Final Report for GW11-001
Integrating pastured poultry with crop production is on the rise in California due to high demand for pastured products and a desire by farmers to close on-farm fertility cycles. This project examined pastured poultry/crop systems using grower surveys, soil quality and crop growth investigation, and soil pathogen research. In summary, this research finds that pastured poultry/crop systems can be profitable to farmers and that certain crops can be grown in these agroecosystems without the addition of supplemental fertilizers. However, further attention to soil P management is critical, and integrated systems should be managed carefully to avoid cross-contamination of crops by pathogens.
In the last 15 years, a number of factors have converged to make pasture-raising poultry and integrated poultry/crop agriculture practices of interest to farmers, scientists and the public. These have been: 1) a rise in fertilizer prices and a desire by farmers to cycle nutrients on-farm, 2) research by nutrition scientists demonstrating the health benefits of pasture-raised livestock, and 3) public concern for the animal welfare of birds raised in indoor systems.
As the cost of fossil fuel-based fertilizers rises, interest in using animal manure as a fertilizer has grown (1). Integrated agroecosystems represent an innovative way of affording a fertilizer, as the sale of animal products can partially or entirely cover the cost of animal and manure production. Pasture-based systems represent a further innovation, as pasture is tilled less frequently than crop fields, leading to decreased erosion and higher carbon storage (2,3). With animals on pasture producing marketable products, pastured poultry/crop systems can become an economically viable way to apply manure and maintain a multi-year low-till “cover crop.”
Recent research by nutrition scientists has demonstrated increased human health benefits from consuming pasture-raised animal products as compared to conventionally produced animal products. Pasture naturally contains higher levels of fatty acids than grain-based feed (4). In poultry, desirable fatty acids are directly absorbed from the intestine into tissue (5). As such, pasturing poultry significantly increases the n-3 (omega-3) fatty acid content of meat and the vitamin A, vitamin E and n-3 fatty acid content of eggs in comparison to caged birds with no access to pasture (6).
Finally, public concern for the animal welfare of birds raised in indoor systems continues to rise, and popular publications highlighting pastured poultry (7,8) have contributed to the perception that humane alternatives exist.
- Interview growers and specialists with management and budget questions based on points identified as critical by farmer collaborators.
Analyze benefits and challenges of raising pastured poultry.
Determine whether fields that have been planted with pasture and grazed with poultry are suitable for crop cultivation with minimal addition of fertilizers, composts or cover crops.
Quantify crop growth via greenhouse experiments from poultry pasture and control fields.
Determine whether foodborne pathogens pose a problem for crops grown under pastured poultry/crop systems via literature review.
Analyze treatment and control soils for E. coli O157:H7, Campylobacter and Salmonella.
Share results and support informed producer adoption via publications, workshops and presentations.
This project utilized interdisciplinary research methods to complete three major studies: (1) farmer survey, (2) soil and crop growth study and (3) pathogen investigation.
METHODS FOR FARMER SURVEY
Survey administration occurred between April and August 2010. Requests for participation were sent out to all poultry farmers in the California Eat Wild network (www.eatwild.com), California Certified Organic Farmers (CCOF) database and by word of mouth. The response rate for the survey was 62% of 29 requests for participation. The survey instrument addressed background information regarding location of farm, organic certification, quantity of farm animals and acreage of crops. Producers were asked to comment on the benefits and challenges of raising poultry, as well as on specific management practices (e.g., managing predators, maintaining pasture). Farmers were then asked to comment on the profitability of pastured poultry and what stimulated them to raise pastured poultry. All questions were open-ended, allowing farmers to provide as much information as they preferred. Survey responses were coded by topic (9). For example, responses to the question on what inspired farmers to work with poultry were coded as “exposure to Joel Salatin,” “profitability” and “pest control.” Themes and relationships between coded variables were assessed quantitatively. For example, profitability was analyzed for a relationship to farm product (e.g., meat vs. eggs).
