Agricultural Phosphorus Research Articles

Phosphorus in the Minnesota River Basin: The debate over its source and ways to mitigate impacts

Phosphorus in the Minnesota River Basin: The debate over its source and ways to mitigate impacts

Баланс фосфору в ґрунтах і землеробстві України

Баланс фосфору в ґрунтах і землеробстві України

Characterization of Single Superphosphate Powders – a study of Milling Effects on Solubilization Kinetics

Conventional single superphosphate (SSP) is known as one of the most important and common sources of phosphorus in agriculture. Despite SSP has been widely produced as a fertilizer, a few studies have been done to describe the fundamental aspects of this P-fertilizer, i.e., phase composition, thermal degradation behavior, and solubility kinetics. Therefore, this paper reports on the detailed characterization of SSP powders by correlating their properties with particle size and surface area. Commercial SSP fertilizers were milled under different conditions and the resulting powders were characterized by X-ray diffraction, thermogravimetric analyses, scanning electron microscopy, FT-IR spectroscopy, and solubilization tests. It was observed that short milling times favored the solubilization kinetics, whereas long milling times were deleterious due to agglomeration effects. It was pointed out that agglomeration plays an important role in phosphate availability. These results provided a deeper understanding of SSP powders in microstructural terms, and may be used as a foundation for the development of novel strategies of alternative production of phosphorus fertilizers.

Managing agricultural phosphorus to minimize water quality impacts

Eutrophication of surface waters remains a major use-impairment in many countries, which, in fresh waters, is accelerated by phosphorus (P) inputs from both point (e.g., municipal waste water treatment plants) and nonpoint sources (e.g., urban and agricultural runoff). As point sources tend to be easier to identify and control, greater attention has recently focused on reducing nonpoint sources of P. In Brazil, agricultural productivity has increased tremendously over the last decade as a consequence, to a large extent, of increases in the use of fertilizer and improved land management. For instance, adoption of the “4R” approach (i.e., right rate, right time, right source, and right placement of P) to fertilizer management can decrease P runoff. Additionally, practices that lessen the risk of runoff and erosion, such as reduced tillage and cover crops will also lessen P runoff. Despite these measures P can still be released from soil and fluvial sediment stores as a result of the prior 10 to 20 years’ management. These legacy sources can mask the water quality benefits of present-day conservation efforts. Future remedial efforts should focus on developing risk assessment indices and nonpoint source models to identify and target conservation measures and to estimate their relative effectiveness. New fertilizer formulations may more closely tailor the timing of nutrient release to plant needs and potentially decrease P runoff. Even so, it must be remembered that appropriate and timely inputs of fertilizers are needed to maintain agricultural productivity and in some cases, financial support might also be required to help offset the costs of expensive conservation measures.

Agricultural soil acidity and phosphorus leaching risk at farm level in two focus areas

ABSTRACTPoland has the largest agricultural area within the Baltic Sea drainage basin and reducing the risk of phosphorus (P) and nitrogen (N) leaching from Polish soils to water is therefore essential. Increased acidity is known to reduce soil fertility and may trigger P leaching from non-calcareous soils. As part of advisor training, 25 farms each in Pomerania and north-western Mazovia were visited and 1500 ha arable soil, including 180 ha grassland soil, were monitored in 2013–2014. The soil was mainly coarse textured, but 25% of the Pomeranian farms were dominated by silty or clayey soils. More or less regular drainage systems were found on 20% of the farms, while 50% had simpler, older (>30 years) systems with a few single pipes. The farmers often used only ammonium sulphate or other acidifying N mineral fertiliser. Median pH on the Pomeranian farms, analysed in potassium chloride solution [pH(KCl)], was 5.2 and liming was advised for fields on most (72%) of these farms. Soil P content, measured by double-lactate extraction (PDL), was positively and significantly correlated (Pearson coefficient 0.57; p < .001) with soil pH and was generally higher for pig farms. Mean PDL (P given in elemental form) tended to be lower on dairy farms and arable farms and was significantly lower (mean 51 mg PDL kg−1 soil) on mixed farms (with just a few cows and poultry) than on pig farms (mean 122 mg PDL kg−1 soil). Farm-gate balances indicated deficits of P and potassium (K) on many of the small mixed farms in Pomerania and the soil can be expected to be nutrient depleted. In contrast, the pig farms demonstrated surplus farm-gate P balances (mean 27 kg ha−1). The P leaching risk is discussed relative to soil threshold values and to results from Swedish long-term field experiments.

