Abstract Phosphorus index (PI) is a risk-assessment tool that combines phosphorus (P) source factors and transport factors to rank the vulnerability of fields to P losses. Here we present the structure and concepts of conditional PI, developed as an educational and P-management tool adjusted for Swedish conditions. Because the significance of certain factors for P losses depends on their interplay with other factors, conditional rules are needed for a more accurate process description and quantification. Accounting for P losses through the soil profile, separate calculations for reactive and unreactive P and a changed approach to P loss assessment from erosion losses are some of the new features included in the tool presented here. The performance of the tool was tested by comparing the calculated PI values with measured annual P transport from seven observation fields included in a Swedish water quality monitoring program. This first test indicated that the tool could be used successfully for P loss risk assessment.

The proceedings from the Nordic Phosphorus workshop, February 2004, address the role of decision tools in the process of abating phosphorus (P) losses from agricultural land in the Nordic and Balti ...

Abstract. The practice of large phosphorus (P) additions to agricultural land has resulted in an increased depletion of limited mineable rock phosphate resources, P accumulation in soils with an increased risk for P losses, and intensified eutrophication and deterioration of water quality in recipient water bodies. A number of measures have been used to reach balance between P inputs and outputs in agricultural systems, with the goal of achieving improved P use efficiency, sustained high crop yields and reduced P losses. This paper discusses how this goal may be achieved. Results from a Swedish long‐term fertility experiment combined with results of a P leaching study using a selection of soils from the fertility experiment are used to evaluate the effects of a balanced P system on yields, soil P levels and P leaching. Three P fertilizer application strategies are compared (zero P, replacement P, and a treatment where surplus P fertilization was used to achieve a rapid increase in the soil P status). The replacement P strategy appeared to be the most sustainable system but P fixation in this system must be accounted for. When surplus P rates were applied, increased crop yields were counterbalanced by poorer use efficiency and P accumulation in soil. Topsoil P content was a poor predictor of P leaching. Instead, balancing P inputs and outputs represents a first step in the management of P losses, but additional, site‐specific measures are required to counteract site‐specific factors responsible for P losses.

Abstract. To establish strategies for sustainable nutrient management, the priority of each identified element for different user groups and the issue of data transferability from one scale to the next need to be addressed. This is important to avoid developing policies and strategies using inaccurate data. This paper provides a thorough background on such issues and provides data from specific case studies to reflect the impact of scale on the usability and transferability of data. These data show that using information obtained in a laboratory setting for larger scales can generate major errors. Data are also provided regarding the spatial variability in total N and total P measured at different sub‐watersheds within a large watershed. Results from this case study indicate that there is a definite spatial variability in N and P loadings, which makes it difficult to transfer and extrapolate from data measured at one sub‐watershed to the entire watershed. Therefore, it can be concluded that using either measured or simulated data obtained at a small scale to respond to questions for larger scales may be erroneous. Such difficulty may be due to the inherent spatial variability in soils, nutrients, biology and other features of the landscape.

Abstract. To establish strategies for sustainable nutrient management, the priority of each identified element for different user groups and the issue of data transferability from one scale to the next need to be addressed. This is important to avoid developing policies and strategies using inaccurate data. This paper provides a thorough background on such issues and provides data from specific case studies to reflect the impact of scale on the usability and transferability of data. These data show that using information obtained in a laboratory setting for larger scales can generate major errors. Data are also provided regarding the spatial variability in total N and total P measured at different sub‐watersheds within a large watershed. Results from this case study indicate that there is a definite spatial variability in N and P loadings, which makes it difficult to transfer and extrapolate from data measured at one sub‐watershed to the entire watershed. Therefore, it can be concluded that using either measured or simulated data obtained at a small scale to respond to questions for larger scales may be erroneous. Such difficulty may be due to the inherent spatial variability in soils, nutrients, biology and other features of the landscape.

