Debate continues over the relative merits of organic and conventional growing systems. In the research described here, two cultivars of carrot, five of cauliflower and five of bulb onions were grown either in an organic system or a conventional one. In the organic system, weeds were controlled by mechanical means and pests were often controlled by insect-proof nets over the crop. With conventional crops, chemical control measures could be used for pests and weeds.
The two systems were compared in adjacent fields over at least three years. The relative performances of the various cultivars were similar in both systems. Yields of cauliflower and onion were higher under the conventional system but carrot yields were the same in both. However, the number of marketable cauliflower heads was not affected by the growing system and the organically grown onions had been sown later to make weed management easier.
The main quality defect in conventionally grown cauliflowers was "hollow stem" while it was slug damage in the organically grown crop. Conventionally grown carrots suffered more damage from carrot root fly while organically grown carrots had more morphological defects. Conventionally grown onions suffered more from diseases.
Yields and the Extent and Causes of Damage in Cauliflower, Bulb Onion, and Carrot Grown Under Organic or Conventional Regimes by Dresboll, Bjorn and Thorup-Kristensen (2008). Journal of Horticultural Science & Biotechnology 83 (6): 770-776. The authors' abstract of their manuscript can be seen in full at www.jhortscib.com.