Biodiversity: Three replicated trials from Canada, Poland and Spain (including one also controlled, one also randomized and one also controlled and randomized) showed that adding mulch to crops (whether shredded paper, municipal compost or straw) increased soil animal and fungal numbers, diversity and activity. Of these, one trial also showed that mulch improved soil structure and increased soil organic matter.
Nutrient loss:One replicated study from Nigeria found higher nutrient levels in continually cropped soil.
Erosion: Five studies from India, France, Nigeria and the UK (including one controlled, randomized, replicated trial, one randomized, replicated trial, two replicated (one also controlled), and one controlled trial) found that mulches increased soil stability, and reduced soil erosion and runoff. One trial found that some mulches are more effective than others.
Drought:Two replicated trials from India found that adding mulch to crops increased soil moisture.
Yield:Two replicated trials from India found that yields increased when either a live mulch or vegetation barrier combined with mulch was used.
Biodiversity: Five controlled trials from China and India (four also randomized and replicated), and one study from Japan found higher microbial biomass and activity in soils with a mix of manure and inorganic fertilizers. Manure alone also increased microbial biomass. One trial found increased microbial diversity.
Erosion: One controlled, replicated trial from India found that mixed amendments were more effective at reducing the size of cracks in dry soil than inorganic fertilizers alone or no fertilizer.
SOC loss: Four controlled, randomized, replicated trials and one controlled trial from China and India found more organic carbon in soils with mixed fertilizers. Manure alone also increased organic carbon. One trial also found more carbon in soil amended with inorganic fertilizers and lime.
SOM loss: Two controlled, randomized, replicated trials from China and India found more nutrients in soils with manure and inorganic fertilizers. One controlled, randomized, replicated trial from China found inconsistent effects of using mixed manure and inorganic fertilizers.
Yield: Two controlled, randomized, replicated trials from China found increased maize Zea mays yield in soils with mixed manure and inorganic fertilizer amendments.
Nutrient loss:Three of five replicated trials from New Zealand and the UK measured the effect of applying nitrification inhibitors to the soil and three found reduced nitrate losses and nitrous oxide emissions, although one of these found that the method of application influenced its effect [Thompson]. One trial found no effect on nitrate loss. One trial found reduced nutrient and soil loss when aluminium sulphate was applied to the soil.
Soil organic matter: Five of six studies (including three controlled, randomized and replicated and one randomized and replicated) from Australia, China, India, Syria and the UK testing the effects of adding chemical compounds to the soil showed an increase in soil organic matter or carbon when nitrogen or phosphorus fertilizer was applied. One site comparison study showed that a slow-release fertilizer resulted in higher nutrient retention. One study found higher carbon levels when NPK fertilizers were applied with straw, than when applied alone, and one replicated study from France found higher soil carbon when manure rather than chemical compounds were applied.
Yield: One replicated trial from India and a trial from the Philippines showed that maize, wheat and rice yield increased with increased fertilizer application.
Biodiversity:One randomized, replicated experiment from Belgium found increased microbial biomass when crop remains and straw were added.
Compaction:One study from India found improved soil structure when straw was incorporated. One before-and-after trial from the UK found that incorporating straw residues by discing (reduced tillage) did not improve anaerobic soils (low oxygen levels) in compacted soils.
Erosion: Two randomized, replicated studies from Canada and India measured the effect of incorporating straw on erosion. One found straw addition reduced soil loss, and one found mixed effects depending on soil type.
Nutrient loss:Four replicated studies from Belgium, the UK and the USA (one also controlled, one also randomized, and two also controlled and randomized) reported higher soil nitrogen levels when compost or straw was applied, but mixed results when processed wastes were added. One also found reduced nitrate leaching when straw was incorporated. One replicated study from China and the Philippines found mixed results depending on site.
Soil organic carbon: Six studies from China, Denmark and India measured the effect of incorporating plant material into the soil. All (including one replicated, two randomized, replicated studies, one controlled, randomized, replicated studies and one controlled before-and-after site comparison) found higher carbon levels when plant material was added. One found higher carbon levels when straw was applied along with NPK fertilizers. One also found larger soil aggregates. One replicated study from China and the Philippines found mixed results depending on site.
Yield:One replicated trial from Denmark found higher barley yield when straw was incorporated. One trial from the Philippines found higher grain yields when crop remains were incorporated earlier in the season.
Biodiversity loss: Three controlled, replicated studies from the UK and USA found higher microbial biomass when manure or compost was applied, and higher microbial respiration when poultry manure was applied.
Erosion:One controlled, randomized, replicated study from India found lower soil loss and water runoff with manure application in combination with other treatments.
Nutrient management:Four studies from Canada, Spain, the UK and the USA measured the effect of a variety of manure types on soil nutrient levels. Of these, three randomized, replicated studies (two also controlled) found reduced nutrient loss and higher nitrogen levels when farmyard or poultry manure was applied. One also found lower nutrient loss when farmyard manure (rather than poultry manure or slurry) was applied in winter rather than autumn. One controlled replicated study found higher nitrate leaching.
Soil organic carbon: Four studies (including three controlled, replicated studies (one also randomized) and a review) from India, Japan and the UK found higher carbon levels when manures were applied.
Soil organic matter:One controlled, randomized, replicated study from Turkey found higher organic matter, larger soil aggregations and a positive effect on soil physical properties when manure and compost were applied. Two studies from Denmark and Germany found no effect of manure on organic matter levels.
Yield: Four controlled, replicated studies (including three also randomized) from India, Spain and Turkey found higher crop yields when manures or compost were applied. One study found higher yields when manure were applied in combination with cover crops.
Two controlled, replicated trials in Spain and the United Kingdom measured the effect of adding wastes to the soil. One trial found that adding municipal compost to semi-arid soils greatly reduced soil loss and water runoff. One found mixed results of adding composts and wastes.