1. Sistemas de cultivo, riego y control de agua en el área de Tlaxcala;Abascal;Arqueología I,1975
2. Effects of pH and phosphorus rates on soil-solution phosphorus and phosphorus availability;Adams;Soil Sci.,1985
3. Chemical Analysis of Ecological Materials;Allen,1989
4. Assessing organic phosphorus in soils;Anderson,1980
5. Soil Nutrient Bioavailability;Barber,1984