Integrating Poultry: Soil Health and Crop Yield Improvements in Organic Vegetable Systems

Project Director: Anne Carey, Iowa State University

Project overview

Integrating livestock into organic production systems can provide several benefits, including (1) improving soil health and structure, (2) boosting soil nutrient cycling and availability, (3) increasing crop yield, and (4) enhancing overall farm resiliency. 

Organic vegetable systems are more delicate than other production systems and can be adversely impacted by compaction via ruminant grazers (i.e. cattle); as such, chickens/poultry have been explored as an alternative. Previous studies have predominantly focused on the soil health and yield impacts of imported chicken manure, with fewer addressing the impacts of directly integrating poultry into vegetable crop rotations. 

This study assesses the impacts of poultry integration on soil health, crop yield, and weed/cover crop biomass in several vegetable crop rotations.

Farmer takeaways

  • Poultry integration may increase plant-available nitrogen (PAN) and soil K. 
  • Poultry integration may enhance soil P accumulation over time. 
  • Poultry integration may enhance water filtration in vegetable cropping systems, with lesser impacts on other physical soil properties including bulk density and aggregate stability. 
  • Poultry integration may enhance vegetable crop yields by up to 96%, but influence crop types differently. 
  • Poultry integration may serve as a promising method of improving soil heath, enhancing nutrient cycling, diversifying income, and boosting yields in organic vegetable production systems, but the practice needs to be monitored carefully to prevent excess nutrients from accumulating and potentially contaminating groundwater sources.

Project objectives and approach

Establishing Vegetable-Poultry-Cover Crop Rotations

Three treatments (rotations) were established: (Control/Treatment 1) vegetable/vegetable/winter cover crop (no poultry), (Treatment 2) vegetable/poultry/winter cover crop, and (Treatment 3) vegetable/summer cover crop/poultry/winter cover crop. During each growing season, all phases would take place. The same vegetables were planted in each treatment within the same growing season, with the exception of the control group, which necessitated a second (new) vegetable crop planting in place of either poultry or a summer cover crop. In accordance with recommended practices for organic vegetable production, the vegetable crop family was rotated between years. 

Vegetable Crop Varieties & Rotation Timelines

In Year 1, spinach was planted in all three treatment groups, followed either by poultry (Treatment 2), a summer cover crop blend of cowpea and teff (Treatment 3), or mini butternut squash (Control). Two months after the summer cover crop was seeded, poultry were introduced (Treatment 3). All three treatments were seeded with a winter cover crop blend of cereal rye and Austrian winter pea for the winter season. 

In Year 2, leaf lettuce was planted in all three treatment groups, followed either by poultry (Treatment 2), summer cover crop (Treatment 3), or bell peppers (Control). The same timeline was applied to Year 2, with poultry integration two months post-summer cover crop seeding, followed by winter cover cropping. 

In Year 3, broccoli was planted in all three treatment groups, followed either by poultry (Treatment 2), summer cover crop (Treatment 3), or sweet potatoes (Control). The same timeline applied. 

Data Collection & Analysis

Soil samples were collected three times each season: spring, summer, and autumn. Additionally, marketable vegetable biomass (yield) was measured during each harvest.

Key findings

Poultry integration may result in greater plant-available nitrogen (PAN), phosphorus (P), and potassium (K) than in vegetable crop rotations without poultry

  • At the end of the three-year trial, plant-available nitrogen (PAN; nitrate and ammonium) was significantly higher in the vegetable/poultry/winter cover crop (Treatment 2) and vegetable/summer cover crop/poultry/winter cover crop (Treatment 3) rotations (101% and 106%, respectively) than for the Control group. 
  • After three years, soil P was 68% higher for Treatment 2, 73% higher for Treatment 3, and 38% higher for the Control than at the beginning of the study. 
  • After three years, soil K was 34% higher for Treatment 2, 49% higher for Treatment 3, and 4% lower for the Control than at the beginning of the study.

Poultry integration may enhance water filtration, but may have lesser impacts on soil bulk density, aggregate stability, soil pH, and soil organic matter

  • Water filtration (measured as hydraulic conductivity, cm/h) was approximately 2.5 and 5 times greater for Treatments 2 and 3, respectively, than for the non-poultry Control group. 
  • No significant differences in soil bulk density, aggregate stability, soil organic matter (SOM), cation-exchange capacity (CEC), or soil pH were observed between treatment groups or growing seasons. This might be due to the fact that the duration of the study was relatively short (three years); as such, additional studies are needed to understand the long-term impacts of poultry integration on soil physical properties. 

Summer cover crop and poultry integration may provide the greatest benefit to soil health

  • Earthworm abundance was significantly higher than the Control for the vegetable/summer cover crop/poultry/winter cover crop (Treatment 3) rotation, but not for the vegetable/poultry/winter cover crop (Treatment 2) rotation, suggesting that both poultry manure and summer cover crop residue are beneficial for establishing an earthworm-conducive environment. 
  • The summer cover crops utilized some of the plant-available nutrients following the Phase 1 vegetable harvest without impacting the growth of the subsequent winter cover crops and vegetable croppings, suggesting that a summer cover crop may present an opportunity to mitigate excess nutrient runoff/water contamination without compromising future vegetable yields. 

Vegetable yields may be improved through poultry integration

  • Significantly higher leaf lettuce yields were observed for Treatments 2 (96%) and 3 (86%) than for the non-poultry Control group. However, no significant yield differences were observed between treatments for the broccoli growing season, suggesting that poultry manure impacts vegetable crop performance differently by crop type/species.

Resources

Anne M. Carey, Cole R. Dutter, Khadija Mbacke, Marshall D. McDaniel, Ajay Nair, Integrating poultry improves soil health and vegetable yield in organic, cover-cropped system, Agriculture, Ecosystems & Environment, Volume 382, 2025,

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Location

Iowa

Collaborators

Cole Dutter, Iowa State University
Khadija Mbacke, Iowa State University
Marshall McDaniel, Iowa State University
Ajay Nair, Iowa State University

Region

North Central

Topic

Soil Health, Crop Nutrient Management, Weed Management, Cropping Systems, Livestock Feeding, Livestock Well-Being

Category

Vegetables/Fruits, Livestock

Year Published

2025