Proceedings

Biosolids disposal in wild environment is a controversial subject. Here we studied the effect of
season and rate of biosolids surface application in semiarid rangelands at central Mexico. Two
alkaline soil types were involved that differ in parental substrate (calcareous and igneous). One
or two application dates (summer and winter) were tested at four doses (0, 3.5, 7 and 10.5 t/ha).
Response variables were biomass and heavy metal content. Increase of perennial grasses
biomass differs among doses when application of biosolids was in summer or in summer +
winter. When biosolids were applied in summer or summer + winter, Cr and Ni concentration in
plants declined, while Cu and Zn increased. In igneous soil Cr and Zn uptake were different
among grasses and herbs. The concentration of Cr, Pb and As in wild plants were not affected
by biosolids rates applied. In the studied region two applications of biosolids per year at rates
not higher than 10.5 Mg ha-1, promote the biomass production of perennial grasses with not
significant increase in the concentration of metals.

KEY WORDS
Biomass, biosolids, Chihuahuan desert, grasses, heavy metals, land application, seasonal
effect, semiarid soils.