Final report for GNC17-236
Integrated systems have the potential to provide an array of benefits to producers, the land they manage, and the environment. Through the proposed project titled “Integrating Poultry and Cover Crops into Vegetable Production for Soil Health”, we will investigate changes in soil properties, crop performance, poultry health, and farm profitability over three growing seasons. Treatments will compare two vegetable-poultry-cover crop rotations with a typical vegetable-cover crop rotation system and determine its effects on soil health, poultry health, vegetable crop performance, and economic feasibility, and prevalence of food-borne pathogens in soil, especially following pasture-raised poultry. The hypothesis is that the implementation of integrated systems will increase soil health while also increasing farm profitability and resiliency. Producers will receive access to the results via field days at the research station, poster presentations at annual growers' conferences, written extension bulletins, and a peer-reviewed journal publication.
Organic producers are constantly looking for new methods to improve soil health while also improving farm profitability. Changing from specialized to integrated systems has the potential to achieve that goal. A production system focusing solely on crops has led to a loss of knowledge especially in the areas of effectively integrating crops and livestock to benefit the entire production system including the soil. For these reasons, this project aims to increase knowledge of integrating poultry into a vegetable and forage based system, the use of slower growing breeds of poultry, and reduction of off farm inputs from the use of live animals in a rotation. This study will outline specific infrastructure requirements necessary to raising poultry outdoors and address the day-to-day knowledge necessary for producing these birds for profit. We will identify cover crops that work well in an integrated system doubling as soil health builders and poultry forage, and evaluate the economic feasibility of integrating poultry.
This project hopes to increase grower adoption of integrated systems among vegetable producers in the NCR-SARE region.
In the effort to determine the effects of an integrated cropping system suitable for vegetable growers this project is investigated changes soil properties and poultry health over three growing seasons in a vegetable-chicken-cover crop integrated system. A total of three treatments were designed (Fig. 1) to compare two vegetable-poultry-cover crop rotations with a typical organic vegetable-cover crop rotation system. The hypothesis is that the implementation of integrated systems will increase soil health while also increasing farm profitability and resiliency.
The study was carried out at the Iowa State University Horticulture Research Station in Ames, Iowa (lat. 42°06'24.4"N long. 93°35'22.5"W) on certified organic land and conducted during 2017, 2018, and 2019. The soil type is classified primarily as a clarion loam. Precipitation and temperature for all years are presented in (Table 1). On 3 March 2017 before the start of the study, baseline soil samples were collected (Table 2).
Treatment rotations included three distinct crop rotations and each experimental plot was 4.5m x 7.5m. Rotations included vegetables, cover crops and chickens rotated within a single season on the same plot each year. Each rotation was replicated four times using a randomized complete block design. Vegetable crops used were different each year to demonstrate a typical organic vegetable enterprise where crops of the same families are not planted year after year. The rotations/treatments were vegetable-chicken-cover crop (V-P-CC), vegetable-cover crop-chicken (V-CC-P), and vegetable-cover (V-CC). In 2017, V-P-CC was Broccoli (Brassica oleraceae var. Italica cv. ‘Belstar’, Seedway Hall, NY), red ranger chicken (Welp Hatchery, Bancroft IA), and cereal rye (Secale cereal VNS) (Albert Lea Seeds, Albert Lea, MN). V-CC-P was broccoli, a cover crop mixture of crimson clover (Trifolium incanatum) (Green Cover Seed, Bladen, NE) and oats (Avena sativa, Albert Lea Seeds, Albert Lea, MN), and red ranger chicken. V-CC followed the same pattern as V-CC-P but instead of Red Ranger as a third component romaine lettuce (Lactuca sativa cv. ‘Holon’) (Johnny’s Seeds, Winslow, ME) was planted. In 2018 and 2019, rotations followed the same sequence except for changes in the vegetable crop grown. A timeline for each field activity for each rotation is presented in (Table 3). Details of each rotation year are described in Appendix I.
Vegetable crop production
Vegetable crops used were Broccoli (Brassica oleraceae var. Italica cv. Belstar, Seedway Hall, NY) transplanted in all treatment plots on 17 April 2017, lettuce (Lactuca sativa cv. ‘Holon’) (Johnny’s Seeds, Winslow, ME) transplanted in V-CC plots on 13 September 2017. In 2018, five romaine lettuce (Lactuca sativa cv Coastal star, Paris Island, Greene towers, Jericho, Freckles) cultivars were transplanted on 24 April 2018 to V-P-CC and V-CC-P treatments. Five pepper (Capsicum annum cv. Milena, King of the north, Golden California wonder, California wonder, Sweet chocolate) cultivars were transplanted to V-CC on 16 May 2018. Spinach (Spinacia oleracea cv. Corvair, Acadia, Regiment, Butterflay, Renegade ) was direct seeded to all plots on 16 April 2019. Five carrot (Daucus carota cv. Miami, Nantes fancy, Napoli, Negovia, Yaya) cultivars were direct seeded to V-CC on 7 August 2019. Lettuce and pepper in 2018 and spinach and carrot in 2019 were part of an organic cultivar trial (data not presented here).
