Principle component analysis (PCA) and biplots for protein and ionome concentration in rice grain in response to CR and ORF. (CR: conventional rice planting system; ORF: organic rice-frog coculture system). (A) Sample scores for CR and ORF at 2013; (B) loading scores of protein and ionome at 2013; (C) sample scores for CR and ORF at 2014; (D) loading scores of protein and ionome at 2014.