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Wheat Response to Sodium Uptake under Zonal Saline-Sodic Conditions¹

ABSTRACT

Plants growing in saline-sodic soils are usually subjected to the zonal distribution of salts. The ability of a root system to tolerate high levels of soluble salts and in particular high levels of Na⁺ is partially due to the compensatory uptake of water and ions in the more favorable regions, thus leading to an improved water and nutrient status of the plant. The objective of this investigation was to determine the uptake of Na⁺ under zonal saline-sodic conditions and to determine what impact Na⁺ accumulation had on the overall water, nutrient and growth status of the plants. The experiment was conducted in lysimeters packed with four soil types, with wheat as the test crop. Electrical generating plant blowdown water (EC 6.9 dS/m) was used as the irrigation source on the treated lysimeters. A 10% leaching fraction was imposed on all lysimeters. Sodium-22 was applied to each of the salinized lysimeters at different times to establish different ²²Na positions with depth. Plant and soil samples and soil solution extracts were taken during the experiment and analyzed for Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^-, and ²²Na. Electrical conductivity was also measured on soil and extracted soil water samples. Fresh to dry weight ratios of the plant and yield estimates were also obtained. An excellent correlation was found between the depth weighted EC_SE/ and the cumulative evapotranspiration. Incorporating the fractional water uptake (W_J) with the EC_SE/ values with depth improved the correlation between EC_SE/ and the cumulative evapotranspiration. Plants that had higher dry matter production and evapotranspiration rates also had higher Na⁺ accumulation. This we believe was manifested by a positive response to more favorable EC_SE/ regions where Na⁺ was effectively used in osmoregulation. Sodium-22 results indicated that the regions closest to the surface were the most active in terms of Na⁺ uptake. Finally, as the evapotranspiration rate decreased so did the yield and this was directly linked to soil type. Yield estimates as high as 7.5 Mg ha^–1 were obtained on the soils with the higher CEC and water holding capacities.

¹ Contribution from Dep. of Soil & Environmental Sciences, Univ. of California, Riverside, CA 92521.

² Staff Research Associate, Assistant Professor of Soil Science, Professor of Soil Physics, Director of Laboratory of Biomedical and Environmental Sciences, UCLA, and Professor of Soil Physics, respectively.

Received for publication May 23, 1983. Accepted for publication September 9, 1983.