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Providing evidence to improve practice

Action: Other biodiversity: Add compost to the soil Mediterranean Farmland

Key messages

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Amphibians (0 studies)

Birds (0 studies)

Invertebrates (1 study): One replicated, controlled study from the USA, found no differences in invertebrate biodiversity between plots with or without added compost.

Mammals (0 studies)

Plants (4 studies): Four replicated, controlled studies (three randomized) from Italy, Spain, and the USA found more plant biomass in plots with added compost, compared to plots without added compost. One of these studies also found more plant cover and faster tree growth in plots with added compost. Another one also found sixteen species of rare plants only in plots with added compost. Another one found more plants in plots with added compost, compared to plots without added compost, in one of two years, but found similar numbers of plant species in plots with or without added compost.

Reptiles (0 studies)

Implementation options (0 studies)

Supporting evidence from individual studies

1 

A replicated, controlled study in 2001–2003 in a degraded wood pasture in Catalonia, Spain, found more plant cover, more plant biomass, and faster tree growth in plots with added compost, compared to plots without added compost. Plants: More plant cover, more herbaceous biomass, and faster oak tree Quercus humilis growth were found in plots with added compost (cover: 89% vs 60%; biomass: 2,700 vs 1,700 kg dry weight/ha; growth: 41 vs 34 cm/year). Methods: Composted sewage sludge was added to five treatment plots (10 t dry matter/ha), but not five control plots (no compost). Each plot was 20 x 5 m. To restore the wood pasture, shrubs and small trees were crushed and scattered on the soil, and grass seeds were sown. Soil was collected in soil cores (10 cores/plot, 0–20 cm depth).

 

2 

A replicated, randomized, controlled, paired study in 2008–2011 in grazed annual grasslands in California, USA, found more plant biomass in plots with added compost, compared to plots without added compost. Plants: More plant biomass (measured as carbon) was found in plots with added compost (50–175 more g C/m2/year, above ground, dry weight). Methods: Composted organic green waste was added to three treatment plots (129 g total N/m2), but not six control plots, at each of two sites (coastal grassland in Nicasio and valley grassland in Browns Valley). The plots were 25 x 60 m. Above-ground plant biomass was measured at the end of the growing season (1,800 cm2/plot).

 

3 

A replicated, randomized, controlled study in 2007–2013 in a fallow field in Campania, Italy, found more plants and plant biomass in plots with added compost, compared to plots without added compost. Plants: More plants were found in plots with added compost, compared to plots without it, in one of two years (2013: 1,023 vs 473 individuals/m2). More plant biomass was found in plots with added compost, compared to plots without it, in both years (2012: 401 vs 119 g dry weight/m2; 2013: 301 vs 111). Similar numbers of plant species were found in plots with or without added compost (12–21 species). Methods: Compost was added to four treatment plots (2007–2009: 30 Mg/ha dry weight; 2010–2013: 15 Mg/ha dry weight), but not to four control plots. The plots were 10 x 5 m. The compost was made from municipal solid waste and urban yard trimmings. The compost was added, and plots were tilled, in April each year (20 cm depth). Horticultural crops were grown in 2007–2011. In March 2012 and 2013, all plants (spontaneous growth) were collected from 1 x 1 m quadrats in each plot.

 

4 

A replicated, controlled study in 2014 in 29 organic vegetable fields on the Central Coast, California, USA, found no differences in invertebrate biodiversity between plots with or without added compost. Invertebrates: Similar numbers of invertebrates and invertebrate families were found in plots with or without added compost (data reported as model coefficients). Methods: In each of 29 vegetable fields, compost was added to one plot, but not to one adjacent plot (5 x 5 m plots), 1–2 months before lettuces were planted (25 t compost/ha, made from cow, chicken, and green manures). Lettuces were planted in spring (5–28 March) and summer (30 May–5 July). Invertebrates (insects, springtails, and spiders) were collected in pitfall traps (three/plot, 7.5 cm diameter) and pan traps (two/plot, blue and yellow, 15 cm diameter) after 48 hours of trapping (one sample when lettuces were seedlings and one when mature).

 

5 

A replicated, randomized, controlled study in 2008–2012 in two grazed grasslands in California, USA, found more plant biomass in plots with added compost. Sixteen species of rare plants were found only in plots with added compost. Plants: Before grazing, more plant biomass was found in plots with added compost, compared to plots without it (coastal prairie: 41% more; valley grassland: 71% more). Higher plant diversity was found in plots with added compost, compared to plots without it, in one of eight comparisons (coastal prairie, 2009: 7.5 vs 6 species/m2; Shannon evenness index). In the valley grassland, increases in the relative abundance of three grass species, and decreases in that of two forb and one bulb species, were found in plots with added compost, compared to plots without it. In the coastal prairie, sixteen rare species (<5% of observations) were found only in plots with added compost. The abundance of an invasive grass (medusahead Elymus caput-medusae) was lower in plots with added compost, in one of four comparisons (13% lower abundance in plots with compost), but that of an invasive forb (Carthamus lanatus) was no different. Methods: In December 2008, composted green waste (7 kg dry matter/m2, 129 g N/m2, C to N ratio of 11) was added to three plots at each of two sites (one valley grassland and one coastal prairie, both dominated by non-native annuals), but compost was not added to three control plots at each site. All plots (25 x 60 m plots) were in cattle-grazed paddocks (15 ha, rotationally grazed to 84 g standing/m2).

 

Referenced papers

Please cite as:

Shackelford, G. E., Kelsey, R., Robertson, R. J., Williams, D. R. & Dicks, L. V. (2017) Sustainable Agriculture in California and Mediterranean Climates: Evidence for the effects of selected interventions. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.