In Holland the genetic increase of the yield of silage maize rye grass varieties in 25 years variety comparison is average 173 kilogram dry matter per hectare per year, analyses of Wageningen University & Research shows. Above this there was an non-genetic increase of 65 kilogram dry matter per hectare per year. So the average total increase was 238 kilogram dry matter per hectare per year. The main factors of the non-genetic increase are earlier planting and higher temperature during the growing season. However: practical farming showed an average increase of only 195 kilogram dry matter per hectare per year.