Legumes dense sowing with peas as an alternative method for nitrogen fertilization in organic fruit growing.

The purpose of the present work was to examine the potential of dense sowing with legumes (peas) to be used as alternative nitrogen source in organic fruit production. Based on several publications it can be hypothesized that the utilization of legume seed nitrogen can be improved by sowing compared to application as seed meal. This can be explained by germination process causing an initial decrease in legume C:N ratio, which is the predominant determinant of nitrogen mineralization. In a three-year-trial the NO3-N-fertilization effect of a pea sowing with high plant density and incorporation of the seedlings after a short growing period was examined. In randomized beds different plant densities and incorporation stages of the peas were tested compared to a not fertilized control. In addition, the pea dense sowing was examined for two years directly sowed in the tree rows of an organic apple-orchard (variety “Topaz”) in comparison to a non fertilized control and the commercial organic fertilizer "Bioilsa". In the bed trials an adequate nitrogen fertilization effect could be measured in most of the treatments in the weeks after incorporation of the seedlings. Thereby the available nitrate (NO3-N)-content in the weeks after incorporation was between 17 and 55 kg NO3-N/ha higher than in the not fertilized control. However, treatment with longer growing period and later incorporation initially leads to reduced NO3-N -content in the soil. In the tree rows a comparable N fertilization effect of the peas dense sowing could be measured. In the treatment with pea dense sowing available NO3-N-contents in the weeks after incorporation of the seedlings were up to 51 kg NO3-N/ha higher than in the unfertilized control.