Responses Of Winter Wheat Varieties From Different Eras To Planting Density In Loess Plateau

Fine cultivar and suitable planting density are fundamental for improving wheat yield.However, our knowledge on the response of winter wheat cultivars to planting density duringwheat varietal replacement in the semi-arid zone has been largely inadequate. Here, we try todetermine the influence of planting density on the growth of aerial parts, root system growth,water-use efficiency （WUE）, grain yield and factors responsible for wheat grain yield, etc.during wheat varietal replacement in the Loess Plateau. Seven cultivars introduced between1940s and2000s in the Loess Plateau were grown in the field at three different kinds ofplanting density (100x104plants hm^-2,250x104plants hm^-2and350x104plants hm^-2). Noirrigation was given during the whole experiment. Results are as follows.1. The growth of the aboveground part of winter wheat was influenced by both plantingdensity and variety. Per plant biomass, tiller number and photosynthesis at flowering alldecreased with the increasing of planting density, and leaf area index （LAI） reaches thehighest at the middle density. Compared with the old varieties, the biomass per plant andphotosynthesis at flowering stage in modern varieties showed an upward trend in all thedensity treatment, but tiller numbers reduced at maturity stage, and the LAI increased only atthe lowest density.2. The growth within the root system in winter wheat was influenced by planting density,but varied due to varieties. Fengchan3had the maximum root dry matter weight, and thelargest deep root system at the lowest density, but Changhan58reached the maximum root drymatter weight and the largest deep root system at the highest density and other varieties at themiddle density. Compared with the old varieties, wheat root system was optimized, root drymatter density was significantly reduced; deep root system increased and the suitable plantingdensity increased in the modern variety.3. Both wheat yields and harvest index showed an upward trend during wheat varietalreplacement. As for the modern variety Changhan58, which have the optimum density tolerance, both the maximum harvest index （HI） and the highest grain yield occurred at thehighest planting density (350x104plants hm^-2).4. Except for grain weight, other factors responsible for wheat grain yield were allinfluenced by both planting density and variety. Planting density had no significant effect onwheat grain weight; however, they showed an upward trend during wheat varietal replacement.The influence of planting density on the number of spikes per unit area and the grain numberper spike of winter wheat is significant, but no significant trends could be seen during winterwheat variety replacement. Interestingly, the grain weight per ear all showed steadily upwardtrends with wheat varietal replacement at different planting densities （except for1970Scultivar Hanxuan10）.In summary, our findings revealed that winter wheat cultivars varied widely in theirresponses of growth and development and grain yield to planting densities in the semi-aridareas of the Loess Plateau. Besides, the significant changes in winter wheat during varietalreplacement in the semi-arid areas of the Loess Plateau may be optimization in root system,reduction in plant height and improvement in both water-use efficiency and density tolerance,which contributing to yield enhancement.