Optimizing Strawberry Yield in Controlled Environmental Agriculture – Environmental parameters

Optimizing the growing environment is crucial to getting the best possible yield. It is not enough to just purchase a high-end lighting solution if other parameters in the growth chambers aren’t met. Optimal humidity, CO2 levels, temperature, lighting, fertigation, disease, and possible pest control all need to be considered and monitored. 

Optimal humidity 

For strawberries (Fragaria x ananassa) the optimal relative humidity is between 65-75%, if it goes over, strawberries are in a great risk of fungal disease like Botrytis fruit rot (Gray mould) caused by Botrytis cinerea fungus. This rot can be spotted as a fuzzy grey coat in the blossoms or ripe berries. Optimal humidity affects also the rate of flowering, obtaining the ideal range can ensure lots of flowers and greater yield. You can observe the leaves of the plants to know if the humidity is optimal, crispy leaves and humidity is too low, or wilting leaves and humidity is too high. Of course, other factors can also affect leaves, such as nutrient deficiencies, light burns, or insufficient irrigation. Optimal humidity ensures the soil stays moist, but that roots will not suffocate. Strawberries need fluffy soil and room for roots to breathe, drip irrigation is the best way to go and it’s best to let the topsoil dry between watering. Misting strawberries is not advised, especially in a closed environment, because it can lead to disease development. 

Equip your growth chamber with an adequate dehumidifier, good ventilation, and sensors to measure and monitor the humidity levels. 

CO2 

It is essential for plants to have CO2, and in a closed environment, it’s even more important to keep optimal levels for photosynthesis to happen. This is when a plant converts the energy from light to sugar, during photosynthesis plants absorb CO2 and then release oxygen. Elevated levels of CO2 increase biomass production and photosynthesis rate. CO2 levels in the air are measured as parts per million (ppm), and for strawberries, the optimal levels are between 650-950 ppm.  

The yield can be considerably enhanced considerably with optimal elevated CO2 and LED light combinations.

Temperature 

Strawberries can be sensitive to temperature and require different temperatures in different growth stages, at different times of day, and with different cultivars. Although good fruit yield is a sum of all the environmental components, temperature contributes greatly to the overall quality and traits of the crop. 

Temperature fluctuations can increase the sugar content in fruits during the light and dark periods. Rising temperatures can negatively affect the sugar content and photosynthetic rate, but the temperature can be kept optimal in a controlled environment in this crucial stage. The best berry sugar content can be obtained with day and night temperatures such as 25/12°C and will be decreased at high day and night temperatures such as 30/22°C. Fruit and root development favors lower day temperatures of 18°C. A decrease in temperature can initiate flower production at an optimal temperature of 15–18°C. Still, too low a temperature during embryo development can harm fruit size, weight, and shape. Some cultivars tolerate higher temperatures better than others. 

Depending on the cultivar, optimal temperatures for strawberries vary between 18 °C and 25 °C, and night temperatures range between 12 °C and 18 °C.  

 Fertilizers 

The most important mineral fertilizers for any plant are nitrogen (N), phosphorus (P), and potassium (K), with N being the most important one as it is involved in a wide range of functions in the plant. Too low levels of N can decrease the whole yield and cause stunted growth. Too much N can inhibit root growth and flowering. K is extremely important for fruit production and overall plant growth. The K amount can almost double that of N, and optimal EC ranges around 1 ms/cm, but this varies between growth stages and varieties. The preferred soil pH for strawberries varies between 5.3 and 6.5. Too high a pH can limit the nutrient uptake of the plant. Finding the optimal nutrient cocktail depends on the cultivar and whether you have day-neutral, June-bearing, or everbearing plants. 

Disease and pest control 

As vertical farming happens in a closed environment, controlling possible pests and diseases is easier. This way, we can avoid soilborne and airborne diseases in outdoor scenarios. Depending on where the seedlings are coming, buying them from seedling producer or propagating through tissue culture, the amount of already existing plant pathogens can vary considerably. When planting seedlings, they can be pre-treated with suitable fungicides to prevent molds. Insect pests should be minimal in a closed environment but are not always absent. For example, we can carry aphids in our clothes and spores in our shoes. This is why paying close attention to hygiene and disinfection of tools and protective gear when entering a closed space is important. If your plants catch diseases and pests, you can still use your choice of biocontrol or pesticides and fungicides to get them under control. 

References: 

Bunce, J.A. 2001. Seasonal patterns of photosynthetic response and acclimation to elevated carbon dioxide in field-grown strawberry. Photosynthesis Research 68; 237-245. 

Lieten, P. 2000. The effect of humidity on the performance of greenhouse grown strawberry. In IV International Strawberry Symposium 567; 479-482. 

Shiow, Y. W. & Mary, J, C. 2000. Temperatures after bloom affect plant growth and fruit quality of strawberry, Scientia Horticulturae. 85(3);183-199, 

Sonsteby, A., & Heide, O. M. 2009. Temperature limitations for flowering in strawberry and raspberry. Acta Horticulturae, 838; 93-7. 

Yilian, T., Xun, Ma., Ming, L. & Yunfeng, W. 2020. The effect of temperature and light on strawberry production in a solar greenhouse, Solar Energy. 195; 318-328. 

Wu, Y., Li, L., Li, M., Zhang, M., Sun, H., & Sigrimis, N. 2020. Optimal fertigation for high yield and fruit quality of greenhouse strawberry. PLoS One, 15(4), e0224588.