Primary Studies On Allelopathy Of Root Exudates Of Main Crops And Continuous Cropping Of Soybean

In recent years, the phenomenon of continuous soybean became very serious in Heilongjiang province. As to continuous cropping, both adverse-resistance and production decrease dramatically. The continuous soybean was pervasive and with significant obstacles. The root secretion in continuous cropping obstacles played the role directly or indirectly. More and more experiments prove that the continuous cropping obstacles had something with allelopathy of the root secretion. Allelopathyeffect was one of the important reasons. This experiment used soybean for materials, normal soil and continuous cropping soil for planting soybean in pots, and collected root secretion, identifid the root exudates of soybean, contrasted the differences between soybean rotation and continuous soybean, using soybean, corn, and wheat for the selecterd crops. By testing seed germination index, seedling morphological index (stem length, stem fresh weight, primary root length, root fresh weight of dedifferentiation etc) and physiological indexes (root vigor), compared allelopathy of the main cropping to seedling stage with the one of continuous cropping. Specific research results were as follows:1 From two kinds of soybean root secretion, we detected, acid and glycol esters, phenol, hydrocarbon, benzene, amides, naphthalene, aldehydes and ketones material and other hydrocarbons derivatives. In the extractive of root extract of continuous soybean, high concentration were (E)-2- butenoic acid,7-9- dimethyl-hexadecane, methyl- succinic acid, 2- ethyl -1- lauryl alcohol, eicosane, undecanal, which were not detected in soybean secretion of main crops. The allelopathy in these substances of continuous soybean needed to be further studied.2 Root secretion of soybean rotation had inhibition to seed germination, with increasing concentration and inhibition, which had significant effect of soybean seed germination and inhibition of germination rate,For seed germination and germination rate of wheat and corn, it showed promotion..3 The root secretion of main soybean and continuous crops showed inhibition to root activity of soybean seedlings, SOD activity. With the concentration became bigger, the inhibition strengthened. The inhibition rates of main crops with 2x concentration on the stem length, stem weight, primary root length and root weight were respectively 45.2%, 30%, 50%, and 18.6%, while continuous cropping with 2x concentration for above are 57.4 %,32.5 %, 56.4%,23.2%. Under the same concentration, the root exduates of continuous soybean had higher allelopathy against soybean than soybean rotation.4 Root secretion of main crops soybean promoted the allelopathy in plant morphology and physiological indexes for materials selected. With the concentration became bigger, the allelopathy strengthened. Continuous crops promoted allelopathy for above factors more dramatically.5 With the concentration of root secretion of main cropping soybean increased, the effect for selected plant---wheat's seed germination, germination rate, root vigor and SOD activity became bigger, and MDA content of wheat decreased. But wheat length and fresh weight, primary root length and root fresh weight all indicated that promotion of high concentration and inhibition of low concentration. With the concentration of continuous soybean increased, it showed inhibition both for root vigor, SOD activity and stem length, stem weight, root length, root weight .