EFFECTS OF SOIL-MANAGEMENT ON CROP NITROGEN AND INSECT DAMAGE IN ORGANIC VS CONVENTIONAL TOMATO FIELDS

To detect if different soil management practices had an impact on the crop in terms of tissue nitrogen, and thereby influenced herbivore dam age, tomato plants from 20 subplots were sampled on each of 17 commerc ial farms representing a wide variety of management practices. Nitroge n level was measured as total Kjeldahl N in the shoot and in the leafl ets. Characteristic damage by thrips, leafminers, flea beetles, and st rip-feeding insects (primarily Lepidoptera) were recorded as percent o f leaflets damaged. Tissue N varied widely among plants both within fi elds and among sampled farms which included conventional and organic m anagement schemes. However, damage to tomato foliage did not increase with increased N content of the crop. Instead, a weak negative correla tion between tissue N and herbivory was detected. Compared with tissue N, transplant date was a much better predictor of herbivory on the to mato crop.