Impacts of gypsum and winter cover crops on soil physical properties and crop productivity when irrigated with saline water

Published source details Mitchell J.P., Shennan C., Singer M.J., Peters D.W., Miller R.O., Prichard T., Grattan S.R., Rhoades J.D., May D.M. & Munk D.S. (2000) Impacts of gypsum and winter cover crops on soil physical properties and crop productivity when irrigated with saline water. Agricultural Water Management, 45, 55-71.
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This study is summarised as evidence for the following.

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

Crop production: Grow cover crops in arable fields

A replicated, randomized, controlled study in 1991–1993 in an irrigated tomato field in the San Joaquin Valley, California, USA, found lower tomato yields in plots with winter cover crops, compared to winter fallows. Crop yield: Tomato yields were lower in plots with cover crops, compared to fallows, in one of two years (in 1991: 76–84 vs 97 t/ha). Methods: There were four plots (93 x 7 m plots) for each of three winter cover crops and one control (winter fallow). The cover crops were Hordeum vulgare barley, Vicia dasycarpa Lana woollypod vetch, or a barley-vetch mixture, seeded in October 1991–1992 and incorporated into the soil in March 1992–1993 (15–20 cm depth, rotary tiller). Tomato seeds were planted in April 1992–1993. All plots were fertilized (12 kg N/ha before planting the tomatoes), but only plots that had not been cover cropped with vetch were sidedressed (168 kg N/ha, when thinning the tomatoes). All plots were irrigated with saline water (at rates to replace evapotranspiration).
Soil: Grow cover crops in arable fields

A replicated, randomized, controlled study in 1991–1994 in an irrigated tomato field in the San Joaquin Valley, California, USA, found more organic matter and nitrogen, and higher soil stability, in soils with winter cover crops, compared to winter fallows. Organic matter: More organic matter was found in soils with cover crops, compared to fallows, in some comparisons in the spring (e.g., spring 1994: 1.05–1.15% vs 0.70%, 0–15 cm depth; number of significantly different comparisons not clearly reported). Nutrients: More nitrogen was found in soils with cover crops, compared to fallows, in some comparisons in the spring (e.g., spring 1993: 0.75% vs 0.90% total nitrogen, 0–15 cm depth; number of significantly different comparisons not clearly reported). Soil erosion and aggregation: More stable soils were found in plots with cover crops, compared to fallows (data on percentage of water-stable aggregates reported as model results). Methods: There were four plots (93 x 7 m plots) for each of three winter cover crops and one control (winter fallow). The cover crops were Hordeum vulgare barley, Vicia dasycarpa Lana woollypod vetch, or a barley-vetch mixture, seeded in October 1991–1993 and incorporated into the soil in March 1992–1994 (15–20 cm depth, rotary tiller). Soil samples were collected in spring and autumn (0–15 cm depth).
Pest regulation: Grow cover crops in arable fields

A replicated, randomized, controlled study in 1991–1994 in an irrigated tomato field in the San Joaquin Valley, California, USA, found similar amounts of fungus in soils with winter cover crops or winter fallows. Pest numbers: Similar amounts of Rhizoctonia solani fungus were found in soils with cover crops or fallows (0.3–1.7 vs 1.3 colony forming units/100 g dry soil). Methods: There were four plots (93 x 7 m plots) for each of three winter cover crops and one control (winter fallow). The cover crops were Hordeum vulgare barley, Vicia dasycarpa Lana woollypod vetch, or a barley-vetch mixture, seeded in October 1991–1993 and incorporated into the soil in March 1992–1994 (15–20 cm depth, rotary tiller). Fungus colonies were measured in soil samples, collected in spring 1994 (0–15 cm depth).