Why are median phosphorus concentrations improving in New Zealand streams and rivers?

McDowell, R. W.; Hedley, M. J.; Pletnyakov, Peter; Rissmann, Clint; Catto, W. D.; Patrick, W. W.

doi:10.1080/03036758.2019.1576213

Cited by 22 publications

(15 citation statements)

References 87 publications

(75 reference statements)

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“…Soil test P analysis was never designed to inform P loss risk to waterbodies, and STP level is only one of a number of factors influencing catchment P export. A statistical linkage between regional variation in STP levels and catchment P flux is therefore difficult to establish (Ekholm et al, 2015; McDowell et al, 2019). However, given the variable and often short‐term effectiveness of soil conservation, buffer strips, and wetlands (Dodd and Sharpley, 2016), more active drawdown of high STP soils would in theory help deliver more long‐term and long‐lasting environmental gains by reducing source P mobilization: the APLE model predicted 18 to 55% P loss reductions were potentially achievable in our study catchments.…”

Section: Resultsmentioning

confidence: 99%

A Global Perspective on Integrated Strategies to Manage Soil Phosphorus Status for Eutrophication Control without Limiting Land Productivity

et al. 2019

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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−1 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. Core Ideas Sensitive management of soils and soil P fertility is critical for limiting water quality degradation. Maintaining soil test P (STP) at or below the agronomic optimum reduces the eutrophication threat. STP drawdown in combination with erosion control reduced catchment P loss by up to 62%. The APLE model quickly quantified the magnitude and timescale of potential P loss reductions.

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Section: Resultsmentioning

confidence: 99%

A Global Perspective on Integrated Strategies to Manage Soil Phosphorus Status for Eutrophication Control without Limiting Land Productivity

et al. 2019

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“…However, a lack of quality rock and poor agronomic effectiveness (Simpson et al, 1997) in areas where the soil pH is ≥6 and rainfall is <800 mm has limited market penetration in Australia. Similarly, use of PR for direct application is a small proportion (4%) of the New Zealand market (McDowell et al, 2019). Less water soluble superphosphates (e.g., the SuperSR range of products from CSBP Fertilizers and lime‐reverted SSP in New Zealand, often termed dicalcic phosphates ), which are basically di‐calcium phosphate dihydrate formed by treatment of SSP with lime, are sometimes used, but the agronomic efficiency of these products is usually greater than SSP only in situations where P leaching is significant (i.e., course‐textured soils in high‐rainfall environments) (Edmeades, 2000).…”

Section: Common Phosphatic Fertilizers Applied To Pastures and Their mentioning

confidence: 99%

“…For example, when appropriate P mitigation strategies were applied to 14 catchments in New Zealand, P exports were estimated to be halved with minimal impact on farm profitability (<2% of farm earnings before interest and tax) (McDowell, 2014). In New Zealand, semiquantitative evidence suggests that despite intensive land use expanding, good management practice combined with increasing awareness of P and critical source areas, and their reinforcement through voluntary processes and regulation, has seen stream water P concentrations decrease in the last 10 years (McDowell et al, 2019). …”

Section: Concluding Commentsmentioning

confidence: 99%

Direct Exports of Phosphorus from Fertilizers Applied to Grazed Pastures

Nash¹,

McDowell

Condron

et al. 2019

J of Env Quality

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Since its discovery in 1669, phosphorus (P) in the form of fertilizer has become an essential input for many agroecosystems. By introducing a concentrated P source, fertilizers increase short‐term P export potential soon after their application and longer‐term export potential by increasing soil fertility (legacy P). The 4R concept was developed to help mitigate P exports from the fertilizers that sustain agricultural productivity. This review investigates the factors affecting P exports soon after the application of mineral fertilizers to pasture‐based grazing systems and studies quantifying its potential impact in different systems, with an emphasis on Australasia. Initially, P fertilizers and reactions that might affect their short‐term P export potential are reviewed, along with P transport pathways, the forms of P exported from grazing systems, factors affecting P mobilization into water, and studies demonstrating the possible short‐term effects of fertilizer application on P exports. Using that foundation, we review studies quantifying the short‐term impact of fertilizer application in different regions; they show that under poor management, recently applied fertilizer can contribute a considerable proportion (30–80%) of total farm P exports in drainage, but when fertilizer is well‐managed, that figure is expected to be <10%. We then use three model systems of varying hydrology that are common to Australasia to demonstrate the principles for selecting fertilizers that are likely to minimize P exports soon after their application. Core Ideas Fertilizers increase P exports directly or by increasing P cycling. We review P pathways and processes relevant to grazing systems. Direct fertilizer P exports can be comparatively small (<10% of annual exports). Fertilizer selection to minimize P exports in three model systems is demonstrated.

