Soil management to enhance bacterivore and fungivore nematode populations and their nitrogen mineralisation function

Published source details Ferris H., Venette R.C. & Scow K.M. (2004) Soil management to enhance bacterivore and fungivore nematode populations and their nitrogen mineralisation function. Applied Soil Ecology, 25, 19-35.
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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

Crop production: Grow cover crops in arable fields

A replicated, randomized, controlled study in 1995–1998 in an irrigated tomato field in Davis, California, USA, found higher crop yields in plots with winter cover crops, compared to plots without cover crops, but summer cover crops had inconsistent effects on crop yields. Crop yield: Higher tomato yields were found in plots with winter cover crops, compared to plots without them, in one of four comparisons (1996–1997: 104 vs 94 t/ha). Higher tomato yields were found in plots with summer cover crops, compared to plots without them, in one of three comparisons (1996–1997: 108 vs 96 t/ha), but lower yields were found in one of three comparisons (1997–1998: 34 vs 45 t/ha). Methods: Cover crops were planted in different numbers of plots in different years (1995–1996: 16 plots with winter cover crops, eight plots with summer cover crops, 16 control plots without cover crops; 1996–1997: 12 winter, four summer, eight controls; 1997–1998: 28 summer and/or winter, four controls). Plots were 3–4 beds wide and 10 m long. Some summer cover crops were retained over winter, and some were mown and replaced with winter cover crops. Summer cover crops were mixtures of oats and legumes, planted in August–September. Winter cover crops were legumes (Vicia sativa common vetch), planted in November. In spring, cover crop residues were mown and either removed or evenly distributed among all plots and incorporated into the soil. Some plots were irrigated during the cover-cropping season. All plots were irrigated during the tomato-growing season. Herbicide was used on all plots, but no inorganic fertilizer was used.
Soil: Grow cover crops in arable fields

A replicated, randomized, controlled study in 1995–1998 in an irrigated tomato field in Davis, California, USA, found more nitrogen, more nematodes, and a higher proportion of bacteria-feeding nematodes, in soils with cover crops, compared to soils without cover crops. Nutrients: More nitrogen was found in soils with winter cover crops, compared to plots without cover crops, in two of three comparisons (10–31 vs 7–16 µg N/g dry soil, cumulative). Soil organisms: A higher proportion of bacteria-feeding nematodes, compared to fungus-feeding nematodes, were found in soils with cover crops, compared to soils without cover crops, in four of six comparisons (data reported as the Channel Index). Similar numbers of nematodes were found in soils with or without winter cover crops, in 1995–1996 (bacterial or fungal feeders: 3,100–9,800 vs 3,800–8,300 nematodes/litre soil). More nematodes were found in soils with summer cover crops, compared to soils without cover crops, in one of two comparisons in 1995–1996 (bacterial feeders: 12,000 vs 3,900 nematodes/litre soil). More nematodes were found in soils with summer and/or winter cover crops, compared to soils without cover crops, in four of six comparisons in 1996–1997 (bacterial and fungal feeders, in plots with irrigation: 2,300–3,600 vs 400–500 nematodes/litre soil), but similar numbers were found in soils with or without winter cover crops in 1997–1998 (bacterial and fungal feeders: 1,200–3,800). Similar numbers of other nematodes (omnivores and predators) were found in soils with or without cover crops (data not reported). Greenhouse gases: Similar amounts of carbon dioxide were found in soils with or without cover crops (soil basal respiration in 1995–1996: 10–13 µg CO₂/g dry soil/hour). Methods: Cover crops were planted in different numbers of plots in different years (1995–1996: 16 plots with winter cover crops, eight plots with summer cover crops, 16 control plots without cover crops; 1996–1997: 12 winter, four summer, eight controls; 1997–1998: 28 summer and/or winter, four controls). Plots were 3–4 beds wide and 10 m long. Some summer cover crops were retained over winter, and some were mown and replaced with winter cover crops. Summer cover crops were mixtures of oats and legumes, planted in August–September. Winter cover crops were legumes (Vicia sativa common vetch), planted in November. In spring, cover crop residues were mown and either removed or evenly distributed among all plots and incorporated into the soil. Some plots were irrigated during the cover-cropping seasons. All plots were irrigated during the tomato-growing season. Herbicide was used on all plots, but no inorganic fertilizer was used. Soil samples (16 soil cores/plot, 30 cm depth, 2.5 cm diameter) were collected at different times for nutrients (once per week, 1–7, 11, and 14 weeks after incorporating cover crop residues, in spring), greenhouse gases (after 1, 4, and 7 weeks), or soil organisms (four times in summer/autumn, and 1, 4, 7, 11, 14, and 18 weeks after incorporating residues), in 1995–1996. In 1996–1998, soil samples for nutrients and soil organisms were collected less frequently (1996–1997: four times in spring; 1997–1998: once in autumn, once in spring, and once when tomatoes were harvested).