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Providing evidence to improve practice

Action: Crop production: Add compost to the soil Mediterranean Farmland

Key messages

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Crop yield (8 studies): Three replicated, controlled studies (two randomized) from Italy, Spain, and the USA found higher crop yields in plots with added compost, compared to plots without added compost, in some comparisons or all comparisons. Two replicated, randomized, controlled studies from Italy and the USA found inconsistent differences in crop yields (sometimes higher, sometimes lower) between plots with or without added compost. Three replicated, randomized, controlled studies from Spain and the USA found similar crop yields in plots with or without added compost. Of two replicated, randomized, controlled studies from Spain, one study found higher yields of barley straw in plots with added compost, compared to plots without added compost, and one study did not.

Crop quality (0 studies)

Implementation options (1 study): One replicated, randomized, controlled study from the USA found similar crop yields in plots with added compost that did or did not also have added fertilizer.

 

Supporting evidence from individual studies

1 

A replicated, randomized, controlled study in 1995 in a broccoli field in the Salinas Valley, California, USA, found similar broccoli yields in plots with or without added compost. Crop yield: Similar broccoli yields were found in plots with or without added compost (13–15 Mg/ha). Implementation options: In plots with added compost, similar broccoli yields were found with or without added fertilizer (13–15 vs 14–15 Mg/ha). Methods: There were four plots for each of three compost treatments (0, 22, or 44 Mg/ha). Fertilizer (165 kg ammonium nitrate/ha) was added to half (6.1 x 7.7 m) of each plot. The compost was made from green wastes (>30%), cow manure (>20%), spoiled hay (>15%), clay soil (>5%), and crop processing residues. Crops were harvested and weighed on 10, 14, and 17 November 1995.

2 

 

A replicated, randomized, controlled study in 1998–2000 in an irrigated vegetable field in the Salinas Valley, California, USA, found inconsistent differences in crop yields between plots with or without added compost. Crop yield: Higher lettuce yields were found in plots with added compost, compared to plots without added compost, in one of six comparisons (410 vs 390 g dry weight/m2), but lower lettuce yields were found in two of six comparisons (280–390 vs 310–430). No differences in broccoli yields were found between plots with or without added compost (620–640 vs 610–630 g dry weight/m2). Larger lettuce or broccoli plants were found in plots with added compost, compared to plots without added compost, in four of eight comparisons (lettuce: 1,080–1,150 vs 1,030–1,100 g fresh weight/plant; broccoli: 240–270 vs 210–220), but smaller lettuces were found in two of six comparisons (750–1,050 vs 790–1,110). Methods: There were four plots (0.52 ha), for each of four treatments (minimum tillage or conventional tillage, with or without added organic matter). In plots with added organic matter, compost was added two times/year, and a cover crop (Merced rye) was grown every autumn or winter. The compost was made from municipal yard waste, salad packing plant waste, horse manure, clay, straw, and other compost. Lettuce or broccoli crops were grown in raised beds. Sprinklers and drip irrigation were used in all plots. Crops were collected in two 2 m2 areas/plot. It was not clear whether these results were a direct effect of adding compost or growing cover crops.

 

3 

A replicated, randomized, controlled study in 2002–2005 in a barley field in Toledo, Spain, found no difference in grain yields, but found higher straw yields, in barley plots with added compost, compared to barley plots without added compost. Crop yield: Similar grain yields were found in barley plots with or without added compost (0.7–1.9 vs 1.2–1.6 t dry weight/ha). Higher straw yields were found in barley plots with added compost, compared to plots without added compost (3.3–3.4 vs 1.3–1.8 t dry weight/ha). Methods: The compost was made from sewage sludge. There were four plots (10 x 3 m) for each of four fertilizer treatments (20 or 80 t compost/ha, applied once in three years or once/year) and one control (no fertilizer). Plots were fertilized in mid-September and planted in mid-October. Barley plants were harvested (1 m2/plot), in June 2005.

 

4 

A replicated, randomized, controlled study in 2001–2009 in an irrigated orchard in Italy found higher nectarine yields in plots with added compost, compared to plots without added compost. Crop yield: Higher yields were found in plots with added compost, in one of six comparisons (38 vs 26 kg/tree). Methods: There were four plots for each of three compost treatments (5 t/ha in May, 5 t/ha split into two applications, in May and September, or 10 t/ha split into two), and there were four control plots (no fertilizer; plot size not reported). The compost was made from domestic organic waste and urban pruning material (50% each). Compost was tilled into the soil (25 cm depth). Yield was measured in the four central trees of each plot, every year.

5 

A replicated, randomized, controlled study in 2006 in a barley field in the Henares river basin, Spain, found similar barley yields in plots with or without added compost. Crop yield: Similar barley yields were found in plots with or without added compost (1,879 vs 1,825 kg grain and straw/ha). Methods: Composted municipal solid waste (125 kg available N/ha) was added to three treatment plots, but not to three control plots, in January. Plots were 30 m2. Plots were cultivated (5 cm depth) to incorporate the compost into the soil. Barley was planted in January and harvested in June.

 

6 

A replicated, randomized, controlled study in 2009–2011 on two farms in the Salerno district, Italy, found higher crop yields in plots with added compost, compared to plots without added compost, in most crop cycles. Crop yield: Higher crop yields were found in plots with added compost, compared to plots without added compost, in 12 of 14 crop cycles (38–39% higher), but lower yields were found in 2 of 14 crop cycles (23–25% lower). Methods: On each of two farms, there were three plots (7 x 5 m) for each of four treatments (30 or 60 Mg organic matter/ha/year, with a carbon-to-nitrogen ratio of 15:1 or 25:1) and there were three control plots (no organic matter). Organic matter was added in February 2009, February 2010, and June 2011. It was made from the composted organic fraction of municipal solid waste, and it was mixed with wood scraps to control the carbon-to-nitrogen ratio. Between the two farms, one pepper, three melon, four kohlrabi, and six lettuce crops (14 crop cycles) were grown in plastic tunnels. It was not clear whether these results were a direct effect of adding composted municipal waste or wood scraps.

7 

A replicated, randomized, controlled study in 2013 in greenhouses in southeast Spain found higher fruit yields in tomatoes with added compost, compared to tomatoes without added compost. Crop yield: Higher fruit yields were found in tomatoes with added compost, compared to tomatoes without added compost, in one of four comparisons (compost R1, with low doses of mineral fertilizer: 5.8 vs 4.2 kg fresh weight fruit/ha). Methods: There were four replicates for each of four treatments (50.5 t/ha of compost R1 or 40 t/ha of compost R2, with low or medium doses of mineral fertilizer) and two controls (low or medium doses of mineral fertilizer). Mineral fertilizer (Hoagland’s solution) was added in two of three waterings (medium dose) or one of five waterings (low dose). Compost R1 was made from sheep and goat manure. Compost R2 was made from alperujo (olive-mill waste), manure, and olive prunings. Ripe red fruits were harvested each week (91- to 161-day-old plants).

8 

A replicated, controlled study in 2014 in 29 organic vegetable fields on the Central Coast, California, USA, found higher lettuce yields in plots with added compost, compared to plots without added compost. Crop yield: Larger lettuces were found in plots with added compost, compared to plots without added compost (65 g larger, fresh weight). 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). Lettuce weights were measured at maturity in one 1 x 1 m quadrat/plot.

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.