Soil fertility properties on Agave angustifolia Haw. plantations

This study examined the variations in soil physical, chemical and biological properties from Agave angustifolia fields in three sites with different topographic conditions (valley, hill and mountain), in Oaxaca, Mexico, associated with the tillage systems, disk ploughing (DP), animal drawn ploughing (ADP) and minimum tillage (MT), respectively. Plant ages were 1.5-3.5 years (class 1), 3.6-5.5 years (class 2) and 5.6-7.5 years (class 3). Soil samples were taken at two soil depths (0-20 and 21-40 cm) from plots of 4000 m² within each site and plant age classes, during the spring of 2005. The main changes in soil properties were found in the mountain site. Soil bulk density (2.0 g cm^-3), cone penetration resistance (CPR) (3.96 MPa), 0.7 and 1.0 mm water stable aggregates (WSA) (28.3 g kg^-1 and 102.2 g kg^-1, respectively) were higher in the mountain site than in the hill and valley fields. This result is consistent with the rocky substrate beneath the shallow soil. Soil organic carbon (SOC) (23.9 g kg^-1), available N (23.1 mg kg^-1) and soil microbial biomass carbon (SMBC) (969.6 μg g^-1) at the mountain site showed the highest values, suggesting that MT practiced in this topographic condition favours the organic matter accumulation and biological activity. Soil microbial biomass carbon and SOC seem to be the soil properties that were mainly affected by the sites and soil management associated with them. For the three sites, SOC, P_Olsen, available N, exchangeable Na⁺ and SMBC were higher at 0-20 cm depth than at 21-40 cm depth within each site. Exchangeable Ca²⁺ and K⁺, P_Olsen and CPR increased with plant age. In contrast, available N decreased. Soil chemical properties were more affected by the age of the plant than physical and biological properties. Results reported here represent a reference of the fertility properties of soils cultivated with A. angustifolia, which could be used in further studies focused on management and tillage systems.