+proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0

# structural relation
mineral_phase <~ 1*clay_mineralogy_PC1 + clay_mineralogy_PC2 #+ clay_perc + BET_surface_mean_m2g.1

CUE ~ F.A_ratio + CN_soil + pH + landuse 
F.A_ratio ~ 1 + pH + landuse 
CN_soil ~ 1 + landuse + mineral_phase
pH ~ 1 + landuse + mineral_phase

F.A_ratio ~~ CN_soil
pH ~~ CN_soil