DEPENDANCE OF WATER REQUIREMENTS OF LYCOPERSICUM ESCULENTUM PLANTED IN ROCKWOOL ON INCOMING SOLAR RADIATION
The trial showed a high correlation between the water requirement figure suggested by Guernsey Horticultural Research Station viz 284 ml per 100 g cal per cm2 absorbed, and the actual figures 273 and 291 ml obtained in this trial for growing in rockwool.
Percentage utilization was found to be higher than that suggested by Salter (1977). It increased to 100% in the midst of summer, when plant height exceded 300 cm. At this stage average daily solarimeter readings were 678.9 g cal cm2 -1 compared to the highest reading of 447.1 registered in Guernsey in 1978. Hotter climates must adapt a higher utilization figure as suggested. Water applications must also be adapted to daily solar readings, that is at least once every 2 weeks, to ensure slight over irrigation.
Weekly monitoring of pH and ECe was necessary. pH was adjusted to 6.5 (H2O) and the conductivity kept between 1.8–2.5 mS (milli-siemens). High pH was lowered by adding phosphoric acid, high conductivity by lowering the complete nutrient feed concentration by 50% and by allowing slight over irrigation until the desired conductivity reading was obtained.
Growth in the top trusses (8th and higher) were more vigorous than for crops planted in soil. Quality remained excellent throughout and blossom-end rot was negligible due to the even moisture regime created by this irrigation system. For greenhouse crops, the use of a solar integrator for estimating water requirements, can be recommended.