『Abstract
Bioavailable P (BAP) in agricultural runoff represents P potentially
available for algal uptake and consists of soluble P (SP) and
a variable portion of particulate P (PP). Evaluation of the impact
of agricultural management on BAP in runoff will aid assessment
of the resultant biological productivity of receiving water bodies.
Soluble P, PP, and bioavailable PP (BPP) (estimated by NaOH extraction)
were determined over a 5-yr period in runoff from 20 unfertilized
and fertilized, grassed, and cropped watersheds in the Southern
Plains. Soluble P, BPP, and BAP loss in runoff was reduced by
practices minimizing erosion and runoff, with respective mean
annual amounts ranging from 237 to 122, 1559 to 54, and 1796 to
176 g P ha-1 yr-1 (for peanut-sorghum [
Atachis hypogaea L.-Sorghum bicolor (L.) Moench]
and native grass watersheds, respectively). However, as vegetative
cover improved, BAP (SP plus BPP) comprised a larger portion of
total P (TP) loss (29％ for peanut-sorghum and 88％ for native grass).
This results from an increasing contribution to BAP of SP (13％
for peanut-sorghum and 69％ for native grass watersheds) and BPP
to PP (26％ for peanut-sorghum and 69％ for native grass watersheds).
Clearly, P bioavailability is a dynamic function of physiochemical
processes controlling erosion, particle size enrichment, P desorption-dissolution
reactions, and plant residue breakdown, in addition to soil and
fertilizer P management. Hence, the change in trophic state of
a water body may not be adequately reflected by TP inputs only.
To more reliably evaluate the biological response of a water body
to agricultural P inputs, particularly from conservation tillage
practices, it may be necessary to determine BAP in runoff.』
Abbreviations
(Introduction)
Materials and methods
Watersheds
Laboratory analysis
Results and discussion
Concentrations and amounts
Relative bioavailability
Conclusions
References
※SPとTP〔塩酸温浸はOlsen and Sommers（1982）〕による）は、Murphy and Riley（1962）の方法による。生物が利用可能なPは、NaOHを用いたSharpley et al.（1991）による。