Mlv. Fernandes et al., Soil properties affecting phosphorus extraction from portuguese soils by conventional and innovative methods, COMM SOIL S, 30(7-8), 1999, pp. 921-936
The conventional Bray 1, Egner-Riehm, Olsen, and the innovative cation/ ani
on exchange resin membranes (CAERM) and iron oxide-impregnated filter paper
strips (Pi) procedures were compared as phosphorus (P) extractants from 73
representative Portuguese soils. The soils were characterized by wide vari
ability of their pedological, physical, and chemical properties. Eleven FAO
-UNESCO soil units, with prevailing Anthrosol, Calcisol, Cambisol, Fluvisol
, Leptosol, Luvisol, and 10 different textural classes, with prevailing loa
my sand, sandy loam, loam, silty loam, clay loam, silty clay loam, were rec
ognized. The soils showed the following properties: CaCO3 0.0-50.9 g 100 g(
-1), organic matter 0.4-8.4 g 100 g(-1), pH-CaCl2 3.9 to 7.9, cation exchan
ge capacity 1.5-57.6 cmol(c) kg(-1). Soil-P (mg kg(-1)) ranges were: 0.2-18
5.9 for Bray 1, 0.6-307.7 for Egner-Riehm, 1.0-100.5 for Olsen, 1.1-69.4 fo
r Pi, and 0.4-48.8 for CAERM. The P extraction efficiency decreased along w
ith the order Bray 1 > Egner-Riehm > Olsen > Pi > CAERM, with mean values o
f 39.7, 34.6, 20.5, 19.0, and 14.8 mg P kg(-1) soil, respectively. All meth
ods, with the relevant exception of Egner-Riehm, were almost uniformly affe
cted by the considered pedological, chemical and physical features of soils
, and well correlated each other. The following conversion equations, by si
mple linear regressions, were calculated: Olsen-P=4.118+1-0.412*Bray 1-P, R
-2=0.737; Olsen-P=-1.300+1.144*Pi-P, R-2=0.677; Olsen-P-0.760+1.330* CAERM-
P, R-2=0.559; Bray 1-P=-3.064+2.249*Pi-P, R-2=0.602; Bray 1-P=-0.630 0+2.72
2*CAERM-P, R-2=0.538; Pi-P=3.417+1.053*CAERM-P, R2=0.677. After performing
multiple regressions including the CEC as accessory variable, we obtained s
ignificant equations only for the conversions between Egner-Riehm-P and Pi-
P or CAERM-P values, as it follows: Egner-Riehm-P=-24.600+1.630*Pi-P+1.928*
CEC, adj. R-2=0.587; Egner-Riehm-P=-23.303+2.183 *CAERM-P+1.747*CEC, adj. R
-2=0.606. Thus, the innovative Pi-strips and the cation/anion exchange resi
n membranes procedures could represent suitable tools for the assessment of
soil-P status and for P fertilizer recommendations. As the future research
step, we will verify the reliability of the contrasted soil-P tests in pre
dicting plant P uptake and yield response.