John P. Schmidt

Phosphorus loss from an agricultural watershed as a function of storm size.

Phosphorus (P) loss from agricultural watersheds is generally greater in storm rather than base flow. Although fundamental to P-based risk assessment tools, few studies have quantified the effect of storm size on P loss. Thus, the loss of P as a function of flow type (base and storm flow) and size was quantified for a mixed-land use watershed (FD-36; 39.5 ha) from 1997 to 2006. Storm size was ranked by return period (<1, 1-3, 3-5, 5-10, and >10 yr), where increasing return period represents storms with greater peak and total flow. From 1997 to 2006, storm flow accounted for 32% of watershed discharge yet contributed 65% of dissolved reactive P (DP) (107 g ha(-1) yr(-1)) and 80% of total P (TP) exported (515 g ha(-1) yr(-1)). Of 248 storm flows during this period, 93% had a return period of <1 yr, contributing most of the 10-yr flow (6507 m(3) ha(-1); 63%) and export of DP (574 g ha(-1); 54%) and TP (2423 g ha(-1); 47%). Two 10-yr storms contributed 23% of P exported between 1997 and 2006. A significant increase in storm flow DP concentration with storm size (0.09-0.16 mg L(-1)) suggests that P release from soil and/or area of the watershed producing runoff increase with storm size. Thus, implementation of P-based Best Management Practice needs to consider what level of risk management is acceptable.

Low-disturbance manure incorporation effects on ammonia and nitrate loss.

Low-disturbance manure application methods can provide the benefits of manure incorporation, including reducing ammonia (NH3) emissions, in production systems where tillage is not possible. However, incorporation can exacerbate nitrate (NO3⁻) leaching. We sought to assess the trade-offs in NH3 and NO3⁻ losses caused by alternative manure application methods. Dairy slurry (2006-2007) and liquid swine manure (2008-2009) were applied to no-till corn by (i) shallow (<10 cm) disk injection, (ii) surface banding with soil aeration, (iii) broadcasting, and (iv) broadcasting with tillage incorporation. Ammonia emissions were monitored for 72 h after application using ventilated chambers and passive diffusion samplers, and NO3⁻ leaching to 80 cm was monitored with buried column lysimeters. The greatest NH3 emissions occurred with broadcasting (35-63 kg NH3-N ha⁻), and the lowest emissions were from unamended soil (<1 kg NH-N ha⁻¹). Injection decreased NH-N emissions by 91 to 99% compared with broadcasting and resulted in lower emissions than tillage incorporation 1 h after broadcasting. Ammonia-nitrogen emissions from banding manure with aeration were inconsistent between years, averaging 0 to 71% that of broadcasting. Annual NO3⁻ leaching losses were small (<25 kg NO3-N ha⁻¹) and similar between treatments, except for the first winter when NO3⁻ leaching was fivefold greater with injection. Because NO3⁻ leaching with injection was substantially lower over subsequent seasons, we hypothesize that the elevated losses during the first winter were through preferential flow paths inadvertently created during lysimeter installation. Overall, shallow disk injection yielded the lowest NH3 emissions without consistently increasing NO3⁻ leaching, whereas manure banding with soil aeration conserved inconsistent amounts of N.

Grazing Can Reduce the Environmental Impact of Dairy Production Systems

Incorporating managed rotational grazing into a dairy farm can result in an array of environmental consequences. A comprehensive assessment of the environmental impacts of four management scenarios was conducted by simulating a 250-acre dairy farm typical of Pennsylvania with: (i) a confinement fed herd producing 22,000 lbs of milk per cow per year; (ii) a confinement fed herd producing 18,500 lbs; (iii) a confinement fed herd with summer grazing producing 18,500 lbs; and (iv) a seasonal herd maintained outdoors producing 13,000 lbs. Converting 75 acres of cropland to perennial grassland reduced erosion 24% and sediment-bound and soluble P runoff by 23 and 11%, respectively. Conversion to all perennial grassland reduced erosion 87% with sediment-bound and soluble P losses reduced 80 and 23%. Ammonia volatilization was reduced about 30% through grazing, but nitrate leaching loss increased up to 65%. Grazing systems reduced the net greenhouse gas emission by 8 to 14% and the C footprint by 9 to 20%. Including C sequestration further reduced the C footprint of an all grassland farm up to 80% during the transition from cropland. The environmental benefits of grass-based dairy production should be used to encourage greater adoption of managed rotational grazing in regions where this technology is well adapted.

