Effects of High Bulk Density Soil Layers on Root Distribution, Resource Acquisition and Root Morphology of Soybean (Glycine Max), Sicklepod (Senna Obtusifolia) and Palmer Amaranth (Amaranthus Palmeri)

Weed control remains one of the greatest costs for farmers in the U.S. The detrimental effect of weeds is most often expressed, agronomically, through competition for resources. In the southeastern U.S., the two main limitations for crop yields are water and nitrogen. One of the important factors restricting access to these important soil resources is the presence of compacted soil layers. The "hard pans" most often occur as a result of compaction by equipment traffic. Our main hypothesis was that the hardpans might inhibit downward root growth of crops and weeds differently, which could influence crop and weed competitive interactions. The purposes of these studies were (i) to evaluate the ability of roots of three species from a model agronomic system to penetrate through compacted soil layers, and (ii) to compare N acquisition from patches deep in a soil profile beneath compacted soil layers. The species selected for the experiments were soybean (Glycine max L.) and the weeds sicklepod (Senna obtusifolia L.) and Palmer amaranth (Amarnanthus palmeri S. Wats). In 12.7 cm diameter and 32.8 cm high growth columns, downward root growth of the weed species penetrated soil zones with higher bulk densities than four soybean lines. Palmer amaranth was most effective in acquiring 15N labeled nitrogen from buried patches underneath the high bulk density layers. Nitrogen acquisition by sicklepod exceeded that of soybean in the higher bulk density treatments but was less than soybean in the absence of compaction. Root diameters of soybean and sicklepod increased within and below compacted soil layers, while those of Palmer amaranth were unaffected. The results help to explain competitive dynamics between soybean and the weed species in the field.

Author dc:creator

• Place, George Thomas II

Advisors dc:contributor.advisor

• Dr. Dan Bowman, Committee Member
• Dr. Michael Burton, Committee Co-Chair
• Dr. Thomas Rufty, Committee Co-Chair

• sicklepod
• palmer amaranth
• soil bulk density
• soil compaction
• root morphology
• soybean

Statement dc:rights

• I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dis sertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report.

Dc Identifier Other

etd-02202007-124135

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