| There are two problems which the China's agricultural faced at present:the shortage of agricultural water resources and the excessive use of fertilizers.Rational use of polymer materials is also one of important measures to reduce the agricultural water and fertilizer application.Poly-y-glutamic acid(?-PGA)and its derivatives are emerging as high molecular polymers which can be completely degraded and environment-friendly,so it has also attracted the attention of agricultural science and technology workers.This thesis is based on the relevant research content at home and abroad,combined with the National Natural Science Foundation of China,and the conditions for synthesis of ?-PGA SAP by ?-PGA were explored.The effects of ?-PGA and ?-PGA SAP on soil water movement and soil physical properties were studied by indoor soil column experiments,and they were applied to pot experiment.The experiments of normal irrigation and fertilization,low water with 21%irrigation or low fertilizer with 30%fertilization were set up to study ?-PGA and ?-PGA SAP.The effects of ?-PGA and ?-PGA SAP on crop growth and root zone microenvironment are as follows.The main achievements are as follows:(1)The preparation conditions of ?-PGA SAP were studied and explored,and its properties were characterized and determined.The ?-PGA SAP is synthesized by aqueous solution polymerization method.When polyethylene glycol diglycidyl ether(PEGDE)is selected as the crosslinking agent,the content of crosslinking agent was more than 20%of the mass of ?-PGA,the ?-PGA SAP could be synthesized effectively.The results showed that the lowest decomposition temperature of agricultural ?-PGA was 296.9?,and the lowest thermal decomposition temperature of ?-PGA SAP is 239.8?.Agricultural ?-PGA is the typical high molecular water-soluble polymer,and its viscosity increases linearly with the increasing of y-PGA concentration.When the content of PEGDE is 20%?60%of the mass of ?-PGA,the water absorption ratio(distilled water)of the synthesized ?-PGA SAP is between 651.19 g/g?302.91 g/g,and the water absorption ratio(0.90%NaCl solution)is between 44.83 g/g?32.93 g/g,which meets the requirements of Ministry of Agriculture for the absorption range of super absorbent polymer(water absorption ratio:100?700 g/g,salt water absorption ratio:>=30 g/g).The absorption rate of distilled water and 0.90%NaCl solution with different cross-linking agent content decreased significantly after repeated absorption drying.The more contents of cross-linking agent in the ?-PGA SAP,the better liquid absorption stability.The smaller particle size of the ?-PGA SAP,the faster initial liquid absorption rate,and which the shorter time required reaching the stability of the liquid absorption.There is no significant difference in the absorption ratio of ?-PGA SAP with the different particle sizes after being stabilized.(2)It is found that the application of different rates of ?-PGA and ?-PGA SAP in the soil had a certain degree of influence on soil water transport characteristics and soil physical properties based the analysis of soil column experiments.The application of agricultural ?-PGA and ?-PGA SAP in the soil could reduce the infiltration of soil water.And the more amount of?-PGA and ?-PGA SAP applied in the soil,the greater decreasing of cumulative infiltration rate.The same amount of ?-PGA in the soil had a greater decrease of cumulative infiltration than that of ?-PGA SAP.The field water capacity and total available water which could be used with the increasing if ?-PGA SAP application amount,and the retention time of total available water in the soil were significantly prolonged.While ?-PGA in the soil had no significant effect on soil field water capacity and total available water,but it could extend the retention time of soil available water,and there was no significant difference between different application amounts.The application of ?-PGA SAP in the soil could significantly increase the contents of soil water-stable aggregates and the stability of soil water-stable aggregates.However,?-PGA had no obvious effect on water-stable aggregates and soil structural stability.Compared with the control group,the soil porosity of ?-PGA SAP was significantly increased,and the soil porosity of the ?-PGA treatment is also higher than that of the control group,but there was no significant difference between control group and ?-PGA treatment.(3)It was found that the application of agricultural ?-PGA and ?-PGA SAP had a certain degree of influence on the microenvironment of soil in the root zone.The average of soil water content increased with the increasing amount of ?-PGA SAP applied to the soil,but the effect of?-PGA on the average soil water content of winter wheat was not obvious.The contents of nitrate nitrogen and ammonium nitrogen in soil increased with the increase of ?-PGA application amount;the ?-PGA SAP can obviously increase the content of soil ammonium nitrogen,but had little effect on the contents of soil nitrate nitrogen.The increase of ?-PGA and?-PGA SAP could increase the abundance of soil microorganisms(bacteria,fungi and actinomycetes)and the activities of soil enzymes(urease,alkaline phosphatase and sucrose).When the application amount of both them is the same,the abundance of soil microorganisms and the activities of soil enzyme increases in the treatment of ?-PGA were higher than that in the treatment of ?-PGA SAP.After the whole growth period of winter wheat,the addition of ?-PGA and ?-PGA SAP could increase the contents and stability of soil water-stable aggregates which the particle sizes less than 0.25 mm.(4)It was found that the application of agricultural ?-PGA and ?-PGA SAP had no significant effect on the ear length,ear diameter,grain number per ear and 1000-grain weight of winter wheat.The yield of winter wheat increased with the increase of the application amount of agricultural ?-PGA and ?-PGA SAP in the soil.However,when the application amount of ?-PGA and ?-PGA SAP was greater than 0.05%,the increasing speed of the winter wheat yield decreased,which increased by 7.62%or 4.85%respectively compared with the control group.In the treatment of reducing irrigation by 30%,the increase of yield by applying the same amount of ?-PGA SAP was higher than that by applying the same amount of ?-PGA,the ?-PGA SAP have better water holding capacity.When the application amount of ?-PGA was greater than 0.15%,the increase speed of wheat yield was decreased,which was 14.81%higher than that of control group.When the application rate of ?-PGA SAP is greater than 0.10%,the increase speed of wheat yield was decreased,which was 22.46%higher than that of control group.In the treatment of reducing 30%fertilization,the increase yield by applying ?-PGA was higher than that by applying ?-PGA SAP,and ?-PGA showed a better synergistic effect of fertilizer.When the application amount of ?-PGA is more than 0.10%,the increase speed of wheat yield decreased,which was 14.79%higher than that of the control group.When the application amount of ?-PGA SAP was more than 0.15%,the increase speed of winter yield was decreased,which was 13.98%higher than that of the control group.The application of ?-PGA and ?-PGA SAP in the soil could improve the water use efficiency and partial fertilizer productivity.The protein content of wheat kernels was significantly increased by the application of ?-PGA in the soil,while the protein content of wheat kernels was not significantly affected by increasing the application of ?-PGA SAP in the soil.The starch content and reducibility sugar content of wheat kernels were not significantly affected by the application of ?-PGA and ?-PGA SAP in the soil. |
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