METHODS FOR SOIL AND CROP GROWTH STUDY
Research for this segment was conducted on two working farms and via a series of greenhouse trials. Three experiments were conducted: (1) crop plants were grown in a replicated greenhouse experiment using soils from plots with a recent history of pastured poultry and soils from adjacent cropped areas; (2) chemical and biological parameters of soil quality were compared from the same plots on two farms; (3) spatial variation in soil quality was assessed relative to location of poultry coops.
Study sites: Farm A was used as an exemplar of PPAS in a mixed annual/berry agroecosystem. Soil was from the Lockwood series with a clay texture. At this site, hens were the integrated animals, and plots were alternately dedicated to crop and pasture production. Pasture fields were seeded with fescue (Festuca arundinacea), orchardgrass (Dactylis glomerata), ryegrass (Lolium spp.), clover (Trifolium spp.) and trefoil (Lotus corniculatus) and intermittently ranged by hens for two years before being converted back to crop production. At this site, the pasture plot had a two-year history of poultry grazing, and the control field had a two-year history of wheat (Triticum sp.) and popcorn (Zea mays averta). Compost and lime were added to the control field biennially, both at a rate of 2.4 Mg ha-1. Both fields were converted to strawberry (Fragaria sp.) production subsequent to the first day of data collection.
Farm B was used as an exemplar of PPAS in an orchard system. Soil was from the Sorrento series with a sandy clay loam texture. At this site, meat chickens were integrated into a portion of walnut (Juglans regia) orchard on pasture seeded as above. An equivalently sized section of the orchard with no prior history of poultry was used as the control, and both plots had equivalent walnut tree density (100 trees/ha). Chickens had intermittently grazed the PPAS orchard for seven years, while the control orchard had no history of poultry.
Greenhouse trial: To address the question of crop growth response to PPAS independent of farmer management, a series of greenhouse experiments were conducted using soil from PPAS and control plots. From each plot, five gallons of topsoil (0-15 cm depth) were collected from 20 random sub-samples. Soil was then air-dried, mixed well and crushed to approximately 2 mm diameter aggregates. Two bean seeds (Phaseolus vulgaris L. var. Hystyle) were planted on 11/05/09 with Farm A soil and thinned to one shoot on 11/11/09 (n=33). In the same manner, sunflowers (Helianthus annuus L.) were planted on 04/23/10 with soil from Farms A and B and thinned on 04/29/10 (n=174). Containers were arranged in a random formation, misted daily and grown at daytime temperatures of 22.8 to 23.9C for 30 days in the UCSC greenhouse. At 30 days from seeding, plants were clipped at the soil level and measured for height. Plants were then oven-dried at 60C for 36 hours and biomass weighed.
Data collection for soil quality: This study was conducted from 2009 to 2011. Using a stratified composite sampling design (10), 16 composite samples per site were gathered at two depths (0-15 and 15-30 cm). Samples were composited from 15 sample points along eight permanent transects per site in two plots, and sub-samples of each well-mixed composite sample were used for analysis. Inorganic N (11) was measured four times per year (n=256) and analyzed for ammonium-nitrogen (NH4+-N) and nitrate-nitrogen (NO3–N) on a flow injection analyzer (Lachat QuikChem 8000, Milwaukee, WI)(12) at the University of California, Santa Cruz (UCSC). Total C and total N29 were measured twice yearly (n=64), assessed on the VarioMAX CNS analyzer (Elementar, Mt. Laurel, NJ)(13) at UCSC. Soil electrical conductivity (14) was determined twice yearly (n=31, topsoil only) using a conductivity meter (Denver Instrument, Model 250). Extractable sodium bicarbonate P (Olsen P), exchangeable K (ex. K), pH, cation exchange capacity and soil organic matter as determined by weight loss-on-ignition were assessed four times/year (n=128). Air-dried samples were sent to A&L Laboratories (Modesto, CA) for analysis.
