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Forms and lability of phosphorus in humic acid fractions of hord silt loam soil

He, Z., Olk, D.C., Cade-Menun, B.J. (2011). Forms and lability of phosphorus in humic acid fractions of hord silt loam soil, 75(5), 1712-1722. http://dx.doi.org/10.2136/sssaj2010.0355

Abstract

Phosphorus 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 (a fine-silty, mixed, superactive, mesic Cumulic Haplustoll) under continuous corn (Zea mays L.) receiving either inorganic fertilizer or animal manure. Solution 31P nuclear magnetic resonance 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 humicbound P. Fungal phytase released more humic-bound P, which may come from scyllo-inositol P. No additional P was released by including nuclease. Ultraviolet (UV) irradiation 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 hydrolysable P in CaHA fractions, which suggests that UV-labile P in CaHA fractions did not overlap wiThenzymatically 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 increasing our knowledge of P lability for more efficient crop uptake. © Soil Science Society of America.

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