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Conservation of water and nutrients in greenhouses through plant and climate based irrigation control Shelford, Tim

Abstract

The vegetable greenhouse industry in British Columbia is rapidly expanding to meet the world's demands for high quality fresh produce. This expansion puts environmental pressure on the region in the demand for fresh water, and the spread of excess nutrient fertilizer into ground and surface water. To help alleviate the problem, efficient irrigation systems which accurately match crop requirements, need to be developed. To establish a more precise algorithm, new and conventional sensors were examined for their ability to predict and/or measure water use. The sensors that showed the most promise were further developed into two new control algorithms. The first control algorithm utilized light, vapor pressure deficit, leaf, and air temperature, in a statistically developed model to estimate water use. The second control algorithm utilized an off-the-shelf electronic balance to directly measure water use. Water use was measured by summing the change in weight over short time-periods, rather than by examining the absolute weight of the media. Experiments were then conducted to compare these two new algorithms to the current industry-standard light-based approach in terms of irrigation consistency and frequency. It was found that the scale-based approach produced the most consistent amount of leachate indicating that it was most able to supply water as the crop needed it. The equation-based approaches performance was similar to the traditional light-based approach. In terms of frequency the equation and scale-based approach did not always trigger an irrigation every hour indicating that setpoints would have to be adjusted. No algorithm allowed the plants to go for long periods without watering. The scale-based approach has the added benefit of an ability to trigger irrigations at night. All algorithms seemed to work effectively; the water usage of the plants on all three systems was statistically similar. Because the new algorithms are based on different principles, their associated advantages and disadvantages are quite different. To improve irrigation efficiency, a control strategy encompassing all of the techniques evaluated is recommended.

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