Farm nitrogen budgets for the assessment of the effectiveness of agri-environmental measures in the Watershed of the Venice Lagoon

One of the main concerns of the environmental scientists and policy-makers is related to the environmental compatibility of current agricultural systems and, in particular, to the losses of chemical fertilizers and manure in surface and ground-waters, as a consequence of run-off and leaching phenomena. In most cases European recent agri-environmental schemes envisaged specific measures for the reduction of fertilizer rates and the control of manure applications, in order to limit the releases of nutrients in surface and ground-waters. Substantial financial resources are invested in those measures and therefore the issue raises interest in monitoring and evaluating their effectiveness. Nutrient balance indicators are often used for quantitative assessment of the effectiveness of the measures in limiting the environmental impact of farming activities. N-surplus is one of the most commonly used indicators. The paper refers the results of a research project aimed at assessing the outcomes of agri-environmental measures implemented in the Venice Lagoon Watershed with an approach based upon the gross nitrogen balance, called “Nboxes”. The results of applying the Nboxes procedure to a sample of 550 farms set are presented, evidencing the expectations of greater effectiveness in terms of nitrogen surplus reduction from the measure C.5.1.3a and C.5.1.3b (low input farming and buffer strips). Measures supporting improved irrigation systems, controlled drainage and more rational livestock nutritional programmes and technologies, showed instead only limited potential for meaningful contributions to the reduction of nitrogen surplus in cultivated soils.