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 chemical 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 conductivity. Sodium, P and organic C were associated in component II, explaining around 20% of variance. Component III mostly included Ca content. Nitrogen concentration was the major descriptor of component IV, explaining 13% of the total variability. Seasonal variation of main soil chemical characteristics were studied in some representative sampling sites. Conductivity increased at the end of the crop (October) when soil was dry. Available P content was highly variable amongst locations and sampling events, peaking at different moments during the crop. This maybe explained by the different fertilizer application protocole used by land owners. Soil Ca concentration variation followed similar geographical distribution patterns than those previously found for flooding water. Nitrogen content remained at high levels during the crop period, leaching the maximum values at the end. The different sources of flooding water and the fertilization habits can be responsible, in some extent, for the soil chemical characteristics. variability. This could influence notably the biology of this agro-ecosystem