Manure Application Timing and Tillage Influence On Nutrient Loss From Snowmelt Runoff.

Manure can be an important source of plant nutrients for crop production and may improve soil quality. A study was conducted to determine the influence of tillage and manure application timing on nutrient loss in snowmelt run-off. The study was designed to compare three dates of beef feedlot manure application at 40 tons/hectare on untilled and tilled soybean stubble. Eight 4 m2 steel frames were installed in the fall on each tillage area to define individual plots. Treatments were randomly assigned so that each area had two control plots, two that received manure during November, two in January, and two in March. Snowmelt runoff volume (RO) was recorded during March and sub-samples analyzed for ammonium-nitrogen (AM), nitrate nitrogen (NT), total suspended solids (TSS), total Kjeldahl nitrogen (TKN), total phosphorus (TP) and total dissolved phosphorus (DP) from the run-off of each plot. Soil probes were installed at 15 cm (6 in) and 50 cm (20 in) below the soil surface to monitor soil moisture and temperatures for each plot. Mean comparisons of tillage and manure timing were determined with SAS PROC GLM. Snowmelt runoff concentrations and loads of AM, TP and DP trended higher in runoff from manure application treatments compared to the control. The concentration and load (calculated as runoff volume area-1 x concentration) of AM was significantly (LSD 0.1) higher with tilled compared to untilled plots. The November application significantly increased RO amount, AM concentrations and AM, NT and DP load in the snowmelt runoff compared to winter applications.