Tillage and cover cropping affect crop yields and soil carbon in the San Joaquin Valley, California

Published source details Mitchell J.P., Shrestha A., Horwath W.R., Southard R.J., Madden N., Veenstra J. & Munk D.S. (2015) Tillage and cover cropping affect crop yields and soil carbon in the San Joaquin Valley, California. Agronomy Journal, 107, 588-596.
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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
	Crop production: Use reduced tillage in arable fields Action Link
	Soil: Grow cover crops in arable fields Action Link
	Soil: Use reduced tillage in arable fields Action Link

Crop production: Grow cover crops in arable fields

A replicated, randomized, controlled study in 1999–2009 in an irrigated tomato-cotton field in the San Joaquin Valley, California, USA (same study as (10)), found that winter cover crops had inconsistent effects on crop yields. Crop yield: Lower tomato yields were found in plots with cover crops, compared to plots without cover crops, in four of 10 years (95–118 vs 109–128 t/ha), but higher yields were found in one of 10 years (with conventional tillage: 142 vs 132 t/ha). Methods: Rainfed winter cover crops (Triticosecale triticale, Secale cereale Merced rye, and Vicia sativa common vetch) were planted on eight treatment plots, but not on eight control plots, in October 1999–2008. Crop residues were chopped in March. Reduced tillage or conventional tillage was used on half of these plots, in 1999–2009. The plots (9 x 82 m) had six raised beds each. Different numbers of tillage practices were used for conventional tillage (19–23 tractor passes, including disk and chisel ploughing) and reduced tillage (11–12 tractor passes, not including disk and chisel ploughing). Tomato seedlings were transplanted in April 2000–2009. Fertilizer and herbicide were used on all plots, and the tomatoes were irrigated. Tomatoes were grown in rotation with cotton.
Crop production: Use reduced tillage in arable fields

A replicated, randomized, controlled study in 1999–2009 in an irrigated tomato-cotton field in the San Joaquin Valley, California, USA (same study as (8)), found higher tomato yields in plots with reduced tillage, compared to conventional tillage. Crop yield: Higher tomato yields were found in plots with reduced tillage, compared to conventional tillage, in four of 10 years (102–120 vs 62–100 t/ha). Higher cover crop biomass was found in plots with reduced tillage, compared to conventional tillage (4,098 vs 3,609 t/ha). Methods: Reduced tillage or conventional tillage was used on eight tomato plots each, in 1999–2009. The plots (9 x 82 m) had six raised beds each. Winter cover crops (triticale, rye, and vetch) were planted on half of the plots, in October 1999–2008, and crop residues were chopped in March. Different numbers of tillage practices were used for conventional tillage (19–23 tractor passes, including disc and chisel ploughing) and reduced tillage (11–12 tractor passes, not including disc and chisel ploughing). Tomato seedlings were transplanted in April 2000–2009. Fertilizer and herbicide were used in all plots. Tomatoes were grown in rotation with cotton.
Soil: Grow cover crops in arable fields

A replicated, randomized, controlled study in 1999–2009 in an irrigated tomato-cotton field in the San Joaquin Valley, California, USA (same study as (10)), found more organic matter in soils with winter cover crops, compared to soils without cover crops. Organic matter: More carbon was found in soils with cover crops (26–29 vs 23–24 t total C/ha). Methods: Rainfed winter cover crops (triticale, rye, and vetch) were planted on 16 treatment plots, but not on 16 control plots, in October 1999–2008. Crop residues were chopped in March. The plots (9 x 82 m) had six raised beds each. Tomatoes were grown in rotation with cotton. Fertilizer and herbicide were used in all plots, and tomatoes and cotton were irrigated. Soil samples were collected in autumn 2007 (0–30 cm depth, 7.6 diameter soil cores, 6–8 subsamples/plot).
Soil: Use reduced tillage in arable fields

A replicated, randomized, controlled study in 1999–2009 in an irrigated tomato-cotton field in the San Joaquin Valley, California, USA (same study as (5)), found similar amounts of organic matter in soils with reduced tillage or conventional tillage. Organic matter: Similar amounts of carbon were found in soils with reduced tillage or conventional tillage (24–29 vs 23–26 t total C/ha). Methods: Reduced tillage or conventional tillage was used on 16 plots each, in 1999–2009. The plots (9 x 82 m) had six raised beds each. Rainfed winter cover crops (triticale, rye, and vetch) were planted on half of the plots, in October 1999–2008, and crop residues were chopped in March. Different numbers of tillage practices were used for conventional tillage (19–23 tractor passes, including disc and chisel ploughing) and reduced tillage (11–12 tractor passes, not including disc and chisel ploughing). Tomatoes and cotton were grown in rotation. Fertilizer and herbicide were used in all plots. Soil samples were collected in autumn 2007 (0–30 cm depth, 7.6 diameter soil cores, 6–8 subsamples/plot).