Natural Soil Amendments to Reduce Nitrate Leaching in Potato Production

Agricultural pollutants are commonly detected in Wisconsin groundwater around potato production on coarse-textured, low organic matter soils and practical nitrate reduction strategies are needed to address groundwater quality. Soil column studies with loamy sand soil common to the potato production region were conducted to explore the ability of organic soil additives incorporated below the simulated potato root zone to capture nitrogen in leachate water. Soil additives included two biochar types (biochar 400 and biochar 700, both at 5% wt wt^− 1 concentrations) and two papermill residual lignocellulose products (papermill source 1 and papermill source 2, evaluated at 60,525 and 49,320 kg ha^− 1, respectively) injected in the soil amendment zone below the simulated potato root zone. Additionally, one humic acid treatment with 500 kg ha^− 1 dry lignite humic acid incorporated into the simulated potato root zone and 374 L ha^− 1 liquid humic acid incorporated below the simulated potato root zone was included. Nitrogen fertilizer was added at study initiation and midway through the study. Distilled water was added every 14 days during the 14-week study period to simulate high precipitation events and leachate volume was quantified and analyzed for nitrate-nitrite nitrogen content. Leachate volume varied slightly and inconsistently among treatments and compared to soil with no additives. Biochar and papermill lignocellulose products reduced the season flow-weighted nitrate-nitrite nitrogen concentration by up to 7.6 and 34%, respectively, but humic acid was ineffective. Treatment efficacy diminished over time. Further research is needed to investigate soil treatment longevity and response to plant biotic interactions, but the papermill residual products were particularly effective at reducing nitrate-nitrite nitrogen content in leachate in this study.