Soil group

Optimal model

Red soil

(n = 109)

BSP (%) = −1.624Al + 20.628 R = −504^*, p < 0.01

BSP (%) = −15.682Ca² + 31.098Ca + 5.487 R = 0.668^**, p < 0.01

BSP (%) = −21.439Mg² + 43.807Mg + 8.059 R = 0.555^**, p < 0.01

BSP (%) = −240.86Na² + 101.16Na + 8.010 R = 0.455^**, p < 0.01

BSP (%) = 14.408 − 2.082Al³⁺ + 12.698Ca²⁺ + 21.475Mg⁺ + 17.710Na⁺, R = 0.916^**, P < 0.01,

Yellow soil

(n = 45)

BSP (%) = 0.296Al² − 5.327Al + 32.762 R = −0.526^**, p < 0.01

BSP (%) = −16.189Ca² + 33.165Ca + 6.613 R = 0.598^**, p < 0.01

BSP (%) = 17.292Mg² + 33.264Mg + 11.166 R = 0.457^**, p < 0.01

BSP (%) = 25.933K^0.306 R = 0.300^*, p < 0.05

BSP (%) = −414.68Na² + 163.66Na + 4.4735 R = 0.461^**, p < 0.01

BSP (%) = 15.298 − 2.636Al³⁺ + 12.271Ca²⁺ + 26.041Mg⁺ + 11.729K⁺ + 20.603Na⁺, R = 0.888^**, P < 0.01