Organic agriculture is an alternative farming system that relies on fertilizers of organic origin, such as manure and green manure, and sustainable farming practices such as crop rotation. Τhe biggest challenge in organic farming is to apply enough nitrogen to plants, especially when the crop requirements are high. However, how can we achieve this goal, given that the use of inorganic nitrogen fertilizers in organic farming systems is prohibited? One of the most sustainable cropping practices to achieve this is the use of legumes as intercrops or cover crops, as well as in rotations.
Legumes are capable of fixing nitrogen derived from the atmosphere through symbiosis with rhizobial bacteria. Using legumes in crop rotation schemes can improve the availability of nitrogen in soil for the next crop. However, the rate of nitrogen fixation depends on legume species and cultivars, as well as on the rhizobia strains.
It is well known that organic farming is a more environment-friendly cultivation method than conventional farming. However, organic farming has been accused of having a significant impact on greenhouse gas emissions. Conventional systems produce greenhouse gases through the production and application of synthetic fertilizers, while organic systems use animal manure that produces nitrous oxide (a powerful greenhouse gas).
TRUE Case study 22 at the Agricultural University of Athens uses legumes in crop rotations schemes in organic crops of non-legumes, aiming to increase soil fertility and ensure an adequate nitrogen supply to the crop despite the non-use of inorganic nitrogen fertilizers. Previous research has indicated that the level of GHG emissions arising from plant cultivation is influenced by differences in cultural practices, including those dictated by the applied farming system. Thus, the cropping practices may be used as management tools to mitigate GHG emissions in agriculture. This study will compare the environmental impact of organic and conventional cultivation systems and identify wider environmental effects when legumes are used in crop rotation schemes with non-legume vegetables.
Faba bean plants are used for green manure because of their high N fixing activity. These plants are inoculated with rhizobia (or not) to test and improve N fixing activity.
>>> Case Study 22:
Ioannis Karavidas, PhD
AUA uses legumes in crop rotations schemes in organic crops of non-legumes, in order to increase soil fertility and ensure adequate N supply to the crop despite the non-use of inorganic N fertilizers. In winter cultivation period, broccoli (grown organically or not) and Faba bean plants (used for green manure) were cultivated, while fallow plots were used as control.
After the winter crop period, the field was cultivated with Phaseolus vulgaris. Plants were inoculated with rhizobia or not cultivated in organic, and conventional farming systems. Yield, N availability in soil, mineral nutrients in plants tissues, BNf efficiency and greenhouse gases will be assessed.