| The experiment was carried out at the greenhouse of crop cultivation and farming system program of GAU in Mar.-Oct.,2000. Wheat/Broad bean (W/B)was selected to study as trial crop. The differences of physiological and ecological properties of root system between two intercropped crops in whole life and the effects of mineral nitrogen(N) and phosphorous(P) were studied with pot, rhizobox and pond methods, further analyzed the physiological and ecological mechanism of root system to intercropping?s high nutrient use efficiency(NUE). The results showed that: 1. The yield of intercropping was increased obviously compare to monoculture. For all treatments, LER>1. The grain yield of intercopping was 20.97% more than mono-wheat(MW).and 12.26% more than mono-broad bean(MB). The biological yield of intercropping was 22.63% more than MW. and 22.70% more than MB in mature period. The increasing of N and P applvinQ could regulate the grain yield and harvest index. Moreover, applying a little amount of fertilizer would intensify the competition between wheat and broad bean. But, if the amount of fertilizer surpass the saturation. further applying would relax the competition. 2. Under different N and P nutritious level, the peaks of weight. length, length density and surface area of two crops?root in the intercropping was interlace in whole life. All these indexes of two crops decreased progressively wave upon wave in vertical and inlaid with each other. So the nutrient niche of two crops separated in time, and inlaid with each other in space. this characteristic was advantageous to the intercropping to make full use of water and nutrients, and it is a main mechanism for the intercropping's high productivity. N and P nutritious level also had significant relevance with intercropping colonys root length(RL) and root weight(RW), but it had no use to root surface area. In addition, with the change of N and P, the RW and RL changed in the same 3 tendency with that of grain yield. Therefore, using N and P to regulate colony抯 RW and RL, the yield and NUE could be improved. 3. The weight of root nodule in intercropping was 68.3 3% higher than that in monoculture. Intercropped bean's(IB) ability of biological nitrogen fixation(BNF) could be regulated by N and P nutritious level. Lower N was advantageous to BNF. The weight of root nodule under N0 were 71.75% higher than N1,and in same N level, lB's ability of BNF improved with the applying of P, but the effect of P on MB is reverse. 4. In all treatments, the vigor of intercropped wheat(IW) was stronger than that of relevant MW. The SARN and SAR~ in intercropping was 59.05 and 61.50% higher than monoculture respectively, and it could be improved by applying P. Under different P treatments, the root vigor of W/B colony became strongest by middle or middle to low level of N. The amount of N and P absorbed by LW was 118.58% and 122.97% more than MW respectively, but the amount of N and P absorbed by LB was 23.25% and 27.75% lower than MB. The content of total P(TP) remained in intercropping under N1 level was 11.39% lower than MW, and 5.06% higher than MB, but the P remained in intercropping soil was more available than that of monoculture under lower N level. The amount of available N remained in intercropping under lower N level was also more than monoculture. In all treatments under N0, the content of TP remained in interc...
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