Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Plant Science

First Advisor

Tom E. Schumacher


The degree to which soil structure is maintained with different tillage systems following the Conservation Reserve Program (CRP) is unknown. The objectives of this study were to evaluate the effect of tillage systems after simulated CRP on: 1) soil physical properties related to soil erosion and water infiltration and 2) soil microbial activity and biomass. The 8.1 hectare research site enrolled in the acreage-reduction program prior to project initiation was considered to simulate conditions that represented CRP. The soils of the site were Wisconsin-age Tazewell sub-stage glacial till in a Poinsett, Kranzberg, and Waubay soil association. The slope gradient ranged from 3 to 6 percent. Experimental design consisted of a randomized block design with 4 replicates and 7 tillage treatments. The grass check (GC), established in 1984, was an undisturbed alfalfa (Medicago sativa L.)- smooth bromegrass (Bromus inermis Leyss.) mixture. Tillage treatments consisted of fall moldboard plow (MP), fall chisel plow (CP), and no-till (NT90) established in 1990. Additional no-till treatments were established in 1991 (NT91), 1992 (NT92) and 1993 (NT93). Continuous corn (Zea mays L.) was grown on all tillage treatments except for the GC. Measurements used in evaluating soil hydraulic properties included surface residue, surface runoff, soil loss measurements, infiltration, and internal drainage. Measurements evaluating changes in microbial indices included above-ground and below-ground plant biomass, microbial activity using fluorescein diacetate hydrolysis (FDA), and microbial biomass using substrate-induced respiration (SIR). Artificial rainfall was applied at a rate of 63.5 mm hr-1 for a duration of 60 min. Approximately 1/2 and 1/3 of the total water applied was lost as runoff on the MP and CP respectively. Reducing tillage intensity from MP to CP resulted in an 80% reduction in soil loss. Reduced infiltration occurred in the MP compared to all no-till and GC. Time domain reflectrometry was used to measure water content within the soil profile at depths of 10, 20, 30, 40 and 60 cm. The time for the wetting front to reach a given depth increased with depth for all treatments. The largest increase in the time interval for the wetting front occurred between the 20 and 30 cm depth in the MP. Wetting-event time from rainfall initiation until maximum water content for the MP was significantly greater for the 30, 40, and 60 cm depths compared to the other tillage treatments. The percentage of applied water stored within the top 60 cm was similar for all treatments. The percentage of applied water below 60 cm was significantly less for the MP and CP. Few differences in soil physical properties occurred among treatments. Therefore, water content reductions that occurred below 60 cm in the MP and CP appear to be due to less water available for infiltration. Properties affecting microbial indices were measured on the upper backslope landscape position. The MP treatment reduced above-ground and below-ground plant biomass for the surface 10 cm by approximately 80% compared to the GC treatment. Tillage associated with the MP resulted in a 95% reduction in microbial activity at the o to 15 cm depth compared to the GC. SIR resulted in no observable treatment differences. These results imply that total microbial numbers may be similar for all treatments, but the number of microbes active within those treatments may be different. The greater soil loss and water runoff on the MP compared to the no-till treatments appear to be primarily related to the effects of surface cover rather than to internal changes in soil structure. Reduced microbial activity that occurred with increased tillage may lead over time to the deterioration of surface and internal soil structure.

Library of Congress Subject Headings

Conservation Reserve Program (U.S.)
Soil structure
Soil conservation




South Dakota State University



Rights Statement

In Copyright