1a. Objectives (from AD-416)
The overarching objective of our research project is to address current knowledge gaps in understanding and managing the nutrient cycles and pathogen transmission on modern dairy farms. Our specific research objectives are as follows: 1. Determine the effects of dairy cattle diet and dairy herd management (e.g. pasture, confinement, hybrid systems) on manure nutrient excretion, capture, recycling, and loss via gaseous emissions, leaching, and runoff. 2. Determine the effects of dairy manure management practices and cropping systems on crop production, soil properties, and loss of nutrients, sediment, and pathogens (e.g. Cryptosporidium parvum, Salmonella spp., and bovine diarrhea virus) in surface runoff or atmospheric emissions. 3. Determine the effects of timing and rate of dairy manure application on nutrient uptake and nutritional characteristics of fresh and harvested annual and perennial forages. 4. Develop crop management strategies to optimize the exchange of N, P, and K as manure and feed between neighboring dairy and cash grain farms. 5. Develop improved methods for detection and quantification of pathogens in manure, forages, and surface runoff and evaluate effects of management practices on pathogen transport and survival.
1b. Approach (from AD-416)
Improved management of dairy farms requires successfully managing its nutrient flows, both to maximize nutrient use by animals and crops to optimize profit, and to minimize nutrient loss to the environment. We will investigate most aspects of nutrient cycling throughout the dairy-farm system with a variety of methods and at different scales (replicated field plots, field-scale paired watersheds, feeding trials with replicated pens of heifers, etc.). We will also examine pathogen transport and viability at different points in the dairy farm system. Some experiments will investigate only one or two nutrient or pathogen pathways, while others will be more comprehensive, including, for example, surface runoff, gaseous emission, and plant removal. Our research team also has a longer-term goal, which is to integrate information across experiments to more completely describe, quantify, model, and manage the entire dairy-farm nutrient cycle. Achieving this goal will help ensure the existence of sustainable, profitable, environmentally benign dairy farming for coming decades.
3. Progress Report
A paired-watershed study to evaluate runoff losses of nitrogen (N), phosphorus (P), and pathogens from different manure/tillage/crop management systems is in its fifth year. Findings from the first three years (calibration period and early treatment period) were reported in a recently published journal article. A runoff experiment comparing nutrient loss from corralling areas, pastures, and cropped fields was completed in the spring of 2011. Data are being summarized for presentations and publications. Construction of plots to compare different barnyard surface materials (soil, sand, and bark mulch) was completed in 2010 and cows were placed in them. Greenhouse gas emission data were collected, and leachate and runoff samples are being analyzed for N, P, and sediments. The third year of a field trial to evaluate N availability and losses of ammonia and greenhouse gases from different methods and timing of liquid dairy manure application on corn is in progress. A grazing runoff study funded by a grant from the WI Department of Agriculture was initiated in 2010. Through a cooperative agreement with the University of Wisconsin Platteville, surface runoff from eight small pasture watersheds is being sampled and analyzed for sediment, N, and P to compare different grazing treatments. The data will be used to validate our model to predict P loss in runoff from pastures. Also, as part of the study, four dairy grazing farms in WI are being visited four times annually to collect comprehensive herd, feed, manure management, and milk analysis information and feed and manure samples for lab analysis. This information will be used for future model simulations to estimate P loss in runoff from both grazing and confinement. In partnership with the University of Wisconsin, all summaries of studies evaluating supplementation of phosphorus for growing dairy replacement heifers have been completed and submitted for publication. Plot studies evaluating the capacity of fall-grown oat to capture nutrients from manure applications or other commercial fertilizer sources will be seeded in August 2011 with subsequent harvests continuing through late October. Data evaluating the efficacy of a grass-ley system for opening additional windows for summer manure application on dairy farms, including assessments of voluntary intake of manured forages by dairy heifers, was summarized and published. A pathogen laboratory has been established and was approved by USDA in January 2011 to conduct pathogen research at the Biosafety Level 2+. Researchers developed assays for quantifying over a dozen different dairy manure-borne bacteria, protozoa, and virus pathogens in the environment. Findings from analysis of dairy manure-borne pathogens in runoff from the paired-watershed study were presented at the 2011 General Meeting of the American Society for Microbiology. The laboratory began five studies on the transport of manure-borne pathogens in Midwestern watersheds and groundwater aquifers in collaboration with researchers at the US Geological Survey Wisconsin Water Science Center, Iowa Water Science Center, Iowa State University, and the USEPA in Athens, GA.
1. Supplementation of phosphorus for developing replacement heifers: performance. The dietary requirements of phosphorus for replacement dairy heifers and typical levels of phosphorus in feeds are similar, suggesting that the need for supplemental phosphorus in dairy-heifer diets may be minimal. On this basis, dairy producers may be able to capture some savings in mineral costs while limiting the potential environmental burdens created by excreted excess phosphorus. In a study conducted by University of Wisconsin and USDA-ARS scientists at Marshfield (WI), dairy heifers (365) were offered diets with or without supplemental phosphorus. Heifers were evaluated for body weight, external frame size, dystocia (calving difficulty), reproductive efficiency, and first lactation milk production performance. Performance of heifers, or subsequently as first-lactation cows, did not differ for any trait evaluated on the basis of phosphorus supplementation strategy. The amount of phosphorus excreted also was examined, and all excess phosphorus consumed by heifers was excreted in the feces and not retained. These results suggest there is no benefit to feeding phosphorus above recommended levels to dairy heifers, provided phosphorus concentrations in feedstuffs are adequate to meet established feeding guidelines. Adherence to these guidelines should reduce mineral costs for producers, as well as environmental burdens associated with excreted excess phosphorus.
