Fig. 3. Diffuse reflectance Fourier transform infrared spectra of humic acids in a Norfolk soil under different tillage treatments: (3A) conservation tillage treatment (CnT1, 0–5 cm; CnT2, 5–10 cm; and CnT3, 10–15 cm); (3B) conventional tillage treatment (CT1, 0–5 cm; CT2, 5–10 cm; and CT3, 10–15 cm).