Document Type

Thesis - University Access Only

Award Date

2011

Degree Name

Doctor of Philosophy (PhD)

Department / School

Plant Science

Abstract

Recent technology provides the ability to process cellulosic plant material for ethanol production. Previous studies suggest that removal of this material from agricultural fields may or may not affect soil quality over time. The objective of this study was to evaluate the change in soil structure associated with biofuels crop residue management based on measurements of soil hydraulic properties using three independent methods in two different studies. Corn (Zea mays) stover removal and cover crop influences were evaluated in a split-plot randomized block design. The study was established as a no-till corn and soybean (Glycine max) rotation in 2000 at the North Central Agricultural Research Laboratory in Brookings, SD (Latitude: 44.338941. Longitude: -96.792123° WGS 84). In 2005, cover crops were introduced as sub-plot treatments. Three levels of corn biomass harvest were 1. Low (grain only = 10 Mg ha- 1) 2. Medium (grain and stover= 13 Mg ha- 1) 3. High (grain, stover and silage= 23 Mg ha- 1 ). A second study involved a split-plot completely randomized block design comprising corn and switchgrass (Panicum virgatum) over three landscape positions with corn stover removal (17 Mg ha- 1) and grass harvest (4 Mg ha- 1) as sub-treatments at Flandreau, SD (Latitude: 44.077183° Longitude: -96.613039° WGS 84) starting in the year 2007. Three methods; Cornell sprinkle infiltrometer (CSI), Tension infiltrometer (TI), and Compact Constant Head Permeameter (CCHP) were used to evaluate surface, and near surface soil hydraulic properties. Saturated hydraulic conductivity (Ksat) values were obtained from all three methods and compared. The CSI and TI methods gave similar Ksat estimates, while the CCHP estimates were an order of magnitude lower. The CCHP does not involve the soil-air interface in contrast to CSI and TI methods, and may account for the observed differences. The microscopic sorptive length and the mean equivalent pore radius (AllllJ) evaluated with the TI was used as an index of soil structure. The best estimate of the microscopic sorptive length a (m- 1) was obtained over the tension range of - 0.03 to - 0.15 m. A mean equivalent pore radius of 235 μm was observed in treatments where only grain was harvested and was significantly larger (LSDo.os = 24) than in treatments where stover (199 μm) or silage (187 μm) were removed in the corn-soybean rotations at Brookings, SD. The results at Flandreau, SD were similar, with a significantly larger mean equivalent pore radius of 227 μm in corn where biomass was not harvested in comparison to 195 μm when the biomass was removed (LSDo.os = 37). Biomass harvest did not affect the mean equivalent pore radius in the grass plots. Saturated hydraulic conductivity and penetration resistance measurements suggest that biomass harvest did not affect the subsurface soil conditions. The findings in this study indicate that residue retention in arable cropping systems are necessary for sustaining favorable structure of the surface soils similar to the soils used in this study (Calcic Hapludolls; Pachic Hapludolls). Removing grain and stover, the medium residue removal in this study (about 13 Mg ha- 1 of biomass), or harvesting silage, high residue removal (about 23 Mg ha- 1 of biomass) had similar effects on surface structure. Stover removal in this study degraded soil surface structure relative to the control condition of refraining from residue removal. This suggests either a nonlinear effect of residue removal or a threshold effect of residue on soil surface hydraulic properties. In either case, this study indicates that there is a cost to surface hydrological functions if too much corn stover is removed. Perennial grass harvest (single harvest per season in this study) did not affect surface soil structure. Subsurface soil conditions are more difficult to manage through residue retention practices, but residue management may have greater impact over time. Monitoring surface conditions provides the best opportunity for evaluating the impact of residue management for biofuel production. The cover crop management system used in this study had little effect on mitigating the effects of harvesting corn stover on surface soil hydraulic properties. Cover crops other than those used in this study may have a greater impact. There are also other benefits of a cover crop that may have immediate value such as mitigating raindrop impact that were not evaluated in this study. Future studies should concentrate on developing a more detailed response curve using more treatment levels to fine-tune management recommendations.

Library of Congress Subject Headings

Soil structure

Soils -- Quality

Crop residues

Biomass energy

Energy crops

Format

application/pdf

Number of Pages

155

Publisher

South Dakota State University

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