Effect of different agricultural management systems on chemical fertility in cultivated tepetates of the Mexican transvolcanic belt

Volcanic soils in their natural state often require some amelioration to accommodate their use for agriculture. Tepetates are defined as hardened volcanic tuffs derived from geo-pedological processes; they have been partially altered by weathering. Tepetates occupy extensive areas of Mexico's Central Highlands and some of them have been adapted for agricultural use after the mechanical breaking up of this hard material. In their native condition tepetates contain only traces of C, N and available P. So, after their incorporation into agriculture production, the addition of fertilisers becomes necessary to improve soil fertility. In the present work changes in certain chemical and physico-chemical soil properties of cultivated tepetates were studied in the short-term (2002–2005) and medium-term (1986–2005) scales. Experimental plots situated in Tlalpan (State of Tlaxcala) were subjected to the following agricultural management systems: Traditional (Tt), Improved (Ti) and Organic (To). In the short term (4 years), the To management system, in which organic residues and manures were added, led to a decrease in the acidification tendency after cultivation, a recovery of initial exchangeable K + levels, and an increase in soil organic C (SOC), total nitrogen (Nt) and available P (Pa) contents in the Ap horizon. The Ti management, in which crop residues and more chemical fertilisers were added, was especially efficient in increasing the concentration of available P. After 20 years of traditional cultivation, the tepetates showed a decrease in soil pH and exchangeable Mg 2+ and K + values, leading to a decline of the base saturation. These results point to the fragility and low buffer capacity of these systems. In contrast, a tendency of SOC, Nt and Pa accumulation was observed after 20 years of cultivation, influenced by the agricultural management system applied. Tepetates adapted for agricultural use evolved into more fertile substrates over the years of cultivation.