Phosphorus turnover characteristics of soils: Comparison of pot experiment results and modelling by stepwise regression analyses

The phosphorus retention ability of soils depends on several factors and influences the effectiveness of fertilization as well as the release of P from soil to water. In the present study the phosphorus supplying and/or retention ability of soils were estimated by two approaches: biological approach (pot experiments) and modelling (by regression analyses). In the course of the biological approach pot experiments were carried out with soils showing significant differences in total and available P contents. Soil samples were collected from selected plots of 9 sites of the National Long-Term Fertilization Trials (NLFT) after 20 years of fertilization, which represents different agro-ecological regions of Hungary. Site characteristics covered a wide range in pH, carbonate and P content, representing typical soil types of the country. With the statistical approach (modelling), the most important soil properties were included and the role of these factors was evaluated by stepwise regression analyses. From the equations, the contribution of important soil parameters to phosphorus supplying and retention ability could be quantified. The objective of the present study was to find a simple way to compare and evaluate the two approaches in P nutrient turnover of soils. Results of the two approaches were correlated. From these results, a rank correlation was also made from the experimental and calculated results. A very close relationship was observed for the P supply and retention of soils (r value was 0.918 for the N0P0K0 unfertilized control and 0.927 for the N200P200K100 fertilization level). Values obtained with rank correlation were 0.87 and 0.866, respectively, verifying that both methodologies are reliable for estimating the nutrient dynamics in soils and to predict P dynamics in a diverse range of soils

Approaches to calculating P balance at the field-scale in Europe

Policies for mitigating phosphorus (P) loss from agriculture are being developed in a number of European countries and calculation of P balance at farm-gate or field-scale is likely to be a part of such policies. The aim of the paper was to study P balance at the field-scale in 18 countries that participated in the European Union's (EU) European Co-operation in the Field of Scientific and Technical Research (COST) action on Quantifying the Agricultural Contribution to Eutrophication (COST 832). A questionnaire related to P balance at the field-scale was sent to representatives in the 18 countries and all replied. The field as a unit is defined differently in the various European agricultural systems. The identification of the inputs and outputs differ among the countries. For example, P losses may or may not be taken into account in balances. Phosphorus balance at the field-scale is used in all countries in the context of soil analysis and P recommendations for crops and advisory and research purposes, while only a few countries use it for policy purposes (agri-environmental). There is wide variation in P balances between countries in relation to soil fertility and vulnerability of water to eutrophication from nutrients from agricultural sources. In several eastern European countries, Hungary for example, fertilizer P use has dropped to about one tenth of the levels used in the 1980's. Many of these countries now have a negative P balance. In western European countries, by contrast, although fertilizer P use has decreased in recent years, the average input is higher than the average off take, and soil test phosphorus (STP) values remains high and continue to increase in some areas. Twelve different soil extractants for STP are used in Europe, and their interpretation can hinder direct comparisons. Calculating P balance at the field-scale involves approximations in estimating inputs and outputs and spatial variations in fertility in individual fields. Accuracy of data and standardization of methods for calculating balances with inputs and outputs will be a challenge for the future development of a sustainable agriculture in Europe

Release of trace metals to the soil solution from a phosphate rock containing soil at different acid loads

In agricultural practice basic phosphate rocks (PRs) may be efficient P sources if applied on acidic soils. However, due to their potentially toxic elements content environmental hazards may arise. In a laboratory bulk experiment the appearance and accumulation of such elements (As, Ba, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sr and Zn) in the soil solution of an acidic sandy soil was studied after various PR and acid treatments. The degree of pH elevating effect of PR treatments was also tested. In the liquid phase of the PR-enriched soil, metal concentrations were generally lower than in the control sample because their release to the soil solution was influenced less by the amount of the pollutants carried into the soil with PR doses than by the pH increasing and/or solubility altering effect of PR. Acid loads, as expected, considerably increased the concentrations of cation forming elements in the soil solution, but their concentrations – due to the immobilizing effect of PR – decreased in the acid treated soil, as well. Extreme strong acid treatment was necessary to compensate for this effect and, while Ba, Co, Cu and Mn concentrations practically did not change with the increasing PR doses, Cd, Sr and Zn concentrations were eleveated. In contrast, the immobilizing effect of PR in case of Pb dominated even under the extreme acid treatment, its concentration decreased with increasing PR doses. Concentration of the anion forming elements (As, Mo) in the acidic soil solution was negligible even at the highest P dose