Further Attempts to Enhance Forced ‘Sweet Charlie’ Strawberry Yield Through Manipulation of Light Quality in High Tunnels

Abstract

In winter months, U.S. domestic strawberry supply is low and demand is high, and unit price for strawberries is at its highest point during the year. Forcing strawberries in high tunnels during this time might capture this niche market. Since yields are much lower in forced systems, enhancing the light environment to increase yield with colored nets (ChromatiNets; distributed by Polysack, Inc., San Diego, CA) was attempted in 2007–2008 (previously published) without success. In the second year of field experiments in 2008–2009, the experiment was repeated with some modifications. ‘Sweet Charlie’ plugs were conditioned from September 5 to September 26 at 24°C on a 12-hr day/night cycle and were planted September 28 in fertilized plots in a high tunnel (29.3-m long × 4.3-m wide × 3.1-m high). Conditioned plants were also planted outside on mulched, drip-irrigated beds as a control. Red, yellow, and pearl ChromatiNets (24% shade factor, lowest intensity possible) were installed over the top of the high tunnel in 7.3-m wide swathes and a nonnetted plot included. Plants were fertigated weekly with about 3.2 kg N/hectare per week from 15 N–30 P2O4–15 K2O. High tunnels were vented to maintain day temperatures in the range of 25 to 30°C. In the second year's work, marketable berry production began November 21, 2008, and continued until February 27, 2009, without any yield advantage for ChromatiNets. In March, plants appeared exhausted; therefore, the high tunnel was opened and plants were allowed to acclimate to outside temperatures. By April, the outside plots were in full production, yielding more than any high tunnel treatments. In the high tunnel, however, yields resumed, with the red nets tending to yield more than the pearl; no-net control and yellow net yielded similarly, but slightly less, than red. In May, all high tunnel treatments and outside berries yielded similarly. Over all harvest periods, there were no differences in total yields with nets in the second year, similar to the first year. It is probable that in winter, the ChromatiNet shading factor overwhelmed any light quality enhancement, and in longer, warmer, and brighter days, the ChromatiNets may show an advantage.