Broccoli, lettuce, and pepper transplant production was carried out in the Department of Horticulture greenhouses, Iowa State University, Ames, IA, and sown into 72 cell trays using organic potting mix (Beautiful Land Products, West Branch, IA). Transplants were fertilized as needed using an organic 2-4-1 liquid fertilizer derived from hydrolyzed fish (Neptune’s Harvest organic fertilizer, Gloucester, MA). Field plots were fertilized with granular 4-6-4 (Sustane Natural Fertilizer Inc. Cannon Falls, MN) before planting. Plants were hand planted at the Horticulture Research Station into 4.5 x 7.5m plots. Each experimental plot consisted of five beds. Beds were 7.5m long and were spaced 1 m apart. In-row spacing between plants within the bed was 30 cm. Broccoli and lettuce transplants were planted in double rows per bed with 30cm between rows and plants. Pepper plants were transplanted in single rows in each bed with 46cm between plants. Crops were irrigated using drip irrigation and hand weeded as needed throughout the growing season. During the growing season crops were fertilized with organic 2-4-1 liquid fertilizer using an injector (Dosatron, Clearwater, Florida). Plants were monitored and sprayed as needed with DiPel Pro (Valent BioSciences Corp., Osage, IA) (Bacillus thuringiensis v kurstaki) to manage lepidopteran insects pests. Spinach and carrots were direct seeded (four rows per bed with 15 cm between rows) using a Jang seeder (Jang Automation Co., Ltd. Beobwon-ro, Songpa-gu, Seoul, Korea).
Cover crop biomass and C:N Ratio
Each year V-CC-P and V-CC rotations were seeded to oats and crimson clover, using a seeding rate of 112 and 33.5 kg ha-1 , respectively. Seeds were broadcasted by hand and raked into the soil. Overhead irrigation was used to ensure proper germination and establishment of cover crops. In 2018 when peppers were grown in the V-CC rotation, crimson clover was interseeded between the rows at 134 kg ha-1. In 2019, Oats and crimson clover did not establish well and V-CC-P rotations were reseeded with buckwheat on 6 August 2019. In all years, cereal rye was hand broadcasted and incorporated at 112 kg ha-1 in V-P-CC rotation.
Aboveground cover crop biomass for oats and crimson clover was collected from V-CC plots in 2017, V-CC-P in 2018, and from both V-CC-P and V-CC in 2019 by placing a four 25 x 25 cm quadrats randomly throughout the plot and cutting all above-ground growth within the quadrat. Cereal rye biomass was collected at the start of each season in 2018 and 2019 using the methods previously mentioned. Cover crops were dried down to a constant weight at 67 ºC and weighed to determine dry weight. Dried cover crops from 2019 sampling dates were ground to 1mm using a Thomas Wiley Laboratory Mill (Thomas Scientific, Philadelphia PA) and analyzed for total C and N (Ward Laboratories Kearney, NE) (Table 4).
Soil samples were collected four times throughout the season (at planting, after harvest, mid-summer, and end of the season) and analyzed for chemical and physical properties. Mid-summer sampling coincided with the removal of chickens from V-P-CC rotation and the establishment of summer cover crops in V-CC-P and V-CC rotations. At each sampling five, 15 cm cores were collected to create one composite sample. When soil sampling occurred during crop growth five cores were taken between and within a row for a total of two composite samples. All soil samples were analyzed for NO3-N, NH4-N, P, K, Ca, Na, Zn, S, Mg, pH, OM, and CEC (Solum Laboratories, Ames, IA) except in 2017 where the beginning of the season and after harvest samples were not analyzed for Na, S, or Zn. Soil samples after harvest, mid-summer, and end of season 2018 and 2019 were analyzed for micronutrients B, Fe, Cu, and Mn.
Analysis of microbial biomass was performed on end of the season soil samples collected in 2017 and 2018.. Analysis of labile carbon and microbial functional diversity was performed on samples collected at the end of the season in 2017, 2018, and 2019 soils. Additional soil samples were collected at end of season 2018 and 2019 and at planting 2019 and analyzed for presence or absence of E. coli 0157: H7 and Salmonella spp. using a miniVida assay.
