Determinants of Total and Available Phosphorus in Missouri Ozark Highland Forest Soils.

Phosphorus is important factor limiting forest growth in many parts of world, and the amount and availability of soil P declines over time with weathering. Soil phosphorus (P) pools are affected by several factors including geomorphic properties (e.g., slope position and parent materials) and chemical and physical properties (e.g., pH, organic carbon content, mineralogy, and clay content). The objective of this study was to identify the importance of geomorphic and soil properties on total and available P concentrations in forested soils of the Missouri Ozark Highlands. Archived soil samples and soil characterization data used in this work were obtained from fifty pedons sampled at the Missouri Ozark Forest Ecosystem Project (MOFEP) located in south-central Missouri. Additionally, soil chemical analyses were conducted to measure total P, available P, and citrate bicarbonate dithionite (CBD) extractable Fe, Al, and Mn in the samples studied. Linear regression and classification and regression tree (CART) analyses were applied to elucidate relationships between P pools and geomorphic and soil chemical properties. Total P and available P in the soils studied ranged from 15.55 to 410.13 mg kg^-1 and 3.81 to 30.61 mg kg^-1, respectively. Linear regression analyses indicated a moderate correlation of CBD extractable Mn with total P (r² = 0.77), Bray-1 available P (r² = 0.69), and Mehlich-3 available P (r² = 0.71) for soils overlying Eminence bedrock. The CART analysis identified (1) CBD extractable Mn and total organic C as important variables explaining 39 % of the cumulative variation in total P; (2) CBD extractable Mn and exchangeable Ca as important variables explaining 49% of the cumulative variation of Bray-1 available P; and (3) CBD extractable Mn and pH as important variables explaining 55 % of the cumulative variation of Mehlich-3 available P. This research aids in understanding and identifying locations in Missouri Ozark forests where of P pools may be relatively small, thus necessitating careful management and monitoring before and after timber harvest.