Providing evidence to improve practice

Action: Water: Add compost to the soil Mediterranean Farmland

Key messages

Water use (0 studies)

Water availability (4 studies): Two replicated, randomized, controlled studies from Turkey and the USA found more water in soil with added compost, compared to soil without added compost, in some or all comparisons. One replicated, randomized, controlled study from the USA found similar amounts of water in soil with or without added compost. One replicated, controlled study from Spain found that less water was lost as runoff from soil with added compost, compared to soil without added compost.

Pathogens and pesticides (0 studies)

Nutrients (2 studies): One replicated, randomized, controlled study from Spain found more nitrogen, phosphorus, and potassium in runoff from plots with added compost, compared to plots without added compost. One replicated, randomized, controlled study from Portugal found that more nitrate was leached from plots with added compost, compared to plots without added compost, in one of four comparisons.

Sediments (1 study): One replicated, randomized, controlled study from Spain found more organic matter in runoff from plots with added compost, compared to plots without added compost.

Implementation options (1 study): One replicated, randomized, controlled study from Portugal found that similar amounts of nitrate were leached from plots with or without added compost, if the compost was split into two small applications, compared to one large application.

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 amounts of water in soils with added compost, compared to soils without added compost. Water availability: Similar amounts of water were found in soils with or without added compost (17–18% vs 17% water by weight). 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. Soil samples were collected on 24 October 1995 (0–20 cm depth).

 

2 

A replicated, controlled study (year not reported) on a slope in Murcia, Spain, found less water loss in plots with added compost, compared to plots without added compost. Water availability: Less water was lost as runoff from plots with added compost, compared to plots without added compost, after rainfall events (eight initial events: 2.3 vs 6.0 litres water/m2; later events: 6.2 vs 12.6). Methods: Composted municipal waste was added to three treatment plots, but not three control plots (10 x 3 m plots, 15% slope). Runoff water was collected from the lower edge of each plot, after each rainfall event. Enough compost was added to the soil to increase its organic carbon content by 2%. The soil was rotovated to a depth of 20 cm, to incorporate the compost.

 

3 

A replicated, randomized, controlled study in 1995–1999 in farmland in southern Turkey found more available water in soils with added compost, compared to soils without added compost. Water availability: More available water was found in soils with added compost, compared to soils without added compost (0.17 vs 0.09 cm3 water/cm3 soil). Methods: Compost (25 t/ha) was added to three treatment plots (10 x 20 m), but not three control plots. The compost was made of grass, stubble, and leaves. Wheat, sweet peppers, maize, and wheat were grown in rotation. Soils were sampled in 1999, after harvesting the last wheat crop. The difference between water retention at field capacity (–33 kPa) and at permanent wilting point (–1,500 kPa) was used to determine available water content.

 

4 

A replicated, randomized, controlled study in 1998–2000 in an irrigated vegetable field in the Salinas Valley, California, USA, found more water in soils with added compost, compared to soils without added compost, in six of 16 comparisons. Water availability: More water was found in soils with added compost, compared to soils without added compost, in six of 16 comparisons (0.10–0.27 vs 0.07–0.26 g water/g soil, 0–15 cm depth). 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. Soils were disturbed to different depths (conventional tillage: 50 cm with disking, cultivating with a liliston, sub-soiling, bed re-making, and bed-shaping; minimum tillage: 20 cm with a liliston, rollers, and bed-shaping). Soils were collected, along the planting line, with 6 cm soil cores. It was not clear whether these results were a direct effect of adding compost or growing cover crops.

 

5 

A replicated, randomized, controlled study in 2001–2005 in the Guadalquivir Valley, Andalusia, Spain, found more nutrients and sediments in runoff water from soils with added compost, compared to soils without added compost, after rainfall. Nutrients: More nitrate was found in runoff from soils with added compost, compared to soils without added compost, after rainfall (60 mm rainfall/hour: 0.12–0.35 vs 0.07–0.09 mg/litre water; 140 mm rainfall/hour: 0.31–0.67 vs 0.10–0.19). More ammonium was found in runoff from soils with added compost, compared to soils without added compost, after rainfall (60 mm rainfall/hour: 5–9 vs 1 mg/litre water; 140 mm rainfall/hour: 13–23 vs 2–3). More phosphorus was found in runoff from soils with added compost, compared to soils without added compost, after rainfall (60 mm rainfall/hour: 0.2–0.7 vs 0 mg/litre water; 140 mm rainfall/hour: 0.7–1.3 vs 0). More potassium was found in runoff from soils with added compost, compared to soils without added compost, after rainfall (60 mm rainfall/hour: 3.5–6.8 vs 1–1.4 mg/litre water; 140 mm rainfall/hour: 8.5–16.1 vs 0.9–2.5). Sediments: More organic matter was found in runoff from soils with added compost, compared to soils without added compost, after rainfall (60 mm rainfall/hour: 6–9 vs 0 mg C/litre water; 140 mm rainfall/hour: 14–21 vs 0). Methods: There were four plots (9 x 9 m) for each of two treatments (10 or 20 t compost/ha) and one control (no compost). The compost was added in October 2001–2004, and soils were ploughed to a depth of 25 cm. Soils were watered to simulate rainfall and runoff water was collected in October 2002–2005 (60 or 140 mm rainfall/hour).

 

6 

A replicated, randomized, controlled study in 2006–2008 in a cereal field in the Castelo Branco region, Portugal, found that more nitrate was leached from soils with added compost, compared to soils without added compost, in one of four comparisons. Nutrients and Implementation options: With a single application of compost in the spring, more nitrate was leached from plots with added compost, compared to plots without added compost, in 2006/2007 (111 vs 49 kg NO3-N/ha), but not in 2007/2008 (32 vs 23 kg). With a split application (some in spring, some in autumn), there were no significant differences between plots with and without added compost (2006/2007: 107 vs 49 kg NO3-N/ha; 2007/2008: 35 vs 23 kg). Methods: Water in the soil was collected in porous ceramic suction cup samplers (four/plot, 0.6–0.7 m depth, 50 kPa for 24 hours), whenever drainage occurred (October–November and April–May; 16 samples in total). There were three plots (5.6 x 8 m) for each of two treatments (single application or split application of compost) and one control (no compost). The compost was made from municipal waste. Maize was grown in spring–summer, and oats were grown in autumn–winter.

 

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.