Labile carbon and microbial biomass
Labile carbon was determined using permanganate oxidizable carbon (POXC) (Weil et al. 2003; Culman et al. 2012). A microplate spectrophotometer (Bio-Rad iMark; Bio-Rad Laboratories, Hercules, CA) at 550 nm was used to determine absorbance. Microbial biomass carbon and nitrogen was determined using a chloroform fumigation extraction method modified from (Vance et al. 1987). Soil samples were sieved using a #4 sieve. A 15g subsample was dried at 67º to determine gravimetric water content. 50g of sieved soil was fumigated with ethanol-free chloroform for 24 hours. A second set of 50 g samples was extracted with 0.5M K2SO4 in sterile water. After 24 hours, fumigated samples were also extracted. After extraction, the supernatant was transferred to 60ml plastic bottles and a drop of phosphoric acid was added to extend storage. Samples were placed in a -20 ºC freezer until analysis of Total Carbon (TC) and Total N (TN) was to be carried out 20 and 21 December 2018. Fumigated and non-fumigated extracts were analyzed for total organic carbon (TOC) using a Torch Combustion TOC/TN Analyzer (Teledyne Tekmar, Mason, OH). A correction factor (k=0.33) was used to calculate MBC (Sparling and West, 1988). “In brief, organic C from the fumigated (24 h) and non-fumigated (control) soil were quantified by a CN analyzer (Shi- madzu Model TOC-V/CPH-TN). The non-fumigated control values were subtracted from the fumigated values. The MBC was calculated using a kEC factor of 0.45 (Wu et al., 1990). Each sample had duplicate analyses and results are expressed on a moisture-free basis.
Microbial functional diversity
Microbial functional diversity was assessed using community level physiological profile (CLPP). Sole-C-source utilization of culturable heterotrophic soil microbes was characterized by the method of Nair and Ngouajio (2012) with the Biolog-EcoPlate (BIOLOG Inc., CA, USA). The 96 well Biolog-EcoPlate® consists of three replications of 31 individual C sources (Table 5), and a blank that serves as a control. The reduction of a tetrazolium dye which turns purple indicates the C substrate utilization rate of the inoculated microbes. Ten grams of soil were combined with 90 mL of a sterile 0.85% sodium chloride (NaCl) solution, shaken and then incubated for 18 h. After incubation, the solution of NaCl and soil was brought to 10-3 dilution. 150µl supernatant was pipetted into each of the 96 wells of a Biolog-EcoPlate® using a multichannel pipette (Fisher Scientific, Hampton, NH). Immediately after plating, optical density (OD) for day 0 was measured at 590nm, with a spectrophotometer (Bio-Rad iMark; Bio-Rad Laboratories, Hercules, CA). The color change was measured every day for 7 days with OD every 24 h. The day 0 reading was subtracted from each subsequent reading to account for any background coloration. Additionally, the OD value of the blank well was subtracted from the response of the 31 C sources in each replicate. Substrate richness (S), the number of substrates utilized by soil microbes in each sample is a count of the positive OD measurements. Average well color development (AWCD), a combined measure of the diversity and abundance of soil microbes was calculated for each sample on days 1-7 using the following equation:
AWCD = ∑ODi/ 31
The Shannon-Weaver diversity index (H) and Evenness (E) were used as measures of soil microbial diversity and calculated using the following equations (Shannon and Weaver, 1969, Zak et al., 1994):
H = - ∑pi(ln pi) and E = H/log S
Where pi is the ratio of the corrected absorbance value of each well, to the sum of absorbance value of all wells. To reduce bias as a result of differences in inoculum densities, well color responses were normalized by dividing the blanked OD values by AWCD (Garland 1997).
Presence and absence of soil pathogens
Soil samples collected on 6 November 2018 and 8 April and 5 November 2019 were analyzed using an ELFA method (Enzyme Linked Fluorescent Assay) SPR and VIDA bioMérieux SA Chemin de l’Orme 69280 Marcy-l'Etoile – France) for the presence and absence of E.coli 0157: H7 and Salmonella spp. Additionally, spinach samples were collected on 5 June 2019 and the surface was tested for the presence of E.coli 0157: H7 and Salmonella spp. A 1000g sample was collected for each treatment plot from three replications.
