Groundcover Management Systems Comparisons In Apple And Avocado Orchards
Groundcover management systems (GMSs) are essential in fruit production to achieve and sustain orchard productivity over long-term production cycles. The present dissertation compiles four studies evaluating the effects of GMSs on the long-term performance and nutrient dynamics of an apple (Malus x domestica Borkh.) orchard, and on tree growth and production, erosion rates, and root system development of a hillside avocado (Persea americana Mill.) orchard. Four GMSs-pre-emergence herbicides, post-emergence herbicide, a sod cover crop, and bark mulch-were evaluated in the apple orchard. Over 16 years were no consistent long-term trends in fruit yields among GMSs, and long-term responses of trees to groundcover vegetation indicated that trees respond adaptively to compensate for surface vegetation competition. Two Nitrogen (N) budgets were developed for each GMS based on N inputs, internal cycling, and outputs, with and without applied N fertilizer. More than 60% of internal N fluxes were comprised of soil mineralization and recycling groundcover biomass; and harvested fruit represented 70% of N outputs from the system during both years. During the year with N fertilizer, N losses approached 4 and 22% through surface runoff and subsurface leaching, respectively. During the year without N fertilizer, the surface runoff N losses were twice the subsurface leaching N losses in all GMSs. We evaluated three GMSs in a steep hillside avocado orchard in Chile-Bare soil (BS), a vegetation strip (VS), and a groundcover (GC) covering the entire surface of the plots. Three years after tree establishment, trees in the BS plots were significantly bigger and produced more fruit than trees in the VS and GC treatments, but soil physical properties had deteriorated in the BS compared to the other treatments. Runoff volumes, soil erosion, and nutrient losses were consistently higher in the BS than VS and CG treatments. Trees in BS plots had more shallow and thicker roots than in VS and GC. Lifespans of roots in the BS and VS plots were 61% and 47% greater than in the GC plots, respectively. More root production was observed in the non-bearing year than in the bearing year, in all the GMS treatments.
Merwin, Ian Alexander
Walter, Michael Todd; Lehmann, C.Johannes
Ph.D. of Horticultural Biology
Doctor of Philosophy
dissertation or thesis