Doctoral Dissertations


Senshan Yang

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Plant, Soil and Environmental Sciences

Major Professor

David Coffey

Committee Members

John Foss, Fred Allen, Mary Leitnaker


In the prediction of crop development, the procedures to calculate the base temperature in heat unit systems are tedious and deficient in theoretical bases. Little information is available on effects of temperature regimes or temporal temperature distributions on crop development. The objectives of this dissertation were: 1) to develop new procedures for calculating the base temperature in heat unit systems for any crop, 2) to study the effects of temperature regimes for tomato seedlings in the preceding developmental stage on the succeeding developmental stage, 3) to study effects of temperature regimes for tomato transplants before transplanting on the subsequent yield in the field. Tomatoes were planted on different dates in the greenhouse under three temperature levels (average temperatures for each developmental phase were at 17-19 C, 21-23 C, 24-26 C in 1991 and 18-20 C, 20-22 C, and 22-24 C in 1992) and rotated among three temperature levels in such a way that all transplants received approximately the same temperature accumulation at the time of transplanting. Seedling emergence and the time of appearance of the first to sixth leaf were defined as developmental stages 1-6. Seedling emergence to the first and second, the first and second to the third, the third to the fourth, the fourth to the fifth, and fifth to the six leaf appearance were defined as developmental phases 1-6. Temperature and solar radiation were measured. Average temperatures and the number of days for each developmental stage and phase were recorded. Transplant height, stem diameter, leaf length, and weight were measured. When transplants reached the sixth developmental stage, they were transplanted to the field of the University of Tennessee Plant Field Science Laboratory at Knoxville. Tomato fruits were divided into six groups according to fruit size based on the Los Angeles system. Fruit yield and fruit number were measured in each of six groups. The results of this research showed that the four proposed formulas for calculating the base temperature in heat unit systems were superior to the previous procedures in terms of simplicity and mathematical bases. Temperature regimes experienced in the preceding developmental stage affected the succeeding developmental stages. The prediction of seedling development in the greenhouse considering effects of the preceding temperature regimes on the succeeding developmental stages was more accurate than that without considering such effects. Tomato seedling development was controlled by both temperature accumulations and the way temperature accumulations were achieved. Fruit yield and fruit number were significantly affected by temperature regimes experienced by seedlings in the greenhouse before transplanting. A sharp change in temperature regimes either from low to high or from high to low before the fourth leaf appearance appeared to have negative effects on fruit yield in the field. Temperature in the ranges of 18-21 C for seedling emergence and 19-22 C for the first and second leaf appearance resulted in the best quality of transplants.

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