Silvia Pajares

Enzymatic Activity and Carbon Mineralization in Mexican Tepetates Cultivated Under Different Management Practices

Tepetates (hardened volcanic tuffs) occupy large extensions in the Central Mexican Highlands and some of them have been modified for agriculture. In their native condition tepetates contain traces of C, N, and available P. The objective of this work was to study how different agricultural practices affect the labile organic C availability and the enzymatic activity in cultivated tepetates. Experimental plots, cultivated since 1986, were subjected to three agricultural management systems during 2002–2005: Traditional (Tt); Improved (Ti); and Organic (To). In 2002 two new plots were subjected to the traditional system (Rt), and organic system (Ro). Two non-cultivated tepetates were chosen as reference (Tv and Td). In 2005 soil samples were collected at 0–10 cm depth and soil organic C (SOC), total N (Nt), dehydrogenase, β-glucosidase, phosphatase, urease and protease activities, mineralized C (Cm), and potentially mineralizable C (C0) were determined. In 4 years the recently cultivated tepetates (Rt and Ro) increased the values of these variables in relation to the non-cultivated tepetates (Tv and Td), indicating that the incorporation of tepetates to the agriculture improved their biochemical properties. Enzymatic activity, Cm and C0 increased with the years of cultivation and they were significantly higher with Ti and To, suggesting higher SOC availability for microbiology with these managements, likely due to a higher supply of organic substrates because fertilizers with crop residues (Ti) and organic manures (To) were added. Results also demonstrated that an appropriate management of tepetates produces a significant increase of SOC and Nt, leading to an improvement of their biochemical properties.