Each year after harvest of the spring vegetable crop an electric fence was erected around the perimeter of the field to protect chickens from predators. Chickens were integrated into the V-P-CC rotation on 10 July, 28 June, and 11 June in 2017, 2018, and 2019, respectively, and removed on 30 August, 8 August, and 18 July 2017, 2018, and 2019, respectively. Chickens were integrated into the V-CC-P rotation on 15, 7, and 6 of September 2017, 2018, and 2019, respectively and removed on 8 November, 20 October, and 31 October 2017, 2018, and 2019, respectively. Chickens were housed in 1.5. x 1.2 m floorless movable coops (Figure 2) to allow them to forage on vegetables or cover crop residue. One pen per replication was used and housed 9-10 birds on average. Broiler types were Red Ranger (Welp Hatchery, Bancroft, IA) and Imperial (Moyer’s Chicks, Quakertown, PA). Both “breeds” come from Hubbard genetics. Characteristics such as a longer hock, larger leg and thigh, narrow breast, and slow growth are ideal for an outdoor rearing system compared to their conventional Cornish cross counterparts. Red ranger (2017) and imperial (2018 and 2019) chicks were purchased at one day old from their respective hatcheries and brooded for three to four weeks at the Iowa State University Poultry Research Farm until they were moved to the experimental field plots. Temperature and relative humidity (RH) inside the chicken houses were recorded in 2018 and 2019 (Figure 2). During brooding, chickens were fed an organic starter feed (Natures Grown Organics, Westby, WI). Once placed on the treatment plots they received a full balanced ration of organic grower and finisher feed (Natures Grown Organics, Westby, WI). Chicken coops were moved every day to allow access to fresh plant material. To calculate feed conversion ratio (FCR) and average daily gain (ADG) feed consumed and chicken weights were recorded throughout the time they were on the plots, feed and weight data were collected by weighing feed leftover and feed added. Chicken weight data were collected three times throughout the season at two-week intervals. In 2017 all birds from the pen were weighed and the weights averaged to record a whole pen weight. In 2018 and 2019 4-5, birds were randomly selected from the pen for weighing to determine an average pen weight. Birds were removed from plots after foraging for 9 (Red Ranger) and 6 (Imperial) weeks. In 2017 and 2018 birds were sold live to a local farmer. In 2019 birds were taken for processing (Martzahn's Farm Poultry Processing Greene, IA). A bird was removed from the study if health issues prevented birds from meeting their quality of life needs. Euthanasia was performed either by the Iowa State LAR team or protocol personnel according to the approved IACUC protocol.
Soil data were analyzed using proc mixed (SAS) ls means was used to determine the significance of between rotations at a given sampling time. The principal component analysis was used to analyze the carbon substrates utilized from the Biolog ecoplates. The 31 carbon sources were grouped into five categories or types of substrates. Vegetable yield and quality data from the lettuce and spinach crops were analyzed using proc glimmix to determine the effect of rotation on lettuce and spinach yields. Only these two crops were examined in this paper as these crops followed the integration of chickens. Yields of individual cultivars were pooled to analyze total yield for each rotation.
Lettuce heads grown in V-P-CC and V-CC-P rotations in 2018 following the 2017 chicken integration were not significantly different in total weight, total number, dry weight, or head length of lettuce heads (Table 6). The marketable weight of lettuce heads and head diameter was higher for V-CC-P as compared to V-P-CC. There was no difference among spinach total and marketable yield, or dry weight grown in V-P-CC, V-CC-P, and V-CC rotations in 2019 (Table 7) following chicken integration in 2018.
Soil nutrients and chemical/physical properties
At planting, there was no difference in any nutrients or other soil properties among rotations in 2017 (Table 8). NH4-N, NO3-N, total N, S, and Na were significantly higher in V-CC-P than all other treatments in 2018 (Table 8). There was no difference in any nutrients or other soil properties among rotations in 2019 (Table 8).
After harvest, there was no difference in any nutrients or other soil properties among rotations at this sampling time in 2017 (Table 8). In 2018, NO3-N was higher for the V-CC-P rotation as compared to V-P-CC and V-CC (Table 8). Zn was higher for V-P-CC than both V-CC-P and V-CC rotations and V-CC-P was higher in Zn than the V-CC rotation (Table 8). In 2019, Zn was lowest in the V-CC rotation (Table 8). Fe was higher in both the V-CC-P and V-CC rotations in 2019 compared to the V-P-CC rotation (Table 8).
Mid-summer, in 2017 OM was highest in the V-CC rotation compared to V-P-CC and V-CC (Table 8). Na was higher in the V-P-CC rotation compared to V-CC-P and V-CC (Table 8) all other nutrients and soil properties were not significantly different at this sampling time (Table 8). In 2018 and 2019, NH4-N, NO3-N, total N, and Na were higher for V-P-CC compared to both V-CC-P and V-CC rotations (Table 8). In 2019, S and Zn were also higher in V-P-CC compared to both V-CC-P and V-CC rotations (Table 8).
End of season, NO3-N was higher in 2017 for V-CC-P compared to V-P-CC and V-CC (Table 8). V-CC-P was higher in S as compared to V-P-CC (Table 8). OM was higher in V-P-CC and V-CC compared to V-CC-P (Table 8). There were no differences in any soil nutrients or other soil properties among the rotations in 2018. NO3-N was higher in V-CC-P compared to both V-P-CC and V-CC (Table 8).
