Breakdown, uptake and losses of human urine chemical compounds in barley (Hordeum vulgare) and soybean (Glycine max) agricultural plots: Effectiveness of human urine use in agriculture

Due to the increasing global demand of food and fibers, a comprehensive analysis was conducted to assess: (1) if application of human urine to agricultural soil provides enough nutrient to satisfy the crop demand for primary and secondary nutrients; and (2) if breakdown products affect the soil and water quality near-surface and in the aquifer. A biogeochemical reaction network of urine decomposition tested earlier and extended here to include also the N cycle, was integrated in a computational solver describing a soil profile 10 m deep. Barley (Hordeum vulgare) and soybean (Glycine max) were used as test crops in West Wyalong and Moree, New South Wales, Australia. Soil properties, daily precipitation, and evapotranspiration at both locations were used as environmental and boundary conditions. After exploring various scenarios of urine application amount per surface area, frequency, and timing, uptake of primary and secondary nutrients was found to meet the crop demand nearly in full for 2 L/m² amendment of undiluted urine. Uptake increased nearly linearly with increasing application, but the partitioning between uptake, aqueous, protected, and gaseous phases was found to be nonlinear. Net C and N gas emissions from urine decomposition did not bring about particularly high values, which were in line with fluxes from contemporary agricultural practices. With the pH stabilizing at about 5.5 and the salinity increasing by less than 2 mM in the top soil, it was inferred that soil and water qualities were not substantially altered even after 20 years of repeated urine applications.