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