NITROGEN FERTILISATION OF PHASEOLUS VULGARIS (BROWN BEANS)

The supply of nitrogen for brown bean production is limited to 30 kg/ha if the grower wishes to be eligible to receive subsidy from the EC. This limit is not based on the nitrogen requirement of the bean crop and is so low that the application in many cases may be unnecessary. The current experiment was designed to test the hypothesis that reduced nitrogen fertilisation in the spring will not reduce the yield if beans have been grown on the field previously and consequently the bacteria necessary for the nitrogen fixing are available.

Three cultivars of dried brown beans were grown in the 1997 season. The soil analysis in the spring showed a content of 10 kg N ha^-1 previously mineralized nitrogen. In a low fertilised treatment 5 kg N/ha was added and in a normal fertilised treatment 30 kg N/ha. No differences were found between the treatments for any of the cultivars with respect to yield, number of nitrogen-fixing nodules, or plant of dry matter and nitrogen contents. All experimental plots contained about 9 kg N ha^-1 in the autumn.

This experiment indicates that an N_min content of 15 kg N ha^-1 might be enough in the spring. If this figure can be confirmed in future experiments it should be possible to omit nitrogen fertilisation on some fields, or during years with abundant early nitrogen mineralization, without risking a reduced yield.