Figures (4)  Tables (3)

    • Figure 1. 

      The green manure biomass of different varieties cultivation at harvest in saline alkali soil field experiment. 'M1, M2, M3 and M4' represent Aurora, Sanditi, Eureka+, Sardi, respectively, which all belong to Medicago sativa. 'L' refers to Lolium multiflorum. 'B1, B2 and B3' represent Huayouza 82, Huayouza 158, Huayouza 62, respectively, which all belong to Brassica campestris. One-way analysis of variance (ANOVA) was used to assess the differences among treatments. Bars represent the mean values of three replicates ± SD. Values that do not share the same lower case letter are significantly different (P < 0.05) among green manure varieties. Values that do not share the same uppercase letter are significantly different (P < 0.05) at different green manure species (Medicago sativa, Lolium multiflorum, Brassica campestris). *** refers to P < 0.001.

    • Figure 2. 

      (a) Carbon content and (b) carbon store of different varieties cultivated at harvest in saline alkali soil field experiment. 'M1, M2, M3 and M4' represent Aurora, Sanditi, Eureka+, Sardi, respectively, which all belong to Medicago sativa. 'L' refers to Lolium multiflorum. 'B1, B2 and B3' represent Huayouza 82, Huayouza 158, Huayouza 62, respectively, which all belong to Brassica campestris. One-way analysis of variance (ANOVA) was used to assess the differences among treatments. Bars represent the mean values of three replicates ± SD. Values that do not share the same lower case letter are significantly different (P < 0.05) among green manure varieties. Values that do not share the same uppercase letter are significantly different (P < 0.05) at different green manure species (Medicago sativa, Lolium multiflorum, Brassica campestris). * refers to P < 0.05; ** refers to P < 0.01; *** refers to P < 0.001.

    • Figure 3. 

      Soil fertility index of different treatment that returning to the field in saline alkali soil experiment. One-way analysis of variance (ANOVA) was used to assess the differences among treatments. Bars represent the mean values of three replicates ± SD. Values that do not share the same lower case letter are significantly different (P < 0.05) among green manure varieties. Values that do not share the same uppercase letter are significantly different (P < 0.05) at different green manure species (Medicago sativa, Lolium multiflorum, Brassica campestris). ** refers to P < 0.01; *** refers to P < 0.001.

    • Figure 4. 

      Cascading relationships of soil fertility with green manure and soil physicochemical properties. (a) Partial least squares path modelling (PLS-PM) disentangling major pathways of the influences of green manure varieties, soil physicochemical properties, plant C, green manure biomass on soil fertility. Red and blue arrows indicate positive and negative flows of causality, respectively. Solid and dashed lines indicate significant (*, P < 0.05; **, P < 0.01; ***, P < 0.001) and nonsignificant (P > 0.05) levels, respectively. Values on arrows indicate significant standardized path coefficients. R2 indicates the variance of dependent variable explained by the model. (b) Total effects of soil fertility in the PLSPM models for green manure varieties, fast-changing soil properties, slow-changing soil properties, plant C, and green manure biomass.

