Individual study: Winter Cover Crop Growth and Weed Suppression on the Central Coast of California
Brennan E.B. & Smith R.F. (2005) Winter Cover Crop Growth and Weed Suppression on the Central Coast of California. Weed Technology, 19, 1017-1024
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Pest regulation: Grow cover crops in arable fields
A replicated, randomized study in 2001–2003 in an irrigated lettuce field in the Salinas Valley, California, USA, found different numbers of weeds in plots with different species of cover crops. Implementation options: Fewer weeds were found in plots that were cover cropped with mustard, compared to oats, in two of six comparisons (December 2001 and January 2002: 18–21 vs 65–110 g weeds/m2), and also compared to a legume-oat mixture, in three of six comparisons (December 2001, January 2002, and January 2003: 11–21 vs 121–188 g weeds/m2). Fewer weeds were found in plots that were cover cropped with oats, compared to the legume-oat mixture, in two of six comparisons (January 2002 and 2003: 37–65 vs 170–188 g weeds/m2). Fewer weed seeds (Urtica urens burning nettle) were found in plots that were cover cropped with mustard (0–1,300 viable seeds/m2), compared to oats (1,900–6,000) or the mixture (4,300–13,600), but the difference between plots with oats or the mixture was not significant. After the cover crops were incorporated into the soil, fewer weeds were found in plots that were cover cropped with mustard (113 weed seedlings/m2), compared to oats (246/m2) or the mixture (377/m2), in one of two years (2002), but the difference between plots with oats or the mixture was not significant. Methods: One of three cover crops (Avena sativa oats; Brassica hirta and B. juncea mustard; or Vicia faba, Pisum sativum, Vicia sativa, Vicia villosa, and A. sativa legume-oat mixture) was planted in October (2001: three 2.2 x 30 m plots each; 2002: four 3 x 30 m plots each). Weed biomass was sampled in two 30 x 30 cm quadrats/plot in 2001–2002, and in one 100 x 100 cm quadrat/plot and one 30 x 30 cm quadrat/plot in 2002–2003, in December, January, and February. Weed seeds were collected in January, in vacuum samples (30 x 30 cm/plot). Cover crops were mown and incorporated into the soil (rototilled, 15 cm depth) in March 2002 and February 2003. The soil was then watered (5–10 cm water), and weeds were counted in eight 50 x 50 cm quadrats and five 30 x 30 cm quadrats (2002: 36 days after incorporation; 2003: 48 days).