Extending cool season production of vegetables in the high tunnel: balancing heat and light
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Date
2019
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Montana State University - Bozeman, College of Agriculture
Abstract
Montana high tunnel growers face challenges associated with being at a northern latitude and high elevation. The wide seasonal fluctuation in photosynthetically active radiation coupled with wide diurnal temperature swings produces a dynamic growing environment within the high tunnel. This dissertation is comprised of four studies investigating the management of light and temperature and their influences on high tunnel grown crops. Chapter one is an introduction to high tunnels and production strategies. Chapter two discusses the results of the Montana High Tunnel Growers Survey, in which respondents reported that managing the high tunnel environment was their number one challenge. Two thirds of respondents produced crops during the shoulder seasons of spring and fall, a period of time when the climatic conditions are especially dynamic. Chapter three presents the findings on the influences various types of season extension have on light and temperature levels and the impacts they have on the accumulation of growing degree hours, soil degree hours, and daily light integral. While each layer retains heat, moderating the effect of low night air temperatures, it comes at the cost of lower light energy at the crop level. Heat retention performance of high tunnel plus row cover improves as outside air temperature decreases, maintaining crop level air temperature at -3°C despite an outside air temperature of -22°C. Chapter four presents the results of seeding date and row cover effects on the yield and days to harvest of six cool season crops. Row cover within the high tunnel only improved crop yields when outside air temperatures were well below the historical average. The early seeding date in the fall resulted in higher yields and fewer days to harvest, indicating that the two weeks difference between August 15th and August 30th has a large impact on production. Chapter five reports on the influence of low daily light integral has on the production of kale, lettuce, and spinach. While all three responded to increasing light, lettuce had the largest response with a 200% increase in dry weight when the daily light integral increased from 8 to 14 mol m -2 d -1.