Carbon and nitrogen balance of a long-term experiment with vegetable crops

A long-term experiment on three different soils with a vegetable crop rotation was used to calculate the carbon and nitrogen balances of twelve treatments characterised by different fertilisation strategies within a 30 years period. The aim of the investigations was to show which fertilisation strategy led Is) to a maximum carbon gain for the plant soil system and additionally 2(nd)) to a minimum level of nitrogen losses from this system. Other aspects like the quality of the produced vegetable were excluded from these investigations. Under our specific experimental conditions, it was estimated that to get the maximum carbon gain of the plant soil system 1(st)) the produced plant matter should reach the site specific maximum and that 2(nd)) the carbon input by manures should be decreased to a minimum. If we consider additionally aspects of minimisation of nitrogen losses from the system, the mineral N fertilisation could be increased to a level that ensures the site specific maximum of the produced plant matter on the one hand. On the other hand, if we want to guarantee mean N losses of maximum 50 kg N ha(-1) year(-1) in treatments applied exclusively with manures, the total annual N input by organic materials should not exceed 100-150 kg N ha(-1).