| Wheat Xiaoyan 22, as sample material, was planted during 2004-2006 via split-split plot (field experimental design) design method under the dry land condition. The effects of the cultivation mode, nitrogen fertilizer rate and planting density have been studied on the dynamical change of the green leaf area, leaf area index, grain yield, average spike, the average grain number per spike and the distribution of grain number for different spike. The effects on the average weight of thousand grains and its distribution for each spike, the ratio of wheat with different grain grade and the weight of grain have also been studied. It aims to provide the theory support for the high yield and high efficiency wheat planting in the dry and half dry area on the Loess Plateau. The study indicates:(1) During the periods of turning green to maturation, the change of single green leaf area of wheat presents, "low - high - low", a parabola tendency and reaches its maximum at the booting stage. Different cultivation factor has a different influence on the single green leaf area of wheat. Cultivation mode has a remarkable influence on the single green leaf area of wheat only before the period of grain filling (milk filling); increasing the nitrogen fertilizer rate can outstandingly influence the single green leaf area of wheat at different growth stage, while increasing the planting density can lead the single green leaf area of wheat reduced notably except the joint stage. These results show that the effect on leaf area of nitrogen fertilizer rate is greater than that of planting density, which is greater than that of cultivation mode. Cultivation factors interact mutually on the single green leaf area of wheat.(2) There are obvious different influences on the leaf area index of wheat with five cultivation modes. The ditch and grass cover cultivation mode have the highest leaf area index of wheat, but the supplementary irrigation cultivation mode has the lowest leaf area index. In comparison with the conventional cultivation mode, the leaf area index increases by 32.1%, 30.3%, 15.3% and -11.7% with the cultivation mode of ditch, grass cover, film cover and supplementary irrigation respectively. The relationship between nitrogen fertilizer rate and leaf area index shows a parabola tendency, which increases first and then decreases. In three levels of nitrogen fertilizer rate, 120kg/hm2 of nitrogen fertilizer rate has the highest leaf area index. Enhancing planting density can lead obviously increasing of the leaf area index; and the leaf area index of the high planting density increases 25.7% more than that of the lower planting density.(3) Cultivation mode, nitrogen fertilizer rate and planting density have a remarkable or extremely remarkable influence on the wheat's grain number per spike; the interaction between or among of these three cultivation factor is not noticeable. Further analysis indicates that among the three cultivation factors, the planting density has the most influence on the wheat's grain number per spike (F=49.010**), followed by the cultivation mode (F=11.436**), and the least is the nitrogen fertilizer rate (F=3.371**). Among the five cultivation modes, the ditch and film cover cultivation modes have the highest grain number per spike; especially with the ditch cultivation mode, it increases by 6-7 grains per spike and the rate of increment is 14.5%. The grain number per spike with cultivation modes of grass cover and supplementary irrigation are between conventional cultivation mode and ditch cultivation mode. The wheat's grain number per spike increases with the increment of nitrogen fertilizer rate. The high nitrogen fertilizer application (240kg/hm2) and medium nitrogen fertilizer application (120kg/hm2) increase 2.3 grains per spike and 2.2 grains per spike respectively in comparison with no nitrogen fertilizer application. The increment rates are 4.6% and 4.5%, there is a remarkable difference in comparison with no nitrogen fertilizer application. Increasing planting density significantly reduces the winter wheat's grain number per spike.(4) Cultivation mode has an extremely remarkable influence on the grain number per spike at the upper position and middle position, and has a remarkable influence on the grain number per spike at lower position. This indicates that the cultivation mode has significant impact on the distribution of grain number per spike, especially the impact on the upper position and middle position are much greater than the lower position. The nitrogen fertilizer rate only has obvious impact on grain number per spike at the upper position and has little impact on the middle and lower position. The planting density has an obvious impact on the grain number per spike for all of the position, especially more obvious impact on the middle position. In comparison with three cultivation factors, the planting density has the most impact on the grain number per spike, followed by the cultivation mode and the least is the nitrogen fertilizer rate. The interaction between or among with two or three of cultivation factors is not significant. In