The Primary Research About The Physiology Mechanism Of N Efficiency Difference From Maize Varities

The excessive application of nitrogen fertilizer not only lead to decreased utilization rate of nitrogen fertilizer and increased production cost but also result in underground water pollution. People attach more and more importance to the problem. So choosing and breeding maize variety of highly nitrogen fertilizer utilization rate based on different maize genotype is a positive and efficient measure to the problem. But there is few research on the physiological and biochemical base of utilization rate of nitrogen now. This increases difficulties inevitably in choosing and breeding maize variety of highly nitrogen fertilizer utilization rate. So it is imperative to do research in the difference among maize varieties physiologically and biochemically. The three maize varieties of representative nitrogen utilization efficiency were determined through the primary identification of nitrogen utilization efficiency of hybrid maize that widely planted recent years in Shan-xi Province in 2000 and 2001. And the different nitrogen utilization efficiency in varieties was researched physiologically and biochemically in 2003 and 2004. The results show that: 1 There are significant differences in nitrogen uptake and retransfer ability in different maize genotypes before silking time and after silking time. Shan-dan 9 has the most strong uptake ability before silking time and Yu-yu 22 after silking time. Shan-dan 9 has the most strong retransfer ability. There are also differences in nitrogen contribution rate of vegetative mass to seed in different maize genotypes. The highest rate is 90 percent, while the lowest rate is only 40 percent. 2 The character of maize root is important to nitrogen uptake efficiency. It is the relatively growth ability of root that determine nitrogen uptake efficiency but not the size of the root. So it is reasonable to choose character of maize root as a filtration index but unreasonable as the all development stage. 3 The maize varieties of strong nitrogen uptake ability also has strong assimilation ability before silking time . Perhaps because strong assimilation ability can feed back uptake ability of the root and enhance uptake ability. At the same time, strong uptake ability also enhance assimilation ability. But the relationship of the two factor need further research. 4 The quantity of nitrogen uptake is relate to length of life. The content of chlorophyll in the ear position leaf and nitrate reductase activity should not be considered as a index of nitrogen uptake. Through the correlation analysis of the quantity of nitrogen uptake and the dry matter accumulation, we foud that there is a significant positive correlation between the quantity of nitrogen uptake and the dry matter accumulation. It showed that overground matter accumulation accelerate nitrogen uptake of root after silking time . Shan-dan 9 has the highest nitrogen contain rate in silking time but the nitrogen uptake ability is the weakest after silking time. The high nitrogen contain rate in silking time may contribute to the weak nitrogen uptake ability after silking time 5 The content of crude protein in the apparatus overground reduced continually after silking time. The content of crude protein reduced more in the variety of strong nitrogen retransfer ability. It showed that the crude protein degeneration ability contribute to nitrogen retransfer ability. Free amino acids retransfer ability in the leaves and the spike also contribute to nitrogen retransfer ability. The nutrition organs on the ground contribution degree for the nitrogen recycle ability is: spike>leaf>stem. Nitrogen in the stem and spike transfer to seed first.