Rainfed olive farming in south-eastern Spain: long-term effect of soil management on biological indicators of soil quality

Published source details Moreno B., Garcia-Rodriguez S., Cañizares R., Castro J. & Benitez E. (2009) Rainfed olive farming in south-eastern Spain: long-term effect of soil management on biological indicators of soil quality. Agriculture, Ecosystems & Environment, 131, 333-339.
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This study is summarised as evidence for the following.

	Action	Category
	Grow cover crops beneath the main crop (living mulches) or between crop rows Action Link
	Soil: Plant or maintain ground cover in orchards or vineyards Action Link
	Change tillage practices Action Link

Grow cover crops beneath the main crop (living mulches) or between crop rows

A randomized, replicated experiment in 2008 on fine sandy loam soil in Spain (Moreno et al. 2009) found that bacteria counts and activity were highest in the mowed cover crop (0.95 billion/g soil and 1,087 μg PNP/g/h) and lowest when herbicides were added (1.37 billion/g soil and 519 μg PNP/g/h). All treatments had a higher microbial diversity and soil organic carbon levels than the treatment with no cover. There were four long-term treatments in an olive Oleo europaea orchard: tillage (3-4 passes with disk harrow to 30 cm depth and tine harrowing (remove small weeds and smooth the soil surface ready for sowing) in summer), no-till, no cover crop (treated with glyphosate herbicide), cover crop (weeds left to grow) treated with herbicides (in March), and mown cover crop (herbicide-free). Each plot was 11 x 11 m and consisted of 16 olive trees. Each treatment was replicated four times. Two soil samples were taken from the centre of each plot. Soil bacterial numbers and community structure were measured. PNP (purine nucleoside phosphorylase) an enzyme which breaks down proteins, was used as an indicator of bacterial numbers.
Soil: Plant or maintain ground cover in orchards or vineyards

A replicated, randomized, controlled study in a rainfed olive orchard in southeast Spain (years of study not reported, but same study as (5)) found more organic matter and soil organisms in soils with cover crops, compared to soils without cover crops, under olive trees. Organic matter: More organic carbon was found in soils with cover crops, compared to soils without cover crops (8.3–9.9 vs 5.4 g C/kg soil). Soil organisms: More bacteria were found in soils with cover crops, compared to soils without cover crops (950–1,400 vs 32–230 million 16S rRNA copies/g soil). Bacterial diversity was similar in soils with or without cover crops (data reported as Shannon diversity index). Methods: Herbicide was used on four control plots in autumn, but not on eight treatment plots, which had resident vegetation. The resident vegetation was controlled in spring with herbicide (four plots) or mowing (four plots). Plots had 16 olive trees each. Plots were not tilled. Foliar fertilizer was used. Two soil samples were collected in each plot (0–30 cm depth, sampling date not reported).
Change tillage practices

A randomized, replicated experiment in 2008 on fine sandy loam soil in Spain (Moreno et al. 2009) found greater soil organic carbon levels in tilled soil (9.94 g C/kg) and soil with a mown cover crop (9.91 g C/kg) than soil with no cover crop (5.36 g C/kg). Bacteria counts under tillage were lower (233 million/g soil) than under mown cover crops (952 million/g soil) or cover crops plus herbicide (1.4 billion/g soil), but were higher than in the no cover crop (32 million/g soil). There were four long-term treatments in an olive Olea europaea orchard: tillage (3-4 passes with disk harrow to 30 cm depth, tine harrow in summer); no-till and no cover (treated with glyphosate herbicide); cover crop plus herbicide (treated in March); cover crops plus mower (herbicide-free). Each plot was 11 x 11 m and consisted of 16 trees. Each treatment was replicated four times. Two soil samples were taken from the centre of each plot. Soil bacterial numbers and community structure were measured.