Conservation tillage and cover cropping influence soil properties in San Joaquin Valley cotton-tomato crop

Published source details Veenstra J.J., Horwath W.R., Mitchell J.P. & Munk D.S. (2006) Conservation tillage and cover cropping influence soil properties in San Joaquin Valley cotton-tomato crop. California Agriculture, 60, 146-153.
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This study is summarised as evidence for the following.

	Action	Category
	Soil: Use reduced tillage in arable fields Action Link
	Soil: Grow cover crops in arable fields Action Link

Soil: Use reduced tillage in arable fields

A replicated, randomized, controlled, before-and-after study in 1999–2004 in an irrigated tomato-cotton field in the San Joaquin Valley, California, USA (same study as (36)), found that tillage had inconsistent effects on nitrogen in soils. Phosphorus in soils increased after reduced tillage, but it did not change after conventional tillage. Nutrients: After four years, nitrogen increased in soils with conventional tillage (before: 1,300 lb/acre; after: 1,400–1,600), but decreased in soils with reduced tillage, in one of two comparisons (before: 1,400; after: 1,200), and increased in soils with reduced tillage, in one of two comparisons (before: 1,300; after: 1,600). After four years, nitrate increased in soils with reduced tillage, in one of two comparisons (before: 18 ppm; after: 25), but did not change in soils with conventional tillage (before: 16–17; after: 10–19). After four years, phosphorus increased in soils with reduced tillage (before: 7–8 ppm; after: 15–17), but did not change in soils with conventional tillage (before: 8; after: 7–9). 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 1999–2003, and crop residues were chopped in March. Different numbers of tillage practices were used (conventional tillage: 18–21 tractor passes, including disc and chisel ploughing; reduced tillage: 12–13 tractor passes, not including disc and chisel ploughing). Tomatoes and cotton were grown in rotation. Fertilizer and herbicide was used in all plots. Soil samples were collected in spring (before planting) and in autumn (after harvest), in 2000–2004 (0–30 cm depth; number and volume of samples not reported).
Soil: Grow cover crops in arable fields

A replicated, randomized, controlled, before-and-after study in 1999–2004 in an irrigated tomato-cotton field in the San Joaquin Valley, California, USA (same study as (27)), found more carbon and potassium in soils after four years with winter cover crops, but found less carbon and no changes in potassium after four years without cover crops. Cover crops had inconsistent effects on nitrogen in soils. Organic matter: Carbon increased in soils with cover crops, after four years (before: 10,000 lb/acre; after: 12,000), and decreased in soils without cover crops, after four years (before: 10,000; after: 9,000). Nutrients: After four years, nitrogen increased in soils with cover crops (before: 1,300 lb/acre; after: 1,400–1,600), but decreased in soils without cover crops, in one of two comparisons (before: 1,400; after: 1,300), and increased in one of two comparisons (before: 1,300; after: 1,600). After four years, nitrate did not change in soils with cover crops (before: 16–19 ppm; after: 10–16), but increased in soils without cover crops, in one of two comparisons (before: 18; after: 25). After four years, potassium increased in soils with cover crops (before: 258–271 ppm; after: 314–319), but did not change in soils without cover crops (before: 271–278; after: 300–303). Methods: Rainfed winter cover crops (triticale, rye, and vetch) were planted on 16 treatment plots, but not on 16 control plots, in October 1999–2003. 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 was used in all plots, and tomatoes and cotton were irrigated. Soil samples were collected in spring (before planting) and in autumn (after harvest), in 2000–2004 (0–30 cm depth; number and volume of samples not reported).