Study On Nitrogen Competition Between Winter-Wheat And Weed

Weed always grows among crops. If clean up all of weed from the agro-ecosystem, there would be the lack of gene storage in genetics, while the balance would be broken in ecology because of the rupture and lose of food chain. Weed on the one hand is the main factor on baffling crops growth, on the other hand is the important part of agro-ecosystem. Concerning from ecology and genetics, maintaining certain amount of weed is useful for protecting the bio-diversity of agro-ecosystem, and therefore protecting the bio-diversity of the ecosystem in the whole world. Former researches on the nitrogen competition between winter-wheat and weed mostly focused on the strain and yield of winter-wheat and weed, but there was short of the study on the effects of medium nutrition on the nitrogen competition between crops and weed. Our research used the Eun-Orthic Anthrosols soils and Xiaoyan No. 22 as soil samples and test crops, and designed three factors which were fertilization, weed and planting density by using incomplete block design. The planting density is the main treatment, while weed planting is the subsidiary one, and fertilization is the least subsidiary treatment. The planting density includes low level and normal level, and there four types of planting weed in each density level which are not cleaning weed in the whole growth stage (A), cleaning weed in the stage of across winter (B), cleaning weed in stage of reviving (C), and cleaning weed in the stage of booting (D). The treatment of normal planting density includes not applying fertilizer (P0N0), applying only phosphorus fertilizer (PN0), and applying 45kg, 90kg, 135kg and 180kg nitrogen fertilizer per hectare on the base of applying phosphorus fertilizer named (PN45,PN90,PN135,PN180). But the treatment of low planting density includes not applying any fertilizer (P0N0), applying only phosphorus fertilizer (PN0), applying only nitrogen fertilizer (P0N135), and applying phosphorus and nitrogen fertilizers together (PN135). This research using field experiment and lab analysis studied the relationship between the characteristics of weed strain and fertilization in the winter-wheat agro-ecosystem, the competition relations of nitrogen between weed and winter-wheat, the influence and relationship of weed on the yield of winter-wheat and so on. The main results are shown as follows:1. There were 17 types of weed in the experiment blocks which are belonged to 12 sections and 15 categories. Among the weed the amount of Cruciferae weed is the largest which has 3 categories and 5 strains, Composite weed has 2 categories and 2 strains, and other weed belongs to 1 section, 1 category and 1 strain. Analyzing the weed diversity index revealed that the enrichment degree, Simpson and Shannon diversity indices in the low planting density blocks were all higher than those in the blocks of normal planting density, and there was no significant disciplinarily difference between each treatment for the symmetrical indices. The Simpson and Shannon diversity indices for weed in the blocks of applying phosphorus fertilizer were significantly higher than those in the blocks of not applying any fertilizer. Under the treatment of applying nitrogen fertilizer, the enrichment degree, Simpson and Shannon diversity indices for weed were a little higher than those in the control blocks.2. Applying nitrogen fertilizer could significantly increase the density and biomass of weed. The biomass of weed was the highest under the treatment of applying low amount of nitrogen fertilizer. The biomass of weed decreased with the increase of the amount of nitrogen fertilizer applied. Applying phosphorus fertilizer and low planting density both could increase the density and biomass of weed significantly.3. The contents of nitrogen in the main types of weed in the winter-wheat field changed with the winter-wheat growth stages ordered as: the stage of across winter> the reviving stage> the booting stage> the autumn stage. The contents of nitrogen increased significantly with the increase of the amount of nitrogen applied (P<0.05). The total amount of nitrogen absorbed by weed change in the order as: the booting stage> the reviving stage> the autumn stage> the stage of across winter, and the values for different stages had significantly difference (P<0.01). The correlation coefficients between the amount of nitrogen absorbed by weed and the amount of nitrogen applied in the stage of across winter, the reviving stage, the booting stage, and the autumn stage were 0.7241, 0.6593, -0.8041 and 0.2647, all of which did not reach the significant level (r0.05=0.8783). The correlation coefficients for the comparatively ratio of the nitrogen absorbed by weed and the amount of nitrogen applied were 0.684, 0.561, -0.923 and -0.887 respectively (r0.05 = 0.8783), which indicated that although the positive correlation between the amount of nitrogen applied and the amount of nitrogen absorbed by weed was not significant, increase the amount of applying nitrogen could promote the distribution of nitrogen in weed in a certain extent in the former stage of crop growth because the weed competition ability of absorb nitrogen was higher than that of winter-wheat. While, in the medium and last stages of crop growth, the comparative ratio of the nitrogen absorbed by weed and the amount of nitrogen applied was negatively correlated, which revealed that the weed competition ability of absorb nitrogen decreased significantly. The critical stages for the competition of nitrogen between weed and winter-wheat were the stage of across winter and the reviving stage.4. The influence of applying phosphorus fertilizer on each type of weed was not significant, but applying phosphorus fertilizer could increase the amount of nitrogen absorbed by weed. Applying nitrogen and phosphorus fertilizers together could significantly increase the amount of nitrogen absorbed by weed. Under the low level of nitrogen and phosphorus applied, the amount of nitrogen absorbed by weed decreased after the booting stage, but that amount decreased after the reviving stage under normal level of nitrogen and phosphorus applied. Applying phosphorus could advance the decrease stage of weed absorbing nitrogen, and therefore is useful for baffling weed absorbing soil nitrogen in the last stage of crop growth.5. The effect on wheat yield and N uptuke is different, in the different cleaning weed stage. It indicate the critical stages of N competition between wheat and weeds. The yields of winter-wheat is not significant both cleaning weed in the stage of across winter and the reviving stage. Compared with over-winter stage and reviving stage, the yield is significantly.descrease because cleaning weed in jointing stage and no weeding all stages , by 1.9% and 2.0%, respectively. It is indicated that there is an obvious effect on yield of cleaning weed in the different growing stage. There is a great effect on yield of weed lived with crop together between reviving stage and jointing stage, so the best way is cleaning weed in the reviving stage. However, the influences of cleaning weed on the amount of nitrogen absorbed by winter-wheat in the autumn stage go as the order of: not cleaning weed in the whole growth stages> cleaning weed in the booting stage> cleaning weed in the reviving stage> cleaning weed in the stage of across winter. The influences for the stages of cleaning weed on the nitrogen utility efficiency of winter-wheat ranked as: not cleaning weed in the whole growth stages> cleaning weed in the stage of across winter> cleaning weed in the booting stage> cleaning weed in the reviving stage. Weed lived with crop together could improve absorbing nitrogen ability of crop, while the ability for crop of transferring nitrogen to seeds would decrease.