TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Strain: The strain comprises 16 sDNA sequence comprising 1378 bp (SEQ ID NO: 1), given in the specification. Preparation (claimed): Culturing the root nodule nitrogen-fixing bacterial strain RY3 comprises processing and crushing the collected root nodule after sterilizing it to obtain juice, placing the juice to an incubator of 28 degrees C plus minus 1 degrees C on YMA solid culture medium for culturing in dark. The method comprises (a) washing the root system of S. guianensis, cutting off 2 mm root of the root nodule band and washing it; (b) crushing the washed root nodule after sterilizing it, dipping milky juice on the YMA solid culture medium for scribing, reversely placing the scribed plate to a freshness protection package for culturing in dark in an incubator of 28 degrees C plus minus 1 degrees C; (c) starting to check whether there is bacterial colony on the YMA solid culture medium on the third day of culturing, labeling the bacterial colony to record its shape and glossiness; and (d) removing the non-root nodule bacterial colony, selecting out the bacterial colonies, time difference of which for growing single bacterial colony is more than 3 days according to the labeled bacterial colony and the bacterial colonies, growth shapes, bacterial colony size, bacterial colony transparency and refraction under light and bacterial colony color of which are not consistent, scribing and numbering on new culture medium, scribing the plate, which is gradually passivated, processed from microscopic examination and back tying, to YMA inclined surface for storing. Sterilizing in step (b) uses sterile water to wash after soaking it with 95% of alcohol, and adds 0.1% mercury chloride (HgCl2) for sterilizing. The YMA solid culture medium comprises 10 g mannitol, 0.25 g dipotassium phosphate (K2HPO4), 0.2 g magnesium sulfate heptahydrate (MgSO4.7H2O), 0.25 g potassium dihydrogen phosphate (KH2PO4), 0.1 g sodium chloride (NaCl), 3 g yeast and 15 g agar. Preferred Bactericide: The bacteria adsorbent is grass carbon, vermiculite or perlite; the mixed proportion is as follows: 50 g grass carbon to 10 ml bacteria liquid, 15 g vermiculite to 10 ml bacteria liquid, and 15 g perlite to 10 ml bacteria liquid. ACTIVITY - Plant Protectant; Antibacterial.