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ROOT TRAITS OF COVER CROPS AND THEIR INFLUENCE ON SOIL ORGANIC CARBON STABILIZATION
Restricted (Penn State Only)
Amsili, Joseph Pierre
Master of Science
Date of Defense:
July 27, 2018
Jason Philip Kaye, Thesis Advisor
Armen R. Kemanian, Committee Member
Charles Macaulay White, Committee Member
Jonathan Paul Lynch, Committee Member
Cover cropping is a beneficial soil management strategy that leads to increased organic carbon (C) and in the case of legumes nitrogen (N) inputs in between cash crops. Cover crop inputs can help to improve soil organic carbon (SOC) levels, build soil health, and mitigate climate change. While roots play an important role in increasing SOC levels, cover crop root traits remain poorly understood. In chapter 2, I compared the quantity, quality, and spatial distribution of roots in triticale, crimson clover, and canola monocultures as well as a cover crop mixture that contained those three species. Recently, cover crop mixtures have grown in popularity as a way to increase the diversity of services provided by cover crops. I determined cover crop and cash crop root C contributions to cumulative C inputs in the three-year organic grain rotation. Triticale produced more total root biomass C and root biomass C in the between row space compared to other cover crop treatments. The mixture had more 0-5 cm root biomass C than the crimson clover monoculture in spring 2017. Therefore, combining crimson clover with grass and certain brassica species can lead to improved total root biomass production, root distribution, and root length density compared to crimson clover monocultures, while also decreasing root C:N compared to grass species. Cover crop and cash crop roots increased cumulative C input estimates by between 37 % (crimson clover) and 46 % (triticale) compared to shoot C alone. The cover crop mixture led to higher cumulative C inputs compared to monoculture treatments, which was due to higher cover crop biomass C and its influence on the following corn crops biomass C. In chapter 3, I compared the quantity of cover crop rhizodeposition C recovered in different density-particle size fractions of SOC under three cover crop species. Crimson clover led to significantly more rhizodeposition C in the light fraction per gram of root C and per meter root length than canola or triticale. While I hypothesized that higher rhizodeposition quality under crimson clover would lead to a greater proportion of rhizodeposition C being stabilized in heavy fractions of silt and clay, I found the opposite. A larger quantity and proportion of canola and triticale rhizodeposition C was stabilized in silt and clay fractions compared to crimson clover. The short length of the experiment, high N availability, and destabilization of organo-mineral carbon by organic acids may explain this result. Knowledge of root traits and the fate of rhizodeposition C can inform cover crop selection for increasing SOC. The field-scale investigation of root traits added to the limited information that exists on root traits of winter annual cover crops. Root trait measurements revealed that important differences in root production, root-to-shoot (R:S) ratios, between-row roots, and carbon-to-nitrogen (C:N) ratios exist among these cover crops. Cover crop rhizodeposition C, while invisible, represents a significant component of root-derived organic carbon and an important source of carbon leading to the formation of mineral-associated organic carbon.
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