An improved methodology to evaluate crop salt tolerance from field trials
G.van Straten, A.C.de Vos, J.Rozema, B.Bruning, P.M.van Bodegom
- Solid method to estimate salt tolerance parameters from field trials.
- Statistical analysis of parameter bias, uncertainty and correlation.
- Salinity thresholds and zero-observed-effect yields are strongly correlated.
- Partially explains the wide range of salt tolerance reported in literature.
- Proposes ECe90 as robust alternative to threshold or ECe50.
Last week the article "An improved methodology to evaluate crop salt tolerance from field trials" by Dutch scientists Prof. dr. Dr. G. van Straten (Wageningen University), Prof. dr. Dr. P.M. van Bodegom (Leiden University), Prof. dr. Dr. J. Rozema (VU University Amsterdam), Dr. ir. A.C. de Vos (Salt Farm Texel) and Dr. B. Bruning (Salt Farm Texel, Salt Farm Foundation) was published. This article, made on request of Salt Farm Foundation and the Dutch Ministry of agriculture nature and food quality, is about an improved method to identify salt-tolerant crops, and thus to advance saline farming.
One of the problems is that salt tolerance is a complex matter. "In various publications there are large differences in the reported salt tolerance levels between crops, (comparable) varieties, locations and years", says Dr. Arjen de Vos. These inconsistent data hamper the development of salt-tolerant crops and saline agriculture. The new method is reliable and can provide a new basis for a good assessment of the potential of crops under saline conditions. The method not only includes a way to analyze data in a robust and uniform way, but also shows that the salt concentration at which 90% yield is reached is a more reliable way to determine salt tolerance instead of the usual threshold value (maximum salt concentration without loss of yield). The results also show that the potato variety is moderately tolerant in the study instead of the current idea that potato is moderately salt-sensitive. This makes this potato variety suitable for cultivation under salty conditions in many parts of the world. A uniform approach to determining salt tolerance can be the starting point for the development of new salt-tolerant crop varieties that can help millions of farmers.
Salinization affects large parts of the world and millions of farmers are faced with declining yields and many are even forced to migrate. In the coastal area of Bangladesh alone, 27 million people may have to migrate by 2050 because of increasing salinization. Salt tolerant crops can help these farmers increase their yield and income in saline areas.
The salt tolerance of crops is commonly expressed in descriptive parameters such as threshold or 50%-yield soil salinity and shape parameters describing the yield curve. Estimation by visual or simplified ordinary least squares (OLS) regression methods has multiple issues: parameter bias due to uncertainty in soil salinity, lack of independent estimates of the reference yield, questionable robustness of the threshold parameter and missing information about uncertainty and correlation of the parameter estimates. Here, we present a comprehensive OLS method together with an analysis of its statistical properties to alleviate and overcome such issues, on the basis of a numerical experiment that mimics observed yield responses to saline groundwater across a range of salinities in the experimental test facility Salt Farm Texel.
The results indicate under which experimental conditions bias is not a major problem. The method allows estimation of the zero-observed-effect yield from the data, which is relevant to agricultural practice. Estimates for zero-observed-effect yield and threshold ECe are negatively correlated, underlining the difficulty of obtaining reliable threshold values. The estimated confidence regions are reliable and robust against soil salinity uncertainty, but large observation error jeopardizes the confidence intervals, especially for the slope parameter. Data uncertainty alone can be responsible for substantial differences from experiment to experiment, providing a partial explanation for the wide variety in reported parameters in the literature, and stressing the need for long-term repetitions.
Given the lack of robustness of the threshold parameter, we propose to adopt the 90%-yield EC (ECe90) as tolerance parameter. Its confidence bounds can be obtained from a simple reformulation of the original models. We also present uncertainty ellipses as a suitable tool to unite multiple-year estimates. The method is offered as a solid and generic basis for reliable assessment of the cultivation potential of varieties and crops on salt-affected soils.