Sustainable Use of Biosolids in Rangeland Forage Production

Biosolids land application was demonstrated to be a potentially cost effective means for restoring ecological services on disturbed rangelands. By land applying aerobically digested, anaerobically digested, composted and lime stabilized biosolids on rangeland test plots at rates of up to twenty times (20X) the estimated agronomic rate, forage yields were found to increase from 132.8 kg per hectare to 1182.3 kg per hectare.In spite of the economic and environmental benefits associated with increased forage yield, the type of forage generated both before and after biosolids land application was found to be dominated by invasive weeds all of which were characterized as having fair to poor nutritional value. Of the nine dominant plant species identified including; 1) Cheatgrass, 2) Mouse Barley, 3) Bur Buttercup, 4) Mexican Fireweed, 5) Herb Sophia, 6) Bulbous Bluegrass, 7) Clasping Pepperweed, 8) Tall Tumblemustard and 9) Sticky Purple Geranium, only Sticky Purple Geranium is native to United States (US) rangelands. Opportunistic and shallow rooting invasive weeds not only have marginal nutritional value, they also limit the establishment of native perennial grasses and thus, biodiversity. Many of the identified invasive species mature early, a characteristic that significantly increases the wildfire fuel loads.Field results demonstrated that the risk of adverse heavy metal impact on forage quality from land applying biosolids at rates significantly greater than the agronomic rate is minimal when metal concentrations are at or below the pollutant concentration limit. The concentrations of arsenic, cadmium, lead and molybdenum in forage grown on biosolids amended rangelands were all found to be below the analytical detection limit at maximum biosolids application rate equivalent to 20X the estimated agronomic rate. Only copper levels were found to be above the analytical detection limit in forage. Despite the detection of copper in forage, when compared to forage grown on control plots, the impact of biosolids land application on copper levels in forage was found to be negligible.