Date of Graduation

12-2013

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Kristofor R. Brye

Committee Member

Pengyin Chen

Second Committee Member

Kenneth L. Korth

Third Committee Member

Edward E. Gbur

Keywords

Biological sciences, Aggregate stability, Irrigation, Residue, Soil physics, Soil respiation, Soybeans

Abstract

Sustainability in agriculture is paramount to assuring continued production from our most naturally fertile soils. Storing carbon (C) in soil as organic matter through sustainable agricultural management practices can both remove atmospheric C and improve soil quality. The objective of this study was to evaluate the long-term effects of water management (irrigation and dryland), residue management [burn and no-burn, conventional (CT) and no-tillage (NT)] and residue/fertility level (high and low) on soil respiration and aggregate stability in a wheat- (Triticum aestivum L.) soybean [Glycine max (L.) Merr.], double-crop system in a silt-loam soil (Aquic Fraglossudalf) in the Mississippi River Delta region of eastern Arkansas after more than six years of consistent management. To this end, soil respiration was measured every two weeks during the 2011 and 2012 soybean growing seasons. A wet-sieving procedure was used to assess total and size-separated (i.e., 0.25-0.5, 0.5-1, 1-2, and > 2 mm diameters) water-stable aggregates (WSA). Soil respiration was greater under irrigation and CT on the majority of days sampled and averaged 27.4 and 16.3% greater than under dryland and NT management, respectively. Soil respiration was reduced by an average of 9.7% by residue burning, as compared to non-burning. The effects of residue level, achieved by differential N-fertilization, on soil respiration were inconsistent and generally non-significant. Soil water-stable aggregates were unaffected by burning, but were affected by all other field treatments. Total WSA concentrations were 19% greater under CT than NT within the dryland-low-fertility treatment combination. Total WSA concentrations under high-fertility were 18% less than under low-fertility within the irrigated-NT treatment combination, despite greater residue levels produced within the high-fertility treatment. The smallest two size classes (i.e., 0.25 to 0.5 and 0.5 to 1.0 mm) comprised over 80% of the total WSA. The WSA concentrations of the largest two size classes (1- to 2- and >2-mm) were unaffected by all treatments imposed. Understanding how long-term agricultural management practices affect soil C storage and cycling can help improve policies for soil and environmental sustainability throughout the lower Mississippi River Delta region.

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