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Nitrogen (N) losses from agricultural production are a serious problem for environmental quality. In order to tackle this problem the environmental ministers in the EU agreed already 15 years ago on a 50% reduction of the N surpluses (among others in the HELSINKI declaration for the protection of the Baltic Sea dated February 15, 1988). But till today agriculture is far away from meeting this target. In a recent workshop "Roadmaps to more N efficiency" the Institute of Plant Nutrition and Soil Science of the Federal Agricultural Research Centre (FAL) in Braunschweig, Germany evaluated and quantified options for reducing farm N surplus.
The largest among the sources of losses in agricultural production is animal production, this alone accounts in the national N balance for Germany for 30 kg/ha N per annum. Intensive animal production is a consequence of the countries large demand for meat and meat products. Thus, society is also responsible for a high N surplus from animal production. National balances, however, obscure the situations of individual farms where the annual N surplus can range from zero to far above 250 kg/ha N. So-called "unavoidable" losses have a high significance for the calculation of the N surplus. "Unavoidable" losses may occur through leaching, gaseous emissions in the field or during storage. They are considered as factors which can not be influenced by farming practice even when operating according to "codes of good agricultural practice". The suggested site-specific variations for "unavoidable losses" of N for instance for southern Germany range from 40 kg/ha N on light soils (< 5% clay) in rain-laden (> 700 mm/a precipitation) regions down to 5 kg/ha N per annum on heavy soils (> 25% clay) in dry regions (< 600 mm/ha precipitation). But this raises the question if farming on sites which tends to increased losses should be allowed to counteract with higher fertilizer rates the higher risk of yield losses, or shall fertilization be restricted on these sites for the benefit of environmental quality?
It may sound surprising, but in general on livestock farms the amount of surplus N is correlated with the consumption of fertilizer N. This reveals that farmyard manure is still not considered as a full equivalent to manufactured N fertilizers. This is also the main reason why in organic farming surplus N is much lower than compared to conventional farms. This calls in for action in conventional farming to increase the general acceptance of N from farmyard manures and to adopt higher efficiency coefficients. In this context the development in Denmark is an exceptional example: by limiting the use of mineral fertilizer N depending on livestock density, the surplus of the national N balance could be reduced by 48%, while the corresponding loss in cereal yield amounts only to - 0.3t/ha and the loss in cereal quality (crude protein content) only to - 0.5%.
Compared to such austere administrative measures the effects of improved production technique on N efficiency can be called only humble. Most effective, but unfortunately still not very common practice is intercropping. Fodder radish and raphanobrassica for instance accumulate exceptionally high amounts of N already in autumn (up to 200 kg/ha N), thus preventing losses by leaching during winter. The contribution of plant breeding towards increased N efficiency of crop plants focuses especially on the extension of the life span of photosynthetic active tissue and a longer generative phase. Spiking N fertilizers with nitrification and urease inhibitors gain less than an overall 5% more N efficiency. Even worse are the actually reported effects of variable rate application of N fertilizers according to the spatial variability of soil fertility parameters ("Precision Agriculture (PA)") on N efficiency. Still after 15 years of implementation no results proving consistent increases in yields or decreased fertilizer application are available. Quite the contrary: some of the techniques developed in PA may even decrease fertilizer N efficiency, like for instance the use of so-called "N-sensors" when applied on crops with not only nitrogen as growth limiting factor.
Conclusion: there are a number of technologies enabling plant production to improve N efficiency. But before they can prove their significance the overall nutrient management of a farm operation needs to be optimised. A way out of effective but harsh administrative measures are investments in improved education of farm managers towards a higher sensitivity for issues of environmental quality and sustainable development in agriculture.
The contributions of the workshop are available at:
http://www.pb.fal.de/index.htm?page=/home.htm in the section"workshops"
Contact: Prof. Dr. Dr. Ewald Schnug, Federal Agricultural Research Centre (FAL), Institute of Plant Nutrition and Soil Science, Bundesallee 50, D-38116 Braunschweig, phone +49 531 596 2101, E-mail: pb@fal.de
http://www.pb.fal.de/index.htm?page=/home.htm - in the section"workshops": contributions of the workshop
http://idw-online.de/pages/de/news107566 - deutsche Fassung der Pressemitteilung
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Biologie, Informationstechnik, Meer / Klima, Tier / Land / Forst, Umwelt / Ökologie
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