| The experiment was carried out at the experimental station of Hebei Agricultural University in 2001-2003. The results are summed as follows:1. In 2001-2002, 28 wheat varieties (genotypes) were selected to study the yield performance under nitrogen stress condition. It is found that there were obvious differences in grain yield among them. The cluster analysis indicated that the tested varieties could be classified into three categories with different nitrogen use efficiencies (NUE), including high efficiency, middle efficiency and low efficiency, corresponding 2, 7 and 19 varieties in each category. It showed that few varieties with high NUE could be found in the present wheat production. There had not big differences on the capability to nitrogen response in the tested 28 varieties.2. Under the condition without nitrogen application, the total nitrogen concentration in plants at maturity stage showed the highest in varieties of high NUE, then of middle NUE, the lowest of low NUE, and the adverse results were found on plant dry matter weight per area and nitrogen accumulation amount in the different NUE varieties. Then this showed that the high NUE varieties had stronger capabilities of N accumulation and dry matter production in plants under N stress condition. N application obviously increased the grain yields, total N concentration of plants at maturity stage, plant dry matter weights and N accumulation amounts of plants in all tested varieties.3. Wheat N use efficiency can be divided into uptake efficiency (UPE) and utilization efficiency (UTE). There existed types high efficiency, middle efficiency and low efficiency in UPE and UTE in the tested varieties. N application decreased NUE and UTE in all varieties. Similar UPE was found for each variety under different N conditions, indicating the increase of NUE in high NUE varieties under N stress condition came from the increase of UTE. The average value of N response degree changed little in different NUE varieties. Big variation coefficients in statistics were existed in varieties of same NUE category.4. Under N stress condition, the plant height at maturity in high NUE varieties was much higher than those in middle NUE and low NUE varieties. It can be used as one important index to screening wheat variety with higher ability to resist N stress. The spike length, total spikelet number and fruitful spikelet number had no obvious difference in tested varieties. The grain weight and dry matter weight per plant at maturity in varieties with different NUE had the same tendency as those in grain yield and NUE. Compared to N stress, N application increased the plant height at maturity, spike length, total spikelet number and fruitful spikelet number, grain weight dry matter weight per plant at different extent in the tested varieties.5. A follow characteristics on yield components in tested varieties under N stress condition was found as follows: The spike number per area showed the highest in high NUE, then middle NUE, the lowest in low NUE; The adverse effect to the spike number per area was found in kernel number per spike; The per 1000 grain weight was the highest in middle NUE, then high NUE, the lowest in low NUE. The spike number per area had important effect on the NUE and the grain yield under N stress condition. N application increased the spike number per area and kernel number per spike and decreased the per 1000 grain weight in tested varieties. No differences were found on responding to N in three yield components in tested varieties.6. At different levels of N, there were not significant differences on total N concentration at jointing stage, booting stage and maturity stage in tested varieties. There existed a close correlation between the increase of N accumulation amount and enhancement of dry matter weight in plants at each growth stage. The N accumulation amounts in plant during jointing to maturity are the most in high NUE, then in middle NUE, the last in low NUE. The response to N application in the N accumulation amounts in high,...
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