Determinants of total and available phosphorus in forested Alfisols and Ultisols of the Ozark Highlands, USA

- Identifying factors related to soil P forms is critical for sustainable forestry.
- CART analysis helped identify environmental and soil properties affecting soil P.
- CART models explained 71 and 65% of Mehlich-3 P and Bray-1 P variability.
- Extractable Mn was the most important explanatory variable in all CART models.
- Findings are applicable for identifying forest soils susceptible to P depletion.

Phosphorus is an important nutrient limiting forest growth in many parts of world, and soil P forms and concentrations may be associated with a host of soil and environmental attributes in a complex soil landscape. The objective of this study was to identify key environmental and soil properties influencing total and available soil P concentrations in a mixed oak (Quercus L.)-hickory (Carya Nutt.) forest ecosystem. Soil samples and soil characterization data were obtained from fifty pedons sampled at the Missouri Ozark Forest Ecosystem Project (MOFEP) located in south-central Missouri, USA. Additional soil chemical analyses were conducted to measure total P, available P (Mehlich-3 P and Bray-1 P), and citrate bicarbonate dithionite (CBD) extractable Fe, Al, and Mn content. Classification and regression tree (CART) analysis was applied to explain relationships between P concentrations and environmental and soil properties. Total P concentration in the soils studied ranged from 15.6 to 410 mg kg− 1 and the range of available P concentration was 0.29 to 30.6 mg kg− 1. The CART analysis identified variables, primarily soil attributes, explaining 48, 71, and 65% of the variability associated with total P, Mehlich-3 P, and Bray-1 P concentrations, respectively. Extractable Mn was the most important explanatory variable in all CART models (explaining 28-33% of soil P variation). The CART analysis provided a concise framework for coupling soil and environmental variables to understand and identify locations within a complex soil landscape that may be susceptible for nutrient depletion. Furthermore, findings of this research highlight a need to more thoroughly evaluate relationships between Mn and P forms and concentrations in soil.