Metadata for "Data on the effects of crop rotational diversity and nitrogen fertilisation on cereal yields" https://doi.org/10.5878/8af1-0q60

For further information, see methods in the publication Smith et al. Increasing crop rotational diversity can enhance cereal yields, Communications Earth & Environment, accepted article

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Data contain standardised yields of several different cereals collected between 1958 and 2020 from 32 long-term agricultural trials across North America and Europe. Yields per hectare were standardised against the overall mean yield per site across all treatments and years. Treatments include different levels of crop rotational diversity and nitrogen fertilisation.

Additional information on each crop rotation per site is available in the document "Crop rotation information". Including, cropping sequence of all crop rotations, mean yield and standard errors refer to the long-term raw yield mean of each indicator crop per rotation and per external N input level for the period to which the yield data refer (see Supplementary Table 1 in Smith et al, accepted article for data years). Yields are based on 100 % dry weight. Mean yields were calculated regardless of management (except N input), therefore could include yields from different tillage. The number of observations relates to yield observations in our dataset for each indicator crop per rotation and per external N input level. Note that some rotations will have observations for more than one indicator crop. Also listed are the crop rotational diversity metrics, species diversity (SD; based on the inverse Simpson's diversity index; see 'D' below) and functional richness (FR; the number of functional groups included in the rotation; see 'F_types' below) and a list of the specific functional groups present in the rotation (see 'F_comb' below).

The R code used to analyse this data for Smith et al., accepted article, are also available in the additional documents. 


Explanation of variables:
country:	Country yield data was collected in
site:	name of the long-term experiment (LTE) the yield data was collected from
lte:	Abreviation of the LTE
time:	Time is in years since the beginning of each LTE
group:	A grouping variable representing other management techniques not of interest in our study (e.g. tillage). The group variable was used as a random effect in our models to account for this extra variation therefore the ID of each group ID is not relevant but authors can be contacted if necessary. 
rot:	Crop rotation ID (lte + number)
crop:	The indicator crop that the yield refers to (M = maize, O = oats, SB = spring barley, SW = spring wheat, U/S O = undersown oats, WR = winter rye, WT = winter triticale, WW = winter wheat)
fert:	Fertilisation level, high = locally recommended rates of fertilisation or higher, low = lower than local recommendations (see supplementary table 1 for more information on each site and their local recommendations)
D:	Crop rotational diversity - species diversity. We calculated species diversity using the inverse of Simpson's diversity index (Simpson, 1949) defined as 1/∑pi2, where pi is the proportion of individuals of each species. The Simpson index is generally used for measuring spatial diversity based on the proportional abundance of species over a unit area. Here we considered species diversity in time and calculated the proportion of years when a given crop species was grown accounting for the temporal rotational species richness and abundance evenness. 
phenology:	Whether the indicator crop is winter or spring sown
year.f:	Calendar year
leg:	Are legumes present in the rotation - yes or no
bl:	Are broadleaves present in the rotation - yes or no
ley:	Are ley present in the rotation - yes or no
F_types:	Crop rotational diversity - functional richness. How many functional groups are present in the rotation
F_comb:	Which functional groups are present in the rotation (C = cereal, B = broadleaf, LEG = legume, LEY = ley)
s.yield:	Standardised yield - observed yield - site mean yield for a particular crop species. Values are in tonne/ha


References
Simpson, E. H. Measurement of Diversity. Nature 163, 688–688 (1949).