In a sub-study conducted in February 2010, spatial variation in soil quality was assessed for the coop-based system at Farm A. Hens, unlike the meat chickens at Farm B, ranged within their fields during the day, frequently seeking shelter under the coop. This study was conducted to determine whether soil quality values changed with distance from the coop. Samples were taken every 4 m on four 16-m transects at two coops (n=20). Soil samples were collected from a depth of 0-15 cm and analyzed for inorganic N, Olsen P, ex. K, pH, cation exchange capacity and organic matter, using the methods described above.
METHODS FOR PATHOGEN RESEARCH
Soil samples for analysis of Campylobacter spp., Salmonella spp. and E. coli O157:H7 were gathered from two farms in the Central Coast region of California in July 2010. Samples (n=16) were gathered from 3 x 3 m plots at the following locations: beneath a portable coop system (PCS); beneath a meat chicken tractor (MCT); from former poultry pasture where poultry had been excluded from the field for 20 days (20D); and from former poultry pasture where poultry had been excluded for 365 days (365D). Individual samples for analysis were taken from composite samples of 20 locations per plot. Samples were transported on ice and processed upon arrival in the Atwill Laboratory at University of California, Davis.
RESULTS OF FARMER SURVEY
Benefits: Farmers reported the primary benefit of pastured poultry was soil fertility, followed by marketing appeal (Table 1). Approximately one-third of respondents went on to say that enhanced soil fertility contributed to better crop and/or pasture growth. Other common responses were in regards to marketing benefits and the production of quality food as a benefit.
Challenges: The top challenge for pastured poultry growers was predation of birds (Table 2). To deal with predators, 61% of farmers used livestock guardian dogs. Fifty-six percent of farmers used a fence, with 33% of farmers specifying that they used electric fencing. Seventeen percent of farmers protected the birds in a coop or house at night. Overall, the common refrain for dealing with predators was “electric fencing and livestock guardian dogs.” Besides predators, pastured poultry growers were challenged by costs and labor, food safety concerns, the ability to handle large quantities of feed, regulations, pasture growth, a lack of background and constructing appropriate infrastructure.
Profitability: Growers responded at length to the question, “Has raising poultry been a profitable endeavor for you? Why or why not?” Fifty percent of farmers reported direct profitability from pastured poultry. This response was not correlated to whether a farmer had meat chickens versus layers or whether a farm was certified organic. In response to the same question, 78% of growers reported that pastured poultry were indirectly profitable because they attracted new customers to the farm, enhanced customer loyalty, and contributed to savings on fertilizer, fuel and pest control. Specifically, 44% of respondents reported marketing advantages in response to this question.
Breed diversity: Breed diversity was higher for hens than for meat chickens. Among all farms, 21 breeds of layers were represented (Fig.1). Far fewer breeds made up the diversity of meat chickens; six breeds were represented across all 12 farms surveyed with meat chickens. Of these, the industrial Cornish Cross was reared on 58% of the farms. Freedom Rangers (a.k.a. Colored Rangers or Poulet Rouge), a bird known for its livability on pasture, represented 27% of breed richness.
RESULTS OF SOIL AND CROP GROWTH STUDY
Poultry manure as a crop fertilizer: Poultry manure is a known effective plant fertilizer. However, in the initial interviews for this research, many farmers expressed concern that they did not know whether manure deposited in pasture-based agroecosystems was equivalent to a traditional manure application because the lack of mechanical incorporation post-application may have been causing nutrient loss. This was the main driver for this portion of the research.
At the study sites, chickens were determined to deposit manure at a rate of 8.4 to 10.9 Mg ha-1 y-1, sufficient to elevate soil quality parameters, total C, total N, NH4+-N, NO3–N, ex. K, organic matter, cation exchange capacity, electrical conductivity and Olsen P, relative to the control (Table 3).
