The substantial yield gains in silage maize achieved in Germany over the last 25 years are commonly attributed to breeding progress and management innovations. However, a warming trend over the same time period may have contributed considerably to this yield increase, especially in regions (like northern Germany) with suboptimal climatic conditions for maize production, i.e. low temperature and radiation. Our retrospective study aimed to determine the weather-adjusted net increase in silage maize yield. Based on historical yield and weather data from 1986 to 2010 the impact of gradual climate change on yield was estimated by two independent methods:  (1) Simulation with the weather-driven MaisProg model.  (2) Establishing a de-trended climate-yield relationship by first difference linear regression. All calculations were carried out for two distinct silage maize producing regions, Schleswig-Holstein (SH) at the northern tip of Germany with maritime, unfavorably low temperature and irradiation conditions, and Bavaria (BV) in Germany’s south with higher temperature and irradiation. The analyses were conducted separately for two different maturity groups, namely a set of early and a set of mid-early hybrids.

The historical data clearly reflect the pronounced differences between BV with an average yield of over 18 t ha^-1 in 1986 and SH with about 14 t ha^-1. While BV started from a relatively high level, the rate of yield increase until 2010 was low, SH in contrast had a nearly 4 times larger rate. The simulated as well as the de-trended estimates for SH consistently attributed 55% to 75% of yield gains to warming trends. Assuming similar breeding and management progress in BV and SH climate change must have had a negative impact on yield gains in BV. This was less clearly confirmed by the simulated than by the de-trended estimates. With respect to differences between maturity groups our preliminary results indicate a larger breeding and management progress for the mid-early hybrids.