Date of Award:

5-2024

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Committee Chair(s)

Jeanette Norton

Committee

Jeanette Norton

Committee

Jennifer MacAdam

Committee

Grant Cardon

Committee

Matt Yost

Committee

Scott Jones

Abstract

Silage corn production challenges sustainable intensification and soil health in semi-arid environments because the entire aboveground biomass is harvested and removed from the field. An irrigated silage corn field study was conducted over a decade comparing nitrogen fertility sources using a complete randomized block design with four treatments: control with no nitrogen fertilizer (control), low ammonium sulfate at 112 kg N ha−1 (AS100), high ammonium sulfate at 224 kg N ha−1 (AS200), and steer manure compost at 224 kg total N ha−1 (compost). Research focused on the impact of these contrasting nitrogen sources on silage corn production, nitrogen use efficiency (NUE), and soil health indicators.

Yield under compost treatment exhibited a notable 41% increase compared to control but was approximately 31% lower than the average yield under AS100 and AS200 treatments. AS100 achieved a yield comparable to AS200 and demonstrated higher NUE, challenging conventional belief that increased nitrogen application rate ensures maximum yield and profitability. Despite lower yield and NUE, the compost significantly enhanced soil health indicators such as STN, carbon, soil N and C mineralization, soil protein, soil water extractable organic N and C, and soil enzymes.

In summary, multiple-season studies are crucial for understanding carbon and nitrogen dynamics and soil health. Ammonium sulfate fertilizers proved effective in achieving higher silage corn yields and NUE compared to compost treatment. In contrast, compost demonstrated significant enhancement of soil C and N and their indicators, highlighting benefits for overall soil health. The positive shifts in soil health indicators underscore the advantages of combining compost with commercial fertilizers for improved fertility and sustainable soil management. Farmers are encouraged to adopt a balanced approach, incorporating compost alongside commercial fertilizers and implementing soil health practices for sustainable silage corn systems.

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