Soil pH was raised relative to the control at Farm A and reduced at Farm B (Tables 4,5). These results are attributed to the liming effect of the calcium carbonate (CaCO3) in the hen feed at Farm A. PPAS raised soil total C relative to the control at Farm B (Table 5), the site with a seven-year history of PPAS. Soil total N was also increased by PPAS at both sites (Tables 4,5). NH4+-N and NO3–N were increased by PPAS at both sites (Tables 4,5). Soil ex. K was also enhanced by PPAS at Farm B (Tables 4,5). The relevancy of these values to plant growth and yield depends on the type of crop grown with or subsequent to PPAS. In the case of this study, PPAS levels were at least as effective as the input methods growers were using for control soil preparation, as shown by crop growth results in the greenhouse trial (below).
In addition to these chemical changes, soil organic matter was raised relative to the control by PPAS at the 0-15 cm depth for both sites (Tables 4,5). Soil cation exchange capacity was also raised by PPAS relative to the control at Farm B but not Farm A (Tables 4,5), which is explained by the soil type of each site. Farm B had a sandy clay loam with 22% clay content, while Farm A had a clay soil with a 43% clay soil. At Farm A, the control soil had a substantially higher cation exchange capacity than the control Farm B, which is consistent with cation exchange properties of clay. At Farm B, PPAS significantly increased organic matter, which would lead to an increase in measureable cation exchange capacity for a soil not dominated by clay.
Soil P levels were highly increased by PPAS relative to the control at Farm B (Tables 4,5). Loss of P to adjacent waterways can lead to eutrophication (16). Whether soil P levels associated with pastured poultry pose an environmental risk is unique to each farm, as chemical and hydrological factors determine P retention and movement (17). However, suggested threshold values of soil Olsen P for environmental quality are approximately 30-40 mg kg-1 (18, 19). Farm B levels exceeded this threshold for the PPAS treatment, and Farm A levels were close to the lower bound of this threshold in the PPAS treatment. Growers should be aware of this issue and conduct regular soil tests. When soil P reaches unacceptable levels for local conditions, birds should be relocated.
Patchy soil quality: Certain soil quality parameters were patchy within poultry pasture fields where free-ranging hens lived; NH4+, NO3-, Olsen P, and K all significantly decreased with distance from coop (Fig.2). Growers should move coops regularly (2 weeks) to prevent build-up.
Crop growth: These soil quality changes resulted in heavier and taller sunflowers and beans grown in these soils. PPAS soil improved crop growth relative to the control for nearly all parameters, showing a neutral effect only for sunflower biomass at one site. PPAS soil enhanced average bean biomass by a factor of 1.48 (Fig.3, t(30.48)=3.31, p=0.0024). Biomass results for sunflowers, on the other hand, varied by farm. At Farm A, PPAS soil enhanced average sunflower biomass by a factor of 1.08 (Fig.4, t(54.94)=3.56, p=0.0008). At Farm B, there was no significant difference in average biomass between plants grown in PPAS and control soils (Fig.4, t(49.28)=1.51, p=0.1373). PPAS soil enhanced sunflower height relative to the control group by a factor of 1.11 at Farm A (Fig.5, t(57.92)=2.09, p=0.041) and by a factor of 1.06 at Farm B (Fig.5, t(108.17)= 2.30, p=0.023).
RESULTS OF PATHOGEN RESEARCH
Pathogen sampling results found no isolates of E. coli O157:H7 or Campylobacter spp. in any of the samples (Table 6). Salmonella spp. results were unexpected. Two of the samples from actively grazed pasture tested positive; two of the samples from pasture that had been grazed within 20 days tested positive; and two of the samples from the control tested positive. In this case, the control had not been grazed by any domestic animals for 365 days.
Very little research has been conducted on pasture-raised poultry, particularly in regards to pathogens. Crop growers with pasture-raised poultry may want to voluntarily abide by manure application guidelines. One guideline that growers can utilize is the National Organic Program (NOP) policy popularly known at the “90-day rule” and officially known as USDA NOP 7CFR 205.203(c)(1). Specifically, the NOP regulation states that raw manure must be incorporated 90 to 120 days before the harvest of crops grown for human consumption, where 120 days is the minimum for crops that touch the soil, such as lettuce.
