Nutritional quality of lettuce and onion as companion plants from organic and conventional production in north Greece

Abstract

The purpose of this study was to examine the effect of production systems – (organic-ORG or conventional-CONV) and growing season (autumn or spring) of cos lettuce (Lactuca sativa L. var. longifoila cv. ‘Parris Island’) and green onion (Allium cepa cv. ‘Sturon’) as companion planting (the onions and lettuce were grown in the same plot of land), on the yield and quality parameters (mineral composition, phenolic profiles, antioxidant capacity, nitrate content). Soil and meteorological parameters were measured. Lettuce plant in both production system obtained higher content of K, B, Zn, or Fe compared to onion. The general order of the mineral content in both plants was K>Ca>Mg>Fe>Mn>B>Zn>Cu. Organically grown green onions from both growing seasons had higher contents of all macro and micro elements (except Cu) compared to the conventionally grown onions. Lettuce from CONV systems contained more Ca, Mg, Mn, Fe, Cu than that from ORG production. However, no significant difference in total phenols content (TPC) was observed between production system and growing season in lettuce. TPC in green onion was higher compared to lettuce. A similar trend was observed for total antioxidant capacity. The nitrate concentration was significantly higher in lettuce than in onion. Lettuce and onions grown in the fall-winter period contained higher nitrate levels compared to lettuce and onions grown in spring-summer. In conclusion, companion planting can result in an increase in productivity of vegetables per unit area, and can improve net income. At present however, we cannot conclusively demonstrate a higher health-promoting value of ORG lettuce and onion in comparison to lettuce and onion grown by CONV farming methods.