Fallowing_GENERAL

Data extracted in April 2021

Note to the reader: This general fiche summarises the environmental and climate impacts of FALLOWING found in a systematic review of 4 synthesis research papers [1]. These papers were selected from an initial number of 236 obtained through a systematic literature search strategy, according to the inclusion criteria reported in section 4.

As each synthesis research paper involves a number of primary research papers ranging from 35 to 127, the assessment of impacts relies on a large number of results obtained mainly in field experiments (carried out in situations close to real farming environment), and sometimes in lab experiments or from model simulations.

1. DESCRIPTION OF THE FARMING PRACTICE

Description

Fallowing refers to the farming practice in which arable land included in the crop rotation system is left to recover, at least for the whole of a crop year, whether worked (e.g. ploughed) or not and with no intention to produce a harvest [2], including set-aside lands.

Key descriptors

This review includes:
Natural fallow comprises:

bare land bearing no crops at all;
land with spontaneous natural growth that may be used as feed or ploughed;
recently abandoned and set-aside lands (<5 years).

Green fallow: land sown exclusively for the production of green manure
This review does not include short and seasonal fallowing periods of annual crops; i.e., summer or winter fallows, whether soils are left bare or are shown with cover crops or green manures. These two practices are assessed in separate sets of fiches.
This review includes spatial and temporal comparisons between fallow lands and cultivated arable lands. Spatial comparisons were simultaneously conducted between nearby fallows and cultivated lands. Temporal comparisons were conducted in the same land before and during fallowing.

2. DESCRIPTION OF THE IMPACTS OF THE FARMING PRACTICE ON CLIMATE AND THE ENVIRONMENT

We reviewed the impacts of fallowing (either natural or green fallows) compared to cultivated arable lands. The table below shows the number of synthesis papers reporting positive, negative, no effect, or uncertain effects. The numbers between parenthesis indicate the number of synthesis papers with a quality score of at least 50%. Details on quality criteria can be found in the methodology section of this WIKI.

Out of the 4 synthesis papers selected, 2 reported studies conducted in Europe and the 4 have a quality score higher than 50%. Some synthesis papers reported more than one impact.

Table 1. Impacts of fallowing (natural or green fallows) compared to cultivated arable land.

Impact	Intervention	Comparator	Positive	Negative	No effect	Uncertain
Increase biodiversity	Natural fallow	Cultivated arable land	1 (1)	0	1 (1)	0
Increase carbon sequestration	Natural fallow		0	0	1 (1)	0
Increase crop yield	Natural fallow		1 (1)	0	1 (1)	0
Increase crop yield	Green fallow		1 (1)	0	0	0

3. DESCRIPTION OF THE KEY FACTORS INFLUENCING THE SIZE OF THE EFFECT

Only the factors explicitly studied in the reviewed synthesis papers with a significant effect are reported below. Details regarding the factors can be found in the Summaries of the meta-analyses.

Impact	Factors
Increase biodiversity	Fallow area (Ref.5), fallow length (Ref.5)
Increase crop yield	Fallow length (Ref.4), fertiliser recommended dose in post-fallow cropping season (%) (Ref.4), interaction between fertiliser recommended dose and post-fallow cropping season (Ref.4), post-fallow cropping season (Ref.4), site productivity (Ref.4)

4.SYSTEMATIC REVIEW SEARCH STRATEGY

Keywords	TS= ((“fallow” OR “uncrop” OR “non-crop” OR “unplant” OR “unplow” OR “uncultiv” OR “non-cultiv” OR “non-pasture” OR “ungraz”) OR ((“non-productive” OR “abandon” OR “bare” OR “unmanage” OR “extensiv” OR “extensificat” OR “desintensificat” OR “rotation” OR “set-aside” OR “set aside”) NEAR/3 (land* OR crop* OR soil* OR field))) AND TS= ("meta-analy" OR "systematic* review" OR "evidence map" OR "global synthesis" OR "evidence synthesis" OR "research synthesis") AND TS= (agricultur) or TITLE-ABS-KEY ((“fallow” OR “uncrop” OR “non-crop” OR “unplant” OR “unplow” OR “uncultiv” OR “non-cultiv” OR “non-pasture” OR “ungraz”) OR ((“non-productive” OR “abandon” OR “bare” OR “unmanage” OR “extensiv” OR “extensificat” OR “desintensificat” OR “rotation” OR “set-aside” OR “set aside”) W/3 (land* OR crop* OR soil* OR field))) AND ("meta-analy" OR "systematic* review" OR "evidence map" OR "global synthesis" OR "evidence synthesis" OR "research synthesis") AND (agricultur)
Search dates	No time restrictions
Databases	Web of Science and Scopus, run in February 2021
Selection criteria	The main criteria that led to the exclusion of a synthesis paper were if the paper: (1) was out of the scope; (2) the duration of the fallowing was not as defined in the general fiche (we excluded fallow periods shorter than one crop year, or arable land taken out of production for more than 5-6 years); (3) dealt with shifting agriculture (practice usually conducted in tropical forest-agriculture where land is abandoned after cultivation for the regeneration of secondary forests); (4) the effect of fallowing was explored in combination with other practices (e.g. conservation agriculture) and it was not possible to disentangle the sole effect of fallowing; (5) was not a meta-analysis; (6) was not written in English. Synthesis papers that passed the relevance criteria were subject to critical appraisal carried out on paper-by-paper basis. The search returned 236 synthesis papers potentially relevant for the practice object of our fiche. From the 236 potentially relevant synthesis papers, 100 were excluded after reading the title and abstract, and 132 after reading the full text according to the above-mentioned criteria. Finally, 4 synthesis papers were selected for fallowing.

5.LIST OF SYNTHESIS PAPERS INCLUDED IN THE REVIEW

Ref. Num	Authors	Year	Title	Reference	DOI
1	Koshida, C; Katayama, N	2018	Meta-analysis of the effects of rice-field abandonment on biodiversity in Japan	CONSERVATION BIOLOGY, 32(6), 1392-1402.	10.1111/cobi.13156
2	Kaempf, I; Hoelzel, N; Stoerrle, M; Broll, G; Kiehl, K	2016	Potential of temperate agricultural soils for carbon sequestration: A meta-analysis of land-use effects	SCIENCE OF THE TOTAL ENVIRONMENT, 566, 428-435.	10.1016/j.scitotenv.2016.05.067
3	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
4	Van Buskirk, J; Willi, Y	2004	Enhancement of farmland biodiversity within set-aside land	CONSERVATION BIOLOGY, 18(4), 987-994.	10.1111/j.1523-1739.2004.00359.x

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