Winter cover crops affect monoculture maize yield and nitrogen leaching under irrigated Mediterranean conditions

Published source details Salmerón M., Cavero J., Quílez D. & Isla R. (2010) Winter cover crops affect monoculture maize yield and nitrogen leaching under irrigated Mediterranean conditions. Agronomy Journal, 102, 1700-1709.
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This study is summarised as evidence for the following.

	Action	Category
	Water: Grow cover crops in arable fields Action Link
	Crop production: Grow cover crops in arable fields Action Link
	Soil: Grow cover crops in arable fields Action Link

Water: Grow cover crops in arable fields

A replicated, randomized, controlled study in 2006–2008 in an irrigated maize field in the Ebro river valley, Spain, found that less nitrate was leached from soils with winter cover crops, compared to bare soils, but more water was lost through drainage. Water use: Similar amounts of water were used in plots with cover crops or bare soils (130–200 mm estimated evapotranspiration in the cover-cropping season). Water availability: More water was lost through drainage from plots with cover crops, compared to bare soils, in three of 10 comparisons (during the cover-cropping season: 4–7 vs 0–3 mm). Nutrients: Less nitrate was leached from soils with cover crops, compared to bare soils, in four of nine comparisons (during the maize-growing season: 2 vs 7–10 mg NO₃-N/litre; 4–5 vs 23–27 kg NO₃-N/ha). Implementation options: Less nitrate was leached from soils that were cover cropped with barley or winter rape, compared to common vetch, in two of three comparisons (during the maize-growing season: 2 vs 10 mg NO₃-N/litre). Less water was lost through drainage from plots that were cover cropped with barley or winter rape, compared to common vetch, in two of four comparisons (during the cover-cropping season: 0–1 vs 7 mm). Methods: There were three plots (5.2 m²) for each of three winter cover crops (Hordeum vulgare barley, Brassica rapa winter rape, or Vicia sativa common vetch, sown in October 2006–2007), and there were three control plots with bare soil in winter. Similar amounts of nitrogen were added to all plots (300 kg N/ha), but less of it came from mineral fertilizer in plots with cover crops, to compensate for the organic nitrogen that was added to these plots when the cover crop residues were tilled into the soil. All plots were tilled in spring (March 2007–2008) and autumn (October 2006–2007). All plots were irrigated twice/week (drip irrigation, based on evapotranspiration). Maize was planted in April and harvested in October 2007–2008. Soil samples were collected before the cover crops were incorporated and after the maize was harvested (two soil cores/plot, 5 cm diameter, 0–120 cm depth). Drainage volume and nitrate leaching was measured every week (lysimeters, 5.2 m²surface area, 1.5 m depth, 50 litre tank).
Crop production: Grow cover crops in arable fields

A replicated, randomized, controlled study in 2006–2008 in an irrigated maize field in the Ebro river valley, Spain, found lower maize yields in plots with winter cover crops, compared to bare soils. Crop yield: Lower maize yields were found in plots with cover crops, compared to bare soils, in four of five comparisons (barley or winter rape as the cover crops: 14 vs 16–17 Mg/ha). Crop quality: Similar grain quality was found in plots with cover crops or bare soils (530–640 grains/ear; 0.25–0.29 g/kernel). Implementation options: Lower maize yields were found in plots that were cover cropped with non-legumes (barley or winter rape), compared to legumes (common vetch) (14 vs 18 Mg/ha). Methods: There were three plots (5.2 m²) for each of three winter cover crops (Hordeum vulgare barley, Brassica rapa winter rape, or Vicia sativa common vetch, sown in October 2006–2007), and three control plots (bare soil in winter). Similar amounts of nitrogen were added to all plots (300 kg N/ha), but less of it came from mineral fertilizer in plots with cover crops, to compensate for the organic nitrogen that was added to these plots when the cover crop residues were tilled into the soil. All plots were tilled in spring (March 2007–2008) and autumn (October 2006–2007). All plots were irrigated twice/week (drip irrigation, based on evapotranspiration). Maize was planted in April and harvested in October 2007–2008.
Soil: Grow cover crops in arable fields

A replicated, randomized, controlled study in 2006–2008 in an irrigated maize field in the Ebro river valley, Spain, found less nitrogen in soils with winter cover crops, compared to bare soils, in spring, but found more nitrogen in autumn. Nutrients: In spring (after the cover crops), less nitrogen was found in soils with cover crops, compared to bare soils, in 19 of 20 comparisons (1–11 vs 3–43 mg inorganic N/kg soil, 0–120 cm depth). However, in autumn (after the maize was harvested), more nitrogen was found in plots with cover crops, compared to bare soils, in two of 20 comparisons (barley as the cover crop, 0–30 cm depth: 14–15 vs 4–7 mg inorganic N/kg soil). Methods: There were three plots (5.2 m²) for each of three winter cover crops (Hordeum vulgare barley, Brassica rapa winter rape, or Vicia sativa common vetch, sown in October 2006–2007), and three control plots with bare soil in winter. Similar amounts of nitrogen were added to all plots (300 kg N/ha), but less of it came from mineral fertilizer in plots with cover crops, to compensate for the organic nitrogen that was added to these plots when the cover crop residues were tilled into the soil. All plots were tilled in spring (March 2007–2008) and autumn (October 2006–2007). All plots were irrigated twice/week (drip irrigation, based on evapotranspiration). Maize was planted in April and harvested in October 2007–2008. Soil samples were collected before the cover crops were incorporated and after the maize was harvested (two soil cores/plot, 5 cm diameter, 0–120 cm depth). It was not clear whether these results were a direct effect of cover cropping or adding fertilizer.