SEASONAL-VARIATION OF CHEMICAL-PROPERTIES OF RICE FIELD SOILS FROM VALENCIA, SPAIN

Chemical characteristics of the ricefields from Valencia (Spain) were analyzed to improve the understanding of this complex agro-ecosystem. Soil characteristics showed a high pattern of variability. The chemica l variables were associated by means of principal components analysis in four components, explaining more than 83% of the total variability. Component I explained 32% of variability and included mainly K and co nductivity. Sodium, P and organic C were associated in component II, e xplaining around 20% of variance. Component III mostly included Ca con tent. Nitrogen concentration was the major descriptor of component IV, explaining 13% of the total variability. Seasonal variation of main s oil chemical characteristics were studied in some representative sampl ing sites. Conductivity increased at the end of the crop (October) whe n soil was dry. Available P content was highly variable amongst locati ons and sampling events, peaking at different moments during the crop. This maybe explained by the different fertilizer application protocol e used by land owners. Soil Ca concentration variation followed simila r geographical distribution patterns than those previously found for f looding water. Nitrogen content remained at high levels during the cro p period, leaching the maximum values at the end. The different source s of flooding water and the fertilization habits can be responsible, i n some extent, for the soil chemical characteristics. variability. Thi s could influence notably the biology of this agro-ecosystem