Abstract. The practice of large phosphorus (P) additions to agricultural land has resulted in an increased depletion of limited mineable rock phosphate resources, P accumulation in soils with an increased risk for P losses, and intensified eutrophication and deterioration of water quality in recipient water bodies. A number of measures have been used to reach balance between P inputs and outputs in agricultural systems, with the goal of achieving improved P use efficiency, sustained high crop yields and reduced P losses. This paper discusses how this goal may be achieved. Results from a Swedish long‐term fertility experiment combined with results of a P leaching study using a selection of soils from the fertility experiment are used to evaluate the effects of a balanced P system on yields, soil P levels and P leaching. Three P fertilizer application strategies are compared (zero P, replacement P, and a treatment where surplus P fertilization was used to achieve a rapid increase in the soil P status). The replacement P strategy appeared to be the most sustainable system but P fixation in this system must be accounted for. When surplus P rates were applied, increased crop yields were counterbalanced by poorer use efficiency and P accumulation in soil. Topsoil P content was a poor predictor of P leaching. Instead, balancing P inputs and outputs represents a first step in the management of P losses, but additional, site‐specific measures are required to counteract site‐specific factors responsible for P losses.

Abstract Phosphorus index (PI) is a risk-assessment tool that combines phosphorus (P) source factors and transport factors to rank the vulnerability of fields to P losses. Here we present the structure and concepts of conditional PI, developed as an educational and P-management tool adjusted for Swedish conditions. Because the significance of certain factors for P losses depends on their interplay with other factors, conditional rules are needed for a more accurate process description and quantification. Accounting for P losses through the soil profile, separate calculations for reactive and unreactive P and a changed approach to P loss assessment from erosion losses are some of the new features included in the tool presented here. The performance of the tool was tested by comparing the calculated PI values with measured annual P transport from seven observation fields included in a Swedish water quality monitoring program. This first test indicated that the tool could be used successfully for P loss risk assessment.

Phosphorus losses from arable soils contribute to eutrophication of freshwater systems. In addition to losses through surface runoff, leaching has lately gained increased attention as an important P transport pathway. Increased P levels in arable soils have highlighted the necessity of establishing a relationship between actual P leaching and soil P levels. In this study, we measured leaching of total phosphorus (TP) and dissolved reactive phosphorus (DRP) during three years in undisturbed soil columns of five soils. The soils were collected at sites, established between 1957 and 1966, included in a long-term Swedish fertility experiment with four P fertilization levels at each site. Total P losses varied between 0.03 and 1.09 kg ha(-1) yr(-1), but no general correlation could be found between P concentrations and soil test P (Olsen P and phosphorus content in ammonium lactate extract [P-AL]) or P sorption indices (single-point phosphorus sorption index [PSI] and P sorption saturation) of the topsoil. Instead, water transport mechanism through the soil and subsoil properties seemed to be more important for P leaching than soil test P value in the topsoil. In one soil, where preferential flow was the dominant water transport pathway, water and P bypassed the high sorption capacity of the subsoil, resulting in high losses. On the other hand, P leaching from some soils was low in spite of high P applications due to high P sorption capacity in the subsoil. Therefore, site-specific factors may serve as indicators for P leaching losses, but a single, general indicator for all soil types was not found in this study.

Abstract. Preferential flow may enhance phosphorus transport through the soil profile and thereby increase the risks for eutrophication of watercourses. Destruction of continuous macropores in topsoil by tillage provides the possibility for better contact between soil particles and P fertilizer. This is facilitated by incorporation rather than surface application of fertilizer, which should reduce the risk of rapid P transport from the soil surface through the unsaturated zone. To test this hypothesis, undisturbed soil monoliths (0.295 m in diameter and 1.2 m in length) were collected at a field site with a clay soil in which preferential flow is the dominant solute transport mechanism. After three years of observation, average total P loads reached 1.86, 1.59 and 1.25 kg ha–1for no‐tillage, conventional tillage, and conventional tillage where the P fertilizer was incorporated, respectively. More than 80% of total losses were in the form of dissolved P. The tillage treatment had no significant effect on P leaching loads compared to no‐tillage, but the improved contact between soil particles and P fertilizer resulting from fertilizer incorporation significantly reduced P loads during the first year after application of 100 kg P ha–1. However, after further application of 100 kg P ha–1 two years later, there were no significant differences between the treatments.

