1a. Objectives (from AD-416):
The objectives of our project are to: 1) measure N and P loss in runoff from 8 pastures representing different grazing management strategies over at least 2 years; and 2) use the runoff data to validate the ability of our SurPhos model to predict P loss in runoff from grazed pasture.
1b. Approach (from AD-416):
Runoff plots will be established at the UW-Platteville Pioneer Farm in Platteville, WI, and runoff collection systems will be installed. Runoff samples will be collected year-round, and analyzed for total sediment, total N and P, and dissolved P, NH4, and NO3. Initial and annual soil samples will be collected from plots and analyzed. Runoff plots will be stocked with dairy cattle to achieve several management scenarios with variations in diet supplementation and grazing intensity. These grazing strategies will result in different amounts of manure and associated nutrient amounts applied to runoff plots. After grazing periods, the number of dung pats deposited in each runoff plot section will be counted and collected to determine total wet weight, dry matter content, total P and N, and water extractable P. These data will enable quantification of nutrient inputs to the runoff plots in cattle feces. Runoff data will be used to validate our SurPhos model, which simulates dissolved P loss in runoff from surface-applied manure. Validation of the model will determine its ability to accurately simulate P loss in runoff from cattle grazing pastures. SurPhos is currently being adapted to simulate grazing and validating the model with field data from Australia and England and small-plot, simulated grazing data from several locations in the U.S. Information and data from Wisconsin producers will be used to simulate P loss from areas where cows spend time outside, including pasture, over-wintering areas, and barnyards. The physical locations and management practices that represent the greatest risk of P loss will be investigated to assess the ability of alternative practices to minimize that loss.
3. Progress Report:
This report relates to Objective 1 of that project: Determine the effects of dairy diets and herd management on manure nutrient excretions and nutrient losses to the environment. We monitored surface runoff from eight pasture watersheds at the University of Wisconsin Platteville Pioneer farm. We analyzed 117 samples from 19 runoff events for sediment, nitrogen, and phosphorus (P). In the 117 samples, sediment concentrations were very low, averaging only 0.24 g/L. Total P concentrations ranged from 0.5 to 5.2 mg/L, with dissolved P averaging about 85% of total P in the snowmelt samples and 60% in rain-runoff events. These P results are consistent with data in the literature. Based on measured runoff volume and sediment and P concentration data, we estimated annual runoff, erosion, and P loss from the pastures. Annual runoff was 2.6 inches, and annual erosion was very low, at only 0.03 ton/acre. Annual P loss was also very low, at only 1.21 lb total P/acre and 1.03 lb dissolved P/acre. The Annual P Loss Estimator (APLE) model has been able to accurately predict phosphorus loss from the grazed pastures. We also tested APLE with pasture runoff data from 18 studies published in the literature, and found a strong relationship between measured and predicted P loss. This validates that APLE accurately predicts phosphorus loss from pastures.