Photosynthetically Active Radiation and Root-zone Temperature Effects on High Tunnel Primocane Red Raspberry Development

Abstract

High-tunnel primocane red raspberry production is beneficial in the North Central Region of the United States where production is dependent upon the length of the growing season. Advantages of growing Rubus iadaeus L. (red raspberries) in high-tunnels include improved climatic conditions, reduced winter-cane injury, decreased disease incidence, improved berry size and quality, advanced fruit maturation and harvest, and a 50% extension of the harvest season. Improved climatic conditions of high-tunnels also have affected primocane red raspberry growth and production negatively, by reducing shoot growth, fruiting lateral development, yield, and berry quality, due to increased PAR and airand root-zone temperature in high-tunnel systems. With the expansion of high-tunnel primocane red raspberry production in an area with seasonal climatic extremes, such as the North Central Region, there is a need for simple management practices for tunnel environment manipulation. The primary objective of this study was to evaluate the relationship between temperature and irradiance (photosynthetically active radiation, PAR) and their effect on primocane growth, development, and production. Subobjectives of this investigation were to evaluate the efficacy of shadecloth in reducing PAR and air-and root-zone temperature during high-tunnel primocane red raspberry production, and the potential of soil mulch in reducing temperature of high-tunnel primocane red raspberry at the root-zone depth. The influences of PAR and root-zone temperature on vegetative and flowering growth responses of primocane red raspberry ‘Autumn Britten’ were examined. Dormant, one-year-old crowns were planted in 2012, under three identical polyethylene-covered tunnels and in a field plot. A split-plot, randomized complete block design was used. Light transmission through the tunnel polyethylene cover was reduced by 17% before treatments were applied. Whole plot target PAR reduction of 50% was achieved with the addition of shadecloth with a 33% shade