A recent study suggests that the diverse response of wheat yields in previous heat stress experiments may be caused by additional drought stress which is difficult to avoid in heat stress experiments using sandy soil substrate.
Eyshi Rezaei, E., S. Siebert, R. Manderscheid, J. Müller, A. Mahrookashani, B. Ehrenpfordt, J. Haensch, H.-J. Weigel, F. Ewert, 2018. Quantifying the response of wheat yields to heat stress: The role of the experimental setup. Field Crops Research 217, 93-103. doi:10.1016/j.fcr.2017.12.015