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ARS Home » Pacific West Area » Riverside, California » Research » Publications at this Location » Publication #157892
Title: ROOT-ZONE SALINITY: II. INDICES FOR TOLERANCE IN AGRICULTURAL CROPS

Author
item STEPPUHN, H - AGR AND AGRI-FOOD CANADA
item Van Genuchten, Martinus
item Grieve, Catherine

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2004
Publication Date: 1/20/2005
Citation: Steppuhn, H., Van Genuchten, M.T., Grieve, C.M. 2005. Root-zone salinity: II. Indices for tolerance in agricultural crops. Crop Science 45:221-232.

Interpretive Summary: Since 1977, crop tolerance lists have been based on a two-piece linear threshold-slope response model which approximates a more-precise modified discount (sigmoidal) function. Evaluations of direct, analytical, and empirical methods for converting the threshold-slope parameters to those of the discount function resulted in selected conversion procedures with errors of plus or minus 10 percent or less for eight test crops (rye, sorghum, wheat, Harding grass, ryegrass, alfalfa, carrot, and turnip). These selected procedures were used to provide lists of the inherent tolerances for root-zone salinity associated with agricultural crops based on the nonlinear Salinity Tolerance Index. Data of the type produced in this paper (i.e., information describing the ability of crops to tolerate salinity and still produce a measurable agricultural product) are critical to optimal management of salt-affected lands.

Technical Abstract: In the companion paper to this study, Root-Zone Salinity: I. Selecting a Product-Yield Index and Response Function for Crop Tolerance, by Steppuhn, van Genuchten, and Grieve, submitted 2003), six relative crop yield functions were evaluated for describing the response of a spring-wheat (cv: Biggar) to increasing root-zone salinity. The experiment, conducted in Canada's Salt Tolerance Testing Facility, resulted in a declining sigmoid-shape response and was best represented by the modified compound-discount function (Yr=1/[1+(C/C50)exp(sC50)]) which demonstrated the lowest root mean square error. This nonlinear function relates relative yield (Yr) to root-zone salinity (C) measured in equivalent saturated soil-paste extract electrical conductivity with two nonlinear parameters, the salinity level producing 50 percent of the non-saline crop yield (C50) and a response curve steepness constant (s) equal to the absolute value of the mean dYr/dC from Yr=0.3 to 0.7. These discount parameters suggest existence of a single-value salinity tolerance index (STI) equal to the 50 percent reduction in crop yield from that of the non-saline yield plus a tendency to maintain some product yield as the crop is subjected to salinity levels approaching C50, i.e., STI=C50+s(C50). Approximations for C50 and s were identified the threshold salinity (Ct) and declining slope (b) parameters of the well-known threshold-slope linear response function. Several procedures for converting Ct to C50 and b to s offer the linkage between these linear and nonlinear response functions. From the procedures, two regression equations, C50=0.988[(0.5/b)+Ct]-0.252 and s=1.52b, proved the most appropriate for the eight representative field, forage, and vegetable crops tested. The selected conversion procedures were applied to previously published Ct and b values to obtain a list of the relative root-zone salinity tolerance in agricultural crops. In addition to C50 and s, values for p and the ST-Index were computed for each crop. The revised list provides extension personnel and plant growth modelers and parameter values from a nonlinear analog of crop yield response to root-zone salinity.