Fig 1.
Map of 97 sampled farmlands (location is indicated in a red circle with a coordinate) distributed in 7 of 12 barley ago-ecological areas.
The original map was obtained from Natural Earth (http://www.naturalearthdata.com/) and was further processed using software Arcgis 10.2 version.
Fig 2.
Soil properties of 7 barley ago-ecological areas on colors, pH, soil organic C, NH4+-N and NO3--N.
(A) Photo of topsoil colors. (B-E) difference comparison between farmlands in 7 barley ago-ecological areas on pH, soil organic C, NH4+-N and NO3--N respectively. Data were presented as box plots where boxes represent the inter-quartile ranges. The lines across the boxes, the whiskers and the black circles represented the median values, the 10th and 90th percentiles and outliers, respectively. The black dashed line represented the average levels of all samples. The number above the box represented the average level of parameter in each area. *, ** and *** denoted significant differences by Kruskal-Wallis H test in 0.1, 0.05 and 0.01 levels, respectively.
Table 1.
The classifications standards for some soil chemical parameters based on the second national soil census and other previous studies.
Fig 3.
Difference comparison between sampled barley farmlands of 7 barley ago-ecological areas on available P, available k, exchangeable Ca, exchangeable Mg, SO42-, DTPA-Fe, DTPA-Cu, Cl- and available B, respectively.
Data of each soil chemical parameters were presented as box plots (From A to I) where boxes represented the inter-quartile ranges. The lines across the boxes, the whiskers and the black circles represented the median values, the 10th and 90th percentiles and outliers, respectively. The black dashed line represented the average levels of all samples. The number above the box represented the average level of parameter in each area. *, ** and *** denoted significant differences by Kruskal-Wallis H test in 0.1, 0.05 and 0.01 levels, respectively.
Table 2.
Selected principal component in measured soil chemical parameters.
Table 3.
Pearson correlation coefficient among soil chemical parameters in minimum data set (MDS).
Fig 4.
Soil quality index (SQI) on each farmland and difference comparison on 7 barley ago-ecological areas.
(A) Scores for each soil chemical parameter from Minimum data set (MDS) in 97 sampled farmlands and deriving SQI (data were presented by 0–1 normalization); (B) Difference comparison between farmlands of 7 sampled barley ago-ecological areas on SQI. Data were presented as box plots where boxes represented the inter-quartile ranges. The lines across the boxes, the whiskers and the black circles represented the median values, the 10th and 90th percentiles and outliers, respectively. The black dashed line represented the average levels of all samples. *, ** and *** denoted significant differences by Kruskal-Wallis H test in 0.1, 0.05 and 0.01 levels, respectively.
Table 4.
Descriptive statistics of SQI in 7 ago-ecological areas.
Table 5.
Results of regression analyses of parameters from MDS with significant differences in 7 areas.