Simulation of Growth, Fresh Weight, and Size of Individual Tomato Fruits and Total Production Under Water and Nitrogen Limitations

Fruit fresh weight size distribution, water content, and concentration of carbon compounds determine tomato production value for fresh market purposes.  Tomato (Solanum lycopersicum) requires optimum water and nitrogen fertilization to obtain high yield and fruit quality. Crop growth models may be valuable tools to understand the impact of water and N fertilization management on tomato production. The CROPGRO-Tomato model accounts for water deficit effects on processes through two reducing factors called SWFAC (for effects on processes such as photosynthesis) and TURFAC (for effects of water deficit on expansive processes). A similar approach is used to compute daily N stress based on N supply to demand ratio.  Fruit fresh weight and size are presently computed in the model based on simulated dry weight per fruit, a dry matter concentration that varies as a function of fruit physiological age, and a diameter function dependent on fresh weight per fruit.  But there are insufficient connections of CROPGRO’s simulation of water or N stresses to dry matter concentration, timing, and size (fresh weight) growth of individual fruits.  In this work the model was modified to use SWFAC or TURFAC as signals to affect dry matter concentration of fruits, and to alter fresh mass and size.  The signals were also used to affect the timing of fruit growth under stress. Water deficit was allowed to increase the lag of the start of the fruit growth period for later-set fruits, and also used to accelerate maturation resulting in potentially shorter total fruit growth duration.  Thus, these factors were strategically connected to fruit addition and dry matter growth rate of individual fruits and fruit thermal time accumulators.  The CROPGRO-Tomato model, with these modifications, was then evaluated as a tool for predicting the dynamic growth of individual fruit cohorts (size and fresh weight) and total fruit yield for a crop grown under water and N limitations.  Effects of reducing factors SWFAC, TURFAC and NSTRES in the model were suitable to reproduce reduced plant growth and total fruit growth as well as individual fruit size and fresh weight under water and N deficits.  The result was an improved ability of the model to mimic the dry weight and fresh weight growth and dry matter concentration behavior of individual fruits under stress.