Effects of Manure and Tillage on Edge‐of‐Field Phosphorus Loss in Seasonally Frozen Landscapes

• Published in: Journal of environmental quality Vol. 48; no. 4; pp. 966 - 977
• Main Authors: Zopp, Zachariah P., Ruark, Matthew D., Thompson, Anita M., Stuntebeck, Todd D., Cooley, Eric, Radatz, Amber, Radatz, Timothy
• Format: Journal Article
• Language: English
• Published: The American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc 01.07.2019
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq2019.01.0011

Environmental conditions and management practices affect nutrient losses in surface runoff, but their relative impacts on phosphorus (P) loss during frozen and nonfrozen ground periods have not been well quantified. More specifically, the relative importance of manure application, tillage, and soil‐test P (STP) has not been assessed at the field scale. In this study, we compiled a dataset composed of 125 site‐years of data from 26 fields that were continually monitored for edge‐of‐field P loss during snowmelt and storm events. Regression tree analyses were performed to rank the level of influence each environmental and management factor had on nutrient loads. Dissolved P (DP) was the majority of the total P (TP) during frozen conditions, but a small portion of TP during nonfrozen conditions. Manure application had a greater influence on the flow‐weighted mean concentrations (FWMCs) of TP and DP during frozen conditions than during nonfrozen conditions. No‐till resulted in greater TP and DP FWMCs during frozen conditions than conventional tillage, whereas the opposite effect for TP FWMC was seen during nonfrozen conditions. However, regression tree analysis revealed that STP (0‐ to 5‐cm depth) was the most important factor in predicting DP and TP FWMCs during frozen conditions and DP FWMC during nonfrozen conditions. Extremely high STP values were associated with late‐frozen manure applications and grazed pastures. Reducing surface P loss in seasonally frozen landscapes will require prioritizing management strategies that avoid manure application through early‐ and late‐frozen conditions and lead to a drawdown of STP, particularly in the top 5 cm. Core Ideas Monitoring P loss in cold climates is limited by the lack of long‐term, field‐scale studies. Manure applied in late winter results in more P loss during the frozen ground season. Conventional tillage reduces P loss during the frozen ground season. Fields receiving late‐frozen manure applications had extremely high soil‐test P. Regression tree analysis identified soil‐test P as the most important variable for frozen ground P loss.