The Toxic Threshold By Biuret To Crops In The Compound Fertilizer And Research On The Degrading Bacterium Of Biuret

Biuret content in the fertilizer is a harmful product, which has been proved by the researchers. It is produced during the granulation process of urea due to high temperature. The excess content of biuret in urea fertilizer causes damage to the wheat and corn. If biuret content exceeds 1.5 percent, it is not suitable for application to the crops. However, national quality standard of complex fertilizers has not established restrictive quantitative indicators for biuret content.At present, there is no permanent solution to overcome the toxic effects of the biuret content, only some traditional methods:proper handling of plough, reseeding or replanting of the crops and supplementation with other N-P-K compound fertilizers.The purposes of this research are:firstly, to find out the threshold level of biuret for crops which could provide some quantified scientific basis for the national standard formulation of complex fertilizer; Secondly, to use a simple examination method for screening some strains which could degrade biuret; Thirdly, to coloninze the gfp gene into the strains which degrade biuret for tracing colonizaition near the roots of crops in the soil.The solution culture and pot method were used to determine the toxic threshold of biuret on testing the wheat, corn, tomato, rape and rice under suitable fertilized condition. The results of solution culture indicated that biuret content should be less than 35mg,40mg,20mg,15mg,15mg in 1L aqueous solution. The results of pot method proved that the level of biuret was controlled under 1.6%,2.0%,2.0%,2.0%,2.0% in compound fertilizer. Advising the amount of biuret standard of the complex fertilizers is controlled under 1%.The biuret-degrading strain GW-1 was screened out from the soils of Xinjiang,Henan and Nanjing. The biuret-degrading rate of was 76.98% in 20 hrs, which reached up to 100% after 34hrs. It was identified as Klebsiella by the physiological and biochemical methods and sequence analysis of 16S rDNA.The gfp gene was marked to the GW-1 strain successfully and named GW-1-GFP, through comparing to the morphological character, plasmid, fluorescence detection, and biuret degrading ability. The ability of GW-1-GFP degrading biuret was similar to the strain GW-1.The result of HPLC indicated that the strain GW-1-GFP can degrade biuret more than 50% under all the treatments in different soils in 25d,it has a good effect on degrading biuret in the soil.Using the pattern of potted discovered that the strain GW-1-GFP can alleviate the biuret toxicity to crops, comparing to the CK. The strain GW-1-GFP can promote absorbtion of the K and P element.