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

Published source details Atucha A., Merwin I.A., Brown M.G., Gardiazabal F., Mena F., Adriazola C. & Lehmann J. (2013) Soil erosion, runoff and nutrient losses in an avocado (Persea americana Mill) hillside orchard under different groundcover management systems. Plant and Soil, 368, 393-406.
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This study is summarised as evidence for the following.

	Action	Category
	Crop production: Plant or maintain ground cover in orchards or vineyards Action Link
	Soil: Plant or maintain ground cover in orchards or vineyards Action Link
	Water: Plant or maintain ground cover in orchards or vineyards Action Link

Crop production: Plant or maintain ground cover in orchards or vineyards

A replicated, randomized, controlled study in 2008–2011 in an irrigated avocado orchard in Chile found lower crop yields in plots with cover crops, compared to bare soil. Crop yield: Lower avocado yields were found in plots with cover crops, compared to bare soil (1.3 vs 5 kg fruit/tree; 7 vs 27 fruits/tree). Crop quality: Similarly-sized avocados were found in plots with cover crops or bare soil. Methods: Cover crops were grown in five treatment plots, and bare soil was maintained with herbicide in five control plots, in an avocado orchard, on a 47% slope (10 x 50 m plots). The groundcover (Lolium rigidum ryegrass and a legume, Medicago polymorpha) was sown in August 2008 and mown in February 2009–2010 (residues were retained). All plots were fertilized and irrigated. Avocado yield and quality were measured in 2011.
Soil: Plant or maintain ground cover in orchards or vineyards

A replicated, randomized, controlled study in 2008–2011 in an irrigated avocado orchard in Chile found more organic matter and nitrogen, higher pH, less erosion, and higher stability in soils with cover crops, compared to bare soils, between avocado rows. Organic matter: More organic matter was found in soils with cover crops, compared to bare soils (2.6–2.8% vs 2.1–2.2%). Nutrients: More nitrogen (1.0–1.1 vs 0.8–0.9 mg total N/g soil), but similar amounts of nitrate (11–59 vs 8–67 mg NO₃/kg soil), and more potassium (162–197 vs 100–122 mg K/kg soil), but similar amounts of phosphorus (11–15 vs 9–10 mg P/kg soil), were found in soils with cover crops, compared to bare soils. Higher pH was found in soils with cover crops, compared to bare soils (6.8–7.2 vs 6.6–6.9). Soil erosion and aggregation: Less soil was lost in runoff water from plots with cover crops, compared to bare soil (0 vs 1,000–3,400 vs kg/ha/year). More stable soils were found in plots with cover crops, compared to bare soil (32–39% vs 22–29% of soil aggregates were water-stable). Methods: Cover crops were grown in five treatment plots, and bare soil was maintained with herbicide in five control plots, in an avocado orchard, on a 47% slope (10 x 50 m plots). The groundcover (Lolium rigidum ryegrass and a legume, Medicago polymorpha) was sown in August 2008 and mown in February 2009–2010 (residues were retained). All plots were fertilized and irrigated. Soil samples were collected along the tree rows in winter 2009–2011 (0–10 cm depth, 2 cm diameter soil cores). Soil loss was measured in runoff water, in buried barrels downslope of each plot.
Water: Plant or maintain ground cover in orchards or vineyards

A replicated, randomized, controlled study in 2008–2011 in an irrigated avocado orchard in Chile found less runoff, less sediment and nutrient in runoff, and more soil pores in plots with cover crops, compared to bare soil. Water availability: Less water was lost as runoff from plots with cover crops, compared to bare soil (0 vs 3–4 mm). No difference in water retention was found between soils with cover crops or bare soils (9–13 vs 8–13 m³ water/m³ soil), but soils with cover crops had a higher percentage of large pores (4–6% vs 3–4% macroporosity). Nutrients: Less nitrogen (0–5 vs 42–68 g/ha), phosphorus (0 vs 20–24 g/ha), and dissolved organic carbon (0–3 vs 345–637 g/ha) was found in runoff from plots with cover crops, compared to bare soil. Sediments: Less sediment was found in runoff from plots with cover crops, compared to bare soil (0 vs 1,000–3,400 kg soil/ha). Methods: Cover crops were grown in five treatment plots, and bare soil was maintained with herbicide in five control plots, in an avocado orchard, on a 47% slope (10 x 50 m plots). The groundcover (Lolium rigidum ryegrass and a legume, Medicago polymorpha) was sown in August 2008 and mown in February 2009–2010 (residues were retained). All plots were fertilized and irrigated. Runoff was collected in buried barrels downslope of each plot.