More stringent guidelines for leafy greens have been set by the Leafy Greens Marketing Agreement (LGMA) and suggest a wait time of 365 days between manure application and harvest of leafy greens (20). Studies have shown varying lengths of time for pathogen survival in soil and on crops. Nicholson et al. (21) found that E. coli O157, Salmonella spp. and Campylobacter spp. did not survive more than 30 days after land application to sandy arable and clay loam soils. In contrast, Islam et al. (22) found that E. coli O157:H7 survived for 154-196 days in soil fertilized with contaminated poultry manure compost. In the same study, E. coli O157:H7 survived for 74-168 days on carrots and onions and 210 days on leafy greens and root crops. Another study found that Salmonella enterica survived for 231 days in poultry manure compost (23). These results suggest that growers may want to test for pathogens in soil, crop and/or animals. Alternatively, growers may want to adhere to organic regulations or LGMA guidelines.
1 Adeli, A., Tewolde, H., Sistani, K., and Rowe, D. 2010. Comparison of Broiler Litter and Commercial Fertilizer at Equivalent N Rates on Soil Properties. Communications in Soil Science and Plant Analysis 41(20):2432-2447.
2 Cannell, R.Q., and Hawes, J.D. 1994. Trends in Tillage Practices in Relation to Sustainable Crop Production with Special Reference to Temperate Climates. Soil & Tillage Research 30(2-4):245-282.
3 Fornara, D.A., and Tilman, D. 2008. Plant functional composition influences rates of soil carbon and nitrogen accumulation. Journal of Ecology 96(2):314-322.
4 Ponte, P.I.P., Prates, J.A.M., Crespo, J.P., Crespo, D.G., Mourao, J.L., Alves, S.P., Bessa, R.J.B., Chaveiro-Soares, M.A., Gama, L.T., Ferreira, L.M.A., and Fontes, C. 2008. Restricting the intake of a cereal-based feed in free-range-pastured poultry: Effects on performance and meat quality. Poultry Science 87(10):2032-2042.
5 Wood, J.D., and Enser, M. 1997. Factors influencing fatty acids in meat and the role of antioxidants in improving meat quality. British Journal of Nutrition 78(1):S49-S60.
6 Karsten, H.D., Patterson, P.H., Stout, R., and Crews, G. 2010. Vitamins A, E and fatty acid composition of the eggs of caged hens and pastured hens. Renewable Agriculture and Food Systems 25(1):45-54.
7 Salatin, J. 1996. Pastured Poultry Profits. Swope, VA: Polyface.
8 Pollan, M. 2006. The Omnivore’s Dilemma. New York, NY: Penguin Press.
9 Bernard, R.B. 2006. Research Methods in Anthropology: Qualitative and Quantitative Approaches. 4th ed. New York: Altamira Press.
10 Quinn, G.P., and Keough, M.J. 2007. Experimental Design and Data Analysis for Biologists. NY, NY: Cambridge University Press.
11 Allan, D.L., and Killorn, R. 1996. Assessing Soil Nitrogen, Phosphorus, and Potassium for Crop Nutrition and Environmental Risk. In: Doran, J.W., and Jones, A., editors. Methods for Assessing Soil Quality. Madison, WI: Soil Science Society of America.
12 Lachat Instruments (1993). Ammonia (Salicylate) in 2M KCl Soil Extracts, QuikChem Method 12-107-06-2-A. Milwaukee, WI. Lachat Instruments (1993). Nitrate in 2M KCl Soil Extracts, QuikChem Method 12-107-04-1-B. Milwaukee, WI.
13 ISO (the International Organization for Standardization) (1998). Soil quality — Determination of total nitrogen content by dry combustion (“elemental analysis”). ISO 13878:1998(E). Genève, Switzerland, the International Organization for Standardization: 1-5.
14 Smith, J.L., and Doran, J.W. 1996. Measurement and Use of pH and Electrical Conductivity. In: Doran, J.W., and Jones, A.J., editors. Methods for Assessing Soil Quality. Madison, WI: Soil Science Society of America.
