EFFECTS OF SOIL MANAGEMENT ON YIELD, GROWTH AND SOIL FERTILITY IN AN ORGANIC APPLE ORCHARD

The objective of this work was to evaluate the effects of soil management on yield, growth and soil fertility in an organic apple orchard cv. Royal Gala/EM 26 planted in 1994 at 4 x 2 m. In 1999, treatments applied to the inter-row spaces were: 1) permanent cover of alfalfa (Medicago sativa) plus fescue (Festuca arundinacea), FA; 2) permanent cover of strawberry clover (Trifolium fragiferum), SC; 3) seeding of common vetch (Vicia sativa), V; and 4) control (natural vegetation of grasses and legumes which is disked in late winter, the traditional management system used by growers in this region), C. The cover crops were mowed between 3 to 4 times during the growing season and the clippings were left on the ground for natural decomposition. In 2003/2004 total cover crop biomass was recorded. The trial was carried out in the northern Patagonia region of Argentina in a sandy loam soil with a pH of 7.6 and an initial organic matter content of 1.5%. Irrigation was with microjets and the amount of irrigation water was calculated based on Class A Pan readings and crop coefficients. Organic fertilizer (5-5-5) was added annually at a rate of 1.0 kg tree^-1 in equal amounts to each treatment in a radius of 0.4 m around the trunk occupied by natural vegetation. In 2004, five years after the initiation of the treatments, yield was 39, 37, 31 and 26 t ha^-1 and canopy volume was 18.58, 17.20, 16.68 and 12.35 m³ tree^-1 for treatments SC, FA, V and C, respectively. In 2003-2004 cover crop aerial biomass was, 571, 675, 644 and 482 g m^-1, respectively. Soil organic matter increased in the topsoil especially with permanent cover crops but decreased in the C treatment due to both annual soil tillage and less input of groundcover biomass. It is concluded that tree growth and yield are affected by soil management. Perennial cover crops perform better than annual common vetch. Disking is not a recommended practice because it may decrease the content of soil organic matter and lead to poor tree vigor that corresponds to low fruit bearing potential. However, even with the use of permanent cover crops the addition of organic fertilizers is necessary in order to sustain good yields and proper tree vigor.