Degree Type

Dissertation

Date of Award

2019

Degree Name

Doctor of Philosophy

Department

Horticulture

Major

Horticulture

First Advisor

Nick E. Christians

Second Advisor

Adam W. Thoms

Abstract

Compared to other amino acids, the branched-chain amino acids (BCAA) could be effective additives in foliarly applied fertilization products due to the fact that these molecules are aliphatic, non-polar, and relatively hydrophobic. The BCAA leucine (L), isoleucine (IL), and valine (V) are synthesized in plants and essential to growth for most organisms, however, plant catabolism of BCAA is not completely understood. In humans, BCAA have been reported to increase muscle protein synthesis, and that increase was related to the intake ratio of L to IL and V.

The objective of these studies was to investigate whether BCAA could serve as a plant nitrogen (N) source, and to observe the effects of BCAA on creeping bentgrass (Agrostis stolonifera L.) growth when applied as single AA, 2-way combinations, and a 3-way combination. Where BCAA were applied as a 3-way combination, the BCAA ratios of 2:1:1, 4:1:1, 8:1:1, and 12:1:1 (L:IL:V) were evaluated. The BCAA were also evaluated as a standalone N application, and also as a combination with urea as a portion of the total applied N.

Applications of BCAA were compared to urea, an industry standard for N fertilization in turfgrass management, as well as GreenNCrease, a commercially available AA product. These nitrogen sources were compared for their effects on creeping bentgrass performance, color, quality, and growth under controlled environment and field conditions.

Results from the controlled environment studies indicated that when BCAA are applied as a standalone N source in a 2:1:1 or 4:1:1 ratio (3.4 kg-N ha-1), shoot density of creeping bentgrass can be increased by 20-30% and 30-40%, respectively, compared to equal urea N. Those responses were equal to GreenNCrease, a commercially available AA product reported to increase creeping bentgrass shoot density. While no increases in shoot density were observed between the BCAA 8:1:1 and 12:1:1 ratios compared to urea in our controlled environment studies, these ratios did result in material incompatibility as a result of incorporating additional L into the mixture, which has a greater hydrophobicity than IL and V. Material incompatibility was alleviated in these ratios by using a BCAA ratio half-rate (1.7 kg-N ha-1), in combination with urea (1.7 kg-N ha-1). In the controlled environment research, there were no differences between the BCAA ratio half-rate (L:IL:V+N) or full-rate (L:IL:V), when BCAA were applied in a 4:1:1 ratio.

In the field study, creeping bentgrass receiving applications of BCAA 4:1:1 ratio half-rate (4:1:1+N) increased creeping bentgrass shoot density by 27% and 7% compared to equal N from urea and GreenNCrease, respectively. Additionally, the BCAA 4:1:1+N treatment also increased creeping bentgrass leaf N content by 10% and 14% compared to urea and GreenNCrease. There were no differences in shoot density at the end of the study between urea and the other BCAA treatments. Based on the results of these studies, BCAA are best applied in a 4:1:1 ratio, and applying BCAA in a 4:1:1 ratio using a half-rate (1.7 kg-N ha-1) in combination with urea (1.7 kg-N ha-1) will promote the greatest increases in creeping bentgrass shoot density compared to urea under field conditions.

Copyright Owner

Isaac Mertz

Language

en

File Format

application/pdf

File Size

125 pages

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