Conventional, low-input and organic farming systems compared

Abstract

In field experiments at Davis, California, in 1989-92, conventional, low-input and organic management of processing tomatoes, safflower, maize and wheat followed by double-cropped dry beans [ Phaseolus vulgaris], were compared. However, due to inadequate alternatives for weed management and N fertilizer application to wheat for the low-input and organic treatments, a mixture of oats and vetch was substituted for wheat in those two systems, following maize and before double-cropped beans. In addition to the 5 cash crops, the low-input and organic systems utilized N-fixing legume cover crops during the winter-spring season preceding tomatoes, safflower and maize. Tomato yields were significantly lower with the low input system in 1991 and in the organic system in 1989-91 compared with the conventional system, and fruit damage by insects was higher. The lower yields were mainly due to inadequate N supply from the preceding vetch cover crop. The performance of maize was more consistent between treatments than tomatoes, with significant yield differences observed only in 1991 (favouring the conventional system) and 1992 (favouring the low-input system). In 1991 the lower maize yields in the low-input and organic systems were due to inadequate incorporation of the vetch cover crop. In 1992, the conventionally managed maize was grown using a 60-inch bed system (2 rows per bed) rather than in the single-row 30-inch beds used for organic and low-input maize, and this may have adversely affected the moisture available to the roots of the conventionally managed maize. In 1992, the lower yield in the organic than in the low-input maize was due mainly to weed competition for N, light and water. The yields of safflower were similar in all systems in each year except 1989 when it was higher in the conventionally managed crop. However, in 1992 the organic and low-input safflower performed very poorly and had to be disked under and replanted with a catch crop of dry beans. Beans performed slightly better under the organic and low-input systems than the conventional system in some years, but usually there was no significant difference in yields between systems. Wheat performed in the conventional 2-year and 4-year rotations as expected, and yields were near to local averages. It is concluded that a rotation of processing tomatoes, safflower, maize and wheat or winter legume, followed by double-cropped dry beans, is a good rotation to make comparisons between management systems. Proper management of late winter/early spring cover crops is highlighted as a critical factor in the success of organic and low-input systems.