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 damage, tomato plants from 20 subplots were sampled on each of 17 commercial farms representing a wide variety of management practices. Nitrogen level was measured as total Kjeldahl N in the shoot and in the leaflets. Characteristic damage by thrips, leafminers, flea beetles, and strip-feeding insects (primarily Lepidoptera) were recorded as percent of leaflets damaged. Tissue N varied widely among plants both within fields and among sampled farms which included conventional and organic management schemes. However, damage to tomato foliage did not increase with increased N content of the crop. Instead, a weak negative correlation between tissue N and herbivory was detected. Compared with tissue N, transplant date was a much better predictor of herbivory on the tomato crop.