Effects Of Different Nitrogen Management On Grain Yield And Quality Of Winter Wheat Under Heat Stress

The studies were conducted from 2005 to 2006 at the experimental farm of Shandong Agricultural University. Wheat cultivar Jimai 20 with strong gluten and Lumai23 with weak gluten were chosen in this study. The effect of heat stress from middle to last grain filling period and different nitrogen treatments on grain yeild and quality formation was studied. The main results were as fellows:1. Effect of nitrogen management on grain yield under heat stress For the cultivar Jimai20, compared with normal air temperature, the heat stress at the mid and later stages of grain filling reduced the 1000- grain weight , grain yield and harvest index significantly,and the biological yield was reduced too. Under heat stress, the 1000- grain weight of ratio of topdressing nitrogen (1:3) at jointing (N2)was best, and that the grain yield and harvest index were higher than other treatments. For the other treatments , the 1000- grain weight and grain yield of ratio of topdressing nitrogen (1:1) and adding nitrogen at athesis (N3)was beneficial to the ratio of topdressing nitrogen (1:1) at jointing(N1). The ratio of topdressing nitrogen (1:3) and adding nitrogen at anthesis treatment(N4)was the lowest.For the cultivar lumai23, the heat stress from middle to last grain filling period reduced the 1000- grain weight , grain yield significantly, too. Except the biological yield of N2 treatment was increased, the other treatments'biological yields were decreased. Under heat stress, the ratio of topdressing nitrogen (1:1) was changed to 1:3 or adding nitrogen at anthesis could lessen the adverse effects of 1000-grain weight and grain yield under heat stress condition, but on the base of the ratio topdressing nitrogen (1:3), adding nitrogen at anthesis had no accumulation effect.2. Effect of nitrogen management on grain quality under heat stress For the cultivar Jimai20, the wet gluten content was rapidly reduced under heat stress, dough development time and dough stability time were decreased obviously, especially the average dough stability time of every nitrogen treatments under heat stress only occupied 1/6 percent for the normal air temperature treatment. The processing quality changed poorly seriously. To increase the nitrogen application amount at the later growth stage of wheat especially on the base of the ratio topdressing nitrogen (1:3), adding nitrogen at anthesis had positive effect for gluten content,dough development time and dough stability time。For the cultivar Lumai23, the wet gluten content was decreased obviously, and the dough development time and dough stability time were reduced slightly. The nitrogen treatments had little influence to it's grain quality. Under heat stress, the peak viscosity and breakdown were reduced markedly for Jimai20 and Lumai 23. The nitrogen treatments had no significantly effect, but adding nitrogen at anthesis had egative effect.3. Effect of nitrogen management on grain protein content and it's components under heat stressHeat stress from middle to last grain filling period affected the protein synthesis. The protein content obviously reduced after heat stress. Under heat stress, different nitrogen treatments had both some influence to Jimai20 and lumai23. for Jimai20,the nitrogen treatment that base on the ratio of topdressing nitrogen (1:1) and adding nitrogen at ahthesis was benefit for formatting kernel protein. While, the ratio of topdressing nitrogen (1:1) treatment was more benefit for Lumai23.Heat stress from middle to last grain filling period affected protein components accumulation significantly for Jimai20 and Lumai23. Soluble gluten content and insoluble gluten content reduced at varying degree. Different nitrogen treatment affected the protein components more or less. The incorporations as fellows: for Jimai20, the ratio of topdressing nitrogen (1:1) and adding nitrogen at ahthesis was benefit for increasing the monomeric protein content, but the ratio of topdressing nitrogen (1:1) was fit for Lumai23; for the soluble gluten content, N1and N2 treatments had obverse effect for jimai20 and lumai23.; for the two cultivars,N3 treatment had the best influence in all of nitrogen treatments.4. Effect of nitrogen management on starch and it's components under heat stressThe effect of heat stress on amylose content was slight for the two cultivars ,and between nitrogen treatments there were no significant difference. But the obvious decrease of the amylopectin content after heat stress resulted that the starch content was reduced. And the starch content of Lumai123 was higher than Jimai20.Increasing the nitrogen application amount at jointing and adding nitrogen at anthesis were benefit for starch content, but the ratio of topdressing nitrogen (1:1) was more appropriate for Jimai20. And ratio of amylopectin to amylase of heat stress treatments decreased significantly.Correlative analysis indicated that there was a significant positive correlation between amylopectin content,breakdown and pasting temperature, the ratio of amylopectin to amylase were extremely significantly positively correlated to peak viscosity,final viscosity. So we could find out that the decrease of amylopectin content and the ratio of amylopectin to amylase ware the main reason that result in the poor starch quality.5. Effect of nitrogen management on the activity of GS under heat stress At heat stress, the activity of GS of Jimai20 declined obviously and the most sensitive period was 23days after anthesis. But for Lumai23 , the reflection was different in every grain filling periods under heat stress,, the activity of GS was decreased in the other periods except that the activity of GS was slightly increased on 29days after anthesis.Increasing the nitrogen application amount at joining especially adding nitrogen at anthesis could improve the activity of GS of Jimai20. Different nitrogen treatments influenced the activity of GS of Lumai23, increasing the nitrogen application at joining and anthesis had positive means for increasing the activity of GS.6. Effect of nitrogen management on enzymes involved in starch synthesis under heat stressThe activity of GBSS of the two cultivars declined obviously after stress by high temperature and the formation of starch was influenced. Under the ratio of topdressing nitrogen(1:3),the activity of GBSS of jimai20 was the highest. Increasing the nitrogen application at jointing , especially adding nitrogen application at anthesis was propitious to improve the activity of GBSS of Lumai23. Compared with Jimai20, the highest activity of GBSS of lumai23 appeared on 15days after anthesis, which was earlier than Jimai20. And in all of the grain filling stages of Lumai23, the change of activity of GBSS was smaller than jimai20.The activities of SSS of the two cultivars declined markedly after heat stress. There had slight difference among of different nitrogen treatments for Jimai20. The activities of SSS of Lumai23 were all reduced except that the SSS activity on 21days after anthesis was slightly increased. For the nitrogen treatments, increasing nitrogen application amount at the later of wheat growth stage had positive effect for the two cultivars. We could find out that the activity of SSS of Lumai23 was higher than Jimai20's under both normal air temperature and heat stress.In a word, the 1000-kernel weight and grain yield were reduced significantly after heat stress, and the protein and starch content declined obviously. Otherwise, the processing quality changed worsen. The different nitrogen treatments had slight influence in the grain quality. Increasing the nitrogen application amount at the mid and later stages of wheat growth could improve the 1000-grain weight and the grain yield, and it could be used to weaken the negative influence after heat stress.