15 Hilimire, K. 2011. The grass is greener: Farmers’ experiences with pastured poultry. Renewable Agriculture and Food Systems (available on CJO 2011).
16 Sharpley, A.N., Chapra, S.C., Wedepohl, R., Sims, J.T., Daniel, T.C., and Reddy, K.R. 1994. Managing Agricultural Phosphorus for Protection of Surface Waters- Issues and Options. Journal of Environmental Quality 23(3):437-451.
17 Maguire, R.O., and Sims, J.T. 2002. Soil testing to predict phosphorus leaching. Journal of Environmental Quality 31(5):1601-1609.
18 Sheffield, R., Brown, B., Chahine, M., de Haro Marti, M., and Falen, C. 2008. Mitigating High-Phosphorus Soils. University of Idaho Extension [serial on the Internet].
19 do Carmo Horta, M. 2007. The Olsen P method as an agronomic and environmental test for predicting phosphate release from acid soils. Nutrient Cycling in Agroecosystems 77:283-292.
20 LGMA. Commodity Specific Food Safety Guidelines for the Production and Harvest of Lettuce and Leafy Greens 2010 [cited 2010 January 18]; Available from: http://www.caleafygreens.ca.gov/food-safety-practices/downloads?phpMyAdmin=486c4cbf331et607af114.
21 Nicholson, F.A., Groves, S.J., and Chambers, B.J. 2005. Pathogen survival during livestock manure storage and following land application. Bioresource Technology 96(2):135-143.
22 Islam, M., Doyle, M.P., Phatak, S.C., Millner, P., and Jiang, X.P. 2005. Survival of Escherichia coli O157 : H7 in soil and on carrots and onions grown in fields treated with contaminated manure composts or irrigation water. Food Microbiology 22(1):63-70.
23 Islam, M., Morgan, J., Doyle, M.P., Phatak, S.C., Millner, P., and Jiang, X. 2004. Fate of Salmonella enterica Serovar Typhimurium on Carrots and Radishes Grown in Fields Treated with Contaminated Manure Composts or Irrigation Water. Applied and Environmental Microbiology 70(4):2497-2502.
24 Jackson, L.E., Wyland, L.J., and Stivers, L.J. 1993. Winter cover crops to minimize nitrate losses in intensive lettuce production. Journal of Agricultural Science 121:55-62.
25 Wyland, L.J., Jackson, L.E., Chaney, W.E., Klonsky, K., Koike, S.T., and Kimple, B. 1996. Winter cover crops in a vegetable cropping system: Impacts on nitrate leaching, soil water, crop yield, pests and management costs. Agriculture Ecosystems & Environment 59(1-2):1-17.
26 Vadas, P.A., Meisinger, J.J., Sikora, L.J., McMurtry, J.P., and Sefton, A.E. 2004. Effect of poultry diet on phosphorus in runoff from soils amended with poultry manure and compost. Journal of Environmental Quality 33(5):1845-1854.
Educational & Outreach Activities
PUBLICATIONS IN PROGRESS
Hilimire, K., Gliessman, S.R., and Muramoto, J. Soil quality and crop growth under poultry/crop integration.
Hilimire, K. 2011. Pastured Poultry/Crop Systems and Their Effect on Soil Quality, Crop Growth, Food Safety, and Farmer Experience. Doctoral dissertation: University of California, Santa Cruz.
Hilimire, K. 2011. The grass is greener: Farmers’ experiences with pastured poultry. Renewable Agriculture and Food Systems (available on CJO 2011).
Hilimire, K. 2011. Integrated crop/livestock agriculture in the United States: a review. The Journal of Sustainable Agriculture 35(4):376-393.
Hilimire, K. Pastured Poultry in Crop Systems. EcoFarm Conference presentation, Monterey, CA. February 2012.
Hilimire, K. Pastured Poultry/Crop Systems and Their Effect on Soil and Plant Quality, Food Safety, and Farmer Experience. International Agroecology Short Course, Santa Cruz, CA. July 2011.
