Progress in determining nutrient availability in the rhizosphere is re
stricted by a lack of reliable and convenient methods for rhizosphere
soil-water collection. A modified centrifugation method with a fluoroc
arbon (Fluorinert(TM),FC-70) as an immiscible displacement liquid was
developed. Our objectives were to: i) obtain an adequate soil-water vo
lume from a small rhizosphere sample within a reasonable time; ii) col
lect rhizosphere soil-water at container capacity (approximate to 90%
of field capacity) to determine soluble soil ions; and iii) evaluate F
C-70 as an extractant. The soil used was a Beadle clay loam (fine, mon
tmorillonitic mesic Typic Argiustoll) with low and high levels of CaCO
3 (5 and 204g kg(-1)). Soil samples from the rhizosphere of 30-days-ol
d sordan (sorghum (Sorghum bicolor L.), sudangrass (Sorghum sudanese L
.) hybrid seedlings were thin-sectioned at 1-, 2- and 3-mm from the ro
ot surface. The extraction parameters (sample size, volume of extracta
nt, relative centrifugal force and centrifugation time) were varied to
determine optimal values. We obtained adequate amounts of aqueous sol
utions from moist soil (approximate to 6 g) when mixed with 2 mt of FC
-70, packed into a filter unit, and centrifuged for 1 hour at 14,500 x
g. The displaced soil-water was analyzed by inductively coupled plasm
a spectrometry. The modified centrifugation technique with FC-70 offer
s a reliable, rapid, safe, and contamination-free method for obtaining
unaltered soil-water from the rhizosphere, at a moisture content norm
ally found in soil.