Trends Of Nitrogen Use Efficiency For Chinese Maize Cultivars And Their Parents From The1950s To The2000s

Maize is the most widely grown corp in China and the world. Expect for plant density, nitrogen fertilizer was one the most significant agronomic practices for improving maize yield. In China, application rate of nitrogen in maize accelerated markedly from1980s, and excessive application happened in many regions now. The excessive nitrogen fertilizer was waste and led to environmental pollution seriously. It is necessary to optimize nitrogen application amounts and to breed cultivars with high value components of nitrogen use efficient for economic interest&environmental safety.Usually, retrospective analysis may help breeders to refine and/or change their breeding programs in desired direction. The objective of this study was to present maize yield trends and nitrogen use efficiency changes for maize cultivars from the1950s to the2000s in China.In the study, thirty-five maize cultivars were tested, including27hybrids,4double-cross hybrids, and4OPVs that were used extensively from1950to2000in the main maize-growing areas (the spring and summer corn region) in China. Field trials were carried in Langfang in2012-2013and Sanya in2011-2012. The experimental design was a randomized complete block in a split-plot arrangement with nitrogen treatments as the main plots and cultivars&their parents as the subplots. Two nitrogen treatments were used,3replications per treatment. The2nitrogen treatments was:①normal nitrogen applied (HN) with240kg·ha-1,②no nitrogen applied (LN).The main results of the study were as follows:1. Yield and most traits of all cultivars were decreased by low nitrogen treatment significantly, except for tassel branch number, shelling percentage and barren tip with not significant changes. But ASI was increased significantly at low nitrogen level.2. Mean yield of each decade cultivars showed a significant linear increase from the1950s to the2000s at both nitrogen levels. The increase rate at normal nitrogen level was117kg ha-1per year, which is higher than that of low nitrogen treatment (104kg ha-1per year). But the rate differences across nitrogen levels were not significant.3. Mean yield of each decade inbred lines showed a significant linear increase from the1960s to the2000s at both nitrogen levels. The increase rate at normal nitrogen level was25.9kg ha-1year-1, and22.1kg ha-1year-1at low nitrogen treatment. But the rate differences across nitrogen levels were not significant.4. Nitrogen agronomic efficiency of Chinese cultivars increased from the1950s to the 1990s, at an average rate of0.151kg·kg-1·year-1.Then decreased at a rate of0.430kg·kg-1·year-1during1990s-2000s. As for their parents, nitrogen agronomic efficiency increased at an average rate of0.094kg·kg-1·year-1during the early20years (1960s-1980s) and decreased at a rate of0.02kg·kg-1·year-1from1980s till2000s.5. Form the1970s to the2000s, absolute heterosis increased at an averaged rate of34kg ha-1per year. But relative heterosis changed little.6. From the1950s to the2000s, plant height did not change consistently with decade. Ear height, tassel branch number and ASI were decreased; ear leaf area and green leaf number were increased, the trends were more apparently for the single-cross hybrids.7. As for ear, sevel of its traits, shuch as ear length, era diameter, cob diameter and100-kernel weight all showed a significant linear increase from the1960s to the2000s. But barren tip and shelling percentage did not show a certain trend with the decades.