Comparison of rotations over time: When comparing differences within one treatment across sampling times, NH4-N went down from at planting to after harvest for V-CC-P in 2018. All rotations decreased in NH4-N from mid-season to the end of the season in 2019. NO3-N went down from at planting to after harvest, after harvest to mid-season, and mid-season to end of season 2017 for V-P-CC. NO3-N decreased from at planting to after harvest and increased from mid-season to end of season 2017 for V-CC-P. NO3-N decreased from after harvest to mid-season for V-CC 2017. In 2018 NO3-N increased from at planting to after harvest and after harvest to mid-season for both V-CC and V-P-CC. NO3-N decreased for both V-CC and V-P-CC from mid-season to end of season 2018. NO3-N decreased from mid-season to end of season V-CC-P 2018. In 2019 all rotations increased in NO3-N from mid-season to end of the season. TN increased in V-P-CC from after harvest to mid-season 2018 and decreased in V-CC-P from at planting to after harvest 2018. All rotations increased in TN from mid-season to end of season 2019. P increased for V-CC from at planting to after harvest 2017 and decreased for V-CC-P from mid-season to end of season 2017. In 2018 P increased from at planting to after harvest for V-CC and V-P-CC. V-CC-P increased in P from at planting to after harvest 2019. In 2019 V-CC and V-P-CC increased in P from after harvest to mid-season. V-P-CC decreased in P from mid-season to end of season 2019. In 2017 K increased for all rotations from after harvest to mid-season and decreased from mid-season to end the season in V-CC and V-CC-P. Only V-CC-P decreased in K from at planting to after harvest 2018. In 2019 V-CC and V-P-CC increased in K from after harvest to mid-season. V-CC-P increased in K from mid-season to the end of the season. V-P-CC decreased in K from mid-season to end of season 2019. In 2017 Mg increased in all rotations from after harvest to mid-season. In 2019 all rotations increased in Mg from after harvest to mid-season. In 2017 V-CC and V-CC-P increased in Ca from after harvest to mid-season and decreased from mid-season to end of the season. In 2019 Ca increased in V-P-CC from at planting to after harvest. V-CC increased in Ca from after harvest to mid-season. In 2018 Na increased from at planting to after harvest in both V-CC and V-P-CC and decreased for V-CC-P. Na decreased from after harvest to mid-season in V-CC and V-CC-P. in 2019 Na increased from after harvest to mid-season and decreased from mid-season to end of the season in V-P-CC. In 2017 S decreased in V-CC and V-P-CC from mid-season to end of the season. In 2018 S increased in V-CC and V-P-CC from at planting to after harvest and decreased after harvest to mid-season. In 2019 S increased in V-P-CC from after harvest to mid-season and decreased from mid-season to end of the season. In 2018 B increased in V-CC and V-P-CC from after harvest to mid-season. In 2019 B decreased in V-CC and V-P-CC from after harvest to mid-season. In 2019 Cu decreased in all rotations from after harvest to mid-season. From mid-season to end of season V-CC and V-CC-P increased in Cu. In 2019 Fe decreased in V-CC and V-P-CC. Mn decreased in all rotations from mid-season to end of season 2019. In 2019 Zn increased in V-CC-P and V-P-CC from at planting to after harvest. Zn increased in V-P-CC from after harvest to mid-season 2019. Both V-CC and V-CC-P increased in Zn from mid-season to end of season 2019 and decreased in V-P-CC.
In 2017 CEC increased in V-P-CC from at planting to after harvest. Both V-CC and V-P-CC increased in CEC from after harvest to mid-season 2017. All rotations decreased in CEC from mid-season to end of season 2017. In 2019 CEC increased in V-P-CC from at planting to after harvest. CEC increased for both V-CC and V-P-CC from after harvest to mid-season 2019. In 2017 pH increased in V-P-CC from at planting to after harvest and from mid-season to end of the season. In 2018 pH decreased in V-CC from at planting to after harvest, increased from after harvest to mid-season, and decreased from mid-season to end of the season. CEC increased in V-P-CC from after harvest to mid-season 2019. Both V-CC-P and V-P-CC decreased in CEC from mid-season to the end of the season. In 2017 OM decreased in V-CC from at planting to after harvest and increased from after harvest to mid-season. In 2018 OM decreased for all rotations from at planting to after harvest. In 2019 OM decreased in both V-CC and V-P-CC from mid-season to end of the season.
