Date of Award:

12-2020

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Committee Chair(s)

Jennifer Reeve (Committee Chair), Astrid Jacobson (Committee Co-Chair)

Committee

Jennifer Reeve

Committee

Astrid Jacobson

Committee

Jeanette Norton

Committee

Scott Jones

Committee

Urszula Norton

Abstract

Organic dryland winter wheat (Triticum aestivum) growers in the U.S. are faced with high interannual variability in yields. This is related to the low annual precipitation and low soil fertility on the cultivated soils. Improving soil health is the key to increasing and maintaining crop yields. In this study, we compared the effects of different rates (0, 12.5, 25 and 50 Mg DW ha-1 compost and 2 Mg ha manure-1) of large quantities of steer manure compost and the inclusion of cover crops versus fallow on soil health and on carbon and phosphorus dynamics in two organic dryland systems with varying soil characteristics and microclimatic conditions. The two sites are located in Snowville and Blue Creek, Utah. At Snowville, the soil fertility is extremely low, pH is 8.5, and average total annual precipitation is 290 mm. At Blue Creek, the soil is more fertile, pH is 7.2 and average total annual precipitation is 485 mm. The results showed that the compost effect on measured physical, biological and chemical soil health indices (soil moisture, dehydrogenase and phosphatasesenzyme activities, soil organic carbon, Olsen P) were greater than the effects of cover crops at both sites. Differences were also found in phosphorus cycling between the two sites, with potential long-term impacts in soils with extreme low fertility due to lower rate of nutrient mineralization. By applying large quantities of compost (25-50 Mg DW ha-1) once, organic dryland winter wheat farmers can improve soil health, enhance SOM associated water retention and availability, and provide an environment for continuous sustainable wheat yield.

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