Relationships between Microclimate and Yield in Strawberry Low-Tunnel Production Systems.

Availability of fresh strawberry (Fragaria ×ananassa Duchesne ex Rozier) in the U.S. Mid-Atlantic region is largely dependent on production from two states, California and Florida. Regional production is limited to a three to five week period with a June-bearing cultivar and is therefore insufficient to satisfy market demand during periods of low yields. Recent research demonstrated economically viable berry yields could be obtained in Maryland with repeat-fruiting varieties that may address this issue. Relationships between yield and microclimate factors need to be evaluated in order to most effectively design and manage appropriate production systems for these cultivars. In this study, the relationship between yields from five repeat-fruiting strawberry cultivars grown in low-tunnel (tunnel) and uncovered raised-beds (open) versus micro-climate factors was assessed from data collected for three years at USDA-ARS facilities in Beltsville, Maryland. Temperature (T) and light accounted for over 41 percent of the total variance between yield and all microclimatic factors. Differences between tunnel and open systems for maximum 24-h T averaged 3.5, 1.6, and 0.8 degrees-Celcius higher at air, crown, and bed positions. Despite an average 34 percent reduction in daily photosynthetically active radiation, fresh yields were 40 percent, and berry numbers 150 percent, higher for production in tunnel versus open beds. This yield difference was attributed to the warmer T in the tunnel system that resulted in higher weekly yields while also extending the growing season, and higher light use efficiency presumably due to a larger fraction of diffuse solar radiation inside the tunnels. A 4-week floral development period was used as a basis for quantifying the yield versus air (Ta), crown (Tc), and bed (Tb) positions using a beta-distribution function. The resulting optimum T from this function averaged 26.8, 28.6, and 27.9 degrees-Celsius at the Ta, Tc, and Tb levels respectively. Yields were also observed to be linearly correlated with daily light integral when T was below these optimum thresholds. Higher slopes for the relationship of yield versus light were observed for tunnel versus open bed production. Predicted yields using the beta function were shown to match observed values well in either production system, especially when Tc data were used, and can be utilized for improving the production system design and the management.