Labile carbon and microbial biomass
At the end of the season in 2017, there was no difference among treatments in labile carbon (Figure 3). In 2018, V-CC-P was higher in labile carbon than V-CC. In 2019 there was no significant difference among treatments. Labile carbon in V-CC decreased significantly from 2018 to 2019. Microbial biomass carbon (MBC) (Figure 4) did not differ among treatments after harvest 2017. MBC was higher in V-P-CC compared to V-CC at after harvest 2018. MBC was higher for V-CC-P compared to V-CC at end of season 2017 and was higher for V-P-CC than both V-CC-P and V-CC at end of season 2018. MBC increased in all treatments from 2017 to 2018 when comparing after harvest soil samples. MBC decreased in V-CC-P from 2017 to 2018 when comparing the end of season samples.
Microbial functional diversity
Average well color development (AWCD) increased with incubation period (Figure 5) for all after harvest and end of season sampling times in 2017, 2018, and 2019.
After harvest, there was no difference among treatments after harvest in 2017 or 2019. In 2018 AWCD was higher for V-CC than V-CC-P and V-P-CC on day 7. V-CC-P had higher AWCD than V-P-CC. AWCD decreased for all treatments from 2018 to 2019 after harvest.
End of season, There were no significant treatment differences at the end of season 2017, 2018, or 2019. AWCD development increased for all treatments from the end of season 2017 to the end of season 2018 but decreased from the end of season 2018 to the end of season 2019. Treatments did not affect soil bacterial functional diversity index (Shannon–Weaver diversity index) or Evenness at either sampling date for any year (after harvest or end of the season).
The principal component analysis showed some distinct differences between treatments (Figure 6). The proportion of variation explained by PC1 ranged from 39 to 63%. Principal component loadings, comprising of five categories of Biolog-EcoPlateTMC substrates, contributed towards the spread of variables along PC1 and PC2 (Table 9). In 2017 all carbon sources were closely correlated with no treatments having any close association with any of the carbon substrates. In 2018 Amines and Amides were highly correlated with Amino Acids. Microorganisms that utilized carbohydrates were mostly seen in the V-CC rotation. Microorganisms that utilized carboxylic acids, Amines, and Amides and Amino acids were more closely associated with V-P-CC and V-CC-P rotations which were spread widely across both PC1 and PC2. Results in 2019 were similar to 2017.
Presence and absence of soil pathogens
Twelve soil samples (one from each rotation replication) were analyzed for the presence of E. coli O157:H7 and Salmonella spp. on 2 November 2018, 8 April, and 5 November 2019. One soil sample from 2 November 2018 from V-CC was found to be positive for Salmonella but when tested for confirmation, it turned out to be a false positive (Table 10). All soil samples from 8 April 2019 were positive for E. coli O157:H7 (Table 10). One sample from V-P-CC and one from V-CC were initially tested negative with miniVidas® however when samples were plated using selective chromogenic agar media, all samples turned out to be positive (Table 10). One sample from V-CC was found to be positive for Salmonella spp. but when tested for confirmation, it turned out to be a false positive (Table 10). Based upon the confirmation tests, the observations account for the firm presence of E. coli O157:H7 in the soil samples. Soil samples from 5 November 2019 were all negative for Salmonella spp. (Table 10). One sample from V-P-CC and two samples from V-CC were positive for E. coli 0157.
All the spinach samples from 5 June 2019 were negative for E. coli O157:H7 and Salmonella spp. (Table 10).
Chicken FCR and ADG
Feed conversion tended to be lower for birds in V-P-CC compared to V-CC-P (Table 11). ADG varied from 0.07-0.09 (Table 11).
Cover crop biomass additions were low most likely due to the production of oats in sub-optimal conditions. Based on the short amount of time cover crop was grown before termination or chicken integration it would have acted like a green manure adding minimal carbon back to the soil. This is obvious in the analysis where the C:N ratio of oats and crimson clover is similar.
In 2018 lettuce harvested off plots that had chickens integrated into cover crop the previous year had higher marketable yields in number and weight and larger head diameter than those grown in plots that had chickens integrated directly following broccoli. In 2019 there was no difference in yields of spinach for any of the rotations.
Poultry manure as a fertility source can provide all 13 of the essential plant nutrients (Chastain et al., 1999). Nitrogen, sulfur, zinc, iron, and sodium seemed to be most influenced by the integration of chickens. At planting in 2018 V-CC-P was higher in S and Na. After harvest 2018 and 2019 Zn was higher where chickens were integrated. Fe was higher for V-CC and V-CC-P in 2018 and 2019 after harvest. When chickens were introduced directly after vegetable crops Na was higher in all three years. Zn was higher in summer 2019 after chickens were integrated.
