Biosolids effects on tobosagrass and alkali sacaton in a Chihuahuan desert grassland

Environmentally responsible use of anaerobically digested biosolids (municipal sewage sludge) is an increasingly urgent ecological and societal concern. There is relatively little information available on effects of biosolids in arid and semiarid rangelands. The purpose of this research was to evaluate effects of rate, season, and number of consecutive years of biosolids application on tobosagrass (Hilaria mutica) and alkali sacaton (Sporobolus airoides), two commonly occurring native grasses in the Chihuahuan desert grassland. Biosolids were topically applied at rates of 0, 7, 18, 34, or 90 Mg ha-1 either during the dormant season or just prior to the onset of the growing season for 1 yr only, or for 2, 3, or 4 consecutive years: one-half of the experimental plots were provided supplemental irrigation. In general, biosolids increased plant length and aboveground standing crop of these species. Plants responded more to dormant season application than to growing season application in the first year of the study. Carry-over effects from earlier applications on current year's growth were species-specific and depended on growing conditions