Date of Award:

5-2014

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Plant Soils and Climate

Committee Chair(s)

J. Earl Creech

Committee

J. Earl Creech

Committee

Grant Cardon

Committee

Corey Ransom

Committee

Ralph Whitesides

Abstract

Glyphosate-containing herbicides such as Roundup® are a common and highly effective method to terminate alfalfa stands. With the development of glyphosate-resistant (Roundup Ready®) alfalfa, this tool is no longer an option. The purpose of this research was to determine the optimal termination methods to use when rotating from glyphosate-resistant alfalfa into silage corn. Studies were conducted in 2012 and 2013 in Cache Junction and Cornish, Utah using five different combinations of tillage type and timing (fall conventional till, spring conventional till, fall strip-till, spring strip-till, and no-till), four 2,4-D plus dicamba herbicide timings (fall, spring, in-crop, and a control), and four nitrogen rates (0, 56, 112, and 224 kg N ha-1). These tillage types and timings, herbicide timings, and nitrogen rates were tested to determine their effect on compaction measured by penetration resistance, alfalfa re-growth measured by alfalfa stem counts and alfalfa biomass collected before corn silage harvest, corn emergence measured by an emergence rate index, and silage yield, quality, and economic return.

The fall, spring, and in-crop herbicide timings across all tillage treatments controlled ≥ 95% of the alfalfa stem count and 98% of the alfalfa biomass controlling 44% to 71% more than tillage alone. All tillage treatments reduced penetration resistance compared to no-till to or near the depth of tillage. The emergence rate index was higher under fall conventional till, spring conventional till, and spring strip-till and when herbicides were applied in the fall or spring. Silage yield, quality, and economic return were the highest when spring herbicide timing was used with all tillage types and timings and the fall herbicide timing under conventional tillage. Increasing nitrogen rates increased crude protein, milk ha-1, and dry matter yield. However, optimal yield and quality can be obtained with no additional nitrogen fertilizer. First-year silage corn yield, quality, and economic return can be optimized under fall or spring conventional till, strip-till, and no-till at the spring herbicide timing along with the fall herbicide timing for conventional tillage with no additional nitrogen fertilizer.

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