Phosphorus in agriculture, a limited resource.

Abstract Phosphorus (P) is a non-substitutable agricultural nutrient. Traditionally, agriculture was underpinned by natural processes leading to the release of phosphates which are available to crops, phosphate deposition from flooding and air, and often also by the recycling of organic residues. In parts of the world, these traditional P resources came to be viewed as a limiting factor to agricultural production in the nineteenth and early twentieth century. Feeding the current world population is dependent on these traditional P resources plus phosphate rock, which is the product of slow geological processes. Current practices are characterized by substantial P losses from agricultural soils, limited P use efficiency and limited recycling of organic residues to such soils. Continuation of such practices at current agricultural production levels will lead to a depletion of phosphate rock resources. Other potential P resources, such as P in steelmaking slags and landfills, seem relatively small if compared with phosphate rock resources. Phosphorus resources are limited but estimates regarding the timespan for depletion of phosphate rock resources vary much: between about 80 and about 1800 years at the current rate of mining. Phosphorus resources can be conserved by increased recycling of P to agricultural soils, reducing losses from agricultural soils and by improving the efficiency of P use in agriculture.

The knowns and unknowns of phosphorus loading into grains, and implications for phosphorus efficiency in cropping systems.

Inefficient use of phosphorus (P) in agriculture adds to production costs, increases the risk of eutrophication of waterways, and contributes to the rapid depletion of the world's non-renewable rock phosphate supplies. The removal of large quantities of P from fields in harvested grains is a major driver in the global P cycle, but opportunities exist to reduce the amount of P in harvested grains through plant breeding. Using rice (Oryza sativa L.) as a model crop, we examine our current understanding of the process of P loading into grain and its regulation by genetic and environmental factors. We expose a dearth of knowledge on the physiological processes involved in loading P into grains, poor resolution of the genes and networks involved in P mobilization from vegetative tissues to grains, and limited understanding of genetic versus environmental contributions to variation in grain P concentrations observed among genotypes. We discuss potential breeding strategies and highlight key research gaps that should be addressed to facilitate these breeding approaches. Given the strong economic and environmental incentives for a low grain P trait, we suggest that some of the investment and resources currently directed to determining the molecular regulation of P starvation responses in model plant species should be diverted to resolving the physiology, genetics, and molecular regulation of P loading into cereal grains.

A five-year P fertilization pot trial for wheat only in a rice-wheat rotation of Chinese paddy soil: interaction of P availability and microorganism

The need for efficient use of phosphorus (P) in agriculture has been highlighted recently by concerns about the finite amount of P fertilizer resources. However, in the Taihu Lake Region (TLR) of China, farmers’ injudicious and excessive use of P fertilizer has led to a dramatic spike in P accumulation. A five-year (ten consecutive crop seasons) pot experiment was conducted using four paddy soils with three P concentrations (2 P-rich, 1 P-moderate, and 1 P-deficient soils) from the TLR under four P fertilization regimes: P fertilization only for the wheat season (PW), P fertilization only for rice season (PR), P fertilization for both rice and wheat seasons (PR + W), and no P fertilization during either season (Pzero; control). Over 5 years, compared to the PR + W treatment, the PW treatment did not decrease crop yield (P < 0.05) because it could supply enough available P sources (124–210 mg kg-1 labile P and moderately labile P) for crop growth and similar microorganism community composition. Also, compared to the Pzero treatment, applied P fertilization significantly increased the concentration of labile P and moderately labile P. Additionally, applied P fertilization decreased acid phosphatase enzyme activity and increased the total relative abundance of microorganisms significantly in P-rich soil, although they decreased in P-deficient soil. Arbuscular mycorrhizal fungi (AMF) showed significant positive correlations with soil labile P (P < 0.05), which indicated that AMF played important roles in the transformation of P in the soil P pool. P fertilizer applied only for the wheat season may be a viable option for saving P fertilizer and sustaining crop yields in the current rice-wheat rotated system of China, and effective utilization of AMF which are related to P availability in the soil will be important in the future reasearch.

