Sweet and water efficient strawberries – Niab EMR and Delta-T Devices collaborate at WET centre

Smart irrigation resulted in a 7% increase in the yield of strawberries for one large commercial grower, following the trial of a precision irrigation system designed by Niab EMR with equipment from Delta-T Devices and Netafim.

Delta-T Devices is an industry partner of the Water Efficient Technology Centre (WET) based at Niab EMR in Kent supplying sensors and data loggers for both research and commercial projects. Delta-T first appeared alongside Niab at the Innovation Hub in 2016 and became involved in WET the following year.
Yields of strawberries reached 72t/ha at the WET centre in 2020, double that of the industry average of 45 t/ha with a significant reduction in water use.
The initial trials were in small polytunnels, but WET Centre enables industry scale conditions with commercial farm polytunnels and tabletop  configuration, ie where the strawberries are grown on substrate on raised platforms.
The research is focussed on the use of automated irrigation control systems, with as little human intervention as possible.

Smart irrigation

Minimising water wastage is of huge importance given its increasing scarcity. In future, it is anticipated that intensive horticultural growing systems will become increasingly based in urban locations, where very strict water waste prevention protocols (and legislation) are likely to be the norm.
Delta-T’s programmable GP2 Data Logger allows different control algorithms to be set for separate experimental irrigation regimes, and then for researchers to measure and compare the outcome of each approach. These experiments enabled the  key plant stress points to be accurately determined, and the optimum moisture content levels in the growing substrate to be determine at each stage of the life cycle of the strawberry plant.
The aim was to ascertain the minimum amounts of water needed to achieve the desired level of strawberry plant quality and yield.

Colour of growbags impacts growth

Further research has shown even the colour of the plastic on coir growbags can have a big impact on crop growth.
The WET Centre team investigated the correlation between plant water use and vapour pressure deficit (VPD) – using the Delta-T Devices SM150T Soil Moisture and Temperature Sensor and RHT2 Relative Humidity and Air Temperature Sensor.
The outputs of this research have been fascinating – showing that black grow bags absorb sufficient additional solar radiation to create warmer root zones (especially earlier in the growing season), whilst white bags reflect more light up into the canopy of the growing crop (see image below for effects on substrate temperature).
Timing of plant growth and fruiting can therefore be manipulated by something as simple as selecting a specific grow bag colour.

Impact of sheeting on photosynthesis

In addition the sheeting, frames and particularly the row position within the polytunnel structures can affect light availability to plants and thus growth and Class 1 yield. Researchers measured Photosynthetically Active Radiation (PAR) levels within polytunnels using the Delta-T Devices QS5 PAR Sensor. PAR corresponds to the spectral range of radiation that plants require for growth and photosynthesis, and levels seen in 2020 were well above the 10 year average.
To explore the effect of this phenomena the team used the GP2 Data Logger and Controller (connected to QS5 PAR sensors) to automatically open and close venting in the roof of the polytunnels – based on the meeting of pre-set threshold requirements and to adjust the irrigation accordingly.
This system was designed to optimise the phytoclimate as the sun passed overhead and leverage the unusually sunny weather of 2020 to maximise yield to levels otherwise not achievable.