Document Type

Thesis - Open Access

Award Date

2012

Degree Name

Master of Science (MS)

Department / School

Agricultural and Biosystems Engineering

First Advisor

Sushant Mehan

Abstract

Phosphorus (P) availability is influenced by soil properties and depth, creating challenges for nutrient management across agricultural landscapes. This study evaluated two complementary approaches for quantifying P availability and adsorption dynamics in eastern South Dakota soils: Diffusive Gradients in Thin Films (DGT) and P quantity–intensity (Q–I) relationships. The objectives were to (1) quantify bioavailable P using DGT, (2) compare DGT measurements with established soil test P (STP), (3) evaluate Q–I parameters describing P adsorption characteristics, and (4) assess spatial variability in P availability across eastern South Dakota soils. DGT-measured P increased with STP levels and was strongly correlated with Bray-1, Olsen, and Mehlich-3 extractable P. Although considerable site-specific variability occurred, depth-related differences were limited, indicating that soil properties and management factors have a greater influence on DGT-measured P than vertical stratification. These results highlight the need for further research on how fertilization and management practices affect DGT responses and how DGT reflects crop uptake across diverse soils. P adsorption characteristics were evaluated using adsorption isotherms. The Langmuir, Freundlich, and Temkin isotherms were applied to characterize P sorption behavior. The Langmuir model was used to estimate maximum adsorption capacity (Qmax) and binding strength (K). The Freundlich model describes adsorption relative to solution concentration (Kf) and the exponent (n), reflects the nonlinearity of the sorption relationship. The Temkin model was used to evaluate bonding energy (b) and buffering capacity. Qmax values ranged from 190 to 496 mg kg⁻¹ P, with the greatest adsorption capacities in the northeastern South Dakota and decreasing values toward the south. Conversely, K exhibited an inverse spatial pattern. Freundlich and Temkin parameters displayed less consistent regional patterns but highlighted substantial variability in soil sorption behavior. These findings underscore the importance of site-specific P management across the study area. Overall, soils in the region differ substantially in P Qmax, K, and buffering capacity. Continued research across additional soil types and management systems will improve recommendations for P application, environmental protection, and agricultural profitability. Integrating DGT measurements with Q–I analysis provides a promising framework for enhancing P assessment and optimizing nutrient management in heterogeneous agricultural soils.

Publisher

South Dakota State University

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Rights Statement

In Copyright