Development and evaluation of a computer-controlled fertigation system

A computer-controlled fertigation system was developed programmed and teste d for selectively injecting concentrated nutrients into a calculated water supply based on plant water demand Plant water demand was calculated with a new feed-forward evapotranspiration function developed for greenhouse crop s using canopy index factors. Both nutrient concentrations and nutrient rat io choices were possible for specific crops and microclimate conditions in multiple zones. After modifications, calibrations, and enhancements based o n developmental results, the fertigation system produced accurate nutrient concentrations within +/-10 mg/L of expected. The total run-time of the fer tigator; however was not stable, Especially for frequent changes in input d ata and for over-lapping of irrigation periods. Also, diaphragm injector pu mps that were assumed in the initial design to be positive displacement, be came unreliable as lodged particles changed line pressure and restricted th e flow.