VARIABILITY OF SOIL SOLUTION IONS IN FALLOWLAND FIELDS IN CENTRAL SPAIN

R. ROMÁN, R. CABALLERO, A. BUSTOS

Centro de Ciencias Medioambientales. CSIC. Finca Experimental La Poveda. Ctra.
Campo Real km 1.300. 28500 Arganda del Rey, Madrid, Spain. rromán@iai.csic

**Abstract**

Variability of soil solution properties must be assessed for proper
monitoring of many soil processes. Two sampling frames were established in
uncultivated agricultural fields. In the first (300 m2), 15 single plots were
instrumented with porous ceramic cups placed at 0.4 m soil depth. In the second
(2500 m2), 50 single plots were instrumented. Results showed that the coefficient
of variation (CV) of soil solution properties ranged from 30 % for electrical
conductivity (EC) to more than 100 % for Cl- and that a minimum of 40 individual
samples were required to estimate representative values of spatial variability
of soil solution ions for this field (CVs). The coefficient of variation linked
to sample size (CVn) was expressed as a function of CVs of each soil solution
property, and sample size. The error curve model of soil solution properties
shows that, for a stated precision [Standard error (SE) of ± 5%], the
number of samples required was lower than that estimated by standard methods.

**Keywords:** Soil solution, variability composition, statístical, fallowlands
fields