SOIL SOLUTION CHEMISTRY - EFFECTS OF BULKING SOIL SAMPLES

Bulking of soil samples is commonly used to obtain a spatially average d measure of soil properties. This study investigated whether bulking can affect the chemistry of soil solution extracted by the centrifuge drainage technique. The short-range variation within a 1-m-wide pit fa ce was also investigated. Systematic differences were found between th e chemistry of soil solutions taken from bulked and unbulked soil samp les. The soil samples studied were taken on several occasions from the upper and lower part of a Bs horizon. Samples of soil solution extrac ted from replicate bulked soil samples contained significantly (P less than or equal to 0.05) larger amounts of Si, Na, Mg, and K as well as significantly (P less than or equal to 0.05) smaller amounts of Al an d Fe than soil solution from unbulked samples. Bulking reduced the var iation in all solutes measured, although a variation remained in repli cates from the bulked sample. The variation between individual core sa mples taken just a few tens of centimeters apart can be considerable, although the magnitude of variation differs depending on the solute st udied. The results suggest that unbulked soil samples may be preferabl e, especially when Al or Fe chemistry is studied and a centrifuge drai nage technique is used.