Fig 6. Soil NO₃⁻−N, NH₄⁺−N, total N, and organic matter content in different soil layers under different treatments.

Error bars denote standard errors. The different letters in the same soil layer indicate a significant difference (P<0.05) with Turkey’s multiple range test of different amounts of biochar addition either under straw incorporation or not. Definitions of C0, C1, C2 and C3 are given in caption of Fig 2.