The effect of multiple applications of a de-inked papermill biosolid on soil properties and crop growth
An approach was tested, using the biochemical composition of a de-inked papermill biosolid PB, to determine optimum rates of supplemental nitrogen fertilizer needed to meet the requirements to decompose the PB and grow crops. In this study, increasing rates of the PB were applied annually for three years on four different agricultural soils in southwestern Ontario. Supplemental nitrogen fertilizer treatments >= 1 kg N Mg-1 PB were generally sufficient to maintain or increase corn yields on the PB amended soils. Soybean yields were also maintained or increased, on PB amended soils, without needing additional supplemental nitrogen fertilizer treatments. Greater concentrations of soil mineral nitrogen were measured over the growing season at supplemental nitrogen fertilizer rates >= 1 kg N Mg -1 PB. In addition, residual soil mineral nitrogen concentrations, measured at post harvest, were typically below 10 ppm in soils amended with PB, even at the highest rate of supplemental nitrogen fertilizer. Soil physical and chemical properties at the study sites, including bulk density, infiltration, and total carbon, were improved by additions of PB. Other soil chemical properties, such as pH and electrical conductivity, were unchanged in all soils receiving PB. No consistent trends toward increasing the concentrations of heavy metal were observed after two years of de-inked papermill biosolid applications. Earthworm density and biomass, a biological measure of soil health, were increased throughout the study on PB amended soils. This study demonstrated that the nitrogen requirements for decomposition of papermill biosolids can be successfully managed with crop production. A number of benefits attributed to papermill biosolid treatments were also discovered on physical, chemical, and biological properties of agricultural soils.