Soil erosion, runoff and nutrient losses in an avocado (Persea americana Mill) hillside orchard under different groundcover management systems

Abstract

Assess the influence of different groundcover management systems on erosion and runoff processes associated with extremely steep hillside avocado (Persea americana Mill) orchards, in a Mediterranean climate with high rainfall variability. We compared several groundcover management systems at a steep hillside avocado planting in a three-year study: 1) Bare soil (BS), pre- and post-emergence herbicides; 2) Vegetation strip (VS), post-emergence herbicide applied in a 1-m wide strip on the tree row plus groundcover seeded between tree rows; 3) Groundcover (GC), over the entire plot surface. Trees in the BS plots were 44 and 53 % bigger, and had 150 and 250 % higher yields than trees in VS and GC, respectively. Runoff volumes, soil losses, dissolved organic carbon, PO4-P and total N losses were significantly higher in BS than VS and CG treatments. Total soil nitrogen (N) and carbon (C) content, C-to-N ratios, and essential plant nutrient availability were greater in the GC soil than in other treatments. Soil macroporosity and aggregate stability were 8–27 % and 25 % lower, and soil bulk density significantly higher in the BS than the VS and GC systems at the end of the study. Terbuthylazine herbicide concentrations in runoff water from BS plots ranged from 55.4 to 79.9 μg L−1, exceeding maximum allowed levels for drinking water (0.1 μg L−1). Soil erosion and runoff rates from newly planted hillside orchards are not environmentally sustainable under current growing practices where groundcover vegetation is completely suppressed. High sediment losses and herbicide residues in runoff water present serious risk of water source pollution, but these impacts can be reduced by alternative soil management systems.