    • Green manure cultivationTreatmentpHEC
      (us·cm−1)      		Soil organic matter
      (g·kg−1)      		Total N
      (g·kg−1)      		Available N
      (mg·kg−1)
      No-cultivationCK9.04 ± 0.16abc496.33 ± 19.50b5.27 ± 0.14bc0.58 ± 0.05abc38.76 ± 2.03bc
      Medicago sativaM18.50 ± 0.13f429.00 ± 26.21cd4.41 ± 0.78c0.58 ± 0.01ab51.58 ± 2.66a
      M28.72 ± 0.02e470.33 ± 13.32bc5.11 ± 0.42bc0.54 ± 0.01cd49.43 ± 4.35a
      M38.89 ± 0.03d356.67 ± 6.43ef5.63 ± 0.66a0.54 ± 0.02bcd41.89 ± 4.57b
      M48.93 ± 0.03cd391.00 ± 4.36de4.33 ± 0.24c0.53 ± 0.02d50.27 ± 1.61a
      Lolium multiflorumL8.69 ± 0.04e567.67 ± 52.88a5.33 ± 0.46bc0.60 ± 0.01a53.68 ± 3.79a
      Brassica campestrisB19.02 ± 0.04bc363.00 ± 26.91ef5.13 ± 0.11bc0.51 ± 0.01de37.53 ± 3.16bc
      B29.11 ± 0.02ab330.67 ± 12.66f5.07 ± 1.32bc0.51 ± 0.02de38.87 ± 2.33bc
      B39.17 ± 0.01a328.00 ± 28.69f6.00 ± 0.21a0.49 ± 0.01e34.97 ± 5.50c
      CK: no cultivation. 'M1, M2, M3 and M4' represent Aurora, Sanditi, Eureka+, Sardi, respectively, which all belong to Medicago sativa. 'L' refers to Lolium multiflorum. 'B1, B2 and B3' represent Huayouza 82, Huayouza 158, Huayouza 62, respectively, which all belong to Brassica campestris. Data are the mean values of three replicates. Numbers followed by '±' are the standard deviations (SDs). Within a column, values that do not share the same letter are significantly different (P < 0.05).

      Table 1. 

      Soil properties measured under different treatment at green manure harvest in saline alkali soil field experiment.

    • Green manure returnTreatmentpHEC
      (us·cm−1)      		Soil organic matter
      (g·kg−1)      		Total N
      (g·kg−1)      		Available N
      (mg·kg−1)
      No-returningCK9.00 ± 0.14ab591.00 ± 56.45bcd5.84 ± 0.74b0.52 ± 0.01c39.80 ± 1.88d
      Medicago sativaM18.89 ± 0.07bc536.33 ± 32.59d7.92 ± 1.24a0.60 ± 0.01b41.99 ± 4.37cd
      M29.11 ± 0.03a407.33 ± 43.25e8.55 ± 0.80a0.54 ± 0.05c45.70 ± 4.68bcd
      M39.00 ± 0.02ab438.33 ± 49.08e8.36 ± 0.59a0.60 ± 0.02b47.24 ± 4.26bcd
      M48.82 ± 0.02c549.67 ± 15.28cd7.76 ± 0.55a0.63 ± 0.02b51.96 ± 1.87b
      Lolium multiflorumL8.31 ± 0.12e519.00 ± 14.53d7.72 ± 0.88a0.71 ± 0.02a62.58 ± 5.98a
      Brassica campestrisB18.58 ± 0.05d621.67 ± 5.13bc7.75 ± 0.44a0.62 ± 0.02b49.04 ± 8.57bc
      B28.59 ± 0.07d701.33 ± 71.44a7.30 ± 0.46a0.61 ± 0.01b42.43 ± 3.22cd
      B38.64 ± 0.01d627.67 ± 35.53b7.61 ± 0.28a0.68 ± 0.03a48.57 ± 3.73bcd
      CK: no cultivation. 'M1, M2, M3 and M4' represent Aurora, Sanditi, Eureka+, Sardi, respectively, which all belong to Medicago sativa. 'L' refers to Lolium multiflorum. 'B1, B2 and B3' represent Huayouza 82, Huayouza 158, Huayouza 62, respectively, which all belong to Brassica campestris. Data are the mean values of three replicates. Numbers followed by '±' are the standard deviations (SDs). Within a column, values that do not share the same letter are significantly different (P < 0.05).

      Table 2. 

      Soil properties measured under different treatment after green manure return to saline alkali soil field for 30 d.

    • pH (H2O)EC
      (us·cm−1)      		Soil organic matter
      (SOM, g·kg−1)      		Total nitrogen
      (TN, g·kg−1)      		Available nitrogen
      (AN, mg·kg−1)
      Scoring curve#aabbb
      Turning pointU91,500151.2120
      L6.010050.530
      O16.5300
      O28400
      weight0.250.230.070.230.22
      'a' Refers to the 'optimum' curve equation; 'b' refers to the 'more is better' curve equation.

      Table 3. 

      Scoring function values and weights assigned to selected soil fertility parameters.