Abstract
For highly productive regions such as Germany, the increase of wheat grain yields observed throughout the 20th century is largely attributed to the progress in crop breeding and agronomic management. However, several studies indicate a strong variability of the genetic contribution across locations that further varies with experimental design and variety selection. It is therefore still unclear to which extent management conditions have promoted the realization of the breeding progress in Germany over the last 100+ years. We established a side-by-side cultivation experiment over two seasons (2014/2015 and 2015/2016) including 16 winter wheat varieties released in Germany between 1895 and 2007. The varieties were grown using 24 different long-term fertilization treatments established since 1904 (Dikopshof, Germany). Averaged over all cultivars and treatments mean yields of 6.88 t ha−1 and 5.15 t ha−1 were estimated in 2015 and 2016, respectively. A linear mixed effects analysis was performed to study the treatment-specific relation between grain yields and year of variety release. Results indicate a linear increase in grain yields ranging from 0.025 to 0.032 t ha−1 yr−1 (0.304 to 0.387% yr−1) in plots that were treated with combined synthetic-organic fertilizers without signs of a leveling-off. Yields from low or unfertilized plots do not show a significant progress in yield. Responsiveness of mean yields to fertilizer management increases with year of release and indicates small yield penalties under very low nutrient supply. Results highlight the need to consider the importance of long-term soil fertilization management for the realization of genetic gains and the value of long-term fertilization experiments to study interactions between genetic potential and management.
Highlights
Grain yields of wheat considerably increased during the 20th century and more than half of the global wheat production areas still witness yield increases (Ray et al 2012, 2013, Iizumi et al 2014)
Grain yields Grain yields across all plots ranged from 0.05 t ha−1 to 12.67 t ha−1 in 2015 and from 1.59 to 9.32 t ha–1 in 2016 with mean yields over all fertilizer treatments and varieties of 6.88 and 5.15 t ha−1 in 2015 and 2016, respectively
In 2015 maximum yields were achieved under maximum nutrient supply (TIDs 13, 16 and 17, see table 1 for TIDs) while in 2016 six varieties showed maximum yields under slightly reduced fertilization but additional manure supply (TIDs 1, 4 and 5)
Summary
Grain yields of wheat considerably increased during the 20th century and more than half of the global wheat production areas still witness yield increases (Ray et al 2012, 2013, Iizumi et al 2014). Analyzing unbalanced yield data obtained at variety trials or using national yield statistics allows for considering a higher number of data sets and, might be more representative for regional and national yield progress rates Recent statistical methods, such as mixed effects models, allow for deriving the genetic gain even from unbalanced data sets with cultivation conditions strongly changing over time (Smith et al 2005). If assessing variety performance and genetic gains at multiple sites, results are nonlinearly affected by site-specific weather and management conditions during crop growth Considering these uncertainties, it is still questionable, whether breeding has been the main factor for the increase in wheat grain yield. Long-term fertilization experiments provide unique research sites where the performance of crop varieties can be evaluated under a range of highly differentiated soil nutrient equilibriums, located at a single site
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