Effects of biosolids on desert grasslands

Anaerobically digested biosolids were applied to experimental units containing a monoculture of either tobosagrass (Hilaria mutical or alkali sacaton (Sporobolus airoides). Biosolids were applied at varying rates (0, 7, 18, 34, or 90 Mg/ha) during either the winter or summer for 1 year only or for 2 consecutive years. In addition, one-half of the plots were provided supplemental irrigation throughout the growing season. Effects of biosolids on standing crop yield of both species and chemical composition of tobosagrass were evaluated. Both species responded better to winter season application at the end of the first growing season. Standing crop of tobosagrass and alkali sacaton were increased above winter controls for all biosolids rates following winter season treatment. Tobosagrass standing crop was increased from 54 to 147% and alkali sacaton increased from 42 to 100% with winter biosolids amendment. Alkali sacaton showed essentially no response to summer biosolids application at the end of the first growing season. Tobosagrass standing crop was increased above summer controls for the three highest rates following summer treatment. At the end of the second growing season there were no differences between tobosagrass or alkali sacaton plots receiving 1 year only or 2 consecutive years of apphcation with 0, 7, 18, and 34 Mg/ha of biosolids. Standing crop significantly diminished, however, in plots receiving 2 consecutive years of treatment with 90 Mg/ha of biosolids as compared to plots receiving 1 year only treatment at this rate. There were no differences in winter and summer season application in plots that received biosolids for two consecutive years. Standing crop was generally greatest for plots receiving biosolids at either 18 or 34 Mg/ha. Lastly, forage quality of tobosagrass was improved as evidenced by increased total Kjeldahl nitrogen (TKN) at the end of the first growing season. In addition, there was no evidence of trace metal accumulation in these plants.