Persistence of municipal biosolids in a Chihuahuan Desert rangeland 18 years after application

The experimental application of municipal biosolids to degraded arid and se miarid rangelands has been practiced for many years and is becoming more co mmon in the western United States. Previous studies have examined the effec ts of applying biosolids to land areas that have been degraded by one or mo re different factors including overgrazing, fire suppression, and increased drought frequency, duration, or intensity. However,few of these studies ha ve measured the persistence of biosolids in the soil. This study is an atte mpt to recover information from an abandoned reclamation effort in which mu nicipal biosolids were spread on a degraded rangeland on the Jornada Experi mental Range in southern New Mexico. The biosolids were applied in 1979 and were still present in substantial amounts when soil samples were taken in 1997. An estimated 32% of the applied biosolids persisted as fragments grea ter than 2 mm in diameter for almost 20 years. There were no apparent benef its of biosolid application at this site in terms of vegetation establishme nt within the first four years, and there was no correlation between vegeta tion patterns and the concentration of biosolids remaining in the soil in 1 997. It is hypothesized that much of the applied sludge remains in the soil because of the recalcitrant nature of digested biosolids combined with the environmental conditions of soil in and systems. Long-term? results from b iosolid addition experiments in and and semiarid rangelands should be consi dered before the practice is widely, used for reclamation of degraded range land sites.