Document Type

Thesis - Open Access

Award Date

2026

Degree Name

Master of Science (MS)

Department / School

Agronomy, Horticulture, and Plant Science

First Advisor

Péter Kovács

Abstract

Soybean production in eastern South Dakota faces a persistent challenge: cool, wet spring conditions combined with heavy soils limit the adoption of conservation tillage despite its soil health and environmental benefits. Strip-tillage has been proposed as a middle-ground practice capable of providing conservation benefits while maintaining the seedbed quality advantages of conventional tillage. However, its performance in soybean production in South Dakota had not been evaluated prior to this work. This research examined the effects of tillage systems and fertilizer placement-timing, fertilizer rate, and seeding rate on soybean plant development, nutrient uptake, seed yield, chemical composition, and partial net economic returns across two growing seasons at two locations in eastern South Dakota. Field experiments were conducted at the Brookings Research Farm (BRS) and the Northeast Research Farm (NERF) in 2024 and 2025 using a randomized complete block design with a split-plot arrangement. Five tillage and fertilizer placement combinations were evaluated: Fall conventional tillage with broadcast fertilizer, fall strip-till with banded or broadcast fertilizer, and spring strip till with banded or broadcast fertilizer. In addition, three fertilizer rates (0, 180, 224 kg ha-1) and two seeding rates (296,500 and 346,000 seeds ha-1) were included as subfactors. Strip-till systems consistently established greater spring plant populations than conventional tillage. However, treatments differences in biomass accumulation that emerged at the R2 growth stage (full bloom) converged by the R6 growth stage (full seed), reflecting soybean phenotypic plasticity. Seed yield was not significantly affected by tillage system, fertilizer placement, or seeding rate as main effects. Nonetheless, a fertilizer yield response was observed at BRS, where baseline soil phosphorus was comparatively lower. Seed protein, oil, amino acid, and fatty acid composition were stable across management treatments and primarily influenced by environmental and varietal factors. The Critical Amino Acid Value remained consistently near 0.147 across all site-years. Economic analysis using both historical and USDA ERS projected price scenarios showed that conventional tillage generated a significantly higher net partial return at BRS, while all tillage systems were economically equivalent at NERF. These results demonstrate that strip-till is a viable, yield-neutral alternative to conventional tillage for soybean production in eastern South Dakota, with strong economic competitiveness on fields where early-season soil conditions do not create a yield disadvantage for conservation systems.

Publisher

South Dakota State University

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Rights Statement

In Copyright