Effects of Cover Crop Treatments on Apple Trees

Ground cover management systems affect soil quality and health and thereby orchard growth and productivity. There have been few studies in the southern US on the effects of managed drive-rows using cover crops as part of a sustainable apple orchard management system. A field study used treatments of 1) seasonal legumes (cowpea [Vigna unguiculata] and crimson clover [Trifolium incarnatum]), 2) seasonal grasses (millet [Setaria italic] and annual rye [Lolium multiflorum]), or 3) unmanaged natural vegetation drive row plantings, with mowed vegetation blown into the tree row as mulch (mow/blow) nested variable. The legume crop cycles produced more than twice as much cover crop tissue N than grasses or natural vegetation. Soils with legume mulches produced the highest labile N compared to other treatments, and the highest labile N where legumes were mulched to the tree-row with a mow/blow treatment. There was a smaller labile pool C/N ratio for legume treatments and for tree row compared to drive row samples, and the largest N concentration for soils in the tree row with legumes as a mow/blow mulch. After two seasons the labile pool C/N ratio was lower for legumes than other treatments. Tree foliage, had highest N content for the legume treatments. These results indicate that legume cover crop mow/blow management systems may offer a N benefit and be a potential sustainable alternative for orchard management. A greenhouse study was also conducted, pairing the cover crop species of the field study with potted apple trees to examine the effects of both cover crop competition and mulches on tree growth and nutrient status. Apple trees in inert media were grown with and without cover crop competition, and cover crops were cut and mulched to the media surface. Cowpeas and German foxtail millet were studied. Legume cover crops generated more biomass per plant, higher % and total N, and total C. Trees grown in competition with cover crops grew less than those without, and did not recover after cover crop harvest within the duration of the study. Trees with neither mulch nor competition grew better than either competition treatment