Development and evaluation of a computer-controlled fertigation system

A computer-controlled fertigation system was developed programmed and tested 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 crops using canopy index factors. Both nutrient concentrations and nutrient ratio choices were possible for specific crops and microclimate conditions in multiple zones. After modifications, calibrations, and enhancements based on developmental results, the fertigation system produced accurate nutrient concentrations within +/-10 mg/L of expected. The total run-time of the fertigator; however was not stable, Especially for frequent changes in input data and for over-lapping of irrigation periods. Also, diaphragm injector pumps that were assumed in the initial design to be positive displacement, became unreliable as lodged particles changed line pressure and restricted the flow.