Yield trends of temperate cereals in high latitude countries from 1940 to 1998

Wheat is the only temperate cereal for which yield trends have been exhaust ively analysed on both global and national bases. This paper aims (i) to co mpare global yield trends of wheat, barley, oat and rye for the last five d ecades, (ii) to analyse their yield trends in Canada, Denmark, Norway, Swed en and Finland, the northernmost limits for extensive agriculture, and (iii ) using case studies, to assess the relative contribution to yield gains ma de by cereal breeding. Average global yield data from FAO were regressed ag ainst years using linear or bilinear regressions. Yield gains in absolute a nd relative terms were calculated for comparison among countries and cereal s. Data from the literature were used to assess the estimated contributions made by breeding to yield gains. Global yield trends were not standard throughout the 1950-1998 period: rye exhibited a constant yield gain (c. 28 kg ha(-1) y(-1)), while barley and o at showed marked increases until around 1970 (c. 38 and 32 kg ha(-1) y(-1), respectively) but quite modest increases (c. 19 and 5 kg ha(-1) y(-1), res pectively) over the last 30 years. Wheat also showed a bilinear trend with only limited yield gains until the 1960s, followed by a more than 3-fold in crease in rate of yield gain from then on (16 and 40 kg ha(-1) y(-1), respe ctively). However, during the 1990s wheat yield gains have been less than p reviously, Hence, global yields of barley, oat and wheat have increased ver y slowly lately. Trends for each combination of cereals and countries indicated consistently higher yields during the 1990s than at mid-century. In general, wheat yiel d tended to increase at a faster rate than yield of the other cereals. Ther e was a trend in the last decade of low rates of yield increase compared wi th those of previous decades. This was clear for oat and barley, and a simi lar trend is emerging for wheat. This suggests that genetic and/or manageme nt improvements have had less effect in recent times. Furthermore, we found preliminary evidence to suggest that with the exception of wheat in Canada , genetic contributions in northern areas were smaller than those reported for wheat and barley at lower latitudes. Therefore, alternative approaches must be sought for future breeding work under these high latitude condition s.