Agricultural Production in the Netherlands by Natural Supply of Nitrogen

Abstract

ABSTRACT On the basis of what is known from the literature an attempt has been made to estimate the yields in an agricultural system that is supplied with nitrogen from natural sources. For this purpose a model of Dutch agriculture is developed in which only nitrogen is considered as a variable and all other production factors (like phosphate, potassium, water, plant variety, and the skills of the farmer) are considered to contribute to productivity in their usual manner. Because there is a wide variety in natural fertility, Dutch soils have been classified into ten landuse classes. In six classes both arable and grassland farming can take place, while four classes consist of soils that are only suitable for grassland. An estimate has been made per class and per hectare as to how much nitrogen the soil can naturally provide, how much can be fixed by leguminous crops, and the amount of nitrogen that can be recycled as manure when livestock farming is practised. The productivity of the grassland is given in the absence of an external nitrogen source. For the soil classes with mixed farming a distinction has been made between N-producing (including grassland) and N-consuming crops. The effect of legumes on yields of the subsequent crops is taken from field experiments on Dutch soils. Also yields of cereals, potatoes and sugarbeet when nitrogen has never been applied are known from these experiments. Optimal rotations have been suggested for the soil classes so that the proportion of legumes in the rotation is evenly balanced with the production level of the crops. This resulted in a percentage of legume crops (including grassland) of 32–40 and a production level of 70% with respect to the situation in 1977. The most important source of nitrogen is green manuring; farmyard manure from the grasslands is mainly needed to maintain horticultural production. The consequence of such an agricultural system on the food situation in the Netherlands has been determined. In a situation of self-sufficiency there would be enough food for the Dutch population provided that a change was made to a diet of grains and beans with a small amount of meat. Finally, the nitrogen balance of grassland and mixed farms has been given.