Salination of organic soils in the sacramento-San Joaquin Delta of California

Abstract

The Delta is an important agricultural area containing organic soils that are threatened by salinity. To aid in water allocation and management decisions, the maximum salinity level in irrigation water that preserves agricultural production was estimated from data gathered in a field trial to establish the salt tolerance of corn. All of the physical properties measured indicated that the soil under study was typical of organic soils in the Delta and elsewhere. Differences in soil sample preparation were shown to influence salinity measurements from the subsoil. Samples brought to saturation without either grinding or drying gave electrical conductivity measurements in agreement with those for soil water extracted by suction cups. Above average rainfall and water table control during the winter effectively leached the upper soil profile. The ratio between the average electrical conductivity of the soil water in the root zone ( $$\overline {EC}$$ sw ) and the salinity of the irrigation water (EC i) was found to be a function of EC i and not constant. Under present conditions of low EC i (0.2 to 0.8 dS/m) and with normal winter rainfall $$\overline {EC}$$ sw /EC i is about 8. As EC i increases, however, the ratio decreases. At the soil water salinity threshold for corn grain (3.7 dS/m), the average ratio is 1.7 which results in a maximum value of 2.2 dS/m for EC i without yield loss under normal conditions. With subirrigation and below normal rainfall, as in 1981, the maximum value of EC i would be 0.8 dS/m.