Short-term Response on Microstructure and Soil Organic Matter Characteristics after Fertilization Change in an Andic Anthrosol

Agricultural management is mainly driven by soil degradation processes, where the synthetic fertilization regime is an important component in the disconnection of the ecological process that provides stability to soil functions. The soils around Mexico City, inside the Soil Conservation Zone (SCZ), have been used for a long time for agricultural production, depleting the soil organic matter and deteriorating soil structure. In this work, we present how different fertilization management methods could produce short-term changes in both organic matter content and soil structure of volcanic soils (Andic Anthrosols) inside the SCZ. We performed a field experiment where different kinds of fertilization systems were used: synthetic NPK, urea, cattle manure, vermicompost, and fertilization suppression on soil cultivated with Avena sativa L. After the oat harvest, we collected topsoil samples from each treatment to evaluate microstructure in thin sections (morphometry and micromorphology, including visual estimation of the organic residues decomposition), as well as organic matter stock, distribution, and decomposition, tested with a Tea Bag Index (TBI) experiment. Morphometric results showed that the pores' shape, size, and connectivity were improved by organic amendments. The visual evaluation of the degradation of the organic residues evidenced the high decomposition and low stabilization rates under inorganic fertilization and fertilization suppression treatments. However, we did not observe statistical differences in the decomposition rate (k) and stabilization factor (S) derived from the TBI. All findings suggest a) that the use of micromorphological and SOM functional characteristics is suitable for the integral evaluation of short-term changes in soils under agricultural management and b) the synthetic fertilization maintains a poorly structured soil with a low functionality condition that can be improved in a short-term improved with fertilization based on organic amendment addition.