19 



Soils 



Soil physical and chemical properties directly affect the vegetation that can grow in an area. 

 These properties indirectly affect people who plant gardens or harvest natural forest products, such as 

 lumber. These properties also affect wildlife species that depend upon this vegetation for food and 

 cover. 



Unfortunately, the classification of soil types in Mexico is problematic, and a new 

 classification scheme recognizing additional categories, especially in the Yucatan Peninsula, is being 

 prepared (Dunning, 1989). Presently, the soils of Quintana Roo are classified as belonging to the order 

 Rendzinas, suborder Calcomorfics, according to the FAO classification, while according to the USDA 

 classification they are categorized as belonging to the order MoUisols, suborder RendoUs (U.S. 

 Department of Agriculture, 1975). Rendzina soils are shallow; have low fertility levels; can be red or 

 black in color; have good structure and drainage; and have a high content of calcium, carbonates, 

 bicarbonates, and organic matter (Aguilera, 1959). Soil color can vary gready between adjacent sites. 



Soil physical and chemical changes in gardens in the X-Hazil Sur area are similar to those in 

 other tropical sites subject to shifting cultivation (Noguez-Galvez, 1991). In general, after 20 years of 

 fallow the physical and chemical values of the soil stabilize at levels similar to those of soils in late 

 secondary forest. X-Hazil Sur residents, however, now practice a short fallow cycle, replanting about 

 every 5 y, and increasingly complain about decreasing crop yields. 



Noguez-Galvez (1991) conducted a study of soil characteristics in the same area as the present 

 study, and reported the following selected soil chemical and physical properties of garden sites for 1 

 and 70 y of fallow at 0-5 cm of depth: 



Soil chemical properties: Organic matter (8.08% and 10.49%, 1 and 70 y, respectively). Total 

 nitrogen (0.437% and 0.493%), PO4 (12.16 ppm and 16.31 ppm), Ca^+ (59.48 me/lOOg and 

 41.91 me/lOOg), Mg"^^ (3.58 me/lOOg and 3.42 me/lOOg), Na^ (1.04 me/lOOg and 0.96 



