Effects Of Irrigation And Nitrogen Coupling On Root Characteristics, Nitrogen And Water Utilization In Different Summer Corn Genotypes

The experiments were carried out in the maize innovation center of Shandong Agricultural University (N36°18′,E117°12′) and the state key laboratory of crop biology during 2008-2010. In this study, we used different nitrogen use efficiency maize varieties as the experimental materials. Root characteristics and nitrogen flowing and the physiological mechanism of high nitrogen and water use efficiency of summer maize were researched systematically. The main results were as follows:1 Effects of irrigation and nitrogen coupling on yield of different corn genotypesMore nitrogen application and irrigation water both made two varieties'yield, biomass and harvest index significantly increased. Inorganic fertilizer was superior to organic fertilizer in increasing maize yield and biomass. The high nitrogen efficiency varieties had higher yield and biomass than the low ones. The average yield of LY13 was 34.01% higher than the one of LD981, and ZD99 was 32.76% higher than LN14 at yield. The main reason of higher grain yield was higher harvest index, and further was the 1000-grain weight.2 Effects of irrigation and nitrogen coupling on root characteristics in different corn genotypesThe root vigor was high with the fertilizer and irrigation increase for the two varieties. The high nitrogen efficiency variety, LY13 had more rational root morphology and spatial distribution than LD981, the low nitrogen efficiency one. It was manifested that more roots at deeper layer were more conducive to their full use the stable environment at deeper layer to keep higher vigor. LY 13 had excellent root system features, reasonable spatial distribution so that the duration of high-value vitality might be extended and the aging was postponed and thus more water and nutrients were absorbed during the growing stage to meet the requirements for nitrogen absorption.Water stress decreased the root TTC reducing quantity and the bleeding sap intensity significantly, especially for LY13. Water and nutrients absorption were limited by less TTC reducing quantity and the dry weight of shoot and the yield was decreased at last.3 Effects of irrigation and nitrogen coupling on photosynthetic characteristics in different corn genotypesNitrogen and irrigation improved significantly the duration of high net photosynthetic rate and high leaf area index, photosynthetic pigment content, actual photochemical efficiency and maximum photochemical efficiency of the ear leaf for the two varieties after anthesis, and LY13 had greater declines. These values of high nitrogen efficiency variety was significantly higher than LD981 nitrogen inefficient varieties, to accumulate more photosynthesis production, on the one hand, and the powerful root and high root vigor during later stages were guaranteed, on the other hand for grain filling to provide sufficient material source.4 Effects of irrigation and nitrogen coupling on nitrogen utilization in different corn genotypesWith the increase of irrigation water and nitrogen application of two varieties, more nitrogen was accumulated significantly. As for the extent, low nitrogen efficiency variety was far inferior to high nitrogen efficiency variety, compared with applying organic fertilizers, inorganic fertilizer treatment improved crops N absorption, the results manifested that high nitrogen efficiency variety had obvious advantages in accumulating nitrogen. The high nitrogen efficiency variety had a bigger seed set and a stronger adjusting ability which made it have more nitrogen accumulation quantity and more nutrients distributed to the grain. As a result, it had higher nitrogen output rate, contribution and N use efficiency.The soil NO₃^--N contents and ammonia nitrogen volatilize quantity increased with nitrogen application increase, and inorganic fertilizer treatment was significantly higher organic fertilizer treatment. With the increase of irrigation water, soil NO₃^--N leaching to the soil deep layer was intensified and ammonia volatilization rate increased. With development period propulsion, inorganic fertilizer increased the nitrate leaching, while organic fertilizer processing reduced soil NO₃^--N residue. Compared with organic fertilizer, inorganic fertilizer significantly increased volatilization loss, and volatilization rate of inorganic fertilizer processing reached the peak of 6.74 kg N·ha^-1·d^-1 and the highest volatilization loss rate was 52.94%. In comparison to Organic fertilizer processing, the two values were 2.97 kg N·ha^-1·d^-1 and 18.90%, respectively.5 Effects of irrigation and nitrogen coupling on water utilization in different corn genotypesMore nitrogen application raised water use efficiency of two varieties. Grain, dry matter and water use efficiency of organic fertilizer processing were significantly higher compared with inorganic fertilizer processing. Increasing irrigation water improved the grain yield and dry matter accumulation and reduced the water use efficiency. For high nitrogen efficiency variety, ZN99, grain yield, dry matter and water use efficiency were significantly higher than those of LN14, the low nitrogen efficiency variety. These results indicated that the high nitrogen efficiency variety was a high water use efficiency one, too.