GROWTH AND PHOSPHORUS UPTAKE OF TOMATO PLANTS AS AFFECTED BY PLANTING PATTERN, SOIL PHOSPHORUS STATUS, ROOT CHARACTERISTICS, AND CULTIVARS

Phosphorus uptake by a plant depends on the soil capacity to maintain a sufficient phosphorus concentration in solution as well on plant root ability to absorb the phosphorus existing in the soil. Plant species and cultivars have differential ability in P uptake, related to differences in plant growth pattern and root physiological and morphological characteristics. In a field study with optimum P level in soil solution, the relationship of planting pattern in single and twin row on the growth-yield response and P uptake by tomato plants during their developmental period was characterized. Plants in twin row pattern produced higher dry matter, fruit yield and P uptake than plants in single row. Differences in these parameters were also observed when tomato cultivars were compared. Variability in P uptake was in part, related to the differential growth pattern associated with planting design or cultivar. Experiments in laboratory and greenhouse led to the conclusion that phosphorus levels in the soil solution appeared to control P uptake and growth. In a silt loam soil 6.5 (mu)M P concentration in the soil solution was sufficient for near maximum growth of tomato seedlings independent of the cultivar tested. Experiments were conducted to determine the root morphological and physiological characteristics affecting P uptake by tomato cultivars growing under insufficient and sufficient P levels in soil and solution. Also tested was the accuracy of the Claassen and Barber (1976) mathematical model for describing the P uptake by plants growing in soil. The results showed differential P uptake among cultivars growing under sufficient and insufficient P soil conditions. Cultivars with larger root surface and more rapid root growth rate absorbed more P than cultivars with smaller ones. Maximum rate of P uptake (I(,MAX)) decreased with an increase in P supply to the plants. The Michaelis Menten constant (K(,M)) and solution P concentration where net P influx ceases (C(,min)) were not affected by either P supply or cultivar. Satisfactory agreement was obtained between observed and predicted P uptake in this research which indicates that the Claassen and Barber (1976) mathematical model is a useful tool for investigating P uptake by tomato plants growing in soil