Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2011
Publication Date: 9/12/2011
Citation: He, Z., Olk, D.C., Cade-Menun, B.J. 2011. Forms and lability of phosphorus in humic acid fractions of hord silt loam soil. Soil Science Society of America Journal. 75:1712-1722. Interpretive Summary: Phosphorus (P) has long been known to be present in soil organic matter, but little is known about the different P forms in organic matter, or their availability. In this work, we evaluated the P forms present in different components of organic matter from a Hord silt loam soil from Nebraska. Our data indicated that P in soil organic matter was present in multiple forms with different availabilities. This research has the potential to improve P management by incorporating our knowledge of these different availabilities for plant uptake.
Technical Abstract: Phosphorus (P) has long been known to be present in soil humic fractions, but little is known about specific P forms in humic fractions, or their lability. We extracted the mobile humic acid (MHA) and recalcitrant calcium humate (CaHA) fractions from a Nebraska Hord silt loam soil under continuous corn (Zea mays L.) receiving either inorganic fertilizer or animal manure. Solution 31P NMR spectroscopy demonstrated that P in both MHA and CaHA was predominantly present in organic forms, mostly as orthophosphate monoesters. Spiking experiments indicated no phytate present in these humic fractions, but scyllo-inositol P was identified in all samples. Potato phosphatase hydrolyzed some humic-bound P. Fungal phytase released more humic bound P, which may come from scyllo-inositol P. No additional P was released by including nuclease. Irradiation with UV increased soluble inorganic P in MHA fractions, but total hydrolyzable P in MHA fractions did not increase, suggesting that the portion of P that was UV-labile was also enzymatically hydrolyzable. In contrast, UV irradiation increased soluble inorganic P and total hydrolyzable P in CaHA fractions, which suggests that UV-labile P in CaHA fractions did not overlap with enzymatically hydrolyzable P. Fertilization management did not significantly alter the lability of humic P in these humic fractions. This research has the potential to improve P management by incorporating our knowledge of P lability for more efficient crop uptake.