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“…Critical source areas in New Zealand are based on source and transport factors and are calibrated against plot to small catchment scale data. At last count, there were 77 industry or government documents that mentioned CSAs (McDowell et al, 2019). …”

Section: New Zealandmentioning

confidence: 99%

“…From 1994 to 2013, 41% of monitoring sites in catchments dominated by intensively grazed pasture showed decreasing median total P concentrations, and 65% of these same sites were shown to be improving when examined between 2004 and 2013 (Ministry for the Environment and Statistics New Zealand, 2017). McDowell et al (2019) examined reasons for the change and found little evidence that the improvement was caused by a decrease in soil Olsen P concentrations or imported P (e.g., fertilizer), a change to low water‐soluble P fertilizers, or that greater nitrate loads were assimilating P from groundwater or sediments. Possible causes of improvement were that land use change had decreased erosion, more N fertilizer use was assimilating P in the soil, and there was a greater awareness of P as an environmental issue.…”

Section: New Zealandmentioning

confidence: 99%

A Global Perspective on Phosphorus Management Decision Support in Agriculture: Lessons Learned and Future Directions

et al. 2019

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The evolution of phosphorus (P) management decision support tools (DSTs) and systems (DSS), in support of food and environmental security has been most strongly affected in developed regions by national strategies (i) to optimize levels of plant available P in agricultural soils, and (ii) to mitigate P runoff to water bodies. In the United States, Western Europe, and New Zealand, combinations of regulatory and voluntary strategies, sometimes backed by economic incentives, have often been driven by reactive legislation to protect water bodies. Farmer‐specific DSSs, either based on modeling of P transfer source and transport mechanisms, or when coupled with farm‐specific information or local knowledge, have typically guided best practices, education, and implementation, yet applying DSSs in data poor catchments and/or where user adoption is poor hampers the effectiveness of these systems. Recent developments focused on integrated digital mapping of hydrologically sensitive areas and critical source areas, sometimes using real‐time data and weather forecasting, have rapidly advanced runoff modeling and education. Advances in technology related to monitoring, imaging, sensors, remote sensing, and analytical instrumentation will facilitate the development of DSSs that can predict heterogeneity over wider geographical areas. However, significant challenges remain in developing DSSs that incorporate “big data” in a format that is acceptable to users, and that adequately accounts for catchment variability, farming systems, and farmer behavior. Future efforts will undoubtedly focus on improving efficiency and conserving phosphate rock reserves in the face of future scarcity or prohibitive cost. Most importantly, the principles reviewed here are critical for sustainable agriculture. Core Ideas Strategies protecting water bodies are often driven by reactive legislation. Phosphorus management focuses on plant available P and mitigating P runoff. Decision support is based on P transfer, best practices, education, and action. Recent scientific developments have rapidly advanced runoff modeling and education. DS challenges are “big data,” farming systems, and farmer behavior.

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Why are median phosphorus concentrations improving in New Zealand streams and rivers?

Cited by 22 publications

References 87 publications

A Global Perspective on Integrated Strategies to Manage Soil Phosphorus Status for Eutrophication Control without Limiting Land Productivity

A Global Perspective on Integrated Strategies to Manage Soil Phosphorus Status for Eutrophication Control without Limiting Land Productivity

Direct Exports of Phosphorus from Fertilizers Applied to Grazed Pastures

A Global Perspective on Phosphorus Management Decision Support in Agriculture: Lessons Learned and Future Directions

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