Date of Award
Master of Science
Plant, Soil and Environmental Sciences
David L. Coffey
J.R. Brooker, J.G. Graveel
Cabbage (Brassica oleracea Group Capitata), tomatoes (Lycopersicon esculentum), and broccoli (Brassica oleracea Group Italica) were grown at the University of Tennessee Plant Science Field Laboratory, Knoxville, TN in 1988 and 1989. Treatments were administered to these crops to compare the effect of three N levels (136, 270, and 404 kg ha-1), applied preplant or in intervals via drip irrigation, in the presence or absence of black plastic mulch to evaluate the performance of these vegetable crops in a sequential cropping system.
During both years of study, nitrogen from a urea-NH4NO3 mixture was soil incorporated into half of the treatment plots prior to the first planting. The N mixture was applied to the other half of the treatments throughout the growing season in sequential increments via trickle irrigation. Likewise, half of the plots were covered with black plastic mulch, and the other half were left uncovered. Crop yields by grade, along with tissue samples, were recorded from multiple harvests. Soil samples were collected throughout the growing season and leaf tissue samples were taken at harvest. Estimated returns were determined from yields, wholesale prices and budgeted production expenses in order to compare the economic performance of each treatment.
During both years of study, crops receiving the medium and high N levels generally produced higher yields than those receiving the low N level. No consistent differences in crop yields were recorded between the medium and high N level treatments. Nitrate concentrations detected in the soils corresponded to the levels applied in the fertilizer and tended to decline over the season at about equal rates.
Treatments receiving preplant N tended to produce higher yields of the first crop (cabbage), while yields from the second crop (tomatoes) were generally no different between preplant and sequential N treatments. Sequentially cropped broccoli produced higher yields than preplant broccoli in 1989. Despite higher soil NO3- concentrations in sequential treatments, the rate of seasonal NO3- decline in either the sequential or preplant treatments was not significantly different.
Mulched treatments tended to produce higher yields over both years. Nitrate concentrations were generally higher for mulched treatments than for nonmulched treatments and the rate of decline for the soil NO3- concentrations was not significantly different between mulched and nonmulched plots.
The economic analysis revealed that plants from plots receiving preplant N, mulch, and the two highest N levels resulted in the highest net returns. Analysis of treatment components indicates that returns might be improved by combining preplant N application with sequential fertigation, thus potentially benefiting both early and late crops.
Results of this study suggest that the environment of East Tennessee may not be compatible for profitable sequential production of these three vegetables. Double cropping of a cool season crop followed by a high value crop such as tomato appears potentially more profitable for this region.
Burnette, Richard Ronald, "Influence of three nitrogen levels, fertigation and black plastic mulch on sequentially grown vegetable crops. " Master's Thesis, University of Tennessee, 1990.