Impacts of circular agriculture-sanitation systems on hydrological and biogeochemical processes

Abstract:

Broken cycles in food systems cause the waste of vast quantities of organic resources that contribute directly to climate change, food insecurity, and soil and water degradation. The capture of human organic waste streams and transformation into soil amendments offers an abundant and untapped resource. Circular agriculture-sanitation systems capture and safely treat human waste, and return the embodied nutrients and organic matter in excreta and urine to agricultural soils. Closing this “poop loop” can contribute to global climate goals and improve the resiliency of agroecosystems by improving hydrological and biogeochemical processes. We compared crop yields, water and nutrient leaching, and greenhouse gas emissions from soils amended with three sanitation products: compost from ecological-based sanitation, anaerobically digested biosolids, and thermal hydrolyzed biofertilizer. We also compared these amendments with inorganic fertilized and unfertilized controls. All treatments were applied at a rate of 100 kg PAN/ha, only one-time immediately prior to the first planting. Six consecutive cropping cycles of radishes were grown and harvested to determine legacy effects of amendments on crop, water, and soil nutrient dynamics. In the first growth cycle, crop yields from all three organic amendments were not significantly different from each other. These amendments increased crop yields 15±2.2-fold compared to the unfertilized control and 2.6±0.4-fold compared to inorganic fertilized control. In subsequent cropping cycles, crop yields declined for all treatments but at different rates. The carry-over effect of organic amendments on crop production was strongest for compost, which resulted in elevated crop production throughout all cropping cycles. Compost and biosolid amendment improved soil water retention, with 12±2.2% of water lost through leaching, compared to an average loss of 17±0.27% from other treatments. Leachate nitrate and ammonium concentrations from EcoSan compost amended soils were higher, however overall nutrient losses were less due to significantly lower rates of leaching. Biosolids resulted in the highest emissions of nitrous oxide.