Here are some of the key findings to have come out of the WET Centre:
Irrigation run-off in strawberry
With commercial growers typically irrigating their substrate-grown strawberry crops to 15-25% run-off, some early work at the Centre demonstrated how growers could reduce their total water use each season by up to 33%, whilst maintaining the same yields and producing equal or higher quality berries.
Combined with precision irrigation approaches, rainwater harvesting and re-use resulted in 90% water self-sufficiency in 2018, despite the very dry June and July in that year.
The Centre has since compared reducing the level of run-off to 5% and 10%, without seeing any significant difference in yields between these levels, or any compromise in fruit quality.
Choice of bag colour in strawberry
Other early work demonstrated a 5% yield increase from white Cocogreen bags in comparison to black bags, and the team are currently investigating the causes of this.
Powdery mildew risk prediction model
The Centre was also used to demonstrate how the use of the powdery mildew risk prediction model, developed originally by NIAB plant pathologists at East Malling, could lead to a significant reduction in overall fungicide use on an everbearer strawberry variety.
Yields and light interception
Comparisons between the commercial and advanced areas in recent years have demonstrated significant differences in fruit yield using the everbearer Malling™ Champion. In 2020, Class 1 yield was found to be 5% higher in the commercial area, perhaps a result of the higher levels of shading in the advanced area, lowering the photosynthetically active radiation (PAR) at the canopy by 3-7%.
We think that the increased steelwork associated with the roof vents in the advanced tunnels reduces light levels, and this effect is probably exacerbated by the relatively large rainwater collection gutters. However, the more flexible venting control resulted in a 1 °C reduction in temperature in June and July and up to 7 °C in August 2020, and so could have significant benefits in hotter years.
Seasonal yield differences and crop row position
Yield differences have also been recorded between seasons, with Class 1 yields of MallingTM Champion in 2021 being 22% lower than those recorded in 2020. The scientists measure the amount of accumulated photosynthetically active radiation (PAR) each season and the lower yields in 2021 could be attributed to lower light levels.
The differing yields between the commercial and advanced areas, coupled with differing light levels, prompted the science team to start investigating whether differences in PAR were responsible for the variability in yields between individual rows in the advanced area.
Our research so far has shown a strong correlation between light availability (PAR) and Class 1 yields, with the latter differing by as much as 12% in rows just two metres apart within one tunnel bay. This equates to a yield differential of over 11 tonnes per hectare.
There are six rows within each tunnel bay and further investigation revealed that the middle rows (2, 3, 4 and 5) were producing higher yields than the outer rows (1 and 6), with the highest yield being produced in Row 4.
Using an array of precision environmental sensors manufactured by Delta-T Devices, a correlation was found between the highest yields per row and the amount of light reaching the canopy, so the team set out to compare Row 4 with Rows 1 and 6. Row 4 was found to receive 2 hours more PAR per day than Row 1, but strangely, despite both being outside “leg” rows, Row 1 produced higher yields than Row 6. Why?
Like other plants, strawberry has a light saturation point, when photosynthesis plateaus, even with further increases in light levels. We discovered that the efficiency of photosynthesis is highest in Row 4 and also higher in the morning than in the afternoon. We are now testing if the higher-than-expected Class 1 yields in Row 1 could result from the peak in early morning PAR coinciding with the peak in photosynthetic efficiency.
The results will inform our next steps to optimise the available light to each row at key times during the day using different techniques and technologies.
We have also tested the use of white reflective mulches in the leg rows to increase light levels at the height of the crop canopy. We recorded higher light levels above the ground level and up to a point below the crop canopy, but light levels were not increased at the height of the crop canopy.
Ultra violet-blocking film
Work in 2020 also investigated the effects of a UV-blocking film (originally developed as a non-chemical way of reducing pest numbers), on leaf physiology, Class 1 yields and berry quality.
When compared to Malling™ Champion plants cropping under a clear film, Class 1 yields were reduced by 15% under the UV-blocking film; this was due to a reduction in fruit number as individual berry fresh weight was increased slightly, presumably due to the slightly cooler (1 °C) air temperatures under the UV-blocking film.
Again, the loss of yield was strongly correlated with a reduction in the cumulated PAR reaching the canopy. Leaf physiology was also changed, with stomatal conductance and photosynthesis being lowered, and while the former response reduced plant transpirational water loss, the latter resulted in a 0.5% fall in the average berry soluble solids content (%BRIX) over the season.
The knowledge gained by our team on zonal phytoclimates within the tunnel also has enabled NIAB scientists at East Malling to work with one of our funders, Berry Gardens, and colleagues at the University of Reading in an IUK project called ‘BerryPredictor’ to improve harvest forecasts, yield predictions and crop productivity, through the development of thermal time and PAR models.
Nitrogen demand in raspberry
NIAB has developed a nitrogen demand model for the primocane variety MallingTM Bella, which was tested and validated in 2022 by NIAB scientist Carlota Gonzalez-Noguer. The model uses temperatures and PAR to predict dry matter production and therefore nitrogen demand, allowing the production manager to use a feed recipe to match the demand, which could potentially reduce the volumes of nitrogen applied.
Overuse of nitrogen can produce nitrous oxide which is significantly more harmful than carbon dioxide to the environment, so it is important not to apply excessive nitrogen. The nitrogen recipe is updated every two weeks using outputs from the model.
Using MallingTM Bella in 2022, we compared the use of a standard grower feed recipe with a reduced nitrogen recipe which followed the nitrogen demand model. This led to a reduction of more than 50% of the nitrogen used in the standard recipe, although by the end of the season, there was a slight reduction in marketable yield.
The original model had been developed using different glasshouse-grown crops overseas and the generic crop coefficients embedded in the model were not found to be accurate enough for raspberry production in the UK, so NIAB is developing specific crop coefficients for raspberry and are planning to repeat the exercise in 2023 for MallingTM Bella.