carefully to ensure adequate crop nutrition without unnecessarily increasing soil nutrients above the agronomic optimum.

Introduction At a global scale, human activity has increased the flux of N two-fold (Vitousek et al. 1997), particularly driven by large scale fertiliser manufacturing (Fowler et al. 2013). Additionally, the ability to transport inputs and outputs cheaply and extensively has led to substantial growth in agricultural production over the past 50 years with an accompanying 40% increase in world population and extensive urbanisation. However, this has also lead to a spatial disconnection between nitrogen flows required for agricultural production systems and reduced incentives to capture and recycle nitrogen at the farm scale. Moreover, agricultural production systems are inherently in efficiency at capturing nitrogen, with excess nitrogen dissipated into the broader environment. Of the total N applied to agricultural land worldwide only 5–15% is eventually transformed into human food (Erisman et al., 2012). In cropping systems nitrogen use efficiency (NUE) will often range between 35 – 65%, while in more intensive animal systems such as dairy production, NUE will typically range from 15 – 35% (Powell et al. 2010). Major pathways of agricultural N loss to the environment are gaseous emission of ammonia and nitrous oxide, and the leaching of nitrate through soil, with various transformations causing a cascade of potential environmental problems (Galloway et al. 2008). In the past decade, measuring losses for nitrous oxide and the effectiveness of mitigation strategies have received considerable attention due to a policy focus on greenhouse gas emissions. In contrast, grazing based dairy farms in Australia and New Zealand have been encouraged to increase production through greater reliance on imported feed and fertiliser (Thorold and Doyle 2007), with likely greater nitrogen losses per ha. Growing societal expectations for air and water quality, stricter standards from international markets, and increasing costs for purchased nitrogen will mean that improving NUE and reducing nutrient losses will be a necessary part of agricultural production systems. This is likely to require difficult choices to better balance production and environmental goals, particularly for intensive livestock industries such as dairy production.

Many intensively managed soils contain phosphorus (P) concentrations greater than required for optimum production. Soils with P concentrations in excess of the agronomic optimum can have unnecessary losses of P that can adversely affect water bodies. Reducing excessive soil-P concentrations is important for the economic and environmental sustainability of intensive agriculture, such as the Australian dairy industry. However, little is known of decreases in extractable soil-P concentrations when P fertiliser applications are reduced or omitted from soils with P concentrations and properties representative of intensive pasture grazing systems. Decreases in extractable P (calcium chloride (CaCl2), Olsen and Colwell) were monitored for up to 4.5 years for six Australian grazed pasture soils (Red Ferrosol, Brown Kurosol, Grey Dermosol, Brown Dermosol, Podosol and Hydrosol) with contrasting textures and P-buffering indices (PBI). Sixteen treatments consisting of four initial extractable-P concentrations (P-init) paired with four ongoing P fertiliser rates (P-fert) were established for each of the six soils, except on an extremely low-PBI Podosol, where a range of P-init concentrations could not be established. The resultant decreases in P were larger with higher P-init concentration and lower rate of ongoing P-fert, except in the extremely low PBI Podosol where decreases in initially high CaCl2-P concentrations were large irrespective of ongoing P-fert. There was a greater proportional decrease in the environmentally extractable P compared with agronomically extractable P, with mean decreases in CaCl2-P of 57%, Olsen-P of 25%, and Colwell-P of 12%. The P-init concentrations, which were well above agronomic optimum, remained above this target. This study advances scientific knowledge of extractable soil-P concentrations when P fertiliser inputs are withheld or reduced from grazed pasture soils, and aids land and catchment managers in estimating likely changes over time.