Cotton-producing soils in Louisiana average 23 mg kg(-1) arsenic (As)
due mainly to use of As-containing agrichemicals. Bioavailability of s
oil As could become an important management factor if As-tolerant cott
on is rotated with other more sensitive crops. The first step in model
ling As bioavailability and its uptake by plants is to characterize so
il supply of As. We sought to: i) determine the relationships among so
lution As, resin-exchangeable solid-phase As, and As addition, and ii)
examine soil properties that affect these relations. Four diverse sur
face soils were collected from the cotton-producing areas of the state
. Five rates of As from 0 to 200 mg kg(-1) were applied and the soils
allowed to equilibrate at 80% of ''field capacity'' water content for
30 days. Total initial As, As in displaced soil solution, and resin-ex
changeable solid-phase As were determined for each treatment. For all
soils, the concentration of solution As increased curvilinearly with A
s addition, conforming to the equation As-sol = ax(c)+d. Values of ''c
'' describing the curvilinearity ranged from 1.09 to 3.19. Curvilinear
ity was negatively related to both initial solution As and diethylenet
riaminepentaacetic acid (DTPA)-extractable manganese (Mn) (r(2) = 0.99
). DTPA-extractable Mn complexed As from the solution phase. The conce
ntration of resin-exchangeable solid-phase As increased at a decreasin
g rate with As addition. The relation was described by the equation As
-resp = mx(l)+n, where values for the curvilinearity, l, ranged from 0
.048 to 0.986. Concentrations approached a point where the adsorption
sites for this phase became saturated and any additional As remained i
n solution. These relationships provide valuable information for model
ling As uptake by plant roots.