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FOREST, RANGE & WILDLAND SOILS

Water Treatment Residuals and Biosolids Coapplications Affect Semiarid Rangeland Phosphorus Cycling

^a USDA-NRCS, 1502 Progress Ct, Wheatland, WY 82201
^b USDA-ARS Northwest Irrig. and Soils Res. Lab., 3793 North 3600 East, Kimberly, ID 83341
^c Dep. of Soil and Crop Sciences, Colorado State Univ., Fort Collins, CO 80523-1170
^d Dep. of Forest, Rangeland, and Watershed, Stewardship, Colorado State Univ., Fort Collins, CO 80523-1472

^* Corresponding author (jim.ippolito{at}ars.usda.gov).

Land coapplication of water treatment residuals (WTR) with biosolids has not been extensively researched, but the limited studies performed suggest that WTR sorb excess biosolids-borne P. To understand the long-term effects of a single coapplication and the short-term impacts of a repeated coapplication on soil P inorganic and organic transformations, 7.5- by 15-m plots with treatments of three different WTR rates with a single biosolids rate (5, 10, and 21 Mg WTR ha^–1 and 10 Mg biosolids ha^–1) surface coapplied once in 1991 or surface reapplied in 2002 were utilized. Soils from the 0- to 5-cm depth were collected in 2003 and 2004 and were sequentially fractionated for inorganic and organic P (P_o). Inorganic P fractionation determined (i) soluble and loosely bound, (ii) Al-bound, (iii) Fe-bound, (iv) occluded, and (v) Ca-bound P, while organic P fractionation determined (i) labile, (ii) biomass, (iii) moderately labile, (iv) fulvic acid, (v) humic acid, and (vi) nonlabile associated P_o. Pathway analysis showed that humic, fulvic, and nonlabile P_o did not play a role in P transformations. Biomass P_o and moderately labile P_o contributed to the transitory labile P_o pool. Labile P_o was a P source for Fe-bound and WTR-bound inorganic phases, with the Fe-bound phase transitory to the occluded P sink. The Al-bound phase additionally contributed to the occluded P sink. The Ca-bound phase weathered and released P to both the Fe-bound and WTR-bound P phases. Overall, the WTR fraction, even 13 yr after the initial application, acted as the major stable P sink.

Abbreviations: β, standardized pathway coefficients • P_o, organic phosphorus • WTR, water treatment residuals