Physiological and molecular approaches for improving phosphorus uptake efficiency of crops.

Intensive use of phosphorus (P) in agriculture has raised concerns about its sustainability due to potential resource scarcity and its non-judicious use which has led to serious environmental pollution. Plants possess a number of adaptive mechanisms to cope with P stress leading to changes at morphological, physiological, biochemical and molecular levels. A comprehensive understanding of these adaptive responses is required to improve P uptake efficiency, partitioning and utilization, together with other agronomic approaches, which would result in meeting the sustainability challenge of P delivery to crops. The present article briefly covers various plant responses to P stress and molecular strategies that could be used to develop plants efficient in P acquisition.

Past, present, and future use of phosphorus in Chinese agriculture and its influence on phosphorus losses.

Large inputs of phosphorus (P) in chemical fertilizers and feed supplements since 1978 have improved soil P status in arable land in China, but have also created challenges by increasing P concentrations in manure and exacerbating water quality degradation. Arable land in China can be divided into five management zones based on soil P chemistry, with 15–92 % of arable land having lower P status than the agronomic optimum and 0.3–7.2 % having severe risks of P leaching losses. A scenario analysis of soil P budget and agronomic P demand during 2011–2030 highlighted the great pressure China faces in sustainable P management and the need for drastic changes in current practices. This includes new policies to reduce P supplementation of feed and improved P use efficiency by livestock and programs to expand the adoption of appropriate fertilization, soil conservation, and drainage management practices to minimize P losses.

Future agriculture with minimized phosphorus losses to waters: Research needs and direction.

The series of papers in this issue of AMBIO represent technical presentations made at the 7th International Phosphorus Workshop (IPW7), held in September, 2013 in Uppsala, Sweden. At that meeting, the 150 delegates were involved in round table discussions on major, predetermined themes facing the management of agricultural phosphorus (P) for optimum production goals with minimal water quality impairment. The six themes were (1) P management in a changing world; (2) transport pathways of P from soil to water; (3) monitoring, modeling, and communication; (4) importance of manure and agricultural production systems for P management; (5) identification of appropriate mitigation measures for reduction of P loss; and (6) implementation of mitigation strategies to reduce P loss. This paper details the major challenges and research needs that were identified for each theme and identifies a future roadmap for catchment management that cost-effectively minimizes P loss from agricultural activities.

Implementing agricultural phosphorus science and management to combat eutrophication.

Experience with implementing agricultural phosphorus (P) strategies highlights successes and uncertainty over outcomes. We examine case studies from the USA, UK, and Sweden under a gradient of voluntary, litigated, and regulatory settings. In the USA, voluntary strategies are complicated by competing objectives between soil conservation and dissolved P mitigation. In litigated watersheds, mandated manure export has not wrought dire consequences on poultry farms, but has adversely affected beef producers who fertilize pastures with manure. In the UK, regulatory and voluntary approaches are improving farmer awareness, but require a comprehensive consideration of P management options to achieve downstream reductions. In Sweden, widespread subsidies sometime hinder serious assessment of program effectiveness. In all cases, absence of local data can undermine recommendations from models and outside experts. Effective action requires iterative application of existing knowledge of P fate and transport, coupled with unabashed description and demonstration of tradeoffs to local stakeholders.

Harvesting Pollution: Quantifying Agricultural Phosphorus Inputs to Lake Champlain

Harvesting Pollution: Quantifying Agricultural Phosphorus Inputs to Lake Champlain

Managing agricultural phosphorus for water quality: Lessons from the USA and China

