Effect of leguminous green manure crops on white cabbage in organic vegetable production in southwestern Germany

ISHS Secretariat
Effect of leguminous green manure crops on white cabbage in organic vegetable production in southwestern Germany

Vegetables require high amounts of nitrogen (N) and rather low amounts of phosphorus (P). Therefore, fertilization with farmyard manure often results in nutrient imbalances, commonly seen in P oversupply. Leguminous green manures increase the nutrient supply of the successive vegetable crop by the mineralization of residues and the exclusive N input into the soil by biological N2 fixation. This may reduce the need for organic fertilizers in vegetable production and contribute to more balanced nutrient flows. In field trials in 2019 and 2020, different green manures were tested in southwestern Germany. In the preceding October, the winter-hardy cover crops rye (Secale cereale), a mixture of rye with Hungarian vetch (Vicia pannonica), winter pea (Pisum sativum) and winter field bean (Vicia faba) were sown. Bare soil served as the control treatment. After incorporation of the green manures in late May, white cabbage was planted and harvested in October. The green manures influenced cabbage yield due to differences in mineralization rates of crop biomass as indicated by N flows as measured by green manure biomass, chlorophyll status of cabbage leaves, and soil mineral N content (Nmin). The N content of incorporated biomass was higher in peas and field beans (156 and 195 kg N ha-1, respectively) than in rye (97 kg) and the mixture of rye with vetch (131 kg). The carbon:nitrogen ratio in the pure legume stands was significantly lower. The chlorophyll status during cabbage head formation as well as the soil Nmin levels at the time of cabbage planting and onset of head formation was significantly lower in the rye and rye with vetch treatments compared to pea and field bean treatments. This resulted in higher cabbage yields for the pure legume treatments compared to bare soil and the cereal treatments of rye and rye with vetch. Therefore, cultivating legumes as green manure crops during winter is an effective approach to increase yields of subsequent vegetable crops, increase internal N cycling and reduce surplus P. Leguminous green manures can compensate for fertilizers such as farmyard manure or compost in organic farming.

Sophie Stein won the ISHS Young Minds Award for the best oral presentation at the III International Organic Fruit Symposium and I International Organic Vegetable Symposium, which was held virtually in Italy in December 2021.

Sophie Stein, Zentrum Ökologischer Landbau, Universität Hohenheim, Fruwirthstraße 14-16, 70599 Stuttgart, Germany, e-mail: sophie.stein@uni-hohenheim.de

The article is available in Chronica Horticulturae

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organic vegetables
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Young Minds Award Winners