By Zhengxia Dou, PhD 
Professor of Agricultural Systems
University of Pennsylvania

Fig. 1

Situated in the rolling hills of horse country in Chester County, Pennsylvania, New Bolton Center is the large-animal campus of the University of Pennsylvania’s School of Veterinary Medicine (Fig. 1). Established in 1952, the campus encompasses hospital facilities for the care of large animals and diagnostic laboratories serving the agriculture industry. In addition to a diverse population of horses and ponies, as well as sheep, goats, and alpacas, New Bolton Center is home to about 200 dairy cows and 250 sows and their piglets. The university’s dairy and swine herds are critical in supporting Penn Vet’s research and educational missions. 

The 700-acre campus is a collage of permanent pastures (30%), woodland (15%), farmstead and developed land (10%), and cropland (45%). Soils at New Bolton Center are deep, well-drained to somewhat poorly-drained, and formed in metamorphic bedrock. A dense soil layer called fragipan underlies about a third of our crop fields. Fragipans may lead to temporary soil water saturation in very wet seasons, but do not limit crop productivity in our case. 

The New Bolton Center property lies mostly in the Red Clay Creek Watershed with a small sliver of the cropland belonging to the White Clay Creek Watershed. Both creeks flow into the Christina River and then into Delaware Bay. South Brook, a tributary of the Red Clay Creek, flows for about 4000 feet within the land area of the Center before emptying into the creek. The Red Clay Creek is the source water for Hoopes Reservoir that serves as one of the drinking-water supplies for Wilmington, Delaware. 

Water protection and pollution prevention for sustainability at New Bolton Center rely on a complementary and synergistic array of strategies and practices. Installment and implementation of these measures have progressively advanced over the course of more than half a century, from soil and water conservation practices adopted in crop fields prior to the 1990s to a systems-based approach implemented near the turn of the century that integrates precision livestock feeding at the front end with targeted manure management at the back end, to engineered solutions installed in the last decade focusing on stormwater management of the built environment. Current research, innovation, and planning efforts aim to find new pathways forward by developing workable solutions that address sustainability challenges locally and beyond, with water security being an integral element. 

Classic soil and water conservation practices  

Fig. 2 Grassed waterways in crop fields on the east side of New Bolton campus.

Grassed waterways are broad and shallow graded channels designed to move surface water across farmland with minimal soil erosion. Left alone, runoff and snowmelt water will drain toward a field’s natural draws, but the vegetative cover in grassed waterways slows the water flow and protects the channel surface from the eroding forces of runoff water. At New Bolton Center, a system of grassed waterways, collectively over a mile long, was put in crop fields approximately four decades ago. Still in full function today, well-established grasses provide permanent and year-round ground cover, trapping soil particles, filtering, and directing water flow to South Brook (Fig. 2). 

Contour cropping across the slope of a field reduces gully erosion. Compared to up and downhill farming, contouring can reduce soil erosion by as much as 50%. At New Bolton Center, contour cropping is implemented in the large parcel of land that has moderate to steep topography (8% slope). Here, contour plowing is combined with two grassed berms separating 30 acres of contour-plowed crop area ((Fig. 3). By reducing sediment and runoff and increasing water infiltration, contouring promotes better water quality and sustains soil health in the long run.

Fig. 3

Similarly, conservation tillage (no till or reduced tillage, as in contrast to the standard moldboard plowing followed by disking and harrowing) decreases erosion of fine soil particles and improves soil carbon retention. All annual crop acres at New Bolton Center are managed with conservation tillage using a tandem chisel-disk and performed in spring after cover crop harvest and before manure application in preparation for the main annual crop planting.

Cover cropping offers numerous benefits to agroecosystem sustainability. Planted after the main crop harvest in the fall, cover crops help ‘scavenge’ residual soil nitrate left from the main crop season, provide ground cover in the winter to reduce water and wind erosion, meanwhile capturing CO2 through photosynthesis and improving soil’s physical and biological conditions. New Bolton Center practices total coverage of all annual crop acres through cover cropping, with the goal of leaving no agricultural land bare for winter. For the 2020-2021 cycle, cover crops of triticale or rye were planted in 160 acres after the annual crop harvest in September-October. Cover crops are harvested in late April-early May as supplementary forage for the dairy cattle, typically yielding 6-8 tons per acre.

