Seasonal Manure Application Timing and Storage Effects on Field‐ and Watershed‐Level Phosphorus Losses

Abstract

Timing of manure application to agricultural soils remains a contentious topic in nutrient management planning, particularly with regard to impacts on nutrient loss in runoff and downstream water quality. We evaluated the effects of seasonal manure application and associated manure storage capacity on phosphorus (P) losses at both field and watershed scales over an 11-yr period, using long-term observed data and an upgraded, variable-source water quality model called Topo-SWAT. At the field level, despite variation in location and crop management, manure applications throughout fall and winter increased annual total P losses by 12 to 16% and dissolved P by 19 to 40% as compared with spring. Among all field-level scenarios, total P loss was substantially reduced through better site targeting (by 48-64%), improving winter soil cover (by 25-46%), and reducing manure application rates (by 1-23%). At the watershed level, a scenario simulating 12 mo of manure storage (all watershed manure applied in spring) reduced dissolved P loss by 5% and total P loss by 2% but resulted in greater P concentrations peaks compared with scenarios simulating 6 mo (fall-spring application) or 3 mo storage (four-season application). Watershed-level impacts are complicated by aggregate effects, both spatial and temporal, of manure storage capacity on variables such as manure application rate and timing, and complexities of field and management. This comparison of the consequences of different manure storage capacities demonstrated a tradeoff between reducing annual P loss through a few high-concentration runoff events and increasing the frequency of low peaks but also increasing the annual loss.

The Promise, Practice, and State of Planning Tools to Assess Site Vulnerability to Runoff Phosphorus Loss

“…Advances in fate-and-transport models continue to enhance our abilities to simulate P transformations and predict P movement under varieties of agricultural conditions. Vadas et al (2017) and Liu et al (2017) evaluate several approaches to winter manure spreading guidelines using SurPhos and SWAT, respectively, to project water quality outcomes. In comparing winter spreading bans with more flexible approaches that allow manure application depending on site conditions, they report that both strategies reduce field-edge P losses relative to no restrictions.…”

“…In comparing winter spreading bans with more flexible approaches that allow manure application depending on site conditions, they report that both strategies reduce field-edge P losses relative to no restrictions. Over the long-term, Liu et al (2017) show that winter spreading bans can affect greater reductions in watershed P loads, albeit while periodically exacerbating peaks in P concentrations of watershed discharge. Ford et al (2017) describe efforts to adapt macropore flow routines in APEX to better simulate preferential P losses to tile drains in the Western Lake Erie Basin.…”

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

“…Monitoring and understanding agricultural runoff in cold climates is critical; research in Wisconsin has shown that more than half of annual runoff occurs during the winter (Stuntebeck et al, 2011; Good et al, 2012). Furthermore, land application of manure during winter conditions, which represents most of the non‐crop‐growing season and can have reduced infiltration due to frozen or supersaturated soils, produces prime conditions for surface runoff and transport of manure P (Fleming and Fraser, 2000; Liu et al, 2017; Vadas et al, 2017). Evaluating field‐level losses in no‐till fields in Wisconsin, Komiskey et al (2011) reported significant increases in P losses when either solid or liquid manure was applied on frozen snow‐covered fields <1 wk from a subsequent runoff event.…”

Varying Influence of Dairy Manure Injection on Phosphorus Loss in Runoff over Four Years

“…However, site hydrology, management, and weather variability may all serve to obfuscate these relationships (Buda et al, 2009). In particular, P loss dynamics over winter periods may be affected by soil cover, including snow, freeze–thaw, and other site properties influencing hydrology and P availability (Vadas et al, 2007; Liu et al, 2017).…”

“…A variety of studies have concluded that manure injection decreases P loss in runoff (Kovar et al, 2011; Maguire et al, 2011). However, many of these studies rely on rainfall simulation, evaluating manure injection under worst‐case conditions that can inflate losses from surface application by simulating rainfall within several days of manure application (Johnson et al, 2011; Maguire et al, 2011; Liu et al, 2017). Further, longer‐term runoff monitoring studies are limited, and those that are available have not included factors that are common to the Chesapeake Bay region, such as fall application of manure, and rotation to perennial legume forages that often do not receive manure and serve to lower soil P (Daverede et al, 2004; Nord and Lanyon, 2003).…”