RELATIONSHIP OF STRAWBERRY YIELD WITH MICROCLIMATE FACTORS IN OPEN AND COVERED RAISED-BED PRODUCTION

Supply for the fresh strawberry (Fragaria x ananassa Duchesne ex Rozier) market in the U.S. Mid-Atlantic region is frequently supplemented by product grown in states outside the region. The adoption of repeat-fruiting cultivars specially bred for this area can benefit local and regional growers, but production systems suited to meet the cultural needs of these varieties must be evaluated. The relationships between yields from five repeat-fruiting cultivars grown in either uncovered (open) or plastic-covered (tunnel) raised-bed systems and associated microclimate factors were assessed from data collected over a three-year period at the USDA-ARS facility in Beltsville, Maryland. Average in-season yields were 40% higher and berry numbers were 150% higher for production in tunnel versus open systems when averaged across all cultivars, years, and harvests. This yield difference was attributed to warmer temperatures in the tunnel system that enabled extension of the growing season, higher weekly yields, and higher light use efficiency. Temperature and solar radiation accounted for more than 41% of the variance between yield and all measured microclimatic factors. Maximum 24 h temperatures averaged 3.5 degrees C, 1.6 degrees C, and 0.8 degrees C higher, respectively, at the air (T-a), crown (T-c), and bed (T-b) positions in the tunnel system, and daily photosynthetically active radiation was 34% lower in the tunnel system. A four-week period between floral initiation and fruit maturity was estimated as representative of the floral development period and was used as a basis for obtaining cardinal temperatures. The optimum temperature averaged 26.8 degrees C, 28.6 degrees C, and 27.9 degrees C at T-a, T-c, and T-b, respectively. Yields were positively correlated with daily light integral at temperatures below these thresholds, and higher slopes from the relationship of yield versus light were observed for tunnel 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 used for production system design and management.