Nitrogen increased when chickens were introduced and fertilizer was able to be reduced by up to half in 2018 in the V-CC-P rotation indicating that integrating chickens in the fall may increase residual nitrogen for crops the following spring. An indication that the utilization of legume and grass cover crop mixture and chickens may increase the potentially mineralizable nitrogen for the following season. Nitrogen levels varied based on when in the rotation the soil was sampled. It is no surprise that N tended to be higher directly after chicken removal. Our results are in agreement with other studies where nitrogen increased when chickens were present (Miao et al., 2005; Hilimire et al., 2012) and varying N levels based on season and production system (Rudisill et al., 2015). This reduction in fertilizer was not seen in 2019 where there were no differences in the amount of nitrogen in any of the rotations at the start of the season. In 2017 chickens were on the plot longer than 2018 and 2019 which may have played a role in the high residual nitrogen present at planting in 2018.
Although increased P is common with the application of manure Rudisill et al., (2015), there was no significant difference in the amount of P for any of the rotations. Although poultry manure can increase soil fertility nutrient composition of the poultry manure is largely affected by the diet and age of the animals (Lorimor et al., 2004), applying poultry manure by the integration of animals may give inconsistent results. Growers should use soil tests each year to determine N requirements when using an integrated system. This three-year study saw some changes to organic matter between rotations specifically at mid-summer sampling and end of season 2017 where the V-CC rotation was higher in SOM in 2017 than both the chicken rotations and V-P-CC and V-CC were higher at 2017 end of the season than the V-CC-P. Changes in organic carbon may be more easily observed in the 0-5cm depths when looking at short term changes due to management (Acosta-Martinez et al., 2004). SOC can be influenced by crop and cover crops, rotation, and tillage practices (Jagadamma et al., 2019) but, increases in SOM can be slow, and incremental organic matter increased after 15 years of application of dairy manure (Verlinden et al., 2017).
POXC is an indicator for small changes in soil carbon from agricultural management practices (Weil 2003). Cover crops and animal manures have improved active carbon (Blair et al., 2000; Butler et al., 2016; Rudisill et al., 2015). We observed an increase in labile carbon from the end of the first rotation cycle to the end of the second cycle. No differences were observed in 2019. Using reduced tillage with chicken integration may result in additional increases in labile carbon.
Soil microbes are the mediators for critical nutrient cycling and are sensitive to changes in management practices which can sometimes be observed before other changes are detected (Adeli et al., 2010). MBC is increased with poultry litter (Adeli et al., 2010; Nair and Ngouajio, 2012) and in diverse cropping systems (Acosta-Martinez et al., 2004). Similar results were seen in this study where microbial biomass was higher in plots with chicks and cover crops.
Microbial biomass was increased at the end of the 2017 season for V-CC-P and was higher in V-P-CC in 2018 both after harvest and end of the season. Inconsistent results in MBC may be due to an environmental effect and that crop type is more important on the effect of microbiological and biochemical soil properties (Acosta-Martinez et al., 2004). Microbial biomass carbon may be more responsive to management practices than SOM especially at the 0-5cm depth total C may be more affected by the crop type and ground cover as seen with higher total C under perennial pasture vs a continuous cotton cropping system (Acosta-Martinez et al., 2004). Changes in microbial biomass may also be due to the complete removal of vegetation when chickens were in place as this may have meant a reduction in substrates for microbial growth (Acosta-Matinez et al., 2010)
Microbial functional diversity increased after incubation regardless of rotation. The use of cover crops may be a better determinant of the diversity of an agroecosystem and each rotation had cover crops. There were some differences in substrate utilization based on rotation particularly in 2018. In 2017 and 2019 substrate utilization was random and did not depend on treatment.
This system much like other intensive vegetable production systems used tillage to prepare beds for planting and preparation for planting and termination of cover crops. Intensive tillage negatively affects measures of soil health (Butler et al., 2016) and could have reduced the benefits observed from integrating chickens.
Ecoli 0157:H7 and Salmonella SPP. are common perpetrators of foodborne illness. Found in the GI tract of animals their manure harbors it. E. coli 0157:H7 and Salmonella SPP. can then become present in the soil when raw manure is applied. E.coli and Salmonella sampling were negative for all plots in 2018 but positive for E.coli for all plots in the spring of 2019 and only in some plots at the end of the season in 2019. Spinach samples had no pathogens detected when samples in the spring of 2019. FSMA regulations encourage the use of applying only treated or composted manure and waiting a sufficient amount of time before planting or harvesting from fields where manure has been applied (21 CFR subpart I 112.83). Additionally, they urge growers to avoid raw manure coming in contact with growing produce that will be harvested and consumed raw. Studies that examine the potential for contamination of produce when raw manure is applied via live animals are crucial for further decision making on the food safety rule.
