Table 3. Rate of growth of wheat yield by mega-environment, Elite Spring Wheat Yield Trial, 1964–1995. Period   ME1   ME2   ME4   ME5 1964–1978                     Percent per year   1.22   1.72   1.54   1.41     Kg per year   71.6   81.5   32.4   34.9 1979-1999                     Percent per year   0.82   1.16   3.48   2.10     Kg per year   53.5   62.5   87.7   46.1