Linear crop response functions to soil salinity with a threshold salinity level

The response function of a crop yield to soil salinity level is essential in decision‐making in regard to irrigation with saline water. A switching regression approach to estimate the piecewise linear response function with critical threshold level is presented, and the asymptotical stochastic properties of the estimates are described. The empirical estimates, based on grapefruit yield data, are compared with those of a recent published study by Maas and Hoffman (1977) and the statistical significance of the differences is discussed. Finally, the threshold hypothesis is tested empirically against some alternative formulations. It turns out that the ‘threshold hypothesis’ is confirmed.