Orchard Groundcover Management Impacts on Apple Tree Growth and Yield, and Nutrient Availability and Uptake

This study compared various conventional and alternative orchard groundcover management systems (GMSs)— including a crownvetch "living mulch" (CNVCH), close-mowed (MWSOD) and chemically growth-regulated (GRSOD) sodgrasses, pre-emergence (NDPQT) and two widths of postemergence (GLY1.5 and GLY2.5) herbicides, hay-straw mulch (STMCH), and monthly rototillage (tilled)—during 6 years in a newly established apple ( Malus domestica Borkh.) planting. Trunk cross-sectional area and fruit yield were higher in STMCH, GLY, and NDPQT, intermediate in tilled, and lower in GRSOD, MWSOD, and CNVCH treatments after 5 years. Despite N and K fertilizer applications, extractable soil N and leaf N concentrations were reduced under MWSOD and GRSOD, and soil K, P, and B concentrations were greater under STMCH. Leaf K concentrations were usually highest in STMCH trees, even when heavily cropped; leaf K declined below the sufficiency range in GLY, NDPQT, and tilled trees as they began to bear fruit. Leaf Ca was marginally deficient in all trees and was unaffected by GMS. Foliar Mn, Zn, and B concentrations declined rapidly in all treatments during 2 years without micronutrient fertilizers. Leaf Cu was higher in herbicide and tilled treatments where seasonal soil water content was intermediate (22% to 27%) and lower where soil was very wet or dry for most of the 1988 growing season. Multiple regression analysis indicated that leaf N and B and soil organic matter in 1990, and mean soil water content during the unusually dry Summer 1988, were the best predictors of fruit yield in 1990. Phytophthora root rot and meadow vole depredation were serious problems in STMCH and CNVCH trees. GMSs greatly affected tree establishment, nutrition, and yield; each system involves tradeoffs among important short- and long-term impacts on the orchard agroecosystem. Increasing attention is being paid to orchard floor management in order to minimize weed competition and bring today's highly capitalized plantings into full production more quickly. In the humid regions of North America and Europe, herbicided tree rows with mowed-grass drive lanes have become the most common orchard groundcover management system (GMS). Past studies have demonstrated that tree growth, productivity, and nutrient uptake during orchard establishment are maximized at least cost by herbicide GMSs (Haynes, 1980; Hogue and Neilsen, 1987). Currently, serious questions are being asked about the long-term sustainability of herbicide usage (National Research Council, 1989) and the possibility that alternative systems using different groundcover species or management strategies might provide some of the soil conservation benefits of vegetative ground cover- age without excessive weed-crop competition (Skroch and Shribbs, 1986). Several studies of orchard floor management have also indicated the need for more information about specific effects of GMSs on critical factors such as micronutrient availability and uptake by fruit trees (Atkinson and White, 1981; Haynes, 1980; Hogue and Neilsen, 1987). In 1985, we initiated a long-term field experiment to evaluate the relative impacts of alternative orchard GMSs on apple tree growth, nutrient uptake and yield, soil physical conditions and fertility, and the apple pest complex. The effects of