Precision feeding and integrated nutrient management

Precision livestock feeding aims to match dietary nutrient supply with the nutrient requirements of animals, to achieve maximal nutrient use efficiency and minimal losses in animal excreta. Precision feeding of lactating cows with carefully balanced diets can reduce nitrogen and phosphorous intake by 10-30% and excretion by 15-40%. Of particular interest is the disproportionately greater reduction of water-soluble phosphorus in excreta from cows fed less (yet adequate) amounts of phosphorus [1], lowering phosphorus runoff losses by severalfold [2]. 

Fig. 4 Cows at Marshak Dairy are fed a diet that is balanced to meet their nutrient requirements, while excess nitrogen and phosphorus are minimized. Photo credit: Linda Baker

At New Bolton Center’s Marshak Dairy (Fig. 4), different feeding rations are formulated for dry cows, growing heifers, and groups of lactating cows based on their respective physiological cycle and production level. Rations are formulated using the UPenn Dairy Ration Analyzer; re-formulation or adjustment is made to accommodate changes in feed ingredients — for example, adding new forages such as cover crops harvested in the spring — or environmental parameters, for instance, extended hot and humid days limiting cow feed intake and milk yield. Ration formulation for precision feeding involves numerous nutritional parameters; fine-tuning rations for optimal cow productivity and minimal environmental burden is made possible due to our experienced nutritionists as well as the Dairy Ration Analyzer’s built-in optimization program.

Pigs are monogastric and feeding them is less complicated than ruminants like cows. At the Swine Center, at least five different rations are used to feed pigs at different stages of production. Precision feeding is achieved with electronic sow feeders where each sow wears a radio-frequency identification (RFID) tag that uniquely identifies them. They enter a feeding station one at a time, the computerized feeding system reads their electronic ID, and provides them with a specified ration for the day based on their age, weight, and stage of production. This precision feeding ensures maximum productivity while minimizing nutrient loss in the manure. The Swine Center also is certified organic; all rations are made from feedstuffs grown without the use of herbicides or pesticides, further reducing the environmental impact of our pigs.   

Manure nutrient management at New Bolton Center is based on matching crop nutrient uptake needs with the nutrients contained in manure produced on-site. Corn for silage producing 25 tons per acre requires around 120 lbs nitrogen, 25 lbs phosphorus and 30 lbs potassium. In a typical year, 2500 tons of dairy manure solids and horse stable manure, and 4 million gallons of liquid manure are applied to the crop fields, which provide sufficient nitrogen for the crops, but in excess of phosphorus uptake. The liquid manure is surface-applied prior to spring planting, during the growing season after forage cutting, and after corn harvest in the fall. Solids are surface-spread multiple times a year, in cultivated fields typically before annual crop planting and after harvest, as well as in grassed fields following cutting. 

Our dairy production systems at Marshak Dairy also address water conservation. An interesting but little-known fact is that increased milk yield per cow enhances water use efficiency of the whole herd. Today, the average dairy cow in the US uses roughly 1/3 as much water per pound of milk as that in 1950, i.e. water use efficiency is three-fold higher, due to vastly enhanced milk yield. 

Stormwater management in built environment

Retention basins are the most recent addition at New Bolton Center and complement the field-based and animal-centric measures by further enhancing water protection. Retention basins are artificial wetlands planted with water-tolerant vegetation. They are constructed to collect rain that falls on impervious surfaces of the built environment, and to allow this water to percolate and drain slowly, thus eliminating downstream erosion and preventing runoff water from polluting waterways. In the last decade, more than a dozen retention basins of varying size and shape were constructed on the New Bolton Center campus, mostly near the buildings and parking areas (see Fig. 1 for a retention basin clearly visible near the main parking lot). These retention basins are engineered solutions that will serve to improve our water for decades to come. 

