Download soil series, for soil fertility survey. Laboratory analyses of

Boletin Nº20
ISSN 0716-6192
soil series, for soil fertility survey. Laboratory analyses of these studies were
performed, but none presented pyrophosphate-extractable Al. CIREN studies
presented oxalate-extractable Al and Rodriguez’s data, Al determined by ammonium
acetate 1 N to pH 4.8 (Al-NH4OAc). Acid ammonium acetate is not as such strong as
acid oxalate solution, but stronger than KCl unbuffered salt, and it may dissolve
soluble forms of exchangeable sites (Mclean, 1965). Preliminary test showed that
soil C concentration (g kg-1) and oxalate-extractable Al from CIREN’s database were
poorly correlated (R2 = 0.11) and the opposite was true for Al-NH4OAc (R2 = 0.55).
Therefore, Rodriguez’s database was considered. Soils series from each pedon was
classified according to CIREN’s studies. Other properties were selected such as
organic C by Walkley-Black and clay concentration. Clay content determination was
performed by Boyouco’s method, but soil samples were previously treated with H2O2
and then dispersed (Gee and Bauder, 1986). It is widely recognized that clay is not
easily dispersed in Allophanic soils (Shoji et al 1993). We also questions weather
our clay content data were reliable. Clay concentration of allophanic soils were
plotted against the amount of amorphous minerals: Allophane, Imogilite and
ferrihydrite, measured by thermal and X ray spectroscopy (Besoain and Sepúlveda,
1985) in the same modal pedons (Andisols) described by Rodríguez (1993) (Fig. 1).
Clay content was always greater that allophane (most amorphous materials). We
confirm that clay had been effectively dispersed. Data from Rodriguez (1993) were
completed for dry bulk density by clod method and silt content by pipette method,
obtained from CIREN’s database. Mean annual temperature for the site associated to
each pedon was taken from Tosso (1985). Mean annual precipitation was obtained
from DGA (Dirección General de Aguas, unpublished data, 2004). Whether stations
were spatially located in a latitude and longitude coordinates. Mean annual
precipitation were obtained by overlaying whether stations location onto 15 by 15
km grid cell soil series layer in a GIS map 1:250.000 (Homman et al.,1995).
Precipitation to each pedon was based on the 1969 to 1999 data from 20 whether
stations within a grid cell and soil series map.
Conversion of Soil Properties
306
Simposio. Residuos Orgánicos y su uso en Sistemas Agroforestales