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Data extracted in November 2020
Fiche created in November 2023
Note to the reader: This general fiche summarises all the environmental and climate impacts of GREEN MANURE found in a review of 13 synthesis papers[1]. These papers were selected from an initial number of 32 obtained through a systematic literature search strategy, according to the inclusion criteria reported in section 4. The impacts reported here are those for which there is scientific evidence available in published synthesis papers, what does not preclude the farming practice to have other impacts on the environment and climate still not covered by primary studies or by synthesis papers.
The synthesis papers review a number of primary studies ranging from 21 to 339. Therefore, the assessment of impacts relies on a large number of results from the primary studies, obtained mainly in field conditions, or sometimes in lab experiments or from model simulations.
1. DESCRIPTION OF THE FARMING PRACTICE
- Description:
- Fertilisation using green manure is the use of a cover crop sown on an agricultural field to fertilise the soil for the following crop, mainly through the intake of nitrogen.[2]
- Key descriptors:
- Green manure consists of an herbaceous cover crop (either a legume, a non-legume or a mix) grown in alternance to cash crops, that is not harvested, and it is typically killed, chemically or mechanically, ahead of cash crop planting[3]
- The main objective of green manure is to substitute, partially or totally, mineral-nitrogen (N) fertilisers. Consequently, we only included papers where the fertilisation strategy was clearly stated, by comparing the use of green manure to either mineral-N fertilisation or to absence of mineral-N fertilisation.
- We excluded synthesis papers where the fertilisation strategy was not clearly stated. We also excluded synthesis papers that reported impacts of cover crops which are removed from the field (not used as green manure), or that only considered the impacts related to the period cover crops are in the field (no data on fertilisation of cash crops).
2. EFFECTS OF THE FARMING PRACTICE ON CLIMATE AND ENVIRONMENTAL IMPACTS
We reviewed the impacts of green manure (either a legume, a non-legume or a mix cover crop species) compared to bare soil (no cover crop) without any fertilisation and to bare soil with mineral-N fertilisation (Table 1).
The table below shows the number of synthesis papers with statistical tests reporting i) a significant difference between the Intervention and the Comparator, that is to say, a significant statistical effect, which can be positive or negative; or ii) a non-statistically significant difference between the Intervention and the Comparator. In addition, we include, if any, the number of synthesis papers reporting relevant results but without statistical test of the effects. Details on the quality assessment of the synthesis papers can be found in the methodology section of this WIKI.
Out of the 13 selected synthesis papers, 7 included studies conducted in Europe, and 12 have a quality score higher than 50%.
Table 1: Summary of effects. Number of synthesis papers reporting positive, negative or non-statistically significant effects on environmental and climate impacts. The number of synthesis papers reporting relevant results but without statistical test of the effects are also provided. When not all the synthesis papers reporting an effect are of high quality, the number of synthesis papers with a quality score of at least 50% is indicated in parentheses. Some synthesis papers may report effects for more than one impact, or more than one effect for the same impact.
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| Statistically tested | Non-statistically tested | ||
Impact | Metric | Intervention | Comparator | Significantly positive | Significantly negative | Non-significant | |
Increase Carbon sequestration | Soil carbon organic | Cover crop as green manure | No cover crop | 2 | 0 | 0 | 0 |
Decrease GHG emissions | CH4 emission | Cover crop as green manure | No cover crop | 0 | 1 | 0 | 0 |
Decrease GHG emissions | N2O emission | Cover crop as green manure | No cover crop | 1 | 2 | 3 | 0 |
Decrease Nutrient leaching and run-off | N loss | Cover crop as green manure | No cover crop | 1 | 0 | 0 | 0 |
Decrease Pests and diseases | Food crop damage | Cover crop as green manure | No cover crop | 0 | 0 | 1 | 0 |
Decrease Pests and diseases | Weed population | Cover crop as green manure | No cover crop | 1 | 0 | 1 | 0 |
Increase Plant nutrient uptake | Nutrient use efficiency | Cover crop as green manure | No cover crop | 1 | 0 | 0 | 0 |
Increase Soil biological quality | Soil microbial parameters | Cover crop as green manure | No cover crop | 2 | 0 | 1 | 0 |
Increase Soil nutrients | Soil nitrogen | Cover crop as green manure | No cover crop | 1 | 0 | 0 | 1 |
Increase Crop yield | Crop yield | Cover crop as green manure | No cover crop | 5 (4) | 2 | 5 | 0 |
3. FACTORS INFLUENCING THE EFFECTS ON CLIMATE AND ENVIRONMENTAL IMPACTS
The factors significantly influencing the size and/or direction of the effects on the impacts, according to the synthesis papers included in this review, are reported below. Details about the factors can be found in the summaries of the meta-analyses available in this WIKI.
Table 2: List of factors reported to significantly affect the size and/or direction of the effects on environmental and climate impacts, according to the synthesis papers reviewed. The reference number of the synthesis papers where those factors are explored is given in parentheses.
Impact | Factors |
Carbon sequestration | Cover crop management (Ref2) and Cover crop type (Ref2) |
GHG emissions | Cover crop management (Ref2), Cover crop type (Ref2) and NA (Ref6) |
Nutrient leaching and run-off | N cover crop input to soil (Ref12) |
Soil biological quality | Climate (Ref1), Fertilizer rate (Ref1) and Termination type (Ref1) |
Soil nutrients | Cover crop management (Ref2) and Cover crop type (Ref2) |
Crop yield | Climate (Ref12), Cover crop phenology (Ref12), Cover crop type (Ref13), Soil type (Ref10, Ref12) and Tillage (Ref12) |
4. SYSTEMATIC REVIEW SEARCH STRATEGY
Table 3: Systematic review search strategy - methodology and search parameters.