Phosphorus (P) is one of the main nutrients controlling algal production in aquatic systems. Proper management of P in agricultural production systems can greatly enhance our ability to combat pollution of aquatic environments. To address this issue, a decision support system (DSS) consisting of the Maryland Phosphorus Index (PI), diagnosis expert system (ES), prescription ES, and a nonpoint-source pollution model, Ground Water Loading Effects of Agricultural Management Systems (GLEAMS), was developed and applied to an agricultural watershed in southern Sweden. This system can identify critical source areas (CSAs) regarding phosphorus losses within the watershed, make a diagnosis of probable causes, prescribe the most appropriate best management practices (BMPs), and test the environmental effects of the applied BMPs. The PI calculations identified small parts of the watershed as CSAs. Only 10.4% of the total watershed area in 1995 and 5.2% of the total watershed area in 1996 were classed as "high potential P movement." Four probable causes (high P level in soil, excessive P fertilization, stream proximity, and subsurface drainage) and three BMPs (riparian buffer strips, reduced P fertilizer application, and P fertilizer incorporation) were identified by a diagnosis and prescription expert system. The GLEAMS simulations conducted for one selected CSA field for a 24-yr period showed that the recommended BMP reduced runoff P losses by 55% and sediment P losses by 71%, if applied from the first year. Results showed that using DSS may enable us to select a proper BMP implementation strategy and to realize the beneficial effect of BMPs on a long-term basis.

This paper attempts to summarize the most important factors which regulate the impact of preferential flow on leaching of agrochemicals, based on a range of long-term field and lysimeter experiments on pesticides, nitrate and phosphorus. In particular, the role of chemical properties, biological and chemical transformations, and physical exposure to preferential flow pathways are stressed, as well as differences in soil type and the significance of the highly transient nature of climatic boundary conditions. A simple two-region model (MACRO) has been used as a tool to quantify the effects of macropore flow for varying solutes under different agroenvironmental conditions. Some examples are presented which demonstrate that macropore flow can either increase or decrease the leaching of agrochemicals depending on the nature of the solute and the location of the solute in relation to the flow pathways.

Phosphorus losses from agriculture may enhance eutrophication of fresh water bodies. This thesis focuses on preferential flow as a phosphorus transport pathway. Both lysimeter and field plot observations were conducted to evaluate the significance of preferential flow for P losses and to test management practices to reduce P losses. A decision support system was also developed to identify critical source areas, to diagnose probable causes of P losses and to prescribe appropriate site-specific best management practices. Preferential flow pathways are an important transport mechanism for P displacement from topsoil to drain tiles. Substantial drainage losses (on average 4.0 kg P ha-') of surface-applied P fertilizer, as measured in one of the studies included in this thesis, indicate a very effective vertical transport in structured clay soils. High sorption potential of the subsoil is bypassed because only a small part of the total pore volume is active in watedsolute displacement. Incorporation of P fertilizer and an increased contact between applied fertilizer and sorbing soil particles may significantly decrease P losses via preferential flow. Ponded flow conditions enhance P losses not only by enhancing preferential flow, but also by prolonging loading of P into water laying temporarily on the surface or subsurface. During four years of observations, nine high discharge episodes were responsible for, more than a half of the total loads of suspended soil material and P losses from clay plots, although the water volume discharged during these episodes reached, only one fourth of the total discharge. Different parts of the watershed do not contribute equally to total P loads. Identification of high-risk areas, site-specific diagnosis and abatement efforts should reduce the losses more efficiently. For instance, high-risk areas occupied no more than 5-1 0% of the total watershed area, according to decision support system developed in the study included in this thesis. Research at different scales is necessary for better understanding of the P problem, as well as for an easier practical application of research results. Shifting the scales tests the relevancy of the research and helps the identification of the gaps in our knowledge and understanding of the proble