Date of Graduation

8-2017

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Nathan A. Slaton

Committee Member

Trenton L. Roberts

Second Committee Member

Edward E. Gbur

Third Committee Member

Jeremy Ross

Keywords

Chloride, Soybean, Toxicity

Abstract

Chloride toxicity is recognized as yield limiting problem in soybean [Glycine max (L.) Merr.] production. Limited information is available to accurately diagnose and manage Cl toxicity. The only recommendation for Cl toxicity management is to plant an excluder cultivar, however the cultivar Cl sensitivity rating system (excluder, includer, and mixed) does not appear to capture the variability in cultivar Cl tolerance. The objectives of this research were to i) develop critical tissue-Cl concentrations in which yield loss occurs for excluder and includer cultivars and ii) investigate the variability in cultivar Cl ratings. A study was conducted across five site-years using six soybean cultivars including three Cl-includer and three Cl-excluder cultivars. Solution containing Cl was applied to the soil beginning at late vegetative growth with final rates ranging from 0 to 1010 kg Cl ha-1. Critical trifoliolate leaflet-Cl concentrations at the R3 stage were developed by regressing relative soybean yield across leaf-Cl concentration for each cultivar Cl rating. For the second objective, composite trifoliolate leaflet and individual trifoliate leaf samples were collected during reproductive growth from variety trials and analyzed for Cl concentration. The research verified that the yield of Cl-includer cultivars is reduced more (4-20%) than Cl-excluder cultivars (0-8%) in high Cl environments. Relative grain yield declined linearly for cultivars within each Cl rating group with 5% yield loss expected when Cl concentrations at the R3 stage averaged 3923 mg Cl kg-1 for Cl includers and 1885 mg Cl kg-1 for Cl excluders. Across more than 100 cultivars sampled in three Arkansas Soybean Performance Tests, tissue-Cl concentration ranged from <100 to >5000 mg Cl kg-1 and showed no clear groupings of the three cultivar Cl-traits suggesting that many cultivars labeled as includers are a mixture of includer and excluder plants. Chloride concentrations of 528 individual plants from eleven cultivars showed 34% and 31% of the plants had Cl concentrations ≤500 or 1000-2000 mg Cl kg-1 with only one cultivar having a pure population of Cl excluder plants. A new rating system is warranted to more accurately characterize the proportion of Cl include and excluder plants of each cultivar.

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