EFFECT OF CONFINED FERTILIZER RATES ON SALINITY OF ROOT MEDIUM AND TOMATO PLANT GROWTH IN A CLOSED SYSTEM

Objectives of the present study were to determine the least amount of Conserver-applied fertilizer needed to sustain the determinate tomato cv. Pik Red growth and fruit yield and to determine the salinity profiles in root growth medium over time when the least amount of fertilizer was Conserver-applied in the presence or absence of plants in the closed insulated pallet system (CIPS) root pouches. CIPS is a continuous subirrigation-capillary system with fertilizers applied in upward facing Conservers (5-cm sidewall and 3-cm diameter plastic vial) and placed within the peat:vermicultite (1:1, v/v) filled root pouches. Increasing the supply of nitrogen (1.3, 3.9, 5.1, 6.4 or 9 g N per plant) did not significantly affect vegetative growth or fruit yield. Mean marketable fruit yield was 10.2 kg m^-2 per 100 day cycle. Marketable tomato yield was 749 g g N^-1 supplied. When 15 g fertilizer (1.3 g N) was supplied, total dissolved solutes (TDS) in the pouched medium at 100 days after seedling emergence (DAE) were 733 in the upper layer, 1617 in the middle layer, and 188 mg L^-1 in the bottom layer. When salinity profiles with 15 g per plant fertilizer was monitored at different intervals, TDS from day 1 to day 100 in the middle layer of the pouched medium ranged from 100-129% of base level TDS content of 1100 mg L^-1. This indicates that plant available fertilizer did not become either excessive or depleted. TDS in the water reservoir peaked at 500 mg L^-1 on day 20 then decreased to approximately the base level (45 mg L^-1) by day 100. The 15 g per pouch fertilizer in upward-opening Conservers with 12.5 diffusion pathway provided adequate fertilizer to growing-fruiting tomato plants for 100 days, with little or no diffusion into the pallet water reservoir.