Spatial distribution of livestock concentration areas and soil nutrients in pastures

Livestock concentration areas can be significant point sources of nutrient pollution. Our objective was to determine the spatial distribution of livestock concentration areas in pastures at the farm scale, along with the distribution of soil nutrients at the individual livestock concentration area scale. We georeferenced and measured the size of all livestock concentration areas in cool-season grass-legume pastures on five farms (four grazing dairies and a beef cattle farm) in Maryland, Pennsylvania, and New York during two years. Soil of selected concentration areas on each of the farms was sampled to 0 to 5 and 0 to 15 cm (0 to 2 and 0 to 6 in) depths to compare nutrient levels with paired unaffected areas of the pasture. On one farm, we sampled two concentration areas more densely (20 to 25 samples, 0 to 5 cm depth along each of five 100 m [328 ft] transects) to measure spatial distribution of soil nutrients. The transects were arranged radially to encompass variation both up and downslope. We installed runoff plots at three locations on and near the two concentration areas to measure nutrients in surface water runoff from simulated rainfall. On the five farms, concentration areas occurred most frequently at paddock gates (38% of sites). Although fewer in number, concentration areas at feeding sites were often larger than those at gates or other locations and accounted for most (48%) of the area affected by livestock congregation. Most concentration areas were small (median area 100 m2 [1,076 ft2]), isolated (median distance, 61 m [200 ft] from a water body), and surrounded by vegetation. Intensive sampling on one farm showed that soil within 20 to 40 m (66 to 132 ft) of concentration areas was enriched in phosphorus, which contributed to higher phosphorus concentration in the runoff from simulated rainfall compared with the rest of the pasture. Pastures used as holding and feeding areas with highly elevated soil nutrients and no surrounding vegetation to filter runoff represented a direct threat to surface water quality. Many concentration areas, however, were surrounded by vegetation, which would mitigate this risk.

Nitrogen Fate in Drainage Ditches of the Coastal Plain after Dredging

Drainage ditches are a key conduit of nitrogen (N) from agricultural fields to surface water. The effect of ditch dredging, a common practice to improve drainage, on the fate of N in ditch effluent is not well understood. This study evaluated the effect of dredging on N transport in drainage ditches of the Delmarva Peninsula. Sediments from two ditches draining a single field were collected (0-5 cm) to represent conditions before and after dredging. Sediments were packed in 10-m-long recirculating flumes and subjected to a three-phase experiment to assess the sediments role as a sink or source of ammonium (NH4) and nitrate (NO3). Under conditions of low initial NH4-N and NO3-N concentrations in flume water, sediment from the undredged ditch released 113 times more NO3-N to water than did sediment from the dredged ditch. When flume water was spiked with NH4-N and NO3-N to simulate increases in N concentrations from drainage and runoff from adjacent fields, NO3-N in flume water increased during 48 h compared with the initial spiked concentration, while NH4-N decreased. These simultaneous changes were attributed to nitrification, with 23% more NO3-N observed in flume water with undredged ditch sediment compared with dredged ditch sediment. Replacing the N-spiked water with deionized water resulted in two times more NO3-N released from the undredged ditch sediment than the dredged ditch sediment. These results suggest that ditch sediments could represent significant stores of N and that dredging could greatly affect the ditch sediments ability to temporarily assimilate N input from field drainage.

Environmental Impacts of Switchgrass Management for Bioenergy Production

In this chapter, we review major environmental impacts of growing switchgrass as a bioenergy crop, including effects on carbon sequestration, greenhouse gas emissions, soil erosion, nutrient leaching, and runoff. Information from life cycle analyses, including the effects of indirect land use change (iLUC), is examined to quantify the full impact of migration to bioenergy cropping systems on both managed and natural ecosystems. Information on the environmental impacts of switchgrass cultivation is scarce and there exists a critical need for additional research. What limited information there is suggests that switchgrass provides multiple environmental benefits compared to annual crop cultivation. However, benefits generally appear to be similar to other perennial crops.

Environmental and Economic Comparisons of Manure Application Methods on Dairy Farms

A dairy farm simulation model was used to compare the environmental and economic impacts of using alternative manure application methods on a dairy farm in Pennsylvania. Model predictions of ammonia emissions, nitrate leaching, and phosphorus runoff were compared to field measurements following no manure application and five application methods. Application methods included broadcast spreading without incorporation, broadcast spreading with immediate incorporation by tillage, band application with aeration, shallow disk injection, and high pressure injection. Following model evaluation, manure application methods were simulated over 25 years of weather on a representative Pennsylvania dairy farm. Immediate incorporation by tillage and the use of the two manure injection techniques reduced ammonia emissions, but nitrate leaching losses were increased. Reductions in ammonia N loss and runoff loss of P were obtained with the use of shallow disk injection without adversely affecting farm profitability.