| Root exudation of wheat, corn, broad bean and pigeon pre were identified, and biological characteristics of three kinds of root exudation were tested by hydro-culture and germination experiments. Effect of 3-methyl phenol on root growth, soil microbial and enzyme activity, as well as the root vertical distribution and rhizosphere effect of different intercropping systems were comprehensively studied by pot, pond and box experiments. The main results are:1. Root exudation of wheat, corn, broad bean and pigeon pea mainly include organic acid, phenol, hydrocarbon, grease, ketone, mellow, amide, benzene, aldehyde and thiazole et al. It was proved that benzalhyde, 3-methyl phenol and 1,2-Benzenedicarboxylic acid secreted by pigeon pea, wheat and corn respectively were three kinds of allelochemicals, among these 3-methyl phenol has the strongest allelopathic effect. The effect of allelochemical on dry weight of seeding (SDW) is more serious than on dry weight of root (RDW), there is no significant additive effect among the three allelochemicals.Bio-test showed that allelopathic effect of benzalhyde, 3-methyl phenol and 1,2-Benzenedicarboxylic acid at the concentration of 150 X 10-6mol/l on SDW of mono wheat is 0.2043, -0.3287and 0.1181 respectively, and at the concentration of 450 X 10-6mol/l the allelopathic effect is -0.2724, -0.3869and -0.2558 respectively; allelopathic effect of the three kinds allelochemicals on SDW of corn is 0.2667, -0.4641, -0.3628 at the concentration of 150X 10-6mol/l and -0.2376, -0.7971, -0.4422 at the concentration of 450X 10-6mol/l respectively.Allelopathic effect of mixed solution(BPA) which is consisted by three kinds allolochemical solutions at 150X10-6mol/l is weaker than that of 3-methyl phenol at concentration of 450X 10-6mol/l, it indicates that not any of the allelochemicals can carry out additive effect. Negative effect of benzaldhyde and 3-methyl phenol mixed solution(BP) and BRA on germination rate, root dry eight, shoot dry weight of mono wheat are 4.39% and 111.12%, 169.11 % and -417.34%, -42.31 % and -44.33% higher than that of 3-methyl phenol at high concentration; negative effect of BP on germination rate, root dry weight, shoot dry weight of wheat in wheat corn mixed cultured system are 43.32% and -96%, -34.64% and -205.88%, -28.22% and -32.86% higher than that of 3-methyl phenol at high concentration.2. 3-methyl phenol can promote the biomass of different crops at the concentration of 150 X l0-6mol/l.soil , it shows negative allelopathic effect on crops growth as the concentration higher than 150 X 10-6mol/l.soil, the higher of the concentration the stronger of the allelopathic effect; the competitive of intercropped wheat to corn is enhanced by 3-mwthyl phenol, phosphorous supplication can weaken the competitive difference between wheat and corn in intercropping system. Negative effect of 3-methyl phenol on harvest index of inter-crops is more significant than that of the mono-crops.Compared to the control, biomass of mono wheat(MW), mono broad bean (MB) and wheat broad intercropping(IWB) was promoted by 10.76%, 14.74% and13.51% as the treatments were dealt with 3-methyl phenol at the concentration of 150 X 10-6mol/l.soi(A1), 3-methyl phenol at the concentration of 300 X 10-6mol/l.soi (A2) made the biomass of MW, MB and IWB decreased by 0.32%, 4.62% and 6.8%, and atthe concentration of 450X 10-6mol/l.soi (A3) the decrease of the three cropping patterns was 12.47%, 46.71% and 25.10% respectively.Negative effect of 3-methyl phenol was show on biomass of IWB at different phosphorous supplication levels(P0-0, P1-100mg P2O5/kg.soil, P2-200mg/kg.soil), in wheat jointing stage biomass of IWBP0, IWBP1, IWBP2, A2IWBP0, A2IWBP,, A2IWBP2 was enhanced by 38.95%, 0.97%, 15.02%, 34.98%, 13.86%, 14.12% compared to the control respectively, and in flowering stage the biomass was improved by 12.10%, 19.84%, 13.82%, 7.91%, 31.21%, 23.62% respectively; in harvest stage biomass yield of the above six cropping patterns was improved by 11.24%, 7.20%, 17.28%, 0...
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