Influence of biosolids on phosphorus sorption characteristics of a Vertisol in comparison with manures and fertilizer

Abstract

Regulation of manure application in Manitoba has raised the question of whether or not biosolids application should be regulated in the same way. This study examined the effects of biosolids (BIO) applications on P sorption characteristics of a Vertisol in comparison with dairy cattle (DAIRY) and hog (HOG) manures, and monoammonium phosphate (MAP) fertilizer using the classical sorption isotherm and single point sorption index. Pertinent chemical properties and degree of P saturation (DPS) were also determined. The sorption maximum (Smax) in the control was reduced from 655 mg kg-1, to a range of 536–655 mg kg-1 with BIO, 559–650 mg kg-1 with MAP, 402–568 mg kg-1 with DAIRY, and 350–587 mg kg-1 with HOG depending upon the rate of P added. The lower DPS in the soil amended with BIO suggests a lower risk of P loss with biosolids compared with manures. The higher P sorption capacity of biosolids-amended soils compared with soils amended with manures suggest that Ca added with BIO increased the number of P sorption sites by a similar proportion to the amount of P added. Key words: Biosolids, P sorption isotherm, degree of P saturation, labile P, non-labile P