Thomas J. Sauer

In complex landscapes with multiple land uses, it is often difficult to identify the source of contaminant loadings. The objective of this study was to compare nutrient runoff as affected by grazing animal depositions vs. poultry litter application. Simulated rainfall was applied twice to 1.5 by 6.0 m runoff plots of tall fescue (Festuca arundinacea Schreb.) with treatments of no waste (CT), dairy calf feces and urine (DFU), poultry litter (PL), and dairy calf feces and urine with poultry litter (DFU + PL). Chemical properties of the runoff samples including pH, electrical conductivity (EC), C, soluble reactive phosphorus (SRP), total nitrogen (TN), NH₄‐N, NO₃‐N, K, Mg, S, B, Cu, Fe, Mn, Mo, Na, and Zn were determined. Plots receiving poultry litter had significantly greater losses of most nutrient parameters for both rainfall simulations. For the nutrient parameters of primary interest with regard to water quality, 5.0, 29.5, and 21.9% of the TN, NH₄‐N, and SRP applied in the PL treatment were transported in runoff during the first rainfall simulation as compared to 3.9, 5.0, and 15.3%, respectively, for the DFU treatment. Comparable percentages of the applied nutrients were lost from the PL and DFU treatments even though the PL treatment, with the exception of NH₄‐N, provided at least six times the amount of each nutrient. A severe rainfall event shortly after poultry litter application produces significantly greater nutrient losses as compared to similar application of grazing animal depositions at the rates used in the experiment.

Surface runoff of nutrients after land application of animal manures is influenced by climate, physical and chemical properties of the soil, and land use. The objective of this study was to characterize the surface soil properties from a riparian forest to an adjacent ridge top at a site in the Ozark Highlands. Sampling transects (60 m long) were established in five soil map units, 7.6-cm-diameter × 10-cm-deep cores extracted at 3-m intervals, and samples analyzed to determine relevant soil physical and chemical properties. Ponded infiltration measurements were also completed on four of the transects. Soil test phosphorus and phosphorus saturation ranged from 10 to 31.4 mg kg⁻¹ and 9.1 to 18.4%, respectively, and reflect the recent history of limited poultry litter or fertilizer application. Soil samples from each transect had similar average silt content (range = 67.2-73.9%), but the soil in the riparian forest (Razort silt loam) had more clay and significantly less sand and coarse fragments. The Razort soil also had a higher cation exchange capacity (CEC) (20.7 cmol kg⁻¹) and infiltration rate (5.29 cm h⁻¹). Trends in clay content, infiltration rate, and CEC suggest that the riparian forest and adjacent alluvial pasture may act as nutrient sinks in this landscape. Results of this study will be combined with grazing management and hydrologic analyses to develop best management practices for poultry litter applications and to provide baseline data for the assessment of long-term effects of litter application on soil properties.

Differentiation between tillage‐ and residue‐induced effects on soil moisture and thermal regimes is necessary to improve residue management practices. The objective of this research was to quantify the influence of corn ( Zea mays L.) residue age and placement on evaporation from and heat flow in two soils. Soil temperature, thermal conductivity, heat flux, and moisture content were monitored in duplicate monoliths (0.45 [length] by 0.35 [width] by 0.5 [height] m) of Nicollet loam (fine‐loamy, mixed, mesic Aquic Hapludoll) and Monona silt loam (fine‐loamy, mixed, mesic Typic Hapludoll) in a controlled environment chamber. Mass changes of one monolith of each soil were measured with load cells to estimate evaporation. Surface cover types consisted of a bare soil surface (B), fresh residue (F), weathered residue (W), and weathered residue with a 0.15‐m‐wide bare strip (S). Bare‐soil evaporation averaged 9.97 ± 0.66 mm for both soils during a 96‐h period and was reduced to an average of 5.76 ± 0.70 mm with residue cover. Nicollet soil with weathered residue had an average evaporation rate of 1.33 to 1.4 mm d ⁻¹ . By comparison, evaporation rates measured in a field having Nicollet and associated soils with weathered corn residue averaged 1.37 and 1.11 mm d ⁻¹ . Residue cover had no significant effect on thermal conductivity measured at 0.15 m that averaged 1.22 and 1.35 W m ⁻¹ K ⁻¹ for the Nicollet and Monona soils, respectively. Phase shift in soil temperature and average daily conductive soil heat flux were similar for field and chamber measurements but the amplitude of the soil temperature wave and conductive soil heat flux were much greater in the field.

Maintenance of crop residues on the soil surface is promoted as a management practice for reducing soil erosion by wind and water. Crop residue on the soil surface, however, also influences turbulent exchange processes that affect surface water and energy balances. At present, there are very limited data on the aerodynamic properties of residue‐covered surfaces. The objective of this research was to derive estimates of the aerodynamic properties (momentum roughness length z₀, zero‐plane displacement d, and drag coefficient C_d) of fields with standing corn (Zea mays L.) stubble. Wind speed and air temperature measurements were made at six heights above two no‐tillage fields near Ames, IA, in the spring and fall of 1994 and in the spring of 1995. Both sites had standing corn stubble approximately 0.3 m tall at a density of greater than 60 000 stalks ha ⁻¹ and nearly 95% residue cover. An iterative, least‐squares linear regression technique was applied to wind profiles obtained under neutral atmospheric conditions to determine z₀, d, and the friction velocity (u.). Mean values of z₀ and d for each of the three measurement periods varied from 11.8 to 24.3 and 119 to 169 mm, respectively. The ratios z₀/h_s and d/h_s, where h_s is the mean stubble height, averaged 0.058 and 0.53, respectively, for all profiles. The magnitude of zo and d and their weak dependence on wind speed are consistent with turbulent flow over a surface with sparse, rigid roughness elements. The z₀ and C_d were higher for the fall measurement period, suggesting that the loose, fresh residue presented a comparatively rough surface that was then smoothed by weathering and compaction beneath snow.