Doctoral Dissertations

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Plant, Soil and Environmental Sciences

Major Professor

David L. Coffey

Committee Members

Charles A. Mullins, Glen V. Wilson, C. Roland Mote, Fred D. Tompkins


Yield and plant characteristics of tomatoes were evaluated under nitrogen fertilization rates of 0, 112, or 336 kg ha-1 in 1990 and 1991; and two tillage systems, no tillage (NT) and conventional tillage (CT), in 1989, 1990, and 1991. In 1989, tillage treatments had no effect on yield of tomatoes (Lycopersicon esculentum Mill.) . In 1990, nitrogen fertilization rate had little influence on yield or plant characteristics. When differences occurred, treatments receiving 112 or 336 kg ha-1 nitrogen fertilization were significantly different from treatments receiving 0 kg ha-1, but were not different from one another. Although total and marketable yields of NT tillage tomatoes were not significantly different from CT tomatoes, the NT tomatoes produced considerably more fruit and appeared to be more vigorous. In 1991, the addition of nitrogen fertilization increased the average fruit weight of tomatoes, while few differences were observed in plant characteristics. Tomatoes grown under the CT system produced significantly higher yields and much more vigorous plants than tomatoes grown under the NT system, the opposite of what was observed in 1990.

Production of NT tomatoes appears feasible into small grain stubble; however, long term continuous NT is not recommended. A nitrogen fertilization rate of 112 kg ha-1 appeared to be adequate for production of NT tomatoes on the soils of the Cumberland Plateau of Tennessee.

Conservation tillage systems have been shown to reduce erosion. However, results of runoff and infiltration characteristics under tillage systems are not as conclusive. Simulated rainfall events were conducted to evaluate runoff and factors influencing runoff on a Lonewood silt loam (Typic Hapludult) soil with a 6% slope. The antecedent soil water content was observed to be unaffected by tillage treatment. The NT treatment produced considerably more cover in the form of crop residue and plant biomass than did the CT treatment. This additional cover increased the interception of raindrops, thus reducing clay dispersion on the surface. The cover also decreased surface water movement, allowed more time for infiltration, as well as reduced erosion. In general, less runoff occurred from NT plots than from CT plots due to increased infiltration. When runoff did occur, sediment concentrations in runoff were considerably greater from CT plots than from NT plots. Total sediment losses were often an order of magnitude greater from CT plots than from NT plots.

Conservation tillage systems have been found to decrease the quantity of surface runoff. However, the quality of surface runoff from conservation tillage systems is unknown. Water samples collected from individual runoff events were evaluated for metribuzin, NO3-N, PO4-P, and potassium concentrations. When runoff does occur, runoff from NT generally carried higher concentrations of metribuzin, NO3-N, PO4-P, and potassium than runoff from CT, especially in the first simulated rainfall event after agrichemical application. Concentrations were generally higher in runoff from CT later in the growing season due to the greater zone of mixing in CT soils. Concentrations of these agrichemicals were observed to decrease during simulated rainfall events. Total losses of metribuzin, NO3-N, PO4-P, and potassium in runoff were similar for NT and CT in the first two years of this study. During the third year; however, greater losses were observed from the CT plots than from the NT plots due to the significantly greater runoff volumes from CT plots.

Conservation tillage systems reduce erosion and may reduce runoff. Therefore, increased infiltration is often observed with conservation tillage systems. Pan lysimeters were installed to evaluate the effect of tillage treatment on water and agrichemical movement through the soil profile. Greater movement of water, NO3-N, and metribuzin was observed under NT soil than under CT soil. Increased cover of the NT treatment slowed water movement, decreasing runoff and increasing infiltration. The infiltrating water probably entered the undisturbed macropores of the NT systems allowing faster movement of water and less reactivity of fertilizer and pesticides with the soil. This may result in higher resident concentrations in CT soils than in NT soils or visa versa depending upon the hydrological conditions during and following chemical applications. Due to the channelization of the subsurface soil, the small pans (12.7 cm X 30.5 cm) collected flow from an area considerably larger than their size. The two larger pans (45.7 cm X 35.6 cm or 61 cm X 76.2 cm) appeared to produce more accurate flow measurements. Soil water content was observed to be slightly higher under NT soil in the top 15 cm and below 60 cm. However, soil water contents of CT soil was as great or greater between 15 and 60 cm. Residual NO3-N and metribuzin concentrations were generally higher (at least in the top 15 cm) in CT soil than in NT soil. These differences were most likely a result of the water moving through the macropores and by-passing soil matrix pores in the NT soils, while water movement would have been more evenly distributed through CT soils.

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