Dryland Organic Winter Wheat Improvement by the Inclusion of Composted Cattle Manure and Cover Crops

C. Helseth, U. Norton
University of Wyoming
There is much to be learned about organically certified winter wheat (Triticum aestivum, L.) production in very dry and marginally productive regions like the northern high plains.  Some challenges include nutrient management and plant-available moisture.  Composted cattle manure (compost) followed by a fallow containing cover crops may create synergistic benefits that have not been widely adopted in southeastern Wyoming.  Little is known about their longer-term legacies.  These legacies may include improvement of soil health and soil structure.
Research Questions
  • Are there any emerging benefits to soil health of applying compost in an organic winter wheat-fallow system four years following a single application of a high rate of compost?
  • Are there any benefits from the compost application to water-holding capacity of the soil from dynamic precipitation events throughout the growing season?
Study Site
This study was conducted on a 15-year old organically managed winter wheat-fallow rotation located at the University of Wyoming Sustainable Agriculture Research & Extension Center (SAREC) in Lingle, Wyoming (42.14ºN, 104.35ºW).
Site Characteristics:
  • 1,276 m above sea level
  • Sandy clay loam soil
  • Slightly alkaline pH of soil
  • < 1% soil organic matter (SOM) 
  • Mean annual precipitation: 398 mm
  • Mean annual temperature: 7.5º C
September 2015: Compost applied during the fallow phase at the rates of 0, 15, 30, 45 Mg ha-1 (referred to as Control, Low, Medium, and High, respectively)
October 2016: Inorganic fertilizer (IF) applied: 89 kg ha-1 monoammonium phosphate and 120 kg ha-1 ammonium sulfate
May 2019: Cover crop mix containing 56 kg ha-1 Austrian winter pea (Pisum sativum, L.) and 28 kg ha-1 oat (Avena sativa) planted in the fallow phase for a period of six weeks 
September 2018: Winter wheat planted at a rate of 79 kg ha-1
August 2019: Winter wheat grain harvested
Data Collection/Analyses
  • Seasonal soil sampling (spring, summer, fall, and winter)
  • 0-5 cm and 5-15 cm soil sample depths collected using a hand probe
  • Soil moisture analyzed gravimetrically
  • Soil analyzed colorimetrically using spectrophotometry for plant-available nitrogen and phosphorus
Plant-Available Nutrients and Wheat Yield
FIGURE 1: Plant-available phosphorus
Observed changes in plant-available phosphorus throughout the 2019 growing season during the wheat phase.  Sample depth was 0-15 cm.  The Olsen phosphorus extraction method was used and extracts were analyzed colorimetrically on a spectrophotometer. Mean separation occurred during all seasons for the compost treatments with alpha = 0.05.  Plant-available phosphorus is particularily important for wheat grain development.  
FIGURE 2: Plant-available nitrogen
Observed changes in plant-available (inorganic) nitrogen throughout the 2019 growing season during the wheat phase.  Sample depth was 0-15 cm.  Inorganic nitrogen consisted of the sum of NH4+ and NO3- from 2M KCl extracts that were analyzed colorimetrically using a spectrophotometer.  Mean separation did not occur during any season for the compost treatments with alpha = 0.05. Inorganic nitrogen is an important nutrient for many plant physiological processes and development.  
FIGURE 3: Wheat grain yield
Observed mean wheat grain yields for the 2018, 2019, and 2020 growing seasons.  Mean separation occurred with alpha = 0.05 between years.  
Soil Moisture and Precipitation
FIGURE 4: Precipitation for the duration of the study
The actual monthly total accumulations of precipitation that occurred during the study compared the the 30-year average.  The total precipitation for each growing season was 400mm, 457mm, and 210mm for 2018, 2019, and 2020, respectively.  Solid black lines indicate wheat planting.  Dashed black lines indicate wheat harvest.
FIGURE 5: Soil moisture
Observed changes in soil moisture throughout the 2019 growing season during the wheat phase.  Sample depth was 0-15 cm.  Soil moisture was analyzed gravimetrically with soil samples dried in a 105ºC oven for 48 hours.  Mean separation occurred during the summer for the compost treatments with alpha = 0.05.  Compost may have added structure to the soil to improve water-holding capacity from precipitation events.  
Concluding Remarks
Emerging trends are beginning to form in the fourth year after a single large rate of compost application to organically managed winter wheat-fallow rotations in the semi-arid region of southeast Wyoming.  These trends include:
  • Improved soil nutrient content in the form of plant-available phosphorus and inorganic nitrogen
  • Improved soil water-holding capacity during times when there was more moisture than the 30-year average
However, there are no emerging trends of the compost application to wheat yield. 
Contact Information:
Tina Helseth, PhD student, chelseth@uwyo.edu
Dr. Urszula Norton, Advisor, unorton@uwyo.edu
Dr. Mavis Badu, Dr. Lianna Boggs-Lynch, Nick Andrews, Dixie Crowe, Olanre Ebanks, Tara Geiger, Katherine Hunley, Liz Moore, Leann Naughton, Justin Schomerus, and Amelia Zenerino

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