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Effects of Reducing Nitrogen Application on Grain Yield and Nitrogen Utilization and Its Physiological Basis in Wheat

Author: ZhangWeiWei
Tutor: DaiTingBo
School: Nanjing Agricultural College
Course: Crop Cultivation and Farming System
Keywords: wheat reducing nitrogen application yield photosyntheticcharacteristics flag leaf senescence nitrogen uptake and utilization
CLC: S512.1
Type: Master's thesis
Year: 2013
Downloads: 1
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Wheat is one of the main food crops of our country. On the premise of maintaining the yield of wheat, decreasing the nitrogen fertilizer application rates and increasing the nitrogen utilization efficiency is an urgent key problem of Chinese agricultural production.60-70percent of nitrogen fertilizers were used as basal manure in Chinese wheat production. Most of the nitrogen fertilizer was lost because of the slowing growth of wheat root and shoot leading to the weak ability of nitrogen absorbing at the wheat seeding stage. Therefore, reducing the nitrogen fertilizer application rates at seedling stage is an important method to realize the high-efficient and high-yield wheat. Field experiments were conducted with conventional nitrogen treatments (240kgN/hm2, Nitrogen fertilizers were applied at seeding, jointing and booting stages of the wheat with the proportion of5:3:2) as the control, and three nitrogen fertilizer rates (240,180,150Nkg/hm2) were conducted. Base seeding fertilizers were divided into three treatments:base fertilizer (LO), topdressing at the fourth-leaf come out stage(L4),topdressing at sixth-leaf come out stage(L6) to study the effects of reducing nitrogen application rates at the seedling stage on wheat yield and nitrogen utilization and its physiological basis systematically. The main results were as follows:1. Effects of reducing nitrogen application on grain yield and group structure of wheat. The grain yield reduced along with the decrease of nitrogen application rates, but there was no significant differences between N240L0and N180L4, suggesting that N180L4was the optimum nitrogen treatment for reducing nitrogen fertilizers. The grain yield of LO was higher than L4and L6significantly under the N240treatment, L4was higher than LO and L6significantly under the N180treatment, L6was higher than LO and L4under N150treatment, suggesting that the nitrogen fertilizer should be applied later when the nitrogen fertilizers were reduced. Analysis of yield components showed that spike and kernels per spike of N180L4were remained stable compared to the control, but1000-kernel weight increased significantly.The maximum dry matter accumulation amount of each treatment from jointing to anthesis, anthesis to maturity stage was in the N180L4treatment. Under the same nitrogen rates, the dry matter transportation capacity of functional leaves were improved in the N180L4treatment. The maximum dry matter transportation amount, dry matter transportation rate and dry matter transportation contribution rate before anthesis were in the N180L4treatment. Further analysis showed that the percentage of earbearing tiller, leaf area index, pre-anthesis translocation amount, pre-anthesis translocation ratio, and dry matter accumulation amount from jointing to maturity of N180L4treatment increased significantly.All shows that N180L4treatment by raising wheat growth prophase matter transportation and anaphase matter accumulation ability and improving population structure to form a reasonable yield components is the important reason for the grain yield increase.2. Effects of reducing nitrogen application on photo synthetic characteristics and the flag leaf senescence of wheat. Nitrogen fertilizer rates and topdressing stage had significant effects on photo synthetic rate and fluorescence parameters. Photosynthetic rate reduced along with the decrease of nitrogen application rate, but the net photosynthetic rate of N180L4treatment was equal to the check and remained the maximum. Under N240, N180and N150treatments, the maximum photosynthetic rate at different topdressing stage were in LO, L4and L6treatment respectively, which showed that with the decrase of nitrogen application rate, the nitrogen fertilizer applied later could improve the photosynthetic rate of flag leaf of later development stage of wheat.SPAD,(?)PSâ…ˇ and Fv/Fm of N180L4was close to the check and significantly higher than LO and L6treatment. At the same time, the activity of SOD, POD and the content of soluble sugar, cane sugar were higher significantly.And the content of MDA decreased significantly. All showed that nitrogen fertilizer applied later enhanced defending photoinhibition or light damage ability under low nitrogen conditions, delayed the senescence of flag leaf, thus to maintain a higher photosynthetic rate.3. Effects of reducing nitrogen application on nitrogen uptake and utilization. The nitrogen uptake efficiency, nitrogen agronomy efficiency and nitrogen harvest index were higher than the check, LO and L6under the same nitrogen application rate. The nitrogen accumulation at anthesis of N180L4was higher than other treatments. The activity of NR and GS of flag leaf and the content of free amino acid increased significantly, suggesting that the ability of wheat plant nitrogen absorption and assimilation were improved in the N180L4treatment, which supplied a foundation for improving the nitrogen utilization efficiency. Further analysis showed that nitrogen transport amount, transport rate and contribution of pre-anthesis transport to grains of N180L4treatment increased significantly, which showed that nitrogen backwards contributed to nitrogen mobilizing of plants under the low nitrogen conditions, which was the physiological basis of the improvement of nitrogen efficiency.To sum up, N180L4treatment can keep high yield and the nitrogen uptake and utilization efficiency, which is the optimal nitrogen treatment, and the best topdressing stage delays with lower nitrogen fertilizer rate. Through the increase of leaf area index, delay of senescence of flag leaf, improving photosynthetic ability and matter accumulation transport capacity after anthesis, to increase grain weight is the main reason for the high yield. The optimal reducing nitrogen treatment (N180L4) significantly increases nitrogen uptake efficiency, which mainly attributes to the increase of amounts of accumulated nitrogen before anthesis and plant N assimilation and mobilization ability enhancement.

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