ADRIANA CAMPOS1, BARBARA WICK2, HOLM TIESSEN1
1Georg-August-University Göttingen, Crop Sciences -Agronomy in the Tropics and Subtropics, Germany
2Humboldt-University Berlin, Division of Soil Science and Site Science, Germany
The Yucatan Peninsula presents a mosaic of different soils, which is the main cause of their distinguishing chemical characteristics and might originate differences in the mineralisation rate and transformation of nutrients. The principal agricultural practices in the region are the traditional shifting cultivation (Milpa), and Home Gardens. Previous studies showed a decline in soil fertility that may be associated to problems with the sorption of nutrients and organic matter. There is no information about the impact of these agricultural practices on transformation of nutrients, and the possible problems related to moisture content, which plays an important role on the biochemical processes of the soil. Therefore, the study had as objective to evaluate the effect of moisture content on enzymes' activities in the soil. Soil enzymes play an essential role in catalysing reactions necessary for organic matter decomposition and nutrient cycling. Four enzymes were chosen: Acid and Alkaline Phosphatase, 17#17 Glucosidase, and Protease. These give indications on the potential capacity of the soil to carry out specific reactions and can have an important implication in nutrient cycling. The study sites were located in the communities of Hocaba and Xmakuil, Yucatan, Mexico. The sampling was done in the dry season (December 2004). Three ecosystems were studied: Milpa, Home Garden (agricultural systems), and Forest (reference system). The soil samples were taken at 0-10cm depth. To evaluate the effect of moisture on the enzymes' activities, two contrasting moisture contents were employed (50 and 100% WHC) and Control soils (without water). In general, a decrease in enzyme activity was found in the Milpas and Home Gardens in comparison to the Forest, possibly due to lack of appropriate organic substrate (specially in Home Gardens) and to soil degradation. The moisture content had an effect on the enzymes: the highest moisture content produced a decline between 10-73% of enzyme activity in comparison to Control soils. At 50% WHC, there was also a decrease, but the effect was not too pronounced. Protease was the enzyme that reacted most to moisture content.
Keywords: 17#17-Glucosidase, acid and Alkaline Phosphatase, Home Garden, Milpa, Moisture Content, Protease