DEVELOPMENT OF A METHOD TO DETERMINE BIOAVAILABLE PHOSPHORUS LOSS IN AGRICULTURAL RUNOFF

The loss of bioavailable P (BAP) in agricultural runoff can accelerate the eutrophication of receiving water bodies. Although several algal assays and chemical extractions have been proposed to estimate BAP, pr ocedural and theoretical limitations have restricted their widespread use. This study evaluates the use of iron-oxide impregnated paper stri ps (Fe-oxide strips) to estimate the BAP content of runoff from 20 agr icultural watersheds in the Southern Plains during 1988-1990. In the p roposed method, BAP is determined by shaking 50 ml of unfiltered runof f with one Fe-oxide strip for 16 h. Phosphorus is removed from the str ip by 0.1 M H2SO4 and measured. The BAP content of runoff sediment was related (r2=0.92-0.95) to the growth of P-starved algae incubated for 29 days with runoff as the sole source of P. Acting as a P sink, the strips have a stronger theoretical basis than chemical extraction in e stimating BAP in agricultural runoff.