2.2.2. Study characteristics
The period during which studies capture and analyze data has
also varied considerably. Approximately 72% of the previous studies
collected data for less than one year. Because organic systems often
have lower nutrient inputs and rely on nutrients added to the soil
before conversion to organic agriculture, it might take decades for
yields to decline to levels reflecting true organic practices. Due to
potential overestimation, surveys based on short-term data
collection might produce results that are more favorable to organic
farming (Bertilsson et al., 2008). Previous studies employing data
from field surveys and secondary sources were more likely to limit
cross-sectional comparisons to one year or to one crop season,
which is not sufficient to capture the spillover effect of nutrient
residues in the soil. Only a few studies using secondary sources
have employed databases with multi-year data (Meisterling et al.,
2009). In contrast, previous studies using data from farms with
crop rotation and experimental farms were more likely to perform
multi-year comparisons. Studies conducted on the experimental
farms of research centers have sample periods ranging from 10 to
30 years
2.2.2. Study characteristicsThe period during which studies capture and analyze data hasalso varied considerably. Approximately 72% of the previous studiescollected data for less than one year. Because organic systems oftenhave lower nutrient inputs and rely on nutrients added to the soilbefore conversion to organic agriculture, it might take decades foryields to decline to levels reflecting true organic practices. Due topotential overestimation, surveys based on short-term datacollection might produce results that are more favorable to organicfarming (Bertilsson et al., 2008). Previous studies employing datafrom field surveys and secondary sources were more likely to limitcross-sectional comparisons to one year or to one crop season,which is not sufficient to capture the spillover effect of nutrientresidues in the soil. Only a few studies using secondary sourceshave employed databases with multi-year data (Meisterling et al.,2009). In contrast, previous studies using data from farms withcrop rotation and experimental farms were more likely to performmulti-year comparisons. Studies conducted on the experimentalfarms of research centers have sample periods ranging from 10 to30 years
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