Canopy Cover and Root-zone Heating Effects on Fall- and Spring-grown Leaf Lettuce Yield in Ohio

Abstract

<jats:p>Low and high tunnels and root-zone heating systems are proven tools in horticultural production. However, impacts of their separate and combined application on crop yield, composition, and microclimates are underreported. We addressed these gaps in the literature by exposing lettuce (<jats:italic>Lactuca sativa</jats:italic>) to four microclimates established with low and high tunnels and root-zone heating during the spring and fall of 2 years in Wooster, OH. Red-leaved romaine lettuce cultivars Outredgeous and Flagship were direct-seeded into raised beds in both outdoor and high-tunnel settings in early October and late March and harvested multiple times over 4 weeks. Half of all plots in each setting were underlain by electric heating cables, and half were covered with 0.8-mil, clear, vented, low tunnels. A growing medium consisting of peat moss, compost, soil, and red clover (<jats:italic>Trifolium pratense</jats:italic>) hay was used, and all plots were overhead-irrigated. Soil and air temperatures were monitored throughout the experiments, which were repeated four times (2 seasons/year × 2 years). Here, we report primarily on treatment effects on crop yield and related variables. Root- and shoot-zone conditions and cultivar significantly affected leaf biomass in both settings (outdoor, high tunnel), while population was more often affected in the outdoor experiments. Microclimate main effects were more prevalent than cultivar effects or interactions. Leaf yield was greater in low-tunnel-covered and bottom-heated plots than in uncovered and unheated plots. We take these data as further evidence of the potential to alter lettuce yield through root- and shoot-zone microclimate modification, particularly in regions prone to dynamic seasonal and within-season temperature and light conditions. The data also suggest that the relative performance of low and high tunnels in the production of short-statured, quick-cycling crops during fall and spring be more thoroughly evaluated.</jats:p>

The effects of container geometry on water and heat regimes in soilless culture: lettuce as a case study

“…Root zone temperatures have an impact on lettuce performance in field as well as in containerized production systems. For example, higher leaf growth was observed when the root zone temperature increased from around 10 to 20-24 °C (Bumgarner et al 2011). Reduction in root growth was reported for medium temperatures exceeding 35 °C (Du and Tachibana 1994;Lyons et al 2007).…”

Soil Heating and Secondary Plant Covers Influence Growth and Yield of Winter High Tunnel Spinach

“…Like air temperature, soil temperatures inside a HT are higher than soils outside during the winter months. However, soil temperatures within a HT during fall or winter months are often below optimal ranges, particularly at night and on cloudy days (Bumgarner et al, 2011;Hunter, 2010). Although soils have the thermal mass to store heat, once soils become cold, they require significant energy inputs to warm them, particularly if they are moist.…”

“…The use of secondary covers (low tunnels and floating rowcovers) within HTs can increase temperatures around plants beyond that of the HT alone. When secondary covers are used in conjunction with a HT, plants with extra protection may spend a longer period each day at temperatures near or within their optimal range (Bumgarner et al, 2011(Bumgarner et al, , 2012Hunter et al, 2012;Wien et al, 2006). Additional layer of plastic or fabric can increase air temperature adjacent to plants by 5 to 10°C on sunny days and 3 to 5°C at night (Lamont, 2009;Waterer, 2003;Wells and Loy, 1985;Wien et al, 2006).…”

“…They suggested that low tunnels or rowcovers be used inside HT to enhance crop growth when additional heat or insulation is necessary. Thus, the combination of HT and secondary covers not only successfully increases biomass and yields of a range of vegetables (Bumgarner et al, 2011;Hunter et al, 2012), but also exposes plants to temperatures closer to their maximum which may be harmful to productivity.…”

“…The addition of soil heating cables generally leads to an increase in the total yield for early spring grown tomatoes, bush beans, peppers, broccoli, and lettuce (Bumgarner et al, 2011;Hunter et al, 2012;Rykbost et al, 1975) and results in increased yield for winter-grown lettuce (Bumgarner et al, 2011(Bumgarner et al, , 2012Hunter, 2010). Additional heat increased total plant biomass and nutrient uptake by maintaining root zone temperatures above freezing and closer to optimal root temperature.…”