Date of Award

8-2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Committee Member

Dara M Park, Committee Chair

Committee Member

Matt C Smith

Committee Member

William C Bridges

Committee Member

Michael Vassalos

Abstract

Two investigations were conducted in the southern coastal plain Pee Dee region of South Carolina to investigate conservation agriculture practices in row crop fields on soil water and fertility recommendations. Prior to these investigations the Varina sandy loam field was under no-tillage practices for 30 years, and had cover crops integrated into the crop rotation for three years and had not had fertilizer applied for three years.

In the first experiment five soil sampling strategies (0-15 cm, 0-30 cm, 0-60 cm, depth to the Bt horizon [ABRUPT], and from the start of the Bt to 24 cm [BT]) were evaluated over a three-year double-crop rotation. Sampling strategy did not affect crop yields (P>0.5), likely because soil phosphorus ([P]) and potassium ([K]) were found to be high in all samples. Variables influencing bioavailability of P and K (soil pH and CEC) partially explained the minimal influence of soil [P] and [K] on yields. While significant reductions in fertilizer costs between sampling strategies were observed for corn (P = 0.005), economic profit (calculated using the Clemson University Cooperative Extension Enterprise Budgets) for all three crops was related to root architecture and mineralogy.

In a separate investigation, five tillage treatments (no-till (NT), no-till with subsoiling (SS), strip-till with subsoiling (ST), vertical tillage with subsoiling (VT), and disking with subsoiling (D)), were established and maintained, with or without cover crops integrated into the double-cropping rotation, for three years in order to study effects on soil volumetric water content (θv). Cover crops increased θv for certain treatments under corn and soybeans but decreased it under wheat. Wheat yield was also decreased by 10 kg ha-1 when planted after a cover crop. Increased θv was significantly greater when CC were used for tillage treatments that had minimal to no surface disturbance (SS for Corn-2 and NONE for Soybean).

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