Toward a more sustainable future

We have identified areas needing improvement for enhanced water protection. Several pasture fields have sub-optimum plant growth, due to heavy animal use and trampling of vegetation. Strategic animal stocking combined with rotation will allow pasture to recover, increasing plant production and ground coverage while limiting soil erosion and overland water flow. Further, management attention is needed to monitor soil phosphorus to prevent its buildup and reaching levels that may lead to accelerated phosphorus loss. Active stream-bank management of South Brook promises to enhance ecosystem services. Interests in this area are growing through innovative collaborations with key entities in the area such as the Stroud Water Center, William Penn Foundation, and the Water Center at Penn.

Water is literally a matter close to home, as our management decisions and actions directly or indirectly impact water quality or quantity in the immediate watershed. Concerns about water have no borders, as all foods embody water and numerous varieties of foods in our supermarkets come from abroad while Pennsylvania dairy and pork products are sold overseas. Regrettably, the modern food system is inefficient in terms of food use – roughly 1/3 of food produced for human consumption is never eaten but wasted [3]. Additionally, very large amounts of plant residual biomass are routinely generated in the food-drink-fuel processing industries, for example, oilseed cakes, wheat middlings, citrus pulp, and brewers’ grains. Ongoing research at New Bolton Center is dedicated to developing and assessing ways for re-use and upcycling food waste discards and plant biomass as safe and nutritious feedstuffs for livestock [4,5]. Leveraging livestock to promote a circular food system serves multiple sustainability objectives, including water conservation. 

Water, food, soil health, biodiversity, ecosystem services, food system resilience amid climate change are some of the essential elements in the sustainability equation. In the Farm of the Future Symposium [6], a recent multi-week online event jointly organized by the School of Veterinary Medicine and the Weitzman School of Design at Penn, a diverse group of thinkers and doers gathered to work together on opportunities for advancing sustainable agriculture for economically and environmentally viable and humane food systems. A range of exemplary projects, waste strategies, regenerative practices, and design of leading teaching farms and campuses for agricultural and veterinary colleges were explored. The interdisciplinary conversation continues, centering on The Farm of the Future in the United States for sustainability, and ways New Bolton Center can catalyze that future in Pennsylvania and beyond. 


Drs. Linda Baker, Dave Galligan, Corinne Sweeney, Tom Parsons, and Mr. John Toth helped with data gathering and confirmation as well as editing.


Dr. Zhengxia Dou is a professor of agricultural systems at the University of Pennsylvania School of Veterinary Medicine. She has worked on agricultural nutrients and sustainable food security issues. Her current research focuses on crop-livestock integration in the context of the food system. Specific areas of interest include livestock as natural bio-processors for upcycling food waste and plant biomass and systems-based analysis of food waste management technologies to mitigate unintended consequences. Her core interest is in leveraging livestock to promote a circular food system, which in turn can aid the transition toward a resource- and climate-smart society. 


References and links

1. Dou, Z., K.F. Knowlton, R.A. Kohn, L.D. Satter, Z. Wu, G. Zhang, J.D. Toth, and J.D. Ferguson. Phosphorus characteristics in dairy feces affected by diets. J. Environ. Qual. 2002.

2. Ebeling, A.M., L.G. Bundy, J.M. Powell, T.W. Andraski. Dairy diet phosphorus effects on phosphorus losses in runoff from land‐applied manure. Soil Sci. Soc. Am. J. 2002.

3. Food loss and food waste,

4. Dou, Z. Leveraging livestock to promote a circular food system. Front. Agr. Sci. Eng., 2021.

5. Dou, Z., D. Galligan, G. Shurson. “Food waste as untapped resources for climate mitigation.” In: The Role of Agricultural Science and Technology in Climate 21 Project Implementation. Council for Agricultural Science and Technology. Ames, Iowa. 2021. (in press)