| Abstract: Filed experiments were carried out at Yangling and Qishan by using the manual loessial soils in the semi-humid area, which is in the south of the Loess Plateau with 628.8mm precipitation per year. The experiments were designed with different levels of nitrogen application including to apply no nitrogen and 120 kg/ha nitrogen, different cultivars of winter wheat (Xiaoyan 22 and Xiaoyan 503), and various modes of cultivation, which consisted conventional cultivation, the mode of mulching in the whole growing period, the mode of mulching 150 days, the mode of planting with different line distance (there are three lines with closer distance and one line with wide distance), and the mode of intensive rainfall cultivation. Using the results from the above experiments, we studied the effects of winter wheat source-sink change on the yield of winter wheat and its yield structure, which would be concluded as follows:1. It was found out that there was no significant difference of the number of spike between the treatments of removal leaf and not removal leaf. However, the weight of per thousand spikes decreased in various extents after removing leaves at different locations. Compared with CK treatment, there was no significant decrease for the weight of per thousand spikes with the treatment of removing flag leaf, while after removing other leaves, the weight of per thousand spikes decreased significantly. The decrease of that weight with the treatment of removing 1/2 flag leaves was the highest, and the extent of the weight decrease went higher with the increase of the number of removing leaves. The weight per spike with the treatment of removing leaves was lower than that of CK except the treatment of removing flag leaves, the weight per spike with which was similar to that of CK. For the treatment of removing 1/2 flag leaves, the weight per spike decreased most significantly.2. The effects of removing leaves on the number of spike, the weight of per thousand spikes and the weight per spike were different because of various mode of cultivation, different levels of nitrogen application and different cultivars of winter wheat. The number of spike after removing flag leaves under those treatments was higher than that of no leaf removing treatment except that under the treatments of intensive rainfall cultivation mode, the mode of planting with different line distance, the conventional cultivation, and the mode of mulching 150 days. The weights of per thousand spikes under different modes of cultivation after removing flag leaves were lower than that of CK. However, compared with CK, the weight per spike increased after removing flag leaves under the treatments of different modes of cultivation, which referred to the extra compensation effect with removing flag leaves, while removing leaves at other location could restrict the enrich of spike. The number of spike, weight of per thousand spikes and weight per spike for Xiaoyan 22 were higher than those for Xiaoyan 503 significantly. For Xiaoyan 22, which is the type of winter wheat with large spikes, the number of spike decreased after removing leaves. General speaking, removing leaves could reduce the weight of per thousand spikes for all cultivars of winter wheat in experiments except the treatment of removing flag leaves for Xiaoyan 22. Nevertheless, the decrease of weight of per thousand spikes for Xiaoyan 22 under those treatments was higher than that for Xiaoyan 503. The treatment of removing leaves caused the difference of spike weight per thousand for Xiaoyan 22 and Xiaoyan 503 deceasing. The weight per spike for those two cultivars increased under the treatment of removing flag leaves, however, the weight per spike decreased by removing other leaves. The extent of decrease of weight per spike for Xiaoyan 22 was higher under the treatment of removing flag leaves than the extent of that for Xiaoyan 503 under the same treatment. After applying nitrogen, the number of spike, the weight of per thousand...
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