2. User-friendly model developed to predict annual phosphorus loss in runoff. Non-point source pollution of fresh waters by agricultural phosphorus (P) can limit water use for drinking, recreation, and industry. An ARS researcher at Madison, WI developed and validated a user-friendly spreadsheet model (Annual P Loss Estimator -APLE) to predict long-term changes in soil P and P loss in runoff for a wide variety of agricultural conditions. Parts of the model have been incorporated into the WI P Index, and the model is being used to help evaluate and improve predictions by other P Indexes, which are used by producers and their consultants across the US to comply with the USDA 590 nutrient management standards. The APLE model can thus help producers develop management practices to reduce non-point source pollution of water bodies by agricultural phosphorus.
3. Use of a temporary orchardgrass ley opens additional windows for manure spreading. Previously, it was demonstrated that a temporary orchardgrass ley (designated manuring site) was a highly productive source of forage, and it created much needed opportunities for the application of manure during summer months. This is especially valuable within the corn/alfalfa rotations common throughout Wisconsin. In these systems, there are only limited opportunities for manure spreading, which becomes increasingly problematic as confinement dairies become larger. In this study, conducted by University of Wisconsin and USDA-ARS scientists at Prairie du Sac (WI), orchardgrass hay produced from a frequently manured grass ley exhibited excellent forage quality characteristics, as well as high concentrations of phosphorus (P). The latter could reduce needed supplemental dietary P purchases. Concentrations of tissue potassium (K) also were high (3.2%); this is potentially problematic for dry dairy cows because it likely contributes to increased risks of milk fever (hypocalcemia). Cool-season grasses receiving manure are notorious for excessive consumption of K, and this was observed in our work; therefore, feeding these hays in dry cow rations should be avoided. A feed rejection trial with Holstein heifers showed that the application of dairy slurry after each orchardgrass hay harvest did not increase forage rejection relative to hays grown with applications of commercial fertilizers. In the upper Midwest, this ley system potentially could open several summer opportunities for spreading manure, as well as supply producers with an alternative forage to compliment their production of corn and alfalfa silages.
4. Midwest cropping system effects on soil quality. Cropping systems may improve or decrease soil quality depending on the specific crop rotation, nutrient amendments, and tillage practices employed. An ARS researcher in Marshfield, WI, collaborated with Univ. of Wisconsin researchers to determine the effect of six cropping systems in the Wisconsin Integrated Cropping Systems Trial on soil properties after 18 years of continuous treatments. Treatments included three grain-based systems (continuous corn and two grain rotations), two forage-based systems (organic and conventional), and a grass-legume pasture. Results showed that different Midwest long-term cropping systems have significant effects on most chemical, physical, and microbial soil properties (soil quality indicators), primarily the effect of crop type and rotation, manure addition, and intensity of tillage. In particular, the intensively managed grass-legume pasture was higher in most soil quality indicators than all other corn or forage-based systems and had a higher soil quality index. The alfalfa-based systems had higher levels of soil carbon and nitrogen and some physical variables than did the grain-based systems but soil quality indexes were not different. There were few differences in soil quality parameters between the conventional and organic dairy cropping systems, a result explained by the fairly similar crop rotations and manure inputs. Overall, these results indicate that, cropping systems affect several soil quality parameters. However, on these productive, high-organic matter, prairie-derived soils under good management, all of the cropping systems in this study maintained an acceptable level of soil quality.
5. Supplementation of phosphorus for developing replacement heifers: bone development. When phosphorus is fed to cattle in amounts greater than what they can utilize, the excess is excreted in the manure. If phosphorus-rich manure is later spread on farm fields to provide nutrients for growing crops, it also may cause an excess of phosphorus in runoff that can promote the undesirable growth of algae in lakes. For growing dairy heifers, phosphorus is essential for bone growth and development. The amount of dietary phosphorus needed in dairy heifer diets is very similar to that found naturally in many forages comprising typical heifer diets; this suggests that adding supplemental phosphorus to heifer diets may not always be necessary. However, no long-term studies addressing this issue exist; therefore, a study was conducted by University of Wisconsin and USDA-ARS scientists at Marshfield (WI) with dairy heifers ranging from 4 to 22 months of age. Dairy heifers were fed diets with or without supplemental phosphorus resulting in dietary phosphorus concentrations of 0.29 or 0.39%. Our results show that phosphorus supplementation for developing replacement heifers had minimal effect on the extent of frame development, bone density, or bone metabolism. Potentially, this information will help dairy producers and nutritionists formulate heifer rations that contain adequate, but not excessive, amounts of phosphorus so that the growth needs of the heifers are met without adding excess phosphorus to the environment.
Hedtcke, J.L., Posner, J.L., Coblentz, W.K., Hall, J., Walgenbach, R.P., Davidson, J. 2011. Orchardgrass ley for improved manure management in Wisconsin: II. Nutritive value and voluntary intake by dairy heifers. Agronomy Journal. 103:1106-1114.