The Effects of High Tunnels and Bio-degradable Mulch on Fruit Quality of Tomatoes Grown in Northwestern Washington

High tunnels provide season extension by adding heat units which increases the success of tomato production, especially in the cool, marine climate of northwestern Washington. Tomatoes are commonly grown with plastic mulch and there is interest among growers to utilize biodegradable mulch (BDM) to increase sustainability of the production system. Effects of high tunnels and biodegradable mulches (BDM) on fruit quality are not well understood. A study at Mount Vernon, WA in 2010 and 2011 compared high tunnel and open field marketable fruit quality of tomato cv. ‘Celebrity’ grown with three commercially-available mulches marketed as bio-degradable: BioBag® (BB), BioTelo® (BT), WeedGuardPlus™ (WG), an experimental spun bonded poly(lactic acid) mulch fabric (PLA), polyethylene black plastic mulch (PEM), and bare ground (NM). Marketability was based on the USDA standard for fresh-market Grade 1 tomatoes in 2010, and a direct-market standard in 2011. In 2010, open field tomatoes were damaged by a severe epidemic of late blight resulting in insufficient replication to compare high tunnel and open field plots. Within high tunnels in 2010, NM (94.73%) produced significantly more juice than BB (94.25%), WG (94.23%), PLA (94.30%) and PEM (94.12%; p=0.0045); and, BT (94.55%) was juicier than PEM and WG. NM (4.25) produced significantly lower soluble solids (oBrix) than BB (4.67), BT (4.48), PLA (4.63), and PEM (4.69; p=0.0055). There were no statistically significant differences in fruit firmness, pH, and titratable acidity due to mulch treatment in 2010. In 2011, there were no significant differences in fruit quality due to mulch treatment. There were statistically significant differences between high tunnel and open field for juice content (94.40% and 94.08%, respectively; p=0.0078), oBrix (4.72 and 4.98, respectively; p=0.0007), pH (4.17 and 4.09, respectively; p=0.0355), titratable acidity (0.364% and 0.404%, respectively; p=0.0001), and lycopene (10.8 μg g-1 and 8.19 μg g-1, respectively; p=0.0008). Improved fruit quality attributes found in the open fields may have been due to increased mean photosynthetically-active radiation (PAR) which in 2011 was 299 μmol.m-2s-1 inside of high tunnels and 387 μmol.m-2s-1 in the open field.