all of 5 cultivation modes, the cultivation modes of ditch and film cover have a higher grain number per spike for all position in comparison with the other three cultivation modes. The amount of nitrogen fertilizer application only has an obvious impact on the grain number per spike for the upper position, and the grain number per spike for upper position has an increment tendency with increasing of nitrogen fertilizer application. Increment of planting density significantly reduces the grain number per spike for all of the positions. (5) Different cultivation methods have different influences on the occupation ratio of each grain grades of wheat. The cultivation mode has an obvious effect on the ration of the medium gain and small grain wheat, and has little effect on the ration of the large grain wheat. The ratio reaches the highest with the cultivation mode of supplementary irrigation, and reaches the lowest with the cultivation mode of ditch. The nitrogen fertilizer rate and planting density have very small effects on the ration of each grain grade. The ditch cultivation mode has the highest ratio for small grain and the supplementary irrigation cultivation mode has the lowest ration for small grain. The cultivation mode has the most influence on the weight of thousand grains for the large grain and the obvious differences exist among the different cultivation modes; the cultivation mode has a small influence on the weight of thousand grains and there are no obvious differences among the different cultivation modes. The application of nitrogen fertilizer has little influence on the weight of thousand grains for large and medium grain, but has a significant influence on weight of small grains which tends to increase as the enhancement of the application of nitrogen fertilizer. The planting density has no remarkable influence on the weight of thousand grains for the large and medium grain, but has a noticeable influence on the weight of thousand grains for small grain. High planting density has an effect on increasing the weight of thousand grains against the low planting density.(6) Three cultivation factors have remarkable or extremely remarkable effects on the grain weight of spike. The planting density has the biggest effect on the grain weight of spike, followed by the cultivation mode and the nitrogen fertilizer rate is the least. The interaction between the two or among the three cultivation factors is not obvious. In 5 cultivation modes, ditch cultivation mode and film cover cultivation mode have relatively heavier weight than the conventional cultivation mode. As increment of application of nitrogen fertilizer, winter wheat shows its grain weight of spike has a tendency of increasing first and then decreasing. The increment of planting density can reduce the grain weight of spike significantly. The grain yield increases by 38.0%, 20.11%, 7.8% and -11.7% with the cultivation mode of ditch, film cover, grass cover, and supplementary irrigation respectively in comparison to the conventional cultivation mode. The grain yield increases remarkably with the cultivation of ditch and film cover. Along with the enhancement of nitrogen fertilizer rate, the wheat grain output also is increasing. The grain yield reached the highest value of 6994kg/hm2 when the 120kg/hm2 of nitrogen fertilizer rate is applied; but it has a little drop when the 240kg/hm2 of nitrogen fertilizer rate is applied. The grain yield reaches to 6121kg/hm2 and 6562kg/hm2 with the planting densities of 67.5kg/hm2 and 135kg/hm2 respectively. Comparing to the low planting density, the high planting density increases the grain yield by 7.2%. In summary, the cultivation factors have obvious effects on the single green leaf area of drought wheat , leaf area index, grain yield, grain number per spike, grain weight of spike and its distribution; but have little effects on the weight of thousand grains. There exists difference of the influences among the cultivation factors on the other observation characteristic besides the weight of thousand grains. Cultivation factors interact on the green leaf area. In cultivation mode, the ditch cultivation and film cover cultivation have obvious role, especially in the increment of yield. Enhancing the application of nitrogen fertilizer can obviously increase the green leaf area, leaf area index, grain number per spike, grain weight of spike and grain yield. But the higher application of nitrogen fertilizer has negative function for the wheat yield and no obvious positive function. Increasing planting density can increase wheat yield, but it lowers the grain number per spike and grain weight of spike. Its increment of yield has major benefit to the enlarging of plant quantity, i.e. the increment of numbers of spike to compliment. In short, by selecting the reasonable cultivation mode, reasonable nitrogen fertilizer application and suitable planting density, they can accelerate the drought wheat's individual plant growth, the community positive development and finally realize the high production goal. |
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