Role of Mineral Fertilisers in Optimising the Use Efficiency of Manure and Land

Keywords: Food production, manure, mineral fertiliser, nitrogen, phosphorus, use efficiency, Liebig.

The product of the number of people on this planet and their food consumption, as well as the envisaged development of both, necessitate the use mineral fertilisers. One of the reasons is that recycling of NPK-containing wastes is far from perfect in a world in which production, processing and consumption have become spatially disrupted. But even if all wastes were to be efficiently recycled, food production would still have to rely on nitrogen (N) supplements, as N is inevitably lost from all systems. These N supplements consist of biologically fixed N or mineral fertiliser N. The use of both is not without consequences, however. Biologically fixed N competes with other potential uses of scarce land, whereas mineral fertiliser N requires the use of energy including finite fossil fuels.

Comparing the agronomic and environmental effects of crop production systems fully based on organic wastes, including manures, with those fully based on mineral fertilisers is irrelevant. This kind of comparison excludes interactions and seems to forget that many ‘wastes’ are natural by-products of agriculture that simply require handling. There is an indisputable need to improve the use efficiency of N in organic wastes, requiring their optimised rates, composition, treatment, timing and placement. In any case, mineral fertiliser N can be seen as a means to compensate for remaining deficits, thus improving the use efficiency of other resources. Conversely, the use of organic wastes itself can contribute positively to the use efficiency of resources whenever there is need for an improvement of the soil fertility that cannot easily be accomplished with mineral fertilisers only. This paper reviews the above interactions between the use of mineral fertilisers and organic nutrient sources.

Jaap Schröder, Wageningen University and Research Centre, Plant Research International, Agrosystems Department, P.O. Box 616, 6700 AP Wageningen, The Netherlands, and

Peter Sørensen, Aarhus University, Faculty of Science and Technology, Department of Agroecology, P.O. Box 50, 8830 Tjele, Denmark

20 pages, 9 figures, 6 tables, 42 references.