Date of Graduation

12-2021

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor

Kristofor R. Brye

Committee Member

Lisa S. Wood

Second Committee Member

Mike B. Daniels

Third Committee Member

Edward E. Gbur Jr.

Keywords

agriculture, Arkansas, cover crops, Lower Mississippi River Valley, resource conservation, soil health

Abstract

Cover crops are a widely considered practice to improve soil health in the form of erosion control, organic matter additions, and improving water-holding capacity. Despite the well-documented benefits, little is known about the effect of cover crops on soils in the Lower Mississippi River Valley (LMRV), an area historically dominated by intensive cultivated agriculture, with soils prone to erosion, and unsustainable aquifer withdrawals for irrigation. The main objective of this study was to evaluate the effects of cover crops [with cover crops (CC) and without cover crops (NCC)] on near-surface soil physical/chemical- and infiltration-related properties, aggregate stability, and water retention. The secondary objective of this study was to evaluate the effects of sample/measurement placement [in the bed (B) and in the wheel-track (WT) and non-wheel-track (NWT) furrow] in adjacent CC and NCC treatments on the same soil under wide-row cotton (Gossypium hirsutum L.) production. Soil samples were collected and in-situ measurements were conducted between May 2018 and May 2019 across four locations within the LMRV portion of eastern Arkansas. Using a falling-head, double-ring infiltrometer method for 20 minutes, overall- and steady-state infiltration rates were unaffected (P > 0.05) by cover-crop treatment. Across all locations, extractable soil Na content in the top 10 cm was greater (P ≤ 0.05) with NCC (31.6 kg ha-1) compared with CC (21.6 kg ha-1). Soil pH, electrical conductivity (EC), total C (TC), soil organic matter (SOM), and bulk density (BD) in the top 10 cm were also unaffected (P > 0.05) by cover-crop treatment. However, EC and BD were numerically greater with NCC compared to CC, while TC and SOM were numerically greater with CC compared to NCC. Based on a wet-sieving approach for five minutes, averaged across cover treatment and soil depth (0- to 5- and 5- to 10-cm), water-stable aggregate (WSA) concentration differed (P ≤ 0.05) by aggregate size class. Averaged across treatment and soil depth (0-to 5- and 5- to 10-cm), WSA concentration in the 0.25- to 0.5- (0.101 g g-1) was 1.5 times greater than that in the 1.0- to 2.0-mm size class (0.068 g g-1) and was at least 1.2 times greater than that in the 0.5- to 1.0- (0.079 g g-1) and 2.0- to 4.0-mm (0.084 g g-1) size classes, which were intermediate. Averaged across treatment and soil depth, WSA concentration in the > 4.0- (0.097 g g-1) was at least 1.2 times greater than that in the 0.5- to 1.0- and 1.0- to 2.0-mm size classes, which did not differ, while WSA concentration in the 2.0- to 4.0- was 1.2 times greater than that in the 1.0- to 2.0-mm size class. Extractable soil Na content was greater (P = 0.03) in NCC-WT (26.8 kg ha-1) and CC-WT (26.7 kg ha-1), which did not differ, than NCC-B (19.8 kg ha-1) and NCC-NWT (17.5 kg ha-1), which did not differ. Soil BD in WT was 1.1 times greater than the other two placements, while SOM content was greater in CC-WT (30.7 Mg ha-1) than in all other treatment-placement combinations, except for CC-NWT, which did not differ. Similarly, WSA concentration was 2.3 and 1.6 times greater in the CC-NWT and CC-WT combinations, respectively, which did not differ, compared to their corresponding placements under NCC. Though many soil properties did not significantly differ between CC treatments due to the collective variations in background management practices, CC and cash crop species grown, and CC duration, which ranged from less than one year to greater than 19 years, results of this study clearly demonstrated that CC positively affect physical, chemical, and hydraulic properties across a large area. With continued management using CC, soil property differences that were only numeric will likely continue to deviate from one another into the future, at which time the fuller benefits of long-term CC use may be realized.

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