**1. Introduction**

Corn silage is an important crop to dairy producers in the US and globally. A lack of crop residue after silage harvest increases erosion potential and phosphorus (P) and nitrogen (N) transport to surface waters compared to less erosive crops [1–7]. The US dairy industry faces increasing pressure from regulatory agencies and the public to improve on-farm nutrient use efficiency while decreasing environmental impacts [8]. While dairy manure application on silage fields provides needed nutrients and is a source of organic matter for soil quality, it also contributes to runoff P and N losses and greenhouse gas emissions [8].

Nutrient management practices such as manure application methods, tillage practices, cover crops, and grass buffers can reduce erosion and P transport in corn production systems [1–3,5,9–17], however, it is important to recognize that they can also have differential effects on sediment and P transport. For example, cover crops and reduced tillage can decrease erosion and particulate P loss but increase bioavailable P loss in the form of

**Citation:** Sherman, J.F.; Young, E.O.; Jokela, W.E.; Casler, M.D.; Coblentz, W.K.; Cavadini, J. Influence of Soil and Manure Management Practices on Surface Runoff Phosphorus and Nitrogen Loss in a Corn Silage Production System: A Paired Watershed Approach. *Soil Syst.* **2021**, *5*, 1. https://doi.org/10.3390/ soilsystems5010001

Received: 14 November 2020 Accepted: 24 December 2020 Published: 29 December 2020

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dissolved reactive P (DRP) transport in surface runoff [18–20]. With long-term reduced and/or no-tillage, DRP can be increased relative to conventional tillage from a combination of lower erosion, nutrient stratification, and/or dissolved nutrient release from crop residues [21–24]. Snowmelt runoff in cold climates often accounts for a substantial fraction of total annual runoff and N and P loss. Several studies conducted in cold climates report a dominance of DRP in snowmelt runoff compared to particulate P, which tends to be higher with more erosive rainfall events compared to snowmelt [19,25,26]. Establishing a winter rye cover crop after corn silage harvest in the fall can help mitigate dissolved and particulate-bound nutrients in surface runoff, including ammonium-N (NH4 +-N) and nitrate-N (NO3-N) [5,11,27,28]. Grass buffer strips are another commonly recommended BMP to reduce erosion and edge-of-field nutrient loss in agricultural systems [15,29]. Mayer et al. [30] compared data from 88 studies evaluating vegetative buffer N removal effectiveness and concluded adequate vegetation was a critical factor for mitigating erosion and enhancing N attenuation. While plant buffer species did not affect N removal, buffers > 50 m removed N more consistently than 0 to 25 m wide strips.

Research indicates that individual and combinations of best practices can mitigate erosion and surface runoff nutrient loss potential. Much of this is from field plots, however, which largely ignores the dynamic nature and complex hydrology of larger fields/watersheds [31–33]. Evaluating the effectiveness of practices at the landscape and watershed scales is also challenging due to the heterogeneity of runoff processes [34–36]. Paired watershed designs account for inherent physiographic differences between watersheds and can help to isolate management effects on runoff water quality [9,32,37,38]. The objective of this study was to use a paired-watershed approach to quantify the effectiveness of targeted BMPs to mitigate surface runoff nutrient transport from corn silage fields in central Wisconsin (WI) with high runoff potential. Specifically, the following management systems were compared to the typical practice of fall manure application with chisel tillage incorporation (FMT) (see Table S1 for abbreviation guide): (i) fall-applied manure and chisel tillage with the inclusion of a grass-legume buffer strip along the lower field edge (BFMT); (ii) a fall rye cover crop with spring manure application and chisel tillage (RSMT); (iii) fall manure application with spring chisel tillage (FMST).
