Effects of Nitrogen Fertilization on Nitrogen Uptake, Assimilation and Root Activity of Maize (Zea mays L.)
| Autor: | Lamin B. Sonko, 宋珂 |
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| Rok vydání: | 2012 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 100 Maize is one of the cereal crops that require higher amounts of nitrogen (N) to attain higher growth and yield. When water and temperature conditions are ideal, productivity of maize is mainly limited by availability of nitrogen. Nitrogen is a component of a number of compounds, e.g. proteins, nucleic acids and chlorophyll; and plays important role in many of the plants physiological processes. In particular, it is important in the efficient capture and use of solar radiation; it is fundamental to establish the plant's photosynthetic capacity and prolongs the effective leaf area duration. Understanding the physiological and biochemical mechanisms that influence the capacity of maize to take up and efficiently utilize nitrogen is a useful strategy for increasing its nitrogen utilization efficiency, increasing yield and reducing environmental problems. The main aim of this study was to investigate the physiological and biochemical mechanisms which determine nitrogen uptake and metabolism in maize at different soil nitrogen levels, and their implications on maize growth and yield. In this study, two field experiments and one pot experiment were conducted. Glutinous white maize (White pearl) was used as the test variety in all the experiments. The experimental design was a complete randomized design (CRD), consisting of four N fertilizer rates treatments: 0, 90, 180 and 270 kg N ha-1. The physiological parameters assessed were nitrate reductase activity (NRA), dehydrogenase enzyme activity and total nitrogen content and concentration of plant samples. NRA and dehydrogenase enzyme activity were determined only at the pot experiment at 11 and 18 days after emergence. Total N content and concentration in plant tissues was determined using the micro-kjeldahl procedure. Plant growth parameters measured include plant height, leaf number, green leaf area, leaf chlorophyll content and biomass accumulation. Leaf chlorophyll was measured using SPAD-502 meter. Grain yield components were also measured. The results showed that nitrate reductase activity, dehydrogenase activity and total N content and concentration were all significantly influenced by N fertilizer rates. Data obtained indicated that NRA in maize roots was more affected by variations in soil N levels than in leaves. Dehydrogenase activity of maize roots was higher when the plants were younger and was found to decrease as the plants grow and soil N levels started to go down. Nitrogen concentration in plant tissues was higher at early growth stage and decreases as the plants mature. In terms of concentration of N in plant parts, data indicated that a greater proportion of N taken up by maize was concentrated in the leaves. Whiles nitrogen concentration in vegetative parts was significantly affected by N rates, grain N concentration showed no significant difference between all the four treatments in both field experiments. This was due to the potential of maize to maintain a stable supply of N in the reproductive parts by remobilizing N from the vegetative parts. Total N content of the shoot of plants in N fertilized treatments were also significantly higher than those in the control plots because the two factors that determines N content i.e. nitrogen concentration and biomass accumulation were both enhanced by N fertilizer application. All the plant growth parameters assessed in this study were significantly enhanced by N application. Plant height was similar for all the treatments at early growth stage, but at late vegetative stage, significant differences were observed between the higher and the lower N treatments. Maize yield components such as ear weight per plant, number of grain rows per ear and ear weight were all significantly affected by N rates. The highest yield in field experiment one (10.72 tons ha-1) was obtained at 180 kg N ha-1 treatment. In experiment two, the highest yield (10.66 tons ha-1) was obtained at 270 kg N ha-1 treatment. In this study, increasing N rates from 0 to 90 kg N ha-1 and from 90 kg N ha-1 to 180 kg N ha-1 in most cases resulted in an increment in grain yield components; but adjusting from 180 kg N ha-1 to 270 kg N ha-1 did not show any significant increment for all the grain yield components. Higher maize yields recorded in the higher N treatments was as a result of the positive effects that N application had on plants physiological and growth factors. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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