Apple Root Growth, Turnover, and Distribution Under Different Orchard Groundcover Management Systems

Minirhizotrons were used to study root emergence, turnover, and depth distribution of apple (Malus ×domestica Borkh.) rootstocks (M.9/MM.111) under four groundcover management systems (GMSs)—pre-emergence herbicide (Pre-H), postemergence herbicide (Post-H), mowed sod grass (Grass), and hardwood bark mulch (Mulch)—that had been maintained since 1992 in an orchard near Ithaca, NY. Two root observation tubes were installed on both sides of one tree in three replicates for each GMS treatment. Roots were observed by camera at 2- to 3-weekly intervals during the growing seasons of 2002 and 2003 and from whole tree excavations in Apr. 2000. Tree growth and yield observations from 1992 to 2003 showed that Mulch and Post-H treatments produced more tree growth and higher yields than other treatments during most years; the Grass treatment usually had the smallest trees and lowest yields. More root emergence was observed in a light crop year (2002) than in a heavy crop year (2003). Pre-H treatment trees had more total roots and new roots than all other treatments, and trees in Grass plots had fewer total roots than others. Trees in Mulch plots had more shallow roots, and trees in Grass plots had more deep roots than others. Root diameter was positively correlated with overwintering root survival. The Pre-H treatment trees had greater root mortality than other trees during an unusually hot and dry growing season (2002) and this was attributed to higher shallow soil temperatures in this treatment. The GMS treatments affected root number and root depth distribution patterns. Despite microsprinkler irrigation, hot, dry weather conditions coincided with decreased root growth, increased root mortality, and reduced root median lifespan. GMS treatments affected root growth, turnover, and distribution at this orchard, and these differences were linked with long-term trends in tree growth and fruit production in this study.