Document Type

Thesis - University Access Only

Award Date

1998

Degree Name

Master of Science (MS)

Department / School

Plant Science

Abstract

Studies have shown that ten years of establishment in the Conservation Reserve Program (CRP) has provided a number of benefits to the soil and environment. The change in criteria for acceptance into the program in 1995 will result in the expiration of a number of CRP acres within the next 5 years. A survey of South Dakota CRP contract holders indicated that 31 % planned to return these acres to crop production upon contract expiration. When returned to crop production, it is important that sound management takes place so that degraded soil properties that were present prior to CRP do not redevelop. The objectives of this study were to: 1) determine the effects of tillage systems on soil physical properties upon the return of western· South Dakota CRP acres to crop production; 2) determine the influence of conventional tilling after CRP followed by no-till management, because of problems associated with planting into un-tilled sod; and 3) assess the substitution of a legume to function as a green manure in place of traditional "black" fallow in winter wheat crop rotations. The 2. 2 ha study site, located in Lyman County, SD, was enrolled into CRP in 198 8. The soil at the site was a Promise clay (very fine, montmorillonitic, mesic Odie Haplustert). In 1994 the land was returned to crop production. The experimental design used was a randomized complete block consisting of six treatments with four replicates. Plots were subdivided so that each crop was represented yearly. Treatments included: 1. CRP; 2. CT - Conventional Tillage (winter wheat (Triticum aestivum) - "black" fallow); 3. CP - Conservation Tillage (winter wheat - green fallow with limited tillage to meet the conservation compliance plan of 20 % residue cover after planting); 4. NT1 - No-till (winter wheat -green fallow); 5. NT2 - No-till (winter wheat - corn (Zea mays) - green fallow); 6. NT 3 - Conventional breakout of the CRP with no-till practices following the first wheat harvest (winter wheat – green fallow). Soybean (Glycine max) was utilized as the "green" fallow crop. Measurements in 1995, 1996, and 1997 were used to evaluate soil physical properties. Soil properties evaluated were: surface residue, bulk density, unsaturated hydraulic conductivity, seasonal water content of the soil profile, surface runoff, soil water propagation velocity, aggregate stability, microbial activity, and organic carbon content. Surface residue cover varied with tillage treatment used. Surface residue cover was 48 % higher in NT1 than the tilled treatments of CT, CP, and NT3 in 1995. In 1996, surface residue cover in NT1 and NT3 were 64 % higher than CT, while CP was slightly higher than CT. The same was true in 1997, except NT3 was 25 % lower than NT1. Bulk density measurements taken in 1995 ranged between 1.18 (NT3) and 1.30 (CRP) g cm- 3 at the surface. Unsaturated hydraulic conductivity at the soil surface was highest in CT in each study year. This was due to tillage induced break-up of the soil surface, thus reducing the effects of surface sealing and soil particle consolidation. In treatments where no tillage was conducted during the growing season (NT1 and NT3), the unsaturated hydraulic conductivity values were highest. Rainfall in the 1996 and 1997 growing seasons was 30 % higher than normal. · Seasonal profile water content was highest in NT1 under green fallow, while CT (under black fallow) had the lowest seasonal profile water content. While under wheat cropping, treatment differences were similar. Water distribution within the soil profile was distributed unevenly. For example, water content was lowest in the upper 0.6 m under NT2 due to greater water uptake by corn roots the previous year. Water was applied to the soil surface at a rate of 6.36 cm in each study year with a sprinkling infiltrometer. Runoff from tilled treatments was significantly higher than no-till. Runoff from NT3 was slightly higher than from NT1. There was no runoff from CRP. Soil water propagation velocity measurement, in concert with the artificial rainfall event, revealed highest rates under CRP, due to surface organic matter, root channels, and bypass flow (resulting from a drier soil profile). NT1 propagation velocity was higher than CT and NT3 in 1995. Heavy rainfall in 1996 and 1997 resulted in one half the propagation velocities of 1995 due to wetter antecedent soil conditions. However, the differences among treatments in 1996-1997 were similar to those of- 1995. Aggregate stability was slightly higher at the surface in CT and CP, probably due to drier surface conditions at time of sampling. Microbial activity at the surface was highest in NT1 and lowest in CT, a direct result of residue differences. There were no significant differences in organic carbon levels among treatments. This study suggests that surface residue has the most profound effect on soil-water relations. No-tilling into chemically killed sod following CRP resulted in the most favorable conditions for soil and water conservation. By tilling the chemically killed sod, than implementing no till, soil structure may have been altered, but resembled perennial no-till more closely than perennial tillage after residue cover was established. Also, this study indicates that the use of a green legume during the fallow period maintained significantly more water in the root zone for use by the succeeding crop. Finally, this study indicated that by implementing no-till a more intense crop rotation may be applied to cropland in western South Dakota, or similar soils/climates, resulting in increased economic return from each acre while decreasing soil erosion and protecting the environment.

Library of Congress Subject Headings

Conservation Reserve Program (U.S.) Tillage Soil management

Format

application/pdf

Number of Pages

148

Publisher

South Dakota State University

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