Root-zone salinity: II. Indices for tolerance in agricultural crops

Crop Science (Impact Factor: 1.48). 10/2005; 45:221-232.
Source: OAI

ABSTRACT This paper provides the tools for distinguishing levels of tolerance to root-zone salinity in agricultural crops. Such distinction rests on the response of a crop's product yield following the declining, sigmoid-shaped, modified compound-discount function (Y(r) = 1/1 + (C/C50)exp(sC50)) for plants grown as crops exposed to increasing root-zone salinity. This nonlinear function relates relative yield (Y(r)) to root-zone salinity (C) measured in equivalent saturated soil-paste extract electrical conductivity with two nonlinear parameters, the salinity level producing 50% of the nonsaline crop yield (C50) and a response curve steepness constant (s) equal to the absolute value of the mean dY(r)/dC from Y(r) = 0.3 to 0.7. These discount parameters suggest the existence of a single-value salinity tolerance index (ST-Index) equal to the 50% reduction in crop yield from that of the nonsaline yield plus a tendency to maintain some product yield as the crop is subjected to salinity levels approaching C50, i.e., ST-Index = C50 + s(C50). The explicit purpose of this study is to determine if the discount function using biophysically relevant parameters can be applied to historical data sets. Approximations for C50 and s were identified in the threshold salinity (C(t)) and declining slope (b) parameters of the well-known threshold-slope linear response function. Several procedures for converting C(t) to C50 and b to s offer the linkage between these linear and nonlinear response functions. From these procedures, two regression equations, C50 = 0.988(0.5/b) + C(t) - 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 C(t) 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 exp(sC50) and the ST-Index were computed for each crop. The revised list provides extension personnel and plant growth modelers the parameter values from a nonlinear analog of crop yield response to root-zone salinity.

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Available from: Martinus Th. Van Genuchten, Aug 10, 2015
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    • "nerally classified according to the U . S . Salinity Laboratory ( Richards , 1954 ) as medium ( C 2 ) to high ( C 3 ) salinity and of low sodification ( S 1 ) risk present a soil salinization hazard and may cause significant reduction in yield for a large number of crops , especially vegetables and fruits ( Ayers and Westcot , 1985 ; Mass , 1990 ; Steppuhn et al . , 2005 ) . Salinization by irrigation water is a process whereby soluble salts from the irrigation water accumulate in the soil due to inadequate leaching , high water tables and / or high evaporation rates . Soil salinity affects plants directly through osmotic effects , which limit the ability of the plants to absorb water from the soil solu"
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    • "Steepness was 0.0105 and salt index 39.21 for relative PDW. Steppuhn et al., (2005) reported values, 0.055 and 21.5, for steepness and salt index of Kochia based on stem dry weight and EC of saturated soil, respectively. These data show that Kochia is much more salt tolerant than other conventional salt tolerant crops. "
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