Submitted to: International Journal of Fruit Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2008
Publication Date: 10/9/2008
Citation: Tworkoski, T., Glenn, D.M. 2008. Response of Young Apple Trees to Grass and Irrigation. International Journal of Fruit Science. 8:89-108. Interpretive Summary: The floor of orchards must be managed to control pests and to enhance soil properties that provide nutrients and water to fruit trees. Techniques such as cultivation reduce weed competition but can degrade soil and destroy shallow tree roots. As an alternative, vegetative ground cover can stabilize and improve soil properties but competition between fruit trees and ground cover vegetation must be managed. The current experiment determined the root growth, water-use, and relative competitiveness of five grasses that may be possible orchard ground covers. In addition, the effect of surface and subsurface irrigation on young apple trees grown with grasses was investigated in a greenhouse. Subsurface irrigation could selectively provide water to deep roots, such as those of fruit trees, without supplementing water to shallow-rooted ground cover. In this experiment, grasses with shallow root systems (roughstalk bluegrass) used about one-third the water used by grass with deep root systems (tall fescue). Roughstalk bluegrass and tall fescue caused the least and most, respectively, water stress and growth inhibition of apple trees. Grasses with intermediate root depths (red fescues and perennial ryegrass) were intermediate in water use. Apple tree root density increased with depth in response to grass competition and subsurface irrigation. Results from this experiment indicate that it may be possible to combine grass ground cover with subsurface irrigation in an orchard floor management system to provide water and nutrients to the fruit tree while suppressing weeds through managed competition with grass. Field experiments are underway to determine the utility of these techniques as sustainable orchard management practices.
Technical Abstract: Ground covers and irrigation are important components of orchard floor management systems that affect fruit tree vigor and productivity. Three experiments were conducted in a greenhouse to determine the relative water use of candidate ground covers (roughstalk bluegrass (RB, Poa trivialis), Chewing's fescue (CH, Festuca rubra subsp. commutata Gaudin), creeping red fescue (RF, Festuca rubra L. subsp. rubra), tall fescue (TF, Festuca arundinacea Schreber, Fawn), and perennial ryegrass (PR, Lolium perenne L., Saint) and the response of apple trees to those ground covers and to drip irrigation applied at two soilless substrate depths. Grass ground covers with large and deep root systems (TF and PR) used more water than a shallow-rooted grass (RB) and leaf water potential decreased more rapidly in apple trees grown with TF than RB when irrigation was withheld. Although apple tree shoot growth was greater with shallow- than deep-rooted grass, photosynthesis, transpiration, and root biomass distribution were not differentially affected by grass type. When grown with RB or TF, irrigation depth affected apple tree growth. During the first season in the greenhouse, deep irrigation at 37 cm depth increased apple root length density near emitters but shoot growth was less in apple grown with deep irrigation compared with apple grown with surface irrigation (0 cm) and with split irrigation at 0 and 37 cm. During the second season in the greenhouse, deep irrigation was beneficial to trees grown with grass that had large, deep root systems (TF) but it did not completely overcome interference effects of grass on apple trees, regardless of grass root system size or distribution. The results indicate that grasses with shallow root systems may be grown beneath apple trees and that split irrigation at two depths can provide flexibility that is necessary for water management of ground covers and apple trees.