A novel dielectric tensiometer enabling precision PID-based irrigation control of polytunnel-grown strawberries in coir

A - Papers appearing in refereed journals

Goodchild, M. S., Jenkins, M. D., Whalley, W. R. and Watts, C. W. 2018. A novel dielectric tensiometer enabling precision PID-based irrigation control of polytunnel-grown strawberries in coir. Biosystems Engineering. 165 (January), pp. 70-76. https://doi.org/10.1016/j.biosystemseng.2017.10.018

AuthorsGoodchild, M. S., Jenkins, M. D., Whalley, W. R. and Watts, C. W.

The benefits of closed-loop irrigation control have been demonstrated in grower trials which show the potential for improved crop yields and resource usage. Managing water use, by controlling irrigation in response to soil or substrate moisture changes, to meet crop water demands is a popular approach but requires substrate specific moisture sensor calibrations and knowledge of the moisture levels that result in water deficit or overwatering. The use of water tension sensors removes the need for substrate specific calibration and enables a more direct relationship with hydraulic conductivity. In this paper, we present a novel dielectric tensiometer that has been designed specifically for use in soil-free substrates such as coir, peat and Rockwool with a water tension measurement range of 0.7 kPa to 2.5 kPa. This new sensor design has also been integrated with a precision PID-based (drip) irrigation controller in a small-scale coir substrate strawberry growing trial: 32 strawberry plants in 4 coir growbags under a polytunnel. The data illustrates that excellent regulation of water tension in coir can be achieved which delivers robust and
precise irrigation control - matching water delivery to the demands of the plants. During a 30-day growing period vapour pressure deficit (VPD) and daily water use data was collected and the irrigation controller set to maintain coir water tension at the following levels: 0.90 kPa, 0.95 kPa and 1 kPa for at least 7 consecutive days at each level. For each setpoint the coir water tension was maintained by the irrigation controller to within ±0.05 kPa. Meanwhile the polytunnel VPD varied diurnally from 0 to a maximum of 5 kPa over the trial period. Furthermore, the combination of the dielectric tensiometer and the method of PID-based irrigation control resulted in a linear relationship between daily average VPD and daily water use over 10 days during the cropping period.

KeywordsTensiometer; Irrigation control; VPD; Soil-free substrate
Year of Publication2018
JournalBiosystems Engineering
Journal citation165 (January), pp. 70-76
Digital Object Identifier (DOI)https://doi.org/10.1016/j.biosystemseng.2017.10.018
Open accessPublished as green open access
FunderBiotechnology and Biological Sciences Research Council
Funder project or codeDevelopment of a novel tensiomdter to deliver water savings in horticulture and agriculture
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Copyright license
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Accepted author manuscript
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Output statusPublished
Publication dates
Online06 Dec 2017
Publication process dates
Accepted31 Oct 2017
PublisherAcademic Press Inc Elsevier Science

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