Winter cover crops to minimize nitrate losses in intensive lettuce production

Published source details Jackson L.E., Wyland L.J. & Stivers L.J. (1993) Winter cover crops to minimize nitrate losses in intensive lettuce production. The Journal of Agricultural Science, 121, 55-62.
Share Tweet Email

Actions

This study is summarised as evidence for the following.

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

Soil: Grow cover crops in arable fields

A replicated, randomized, controlled before-and-after study in 1989–1991 in an irrigated lettuce field in Salinas, California, USA, found less nitrate, and nitrate depletion, in soils with winter cover crops, compared to bare fallows. Nutrients: At the beginning of spring, less nitrate was found in soils with cover crops, compared to bare fallows, in some comparisons (all cover crops in 1990: 2–6 vs 18–21 µg NO₃-N/g dry soil; one of two cover crops in 1991: 66–79 vs 85–112). After the first rainfall in spring, more nitrate was found in soils with winter cover crops, compared to bare fallows (amounts of nitrate not clearly reported). The inference was that more nitrate was depleted by cover crops over winter, and more nitrate was leached from bare fallows in spring. In early spring, more ammonium was found in soils with winter cover crops, compared to bare fallows (0–15 cm: 2–6 vs 0–1 µg NH₄-N/g soil), but similar amounts were found later in the spring (0–15 cm: 0.5 µg), in 1991. In the lettuce-growing season, similar amounts of nitrate, ammonium, and mineralizable nitrogen were found in plots with winter cover crops or bare fallows (0–60 cm: 9–60 µg NO₃-N/g dry soil; 0–15 cm: 0.2–0.8 µg NH₄-N/g dry soil; 0–15 cm: 3–6 µg mineralizable N/g dry soil). Methods: In 1989–1990, six winter cover crops (Raphanus sativus oilseed radish, Brassica hirta white senf mustard, Brassica alba white mustard, Lolium multiflorum annual ryegrass, Secale cerale Merced rye, and Phacelia tanacetifolia) were grown on three plots each (two 12 m rows/plot), and bare fallows were maintained (with herbicide and hand cultivation) on three plots. In 1990–1991, two winter cover crops (Secale cerale Merced rye and Phacelia tanacetifolia) were grown on six plots each (two 8 m rows/plot), and bare fallows were maintained on six plots. Cover crops were tilled into the soil (15–20 cm depth in March 1990, depth not reported in February 1991). Lettuce was sown in April 1990–1991. All plots were irrigated and fertilized (56–85 kg N/ha, before sowing lettuce). Soil samples were collected in November 1989–1990, January 1990–1991, February 1991, and March 1990 (0–60 cm depth, 4 cm diameter, two cores/plot), weekly from late March to the end of June 1990 (0–15 cm depth), and every 2–7 days from mid-February to the end of March 1991 (0–15 cm depth).
Crop production: Grow cover crops in arable fields

A replicated, randomized, controlled study in 1989–1991 in an irrigated lettuce field in Salinas, California, USA, found similar lettuce yields in plots with winter cover crops or bare fallows. Crop yield: Similar lettuce yields were found in plots with cover crops or bare fallows (290–312 vs 252 g dry matter/m²). Methods: In 1989–1990, six winter cover crops (Raphanus sativus oilseed radish, Brassica hirta white senf mustard, Brassica alba white mustard, Lolium multiflorum annual ryegrass, Secale cereale Merced rye, and Phacelia tanacetifolia) were grown on three plots each (two 12 m rows/plot), and bare fallows were maintained (with herbicide and hand cultivation) on three plots. In 1990–1991, two winter cover crops (Secale cerale Merced rye and Phacelia tanacetifolia) were grown on six plots each (two 8 m rows/plot), and bare fallows were maintained on six plots. Cover crops were tilled into the plots (15–20 cm depth in March 1990, depth not reported in February 1991). Lettuce was sown in April 1990–1991. All plots were irrigated and fertilized (56–85 kg N/ha, before sowing lettuce). Data on lettuce yields were reported for the harvest in July 1991.
Water: Grow cover crops in arable fields

A replicated, randomized, controlled before-and-after study in 1989–1991 in an irrigated lettuce field in Salinas, California, USA, found less water, but less nitrate leaching, in soils with cover crops, compared to bare fallows. Water availability: At the end of winter, less water was found in soils with winter cover crops, compared to bare fallows, at one of three depths (0–15 cm: 9–10% vs 13% soil moisture content), but similar amounts of water were found earlier in the winter (0–15 cm: 8–13% vs 9–14%), in 1991. Nutrients: At the beginning of spring, less nitrate was found in soils with winter cover crops, compared to bare fallows, in some comparisons (all cover crops in 1990: 2–6 vs 18–21 µg NO₃-N/g dry soil; one of two in 1991: 66–79 vs 85–112). After the first rainfall in spring, more nitrate was found in soils with winter cover crops, compared to bare fallows (amounts of nitrate not clearly reported). The inference was that more nitrate was depleted by cover crops over winter, and more nitrate was leached from bare fallows in spring. Methods: In 1989–1990, six winter cover crops (Raphanus sativus oilseed radish, Brassica hirta white senf mustard, Brassica alba white mustard, Lolium multiflorum annual ryegrass, Secale cereale Merced rye, and Phacelia tanacetifolia) were grown on three plots each (two 12 m rows/plot), and bare fallows were maintained (with herbicide and hand cultivation) on three plots. In 1990–1991, two winter cover crops (Secale cereale Merced rye and Phacelia tanacetifolia) were grown on six plots each (two 8 m rows/plot), and bare fallows were maintained on six plots. Cover crops were tilled into the plots (15–20 cm depth in March 1990, depth not reported in February 1991). Lettuce was sown in April 1990–1991. All plots were irrigated and fertilized (56–85 kg N/ha, before sowing lettuce). Soil samples were collected in November 1989–1990, January 1990–1991, February 1991, and March 1990 (0–60 cm depth, 4 cm diameter, two cores/plot), weekly from late March to the end of June 1990 (0–15 cm depth), and every 2–7 days from mid-February to the end of March 1991 (0–15 cm depth).