The accelerated eutrophication of freshwaters and to a lesser extent some coastal waters is primarily driven by phosphorus (P) inputs. While efforts to identify and limit point source inputs of P to surface waters have seen some success, nonpoint sources remain difficult to identify, target, and remediate. As further improvements in wastewater treatment technologies becomes increasingly costly, attention has focused more on nonpoint source reduction, particularly the role of agriculture. This attention was heightened over the last 10 to 20years by a number of highly visible cases of nutrient-related water quality degradation; including the Lake Taihu, Baltic Sea, Chesapeake Bay, and Gulf of Mexico. Thus, there has been a shift to targeted management of critical sources of P loss. In both the U.S. and China, there has been an intensification of agricultural production systems in certain areas concentrate large amounts of nutrients in excess of local crop and forage needs, which has increased the potential for P loss from these areas. To address this, innovative technologies are emerging that recycle water P back to land as fertilizer. For example, in the watershed of Lake Taihu, China one of the largest surface fresh waters for drinking water supply in China, local governments have encouraged innovation and various technical trials to harvest harmful algal blooms and use them for bio-gas, agricultural fertilizers, and biofuel production. In any country, however, the economics of remediation will remain a key limitation to substantial changes in agricultural production.

Factors influencing phosphorus levels delivered to Everglades National Park, Florida, USA.

Everglades restoration is dependent on constructed wetlands to treat agricultural phosphorus (P)-enriched runoff prior to delivery to the Everglades. Over the last 5years, P concentrations delivered to the northern boundary of Everglades National Park (Park) have remained higher than the 8μg L(-1)-target identified to be protective of flora and fauna. Historically, Everglades hydrology was driven by rainfall that would then sheetflow through the system. The system is now divided into a number of large impoundments. We use sodium-to-calcium ratios as a water source discriminator to assess the influence of management and environmental conditions to understand why P concentrations in Park inflows remain higher than that of the target. Runoff from Water Conservation Area 3A (Area 3A) and canal water from areas north of Area 3A are two major sources of water to the Park, and both have distinct Na:Ca ratios. The P concentrations of Park inflows have decreased since the 1980s, and from June 1994 through May 2000, concentrations were the lowest when Area 3A water depths were the deepest. Area 3A depths declined following this period and P concentrations subsequently increased. Further, some water sources for the Park are not treated and are impeding concentration reductions. Promoting sheetflow over channelized flow and treating untreated water sources can work in conjunction with constructed wetlands to further reduce nutrient loading to the sensitive Everglades ecosystem.

Demonstrating the relationship between soil phosphorus measures and phosphorus solubility: Implications for Ohio phosphorus risk assessment tools

Approximately 80% of the land area draining into the western Lake Erie Basin is in Ohio, much of which is agricultural. Therefore, the potential for agricultural phosphorus (P) loading from Ohio is a concern for the water quality of western basin rivers, embayments and open water. This work demonstrates soil P relationships across Ohio soils and its implications for potential revisions of Ohio P risk assessment tools. The objectives were, using a selection of soils representative of soils across Ohio, (i) to determine if soil survey classification (series) could be an indicator of hydrous oxide content and, (ii) to determine if agronomic soil test P (STP) Mehlich 3 (M3-P), Bray P, or alternative measures of soil P saturation (Psat) were comparable to oxalate Psat for predicting P solubility, and therefore, useful for Ohio P risk assessment tools. Results showed no significant difference (P>0.01) in soil hydrous oxide content when grouped by soil series. However, significant (P<0.01) inflection points, reflecting a rapid increase in P solubility, were identified for oxalate P saturation (11.8%), M3-P saturation (12.4%), M3-P extractable P (181mg/kg), and Bray-P extractable P (122mg/kg). This suggests a separate pre- and post-inflection point consideration of STP may be appropriate for revised Ohio P risk assessment tools to better reflect increased post-inflection offsite P transport risk and thereby be sufficiently protective of water quality. Identifying fields with high offsite P transport risk is critical to implementing management decisions to reduce P transport risk to receiving waters including Lake Erie.

