Effect of vetch and broccoli in four-year rotation of organic cucurbitaceous and solanaceous vegetables under Mediterranean conditions

Summary

Vegetables are among the main ingredients of the Mediterranean cuisine and thus enlarging organic local markets increase their demand for a diversity of vegetables. Long-term rotations based mainly on vegetables are rather rare in the Mediterranean countries. A four year experiment was carried out between 2006 and 2010 at Ege University Department of Horticulture in cooperation with CIHEAM Mediterranean Institute of Bari. And two different pre-crops, broccoli and vetch were tested under an organic management system as compared to fallow during the autumn-winter period. The summer main crops were rotated between solanaceous and cucurbitaceous vegetables as tomato (2007), zucchini (2008) pepper (2009) and eggplant (2010). The experiment aimed at recommending sustainable rotation plans for organic vegetable growers in western Turkey. Broccoli represented the farmers’ choice as a winter vegetable prior to the summer crop. Vetch (incorporated) was selected as leguminous green manure well adapted to the regional conditions. All the management including disease and pests were handled according to the organic regulations valid in Turkey and the EU. Soil fertility was maintained by incorporation of crop residues at the end of both cycles and addition of organic-certified commercial compost and compost tea during the main cycle as a standard amendment. Effect of pre crops and main crops on soil organic matter and, primary nutrients, and weed abundance and yield were assessed for each main crop cycle. Soil organic matter values showed significant differences before and after the winter or summer cycle and fluctuated between 0.7 and 3.0 %. Soil N, P and K contents were kept at rich or sufficient levels for four years. The variation in soil organic matter, N, P and K displayed similar trends during in the tested precrop and fallow control plots during the four year period. The broccoli plots had lower soil potassium levels compared to the other two. Weed diversity varied according to the annual climatic conditions however broccoli exhibited a marked weed suppressing effect mainly due to shading and allelopathy.