| In Jiangsu province, wheat production has been developing rapidly in the past decade. Grain yield per unit area has rapidly increased from about 4500 kg ha-1 in 2004 to around 6000 kg ha-1 in 2015. Jiangsu has become one of the provinces achieving wheat high-yield in China. However, the contradiction between high-yield and plant lodging has become an important factor that constraint sustainable increase in grain yield. Therefore, the extension of lodging-resistant varieties and anti-lodging cultural practices, which wheat breeding and cultivation experts propose, are needed urgently in wheat production. In addition, yield loss after lodging is also needed to be estimated in an accurate, rapid and effective way. The study of this thesis was conducted to investigate the causes of lodging and estimate influential degrees of these causes, and then to raise effective strategies and suggestions for decreasing lodging occurrence. The data from 2004 to 2014 wheat growing seasons were collected from the guidance stations of crop cultivation in Jiangsu, and the questionnaire data of 500 wheat producers in 9 cities, including Changzhou, Suzhou, Nanjing, Nantong and so on, were analyzed. Additionally, through utilizing hyperspectral remote sensing technology and using three verities of Guangmingmai 1, Yangfumai 5 and Yangmai 20 as the varieties, the relationships of canopy spectrum reflectance with lodging degree, grain yield and yield components were analyzed at different growth stages to establish two quick and efficient models, i.e. estimating grain yield and severity after wheat lodging. These results could provide a strong judgment for agricultural insurance against disasters, especially for wheat insurance against lodging. The main results were as follows.1. In Jiangsu, wheat lodging occurred in 10 years out of the past 11 years. And the frequency of lodging occurrence was 90.9%. The area of wheat lodging was annually more than 100 000 ha from 2012 to 2014, but the severity of wheat logging varied greatly in different years, possibly due to varied meteorological conditions.2. The data analysis of questionnaire showed that there were many factors resulting in wheat lodging, such as lodging resistance of different varieties, overmuch seedling rates, improper fertilization, and disastrous weather conditions during late growth periods. Compared with other factors, the evaluation index of the effects of variety and seedling rate on lodging was more than 0.5, which was much higher than other factors, and the occurrence probability of lodging caused by variety and seeding rate was more than 50%, which was significantly higher than by other factors. Therefore, variety and seedling rate were the key influential factors resulting wheat lodging. The evaluation index of green-returning fertilizer and post-anthesis weather was between 0.2 and 0.5, and the summed probability was more than 10% when these two factors appeared in the first and second place. Therefore, green-returning fertilizer and post-anthesis weather were the main factors. The evaluation index of jointing fertilizer, spring weather, sheath blight, sowing date, and sowing method was between 0.1 and 0.2, and the summed probability was just a bit more than 5% when these factors appeared in the first and second place. Therefore, these factors could be listed as the secondary factors. Besides, the evaluation index of other factors, i.e. water-logging, grass disaster, basic fertilizer, weather in winter and freezing injury, was less than 0.1, and the summed probability was less than 5% when these factors appeared in the first and second place. Therefore, these factors could be the ordinary factors.3. The results showed that the spectrum reflectance had an increased tendency after lodging, there was a small absorption peak in the visible light wave band (550 nm); and meanwhile there was a trough of wave in the 670 nm; there was one absorption peak and two trough of waves in the near infrared region wave band (1000 nm). At the same level of lodging, the spectrum reflectance was different because of the change of lodging period. In the visible light wave band, the reflectance of late milk stage was higher than flowering period, while the near infrared wave band, to the contrary, during the same lodging period, the more lodging level was, the more obvious difference was. At 760 nm, the correlation relationship between the lodging level and the canopy spectrum reflectance was the highest, and the correlation coefficient (r=0.968**) arrived at a highly significant level (P<0.01).The result indicated that the canopy spectral data could be used to monitor lodging severity in winter wheat.4. The results showed that the degree of lodging significantly affected 1000-grain weight and grain yield. The higher the degree of lodging, the lower 1000-grain weight and grain yield were, with a decrease up to 10.72% for 1000-grain weight and up to 17.69% for grain yield. The correlation coefficients between canopy spectrum reflectance and grain yield were generally on a downward trend between 350 and 690 nm and zoomed up between 690 and 760 nm. The highest absolute value of coefficient was determined at 764 nm, reaching a high level of 0.734. The correlation coefficient between 1000-grain weight and DVI570,670 was the highest. The correlation between grain yield and DVI764,407 was the highest. The inversion model constructed with vegetation index,1000-grain weight and grain yield was more accurate in estimating grain yield, compared to the model constructed with vegetation index of single factor-yield and the model constructed with vegetation index of multiple factor-yield.5. According to the analysis of questionnaire survey, the measures preventing and controlling wheat lodging were divided into five levels. The key regulation factors include using disease-resistant varieties and adopting rational seedling rates. The important regulation factors include jointing fertilizer application and sheath blight prevention. The ordinary regulation factors include digging trenches to drain the waterlogged fields, mechanical row-sowing, choosing suitable sowing date and controlling the content of booting fat fertilizer. The weak regulation factors include weeding, applying root fertilizer, and so on. Besides, the potential regulation factors include rational chemical controlling measures.6. Based on the above analyses, effective strategies combating lodging in wheat production were proposed. Strategically, wheat lodging should be prevented rather than be remedied passively after lodging occurrence. The application of single technology should be replaced with comprehensive and synergetic prevention. The technology is that the combinations of regular measures and physical and chemical methods replaced the integration of regular measures. The policy is that agricultural insurance and protection replaced independent handing by farmers. Additionally, the specific measures were as follows. Firstly, the government should recommend good-quality, high-yield and stress-resistance varieties to wheat producers. Secondly, the government should guide wheat producers to rationally control seedling rate according to varieties, sowing data, soil fertility, and fertilizer and water conditions, to keep wheat population at a proper level. Thirdly, the government should extend soil testing and fertilizer recommendation according to soil fertility, seedling quality and weather to improve the scientific awareness of fertilization application. Fourthly, the government should extend the technology of dig trenches to drain the waterlogged fields, controlling pests and diseases, and chemical control technologies to improve application levels of these technologies. In the end, wheat producers should better manage pests and diseases to reduce yield losses when lodging occurs. |
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