Closing the loop: biosolids to rebuild degraded soils

Biosolids represent a valuable source of soil nutrients and zinc, a trace element that is deficient in many areas. Yet environmental concerns, particularly regarding nitrate leaching, limit the application of biosolids to soil. Biochar, a form of charcoal that is added to soil, is a potential solution. We aimed to determine the effect of biosolids and biochar addition to the uptake of Zn by crop plants and investigate the effects of biochar addition on Zn uptake and nitrate leaching from biosolids amended soil. We tested 10 common crop plants as well as pasture in a pot trial with and without the addition of biosolids and biochar. The effect of biochar on the nitrate leaching from biosolids amended soil was measured in a lysimeter experiment. There were large species differences in Zn uptake from the biosolids and biochar amended soils. Beetroot (Beta vulgaris) and spinach (Spinacia oleracea) showed the greatest increases are good candidates for further biofortification research. Over a five-month period, biochar reduced the nitrate leaching from a biosolids amended soil to levels below an unamended soil. Future work will focus on the performance of the system over the long-term