The Preparation And Agricultural Application Experiment Ofγ-Poly-Glutamic Acid

y-polyglutamic acid is a new type of biological degradable water-soluble polymer, and its unique structure and physical and chemical properties make it have a broad prospect of application in agricultural. The purpose of this study was provide a theoretical basis for the y-PGA’s promotion and application in agriculture. In laboratory, a high productive of y-PGA was obtained from the flask fermentation and100L fermentation test by Bacillus natto ZW-2, using microbiological methods and techniques. Besides, preliminary discussion of the effects of y-PGA was studied on yield, quality and utilization ratio of fertilizer in cabbage and rape pot experiment, as well as the yield, quality and the content of nutrient in soil in greenhouse lettuce trials. The principal conclusions of this study are as follows:1、 Firstly, Screening of fermentation conditions for y-PGA was studied in laboratory. The medium composition and culture conditions were optimized by single factors to determine the composition of the fermentation medium and the basis of fermentation conditions preliminary. Three important factors on yield of y-polyglutamate was selected by Placket-Burman experiment, then the best composition of medium of this three factors by steepest ascent design was as follows:L-sodium glutamate68g/L, NH4CI1.2g/L, K2HPO42.2g/L. Lastly, the optimal prediction yield of y-PGA(36.5018g/L) was achieved by Box-Behnken Design experiment,and the best composition of medium was as follows: glucose40g/L, L-sodium glutamate68.76g/L, NH4C11.16g/L,yeast extract paste3g/L, K2HPO42.16g/L, CaCl20.4g/L, MgSO40.3g/L; and the optimum fermentation conditions was as listed below:inoculum size2%, loading volume80ml/250ml, shaking speed180r/min, initial PH7-7.4, temperature37℃, fermentation time72h.2、Preparation and correction parameters of y-PGA was carried out in100L tank on the basis of optimized fermentation experiments in the flask. The effect of the initial concentration of the carbon source (glucose) and precursor (glutamate) to the growth of Bacillus natto (Bacillus natto) ZW-2and yield of y-PGA was studied by single factor experiments. The results showed that:The number of bacteria can significantly increase in the fermentation broth when the concentration of glucose and sodium glutamate were20g/L and30g/L. Further, the fermentation of y-PGA was investigated by fed-batch culture. The results says that the yield was highest(48.15g/L) when the feeding time was16h after fermentation(prophase of stationary phase of strain), which was significantly higher than the yield obtained by conventional methods of fermentation(34.35g/L). In addition, the effect of different types and different amounts of flocculant to the yield of y-PGA was studied, and the result says that the yield of y-PGA is higher when the amount of alcohol was2.5times fermentation broth.3、In this part, impact of y-PGA on the yield, quality and utilization of fertilizers of potted cabbage and rape was studied.Under the normal conditions of fertilization, compared with no added y-PGA of CK treatment, the results:1)The treatment with y-PGA added can improve plant height and fresh weight of potted cabbage and rape, the extent of height growth in potted cabbage and rape, respectively, was 0.03%-16.88%and3.91%-12.76%. Besides, on the condition of20%reduction in fertilizer, the height of Cabbage and rape respectively increased12.81%and3.12%, and the fresh weight growth of potted cabbage respectively increased9.08%and2.47%compared with the treatment of CK, when the addition of y-PGA reaches5‰;2) The treatment with γ-PGA added can improve the content of Vitamin C and the value of SPAD in potted cabbage and rape, the highest increase of the content of Vitamin C, respectively, was25.24%and20.78%, and the highest increase of the value of SPAD, respectively, is34.27%and16.18%. Besides, the treatment with y-PGA added could hence the nutritional quality, and the maximum decrease, respectively, was29.99%and37.79%;3) The treatment with y-PGA added can improve the utilization efficiency of nitrogen, phosphate and potash in the soil of potted cabbage and rape, and the highest increase, respectively, was39.15%,39.16%,46.15%and34.75%.12.30%,75.05%. Beside, With the amount of fertilizer reduction, the synergies of fertilizer utilization was rose with the addition of y-PGA.4, In this part, impact of y-PGA on the yield, quality and soil nutrients of greenhouse lettuce was studied. The results says:1) The treatment with y-PGA added could improve fresh weight of greenhouse lettuce, the highest increase of the fresh weight was10.54%compared with the treatment of CK when the addition of y-PGA reaches5%o;2) The treatment with y-PGA added could improve the content of Vitamin C. soluble sugar and chlorophyll, and the highest increase, respectively, was132%、14.86%and29.42%. Besides, the treatment with y-PGA added could hence the nutritional quality, and the maximum decrease, respectively, was61.49%;3)The addition of y-PGA have a significant difference of N03-N and NH4-N in soil just11days after fertilizer. When the sampling time was11、18.25、32、39, the highest increase of NO3-N, respectively, was90.41%、234.80%、91.61%、94.42%、121.77%and the highest increase of NH4-N, respectively, was40.73%、31.96%、29.16%、47.60%、55.57%、57.10%compared with the treatment of CK;4) The addition of y-PGA had a significant difference of soil available phosphorus just18days after fertilizer. When the sampling time was18、25、32、39, the highest increase of soil available phosphorus, respectively, was27.37%、35.40%、44.35%and72.64%.