Parameter | Details |
Keywords | WOS: TOPIC: ("crop manur*" OR "green manur*" OR (legum* near/3 fert*) OR ("nitrogen fix* crop*" near/3 fert*) OR ("nitrogen fix* crop*" near/3 amend*)) AND TOPIC: ("meta-analy*" OR "systematic* review*" OR "evidence map" OR "global synthesis" OR "evidence synthesis" OR "research synthesis") |
Time reference | No time restriction. |
Databases | Web of Science and Scopus: run on 01 November 2020 |
Exclusion criteria | The main criteria that led to the exclusion of a synthesis paper are: |
5. SYNTHESIS PAPERS INCLUDED IN THE REVIEW
Table 4: List of synthesis papers included in this review. More details can be found in the summaries of the meta-analyses.
Ref Num | Author(s) | Year | Title | Journal | DOI |
Ref1 | Kim, N; Zabaloy, MC; Guan, KY; Villamil, MB | 2020 | Do cover crops benefit soil microbiome? A meta-analysis of current research | SOIL BIOLOGY & BIOCHEMISTRY, 142, 107701. | 10.1016/j.soilbio.2019.107701 |
Ref2 | Muhammad, I., Sainju, U.M., Zhao, F., (...), Fu, X., Wang, J. | 2019 | Regulation of soil CO2 and N2O emissions by cover crops: A meta-analysis | Soil and Tillage Research 192, pp. 103-112 | 10.1016/j.still.2019.04.020 |
Ref3 | Shackelford, GE; Kelsey, R; Dicks, LV | 2019 | Effects of cover crops on multiple ecosystem services: Ten meta-analyses of data from arable farmland in California and the Mediterranean | LAND USE POLICY, 88, 104204. | 10.1016/j.landusepol.2019.104204 |
Ref4 | Ding, WC; Xu, XP; He, P; Ullah, S; Zhang, JJ; Cui, ZL; Zhou, W | 2018 | Improving yield and nitrogen use efficiency through alternative fertilization options for rice in China: A meta-analysis | FIELD CROPS RESEARCH, 227, 11–18. | 10.1016/j.fcr.2018.08.001 |
Ref5 | Knapp, S; van der Heijden, MGA | 2018 | A global meta-analysis of yield stability in organic and conservation agriculture | NATURE COMMUNICATIONS, 9:3632. | 10.1038/s41467-018-05956-1 |
Ref6 | Han, Z; Walter, MT; Drinkwater, LE | 2017 | N2O emissions from grain cropping systems: a meta-analysis of the impacts of fertilizer-based and ecologically-based nutrient management strategies | NUTRIENT CYCLING IN AGROECOSYSTEMS, 107, 335-355. | 10.1007/s10705-017-9836-z |
Ref7 | Basche, A.D.; Miguez, F.E.; Kaspar, T.C.; Castellano, M.J.; | 2014 | Do cover crops increase or decrease nitrous oxide emissions? A meta-analysis | JOURNAL OF SOIL AND WATER CONSERVATION, 69, 471-482. | 10.2489/jswc.69.6.471 |
Ref8 | Bayala, J; Sileshi, GW; Coe, R; Kalinganire, A; Tchoundjeu, Z; Sinclair, F; Garrity, D | 2012 | Cereal yield response to conservation agriculture practices in drylands of West Africa: A quantitative synthesis | JOURNAL OF ARID ENVIRONMENTS, 78, 13-25. | 10.1016/j.jaridenv.2011.10.011 |
Ref9 | Linquist, BA; Adviento-Borbe, MA; Pittelkow, CM; van Kessel, C; van Groenigen, KJ | 2012 | Fertilizer management practices and greenhouse gas emissions from rice systems: A quantitative review and analysis | FIELD CROPS RESEARCH, 135, 10-21. | 10.1016/j.fcr.2012.06.007 |
Ref10 | Sileshi, G; Akinnifesi, FK; Debusho, LK; Beedy, T; Ajayi, OC; Mong'omba, S | 2010 | Variation in maize yield gaps with plant nutrient inputs, soil type and climate across sub-Saharan Africa | FIELD CROPS RESEARCH, 116 1–13. | 10.1016/j.fcr.2009.11.014 |
Ref11 | Sileshi, G; Akinnifesi, FK; Ajayi, OC; Place, F | 2008 | Meta-analysis of maize yield response to woody and herbaceous legumes in sub-Saharan Africa | PLANT AND SOIL, 307, 1-19. | 10.1007/s11104-008-9547-y |
Ref12 | Tonitto, C; David, MB; Drinkwater, LE | 2006 | Replacing bare fallows with cover crops in fertilizer-intensive cropping systems: A meta-analysis of crop yield and N dynamics | AGRICULTURE ECOSYSTEMS & ENVIRONMENT, 112, 58–72. | 10.1016/j.agee.2005.07.003 |
Ref13 | Miguez, FE; Bollero, GA | 2005 | Review of corn yield response under winter cover cropping systems using meta-analytic methods | CROP SCIENCE, 45:2318–2329. | 10.2135/cropsci2005.0014 |
Disclaimer: These fiches present a large amount of scientific knowledge synthesised to assess farming practices impacts on the environment, climate and productivity. The European Commission maintains this WIKI to enhance public access to information about its initiatives. Our goal is to keep this information timely and accurate. If errors are brought to our attention, we will try to correct them. However, the Commission accepts no responsibility or liability whatsoever with regard to the information on these fiches and WIKI.
[1] Synthesis research papers include either meta-analysis or systematic reviews with quantitative results. Details can be found in the methodology section of the WIKI.
[2] Thromas et al., 2019 https://dicoagroecologie.fr/en/encyclopedia/green-manure/
[3] Basche et al., 2019 https://doi.org/10.2489/jswc.69.6.471