Phosphorus Retention and Remobilization along Hydrological Pathways in Karst Terrain

Karst landscapes are often perceived as highly vulnerable to agricultural phosphorus (P) loss, via solution-enlarged conduits that bypass P retention processes. Although attenuation of P concentrations has been widely reported within karst drainage, the extent to which this results from hydrological dilution, rather than P retention, is poorly understood. This is of strategic importance for understanding the resilience of karst landscapes to P inputs, given increasing pressures for intensified agricultural production. Here hydrochemical tracers were used to account for dilution of P, and to quantify net P retention, along transport pathways between agricultural fields and emergent springs, for the karst of the Ozark Plateau, midcontinent USA. Up to ∼ 70% of the annual total P flux and ∼ 90% of the annual soluble reactive P flux was retained, with preferential retention of the most bioavailable (soluble reactive) P fractions. Our results suggest that, in some cases, karst drainage may provide a greater P sink than previously considered. However, the subsequent remobilization and release of the retained P may become a long-term source of slowly released "legacy" P to surface waters.

Start-up performance of a novel constructed riparian wetland for removing phosphorus from agricultural runoff

The overloading agricultural phosphorus inputs play significant roles in accelerating eutrophication of receiving waters. For the propose of phosphorus removal from agricultural runoff, a field-scale free surface flow constructed riparian wetland system, with cost-effective and easily maintainable design, was constructed for receiving runoff from a small agricultural watershed on the northeastern lakeside rural areas of Liangzi Lake, China. During the start-up period, the system potentially provided a buffering capacity in irrigative and rainy periods. Wetland vegetations grew relatively well during the observed period (1 August–30 October 2012). Furthermore, the growth of vegetations has assisted in transforming the constructed riparian wetland structure to fit well with the surrounding landscape. The reductions in average concentrations of PO4-P and total phosphorus (TP) during the start-up period were approximately 75.6% and 46.5%, respectively. Moreover, the influences of environmental conditions on PO4-P and TP removal and retention in the constructed riparian wetland system were also analyzed. The results indicated that water temperature, conductivity, dissolved oxygen, and pH were important factors controlling phosphorus redistribution in the studied system. Generally, the constructed riparian wetland system preformed satisfactory during the start-up period, and it might be a suitable wastewater treatment tool for farms in poor rural areas.

Distributed and dynamic modelling of hydrology, phosphorus and ecology in the Hampshire Avon and Blashford Lakes: Evaluating alternative strategies to meet WFD standards

The issues of diffuse and point source phosphorus (P) pollution in the Hampshire Avon and Blashford Lakes are explored using a catchment model of the river system. A multibranch, process based, dynamic water quality model (INCA-P) has been applied to the whole river system to simulate water fluxes, total phosphorus (TP) and soluble reactive phosphorus (SRP) concentrations and ecology. The model has been used to assess impacts of both agricultural runoff and point sources from waste water treatment plants (WWTPs) on water quality. The results show that agriculture contributes approximately 40% of the phosphorus load and point sources the other 60% of the load in this catchment. A set of scenarios have been investigated to assess the impacts of alternative phosphorus reduction strategies and it is shown that a combined strategy of agricultural phosphorus reduction through either fertiliser reductions or better phosphorus management together with improved treatment at WWTPs would reduce the SRP concentrations in the river to acceptable levels to meet the EU Water Framework Directive (WFD) requirements. A seasonal strategy for WWTP phosphorus reductions would achieve significant benefits at reduced cost.

Estimation of national and regional phosphorus budgets for agriculture in Turkey

This paper presents national and regional phosphorus (P) budgets for agriculture in Turkey by using Eurostat/OECD common methodology. Regional P budgets presented in this paper are the first estimations for Turkey known to date. In Turkey, the values of P surplus for agriculture (PS) and P use efficiency for agriculture (PUE) in 2011 were 2 kg P ha-1 yr-1 and 77%, respectively. PS values varied from -2 to 15 kg P ha-1 yr-1 among regions in 2011. In 2008, PS and PUE values (0 kg P ha-1 yr-1 and 96%, respectively) were lower than the average EU values (3 kg P ha-1 yr-1 and 104%), including Norway and Switzerland. The relationship between PS values and some socio-economic properties in Turkey regions were also analyzed. According to the results, the correlations of PS with gross domestic product per capita, permanent meadows and pastures share in utilized agricultural area (UAA), population density, illiterate share and arable land share in UAA were statistically significant. We can conclude from the study results that the environmental effect of agricultural phosphorus on water bodies varies greatly both among regions in Turkey and among European countries because of high variations in PS values.