Salinity Effects on Emergence, Vegetative Growth, and Seed Yield of Guar
Francois, L. E. | Donovan, T. J. | Maas, E. V.
Guar [Cyamopsis tetragonoloba (L.) Taub] seed is an important source of galactomannan gum used in food and industrial products. Increased demand and an insufficient domestic supply has led to an increased interest in this crop in the semi-arid western USA where many soils are, or have the potential to become, highly saline. This study was conducted to determine the effect of soil salinity on vegetative growth and seed yield of two cultivars, 'Kinman' and 'Esser,' grown under field conditions. Six salinity treatments were imposed on a Holtville silty clay [clayey over loamy, montmorillonitic (calcareous), hyperthermic Typic Torrifluvent] by irrigating with waters salinized with NaCl and CaCl₂ (1:1 by weight). Electrical conductivities of the irrigation waters were 1.3, 2.5, 5.0, 7.4,10.0, and 12.4 dS/m during the 1st yr, and 1.2, 2.5, 4.5, 5.5, 6.5, and 7.5 dS/m during the 2nd yr. Seed yield of both cultivars was unaffected by soil salinity up to 8.8 dS/m (mean electrical conductivity of the saturated-soil extracts in the rootzone). Each unit increase in salinity above 8.8 dS/m reduced seed yield by 17%, which places guar in the moderately tolerant category for seed production. Reduction in the number of pods per plant and weight per seed were the primary factors contributing to reduced yields. Vegetative growth was decreased 9.6% for each unit increase in salinity above 4.9 dS/m. Plant emergence was determined in greenhouse sand cultures with irrigation waters of 0.8, 4.4, 8.5,11.3,15.7, and 18.8 dS/m. Emergence was unaffected by salt levels up to 8.5 dS/m; greater levels delayed but did not significantly reduce the percent emerged. Contribution from the U.S. Salinity Laboratory, USDAARS, Riverside, CA
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