@article{nelson_parsons_2006, title={Modification and validation of GLEAMS for prediction of phosphorus leaching in waste-amended soils}, volume={49}, DOI={10.13031/2013.22055}, abstractNote={Excess phosphorus applied to soils with low P adsorption capacities can enter surface water via leaching and subsurface transport, thereby negatively impacting water quality. Computer simulation models can be used to describe the effects of management practices on P leaching losses, provided the models are appropriately validated. The objectives of this research were to modify and validate P subroutines in the GLEAMS (Groundwater Loading Effects of Agricultural Management Systems) model to more accurately reflect P sorption and desorption, and then use the modified model to determine crop and waste management effects on long-term P leaching losses below the root zone of a grazed pasture with >20-year history of swine lagoon liquid application and considerable P buildup in the soil profile. GLEAMS was modified with the Langmuir equation to partition labile P between adsorbed and solution phases. The modification improved predictions of percolate P concentrations and soil P accumulation in acid sandy soils receiving waste-based P additions. The modification also increased model sensitivity to changes in crop and P management. The modified model predicted that P-based swine lagoon liquid applications would decrease P leaching by >20 kg ha-1 year-1 compared to N-based applications. Eliminating all P applications decreased the predicted P leaching losses by less than 1 kg ha-1 year-1 compared to P-based swine lagoon liquid application. Results show that P can continue leaching from P-saturated soils even in the absence of P additions.}, number={5}, journal={Transactions of the ASABE}, author={Nelson, N. O. and Parsons, J. E.}, year={2006}, pages={1395–1407} }
 @article{nelson_mikkelsen_2005, title={Balancing the phosphorus budget of a swine farm: A case study}, volume={34}, journal={Journal of Natural Resources and Life Sciences Education}, author={Nelson, N. O. and Mikkelsen, R. L.}, year={2005}, pages={90–95} }
 @article{nelson_mikkelsen_hesterberg_2003, title={Struvite precipitation in anaerobic swine lagoon liquid: effect of pH and Mg : P ratio and determination of rate constant}, volume={89}, ISSN={["0960-8524"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0038182035&partnerID=MN8TOARS}, DOI={10.1016/S0960-8524(03)00076-2}, abstractNote={Because of increased concern about surface water eutrophication from nutrient-enriched agricultural runoff, many swine producers are encouraged to decrease application rates of waste-based P. Precipitation and subsequent removal of magnesium ammonium phosphate (MgNH(4)PO(4) x 6H(2)O), commonly known as struvite, is a promising mechanism for N and P removal from anaerobic swine lagoon effluent. The objectives of this research were to (i) quantify the effects of adjusting pH and Mg:P ratio on struvite precipitation and (ii) determine the rate constant pH effect for struvite precipitation in anaerobic swine lagoon liquid. Concentrations of PO(4)-P in liquid from two anaerobic swine lagoons were determined after 24 h of equilibration for a pH range of 7.5-9.5 and Mg:P ratios between 1:1 and 1.6:1. Struvite formation reduced the PO(4)-P concentration in the effluents to as low as 2 mgl(-1). Minimum concentrations of PO(4)-P occurred between pH 8.9 and 9.25 at all Mg:P ratios. Struvite precipitation decreased PO(4)-P concentrations by 85% within 20 min at pH 9.0 for an initial Mg:P ratio of 1.2:1. The rate of PO(4)-P decrease was described by a first-order kinetic model, with rate constants of 3.7, 7.9, and 12.3 h(-1) at pH 8.4, 8.7 and 9.0 respectively. Our results indicate that induced struvite formation is a technically feasible method to remove N and P from swine lagoon liquid and it may allow swine producers to recover nutrients for off-farm sale.}, number={3}, journal={BIORESOURCE TECHNOLOGY}, author={Nelson, NO and Mikkelsen, RL and Hesterberg, DL}, year={2003}, month={Sep}, pages={229–236} }
 @inproceedings{nelson_mikkelsen_hesterberg_2000, title={Struvite formation to remove phosphorus from anaerobic swine lagoon effluent}, number={2000}, booktitle={Animal, agriculture and food processing waste: 8th Symposium: American Society of Agriculture Engineers, 2000}, publisher={St. Joseph, Michigan: American Society of Agricultural Engineers}, author={Nelson, N. O. and Mikkelsen, R. L. and Hesterberg, D. L.}, year={2000}, pages={18–26} }