Predicting phosphorus retention in two Haplohumult forest soils of northern California

Graduation Date

2015

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Natural Resources: Forest, Watershed and Wildland Sciences, 2015

Committee Chair Name

Susan Edinger Marshall

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Andic soil properties, Phosphorus retention, Humboldt State University -- Theses -- Natural Resources, Forest soils, Phosphorus, Volcanic soils

Abstract

Plant available phosphorus (P) occurs in anionic forms which become unavailable (retained) when iron and aluminum oxides form insoluble phosphate complexes. P-retention is especially likely to occur under acid conditions in soils containing short range order (SRO; poorly crystalline) materials, namely allophane and imogolite. This set of characteristics is common in volcanic-derived forest soils in Pacific Northwest timber regions. P-retention was investigated in Powellton (Fine-loamy, parasesquic, mesic Andic Haplohumults) and Aiken (Fine, parasesquic, mesic Xeric Haplohumults) soil series from Feather Falls and Whitmore "Garden of Eden" sites, respectively. Some soils received heavy fertilization over multiple years; another set of unfertilized soils were compared as a control. Results show that pHNaF (indicator of SRO materials), soil carbon, and New Zealand P-retention decreased with soil depth in both soils. In near-surface horizons, Feather Falls soil had higher pHNaF, carbon content, and P-retention than the Whitmore soil. Unexpected high P-retention at Feather Falls is probably due to the presence of P-fixing organo-metal complexes in Feather Falls surface horizons. TheWhitmore soil shows higher pHNaF and P-retention than Feather Falls in deep horizons. At Whitmore, the drop in P-retention with depth is attributed to decreasing SRO minerals deeper in the profile; at Feather Falls, a simultaneous drop in carbon and SRO minerals contributes to the pattern of P-retention with depth. Fertilized surface soils at Feather Falls showed ten percent less P-retention than unfertilized soils at that site. Fertilization did not affect P-retention at Whitmore. pHNaF was the single best predictor of P-retention, with other important factors including depth, soil carbon, and soil "redness" (a quantitative measure representing iron content) in a mixed-effects regression of P-retention for these soils.

https://scholarworks.calstate.edu/concern/theses/ff3657454

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