Feed conversion ratios for organic hens raised with outdoor access have been reported between 2.07 and 2.81 (Hermansen et al., 2004). Our results are similar to those reported and may be higher due to heat, humidity, or cold stress at times during summer heatwaves and fall cold spells. FCR may also be lower in birds raised on pasture due to less feed consumption overall. Lorenz et al., (2013) found that slower-growing birds on pasture had less feed in their crops and gizzard but higher pasture contents than fast-growing birds. The pasture intake reduces feed efficiency in monogastric whose anatomy is not made for consuming lignin.
Utilizing chickens in an integrated system may require an altered way of thinking from production efficiency to the soil building and farm resiliency services that the animals provide (Hermansen et. al, 2004).
The goal of organic vegetable production is to strive for and build healthy and resilient systems that start with healthy soils. Integrating chicken with the already implemented cover crops in an organic vegetable rotation has the potential to increase soil health indicators such as microbial biomass, and active carbon.
Chicken integration could save on off-farm fertilizer costs and increase resiliency.
Although E. coli was detected in all plots in the spring of 2019 and some plots in the fall of 2019 no pathogens were detected in the spinach crop when leaf surfaces were tested indicating the potential for integrating chickens to be a low-risk soil building management strategy. Although more research is needed to confirm.
Chickens reared on cover crops and vegetable crop residues in the summer and early fall appear to be able to withstand heat and have similar efficiency to birds raised on pasture systems providing growers with a high-value product to diversify their income stream.
Despite the potential benefits of integrating chickens, more research on these systems are required to gain back lost knowledge of effectively integrating animal and vegetable systems for maximum benefit to the producer, the animals, and the environment. Long term studies are needed to gain insight into carbon and nutrient cycling. After seven years of crop-livestock integration, MBC was higher than continuous cotton and after 10 years there were significant changes in SOM (Acosta-Martnez et al., 2010). Birds raised outside are exposed to heat, cold, and predation which could alter the success of the system. Continued evaluation of chicken-vegetable crop systems is needed to determine what factors promote success. Although a few factors may align with livestock systems such as breeds used and forage quality. An optimal system would build soil health, promote the health of chickens, and minimize P accumulation and death of soil cover (as this could affect microbial biomass growth).
Integrated systems should also be evaluated by the environmental and social services they could provide such as reduction of energy used to transport fertilizer to the farm from manufacturers, reduction of nutrient leaching, more biodiverse farms, and those that involve the local community.
Organic vegetable production systems need diversity to be resilient and the potential benefits of doing this with integrated chicken and vegetable production should not be overlooked.
Acknowledgments: Thank you to all that provided guidance and insight; the staff at the Horticulture Research Station, Cameron Hall, at the ISU Poultry Science Farm, and ISU LAR on-call veterinarians.
Funding: This work was supported by the North Central Sustainable Agriculture and Research and Education Service (NC-SARE) [GNC-]. 120 BAE, University of Minnesota | 1390 Eckles Avenue | St. Paul, MN
Educational & Outreach Activities
In July of 2018 Iowa State news service visited and toured the research plot. A video story was created about the project and published on the ISU news website.
In August of 2018 the Iowa Fruit and Vegetable Growers field day was held at the ISU Horticulture Research Station. Around 150 growers of all scales and operations attend this event each year. One of the stops on the field day was the research plot for this study. Attendees observed the research plot and information about the project was described. Growers were able to observe the different treatment plots and how the chickens were housed.
In Agust if 2018 Amy Mayer of Iowa Public Radio published a podcast and blog on harvest public media. http://www.harvestpublicmedia.org/post/little-livestock-could-go-long-way-organic-farm
In September of 2018 STEM students visited and toured the research plot.
Each year a local grower purchases the birds at the conclusion of the study. This collaboration allows for valuable insight into the dressed weights of the birds and cosnumer satisfaction of slower growing birds grown on a pasture and forage system.
This project provided valuable preliminary data for the funding of a multi-institutional collaborative grant to further study the integration of poultry into organic vegetable production systems. This OREI grant will further examine the health of slow-growing birds on pasture, pathogen presence in soil and vegetable crops from the presence of poultry, vegetable yield and quality of organically raised crops, and further investigate soil health parameters of a poultry vegetable integrated system.
After the completion of the 2019 season, we have gained knowledge in the requirements for raising poultry in an alternative production system (outdoors on various forages). We have gained hands-on experience producing pastured poultry as well as gained insights into the use of cover crops for between row weed control on a small scale.
We have gained insight into consumer preferences for pasture-raised chickens for the direct to consumer market. Knowledge was also gained in organic production practices and reporting requirements for organic vegetable production especially for the production of lettuce, peppers, spinach, and carrots.