THE STABLE ISOTOPE CHEMISTRY OF A NATIVE AND IRRIGATED TYPIC NATRARGID IN THE SAN-JOAQUIN VALLEY OF CALIFORNIA

The stable C and O isotope chemistry of native and irrigated Typic Natrargids was examined in order to determine the relationship between the climate and vegetation and the delta **1**3C and delta **1**8O of the native pedogenic carbonates (CaCO//3) and the effect of irrigation on the CaCO//3 in the cultivated soils. Based on the differences in the delta **1**8O of the CaCO//3 in the irrigated and native soils, it was semiquantitatively estimated that between 10 to 40% of the carbonate in the irrigated soils was newly formed or had dissolved and reprecipitated as a result of irrigation, increased biological activity, and the application of chemical amendments.