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An Application of the Maas-Hoffman Salinity Response Model for Boron Toxicity¹

ABSTRACT

The Maas-Hoffman model for salinity tolerance was tested for boron toxicity (reduction in yields only) using wheat (Triticum aestivum L., var. Inia 66R), barley (Hordeum vulgare L., var. Briggs), and sorghum (Sorghum bicolor L., var. Dekalb C42A) as test crops. These crops were grown to maturity in sand cultures containing low to excessive concentrations of boron. The leaf immediately below the Y-leaf was collected at the early spike emergence stage and analyzed for boron. At harvest, the individual grain heads were collected, dried and weighed. Relative grain and shoot yields (Y, %) were related to the boron concentration of the nutrient solution (X, mg B L^–1) using the following equation Y = 100 – m(X – A), where m is the decrease in yield per unit increase in soluble boron above the threshold concentration, and A, the maximum concentration not restricting yield (the threshold). The SALT computer program (van Genuchten, 1983) was used to derive the slope and threshold parameters. The respective threshold concentrations for the grain yields of wheat, barley, and sorghum were found to be 0.3, 3.4, and 7.4 mg B L^–1, respectively, which categorized these crops as being sensitive, moderately tolerant, and very tolerant to boron. The relationship between relative yield and leaf boron was linear for wheat whereas barley and sorghum followed the Maas-Hoffman model. The threshold leaf B values with reference to grain yield were found to be 55, 768, 171 mg B kg^–1, respectively, for wheat, barley, and sorghum. The study indicates that yield under the influence of soluble boron may be fitted to the Maas-Hoffman model for salt tolerance.

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

² Professor of Soil Science, Staff Research Associate, respectively, Dep. of Soil & Environmental Science, Univ. of California, Riverside; Soil Scientist, U.S. Salinity Laboratory, Riverside, CA; and Soil Scientist, Inst. of Soils & Water, ARO, The Volcani Center, Bet Dagan, Israel.

Received for publication August 20, 1984. Accepted for publication October 26, 1984.