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CROP ECOLOGY, MANAGEMENT & QUALITY

Root-Zone Salinity

I. Selecting a Product–Yield Index and Response Function for Crop Tolerance

^a Semiarid Prairie Agricultural Research Centre, Agriculture and Agri-Food Canada, Box 1030, Swift Current, SK, Canada S9H 3X2
^b Soil Physics/Pesticide Unit, George E. Brown, Jr. Salinity Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Riverside, CA
^c Plant Sciences Group, George E. Brown, Jr. Salinity Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Riverside, CA

^* Corresponding author (SteppuhnH{at}agr.gc.ca).

Six empirical functions were compared for describing the product yields of agricultural crops grown while subject to increasing levels of root-zone salinity. The four nonlinear functions fit the test data from a spring wheat (Triticum aestivum L. , cv. Biggar) experiment conducted in Canada's Salt Tolerance Testing Facility closer than the two linear functions. Although each of the four nonlinear declining functions could reasonably describe the data, the modified compound-discount equation recorded the lowest root mean square error and the highest R² value. Additional response data using the nonlinear discount function obtained from 33 separate trials averaged 11% closer in statistical fit and 45% lower in statistical error than the best linear function. The discount function {Y_r = 1/(1 + [(C/C₅₀)^exp(sC50)]} follows a sigmoidal form and relates relative yield (Y_r) to a measure of root-zone salinity (C) such as the solute concentration with an electrical conductivity of an equivalent saturated soil paste extract (EC_e). This function features two parameters, the salinity level producing 50% of the nonsaline crop yield (C₅₀) and the absolute value of the general decline in relative yield with salinity at and near C₅₀, the steepness constant (s). These parameters combine to form a single-value, salinity-tolerance index (ST-Index) consisting of the 50% reduction in crop yield (C₅₀) plus the tendency to maintain some product yield as the crop is subjected to increasing salinity levels approaching C₅₀, i.e., ST-Index = C₅₀ + s(C₅₀). The ST-Index for the Biggar wheat registered 6.44. Approximations for C₅₀ and s can be derived from the threshold salinity (C_t) and declining slope (b) parameters of the threshold-slope linear response function [Y_r = 1 – b(C – C_t)]. Procedures for converting C_t to C₅₀ and b to s offer linkages between these linear and nonlinear response function parameters, and are further explored in this paper's companion. The resulting ST-Index-values equal 6.56, 9.43, and 5.67 for sample field (corn, Zea mays L.), forage (alfalfa, Medicago sativa L. and falcata L.), and vegetable (radish, Raphanus sativus L.) crops, respectively.

Abbreviations: EC_e, electrical conductivity of saturated soil paste extract • EC_i, electrical conductivity of the irrigated water • EC_s, electrical conductivity of test solution • FAO, Food and Agriculture Organization, United Nations • ST-Index, salinity tolerance index

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THIS ISSUE IN CROP SCIENCE

Crop Science 2005 45: xi. [Full Text]  

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				R. Munns, R. A. James, and A. Lauchli Approaches to increasing the salt tolerance of wheat and other cereals J. Exp. Bot., March 1, 2006; 57(5): 1025 - 1043. [Abstract] [Full Text] [PDF]

				H. Steppuhn, M. Th. van Genuchten, and C. M. Grieve Root-Zone Salinity: II. Indices for Tolerance in Agricultural Crops Crop Sci., January 1, 2005; 45(1): 221 - 232. [Abstract] [Full Text] [PDF]