Hilimire, K. Where the Grass is Greener: Pastured Poultry/Crop Systems and Their Effect on Soil Quality, Crop Growth, Food Safety, Farmer Experience, and Sustainability. Guest Lecture for UCSC Agroecology Undergraduate Course, Santa Cruz, CA. November 2010.
FIELD DAYS AND OUTREACH
Hilimire, K. Pastured Poultry/Crop Systems and Their Effect on Soil and Plant Quality, Food Safety, and Farmer Experience. Farmer Workshop at Pie Ranch, Pescadero, CA. July 2011.
California Pastured Poultry/Crop Systems. Grower Newsletter. August 2011. Distributed to 75 growers.
Taken together, these findings suggest that integration of pastured poultry and crop production is a promising alternative agricultural practice. In particular, the combination of enterprises, crops and animals is likely to produce more profit than pastured poultry alone, based on the indirect profits of customer loyalty, marketing, soil quality and pest management reported by growers.
Growers responded at length to the question, “Has raising poultry been a profitable endeavor for you? Why or why not?” Fifty percent of farmers reported direct profitability from pastured poultry. This response was not connected to whether a farmer had meat chickens versus layers or whether a farm was certified organic. In response to the same question, 78% of growers reported that pastured poultry were indirectly profitable because they attracted new customers to the farm, enhanced customer loyalty and contributed to savings on fertilizer, fuel and pest control. Specifically, 44% of respondents reported marketing advantages in response to this question.
This research is of use to farmers seeking to maximize profitability from integrated pastured poultry/crop agriculture and aiming to utilize live poultry as a source of fertilizer.
This research suggests that poultry may combine well with certain crops and not with others. Specifically, poultry may not combine well with leafy greens or other fast-growing plants known to be easily contaminated by manure. Orchard trees may be a suitable alternative. Crops with high P requirements should also be considered because they utilize high soil P concentrations.
This study suggests that seven years of consistent animal activity leads to excessively high Olsen P levels (Farm B). Research should be directed at 1) determining the amount of time birds should be withheld from a field before reintroducing a pasture rotation and/or 2) a stocking density that optimizes soil P levels. At optimal P levels, N levels will likely be inadequate. To add more N, leguminous winter cover crops could be used. N-scavenging cover crops could also be used to minimize N loss and to recycle inorganic N. Radish (Raphanus sativus), mustard (Brassica hirta and Brassica alba), phacelia (Phacelia tanacetifolia), rye (Secale cereale) and annual ryegrass (Lolium multiflorum) are all known nitrogen scavengers (24,25) that could function to recycle nitrogen from poultry manure. Finally, altering supplements added to poultry feed may impact water-soluble soil P levels and is an area of ongoing research (26). Movement of birds within a field needs also to be researched in order to optimize nutrient management. Hot spots can be addressed by determining how long a coop can remain in one location before leading to excessive nutrient accumulations.
Areas needing additional study
Future research needs were identified by this study in regards to chicken breeds and feed. The identification and breeding of locally adapted pasture-hardy breeds of chickens, particularly meat chickens, are important areas of research that could improve these pasture-based agroecosystems. Secondly, research is needed in determining sources of affordable energy-rich feed for birds, especially organically certified ones. Connecting these feed sources to the farm-scale or the local agricultural landscape may also aid farmers in reducing costs and/or improving their ability to cycle nutrients on-farm.
In terms of soil research, areas of concern have been identified that will allow growers to refine the N and P dynamics of these systems in order to maximize soil quality and environmental concern. Future research should be directed at determining the amount of time birds should be withheld from a field before reintroducing a pasture rotation, at stocking densities that optimize soil P levels, at crop and cover crop rotations that optimally follow poultry pasture, and at movement of birds within fields to mitigate nutrient hot spots.
Finally, there is a need for replication of the pathogen study on many farms. Currently, most pathogen research related to alternative agricultural systems has focused on organic poultry. There is a need for more studies that focus specifically on pastured poultry.