Organic matter pools and nutrient cycling in different coffee production systems in the Brazilian Cerrado

Agroforestry and organic systems have been used to reduce the negative effects that conventional coffee cultivation has on soils. In this work, ¹³C-CPMAS-NMR, Fourier transform infrared spectroscopy, elemental composition, classical humus fractionation and the soil fertility status were used to evaluate the impact of these three systems on a Latosol from the Brazilian Cerrado. Continuous input of tree residues promoted changes to the soil organic matter with increase in total organic carbon, humic acids (HA) and light organic matter, mainly in the topsoil. Available P and cation exchange capacity were also increased and the acidity status decreased in the agroforestry system. Moreover, HA from the agroforestry were enriched in O-alkyl C, O-di-alkyl C and alkyl C groups and the organic system resulted in HA richer in carboxyl groups. The conventional system resulted in greater aromatic and methoxyl participation, and lower phenol groups. HA from the agroforestry system were richer in easily degradable structures and the chemical fractionation demonstrated a decrease in both recalcitrant fractions, allowing for a more conservative and sustainable management of soil fertility. The modifications were not as evident in the organic system, probably due to the low organic fertilizer input.