ISHS Acta Horticulturae 491: International Symposium Greenhouse Management for Better Yield & Quality in Mild Winter Climates
TESTING A TENSION OPERATED IRRIGATION VALVE |
| Author: | H. Baugerød |
| Keywords: | Soil tension, cucumber |
| Abstract:
All present irrigation systems fail to fulfil the ultimate goal of supplying each plant with the exact amount of water needed at all times and keeping the soil moisture at the optimum level. Computer models of the water demand used for irrigation control have to take into account climatic conditions and the type and size of plants grown, and when tensiometers are used the problem of representativeness of the sensor site arises. In all cases allowances have to be made for variations in emitter discharge and demand due to local climatic variations in the greenhouse by overwatering some plants. A newly developed drip irrigation valve (Norwegian Patent No 175921) which incorporates a tensiometer, is able to overcome all these shortcomings. One valve can deliver up to ten litres per hour, and can be adjusted to keep soil moisture tension within narrow limits (±5 hPa) in the range of 0 – 120 hPa. The valve responds in a few minutes to changes in soil moisture tension and the valve output increases by 20 per cent per hPa increase in soil water tension over a range of 25 hPa. The increase of water head from 65 to 130 centimeters more than doubles valve output. In a greenhouse experiment with cucumbers grown in peat in ten litres containers and watered individually with the valve the plants received up to six litres per day. The valve output closely followed the level of global radiation outside the greenhouse. | |
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