Synthesis Of Artificial Humic Acid Urea Fertilizer And Effect On Soil Nitrogen Transformation

The low efficiency of crops on nitrogen fertilizer is an urgent problem in agricultural production.The addition of artificial humus acid（A-HA）is an effective way to improve the utilization rate of traditional nitrogen fertilizers in the soil,but its structural heterogeneity reduces its performance.Firstly,in this study,different artificial humic acid fractions with different aromatization degrees and molecular weights were separated by improving the traditional p H fractionation method.Secondly,different artificial humic acid urea fractions（A-HAUs）fertilizers were prepared by melting method and the preparation mechanism was revealed.Finally,soil incubation experiments and root bag planting experiments were conducted to determine the enhancement of soil nitrogen utilization by artificial humic acid urea fertilizer and its regulatory mechanism on soil nitrogen conversion.The main research results of the paper are as follows:（1）Successfully separated A-HA_3-4,A-HA_4-5,A-HA_5-6 and A-HA_6-7 fractions in the p H range of 3-4,4-5,5-6 and 6-7 by continuously adjusting the extract solution p H value.The aromatization degree and the structure of the protonated aromatic carbon decreased with increasing p H of the extract solution.（2）Melt permeation experiments revealed the reaction mechanism of artificial humic acid and urea.During the melting process,the carboxyl and phenolic hydro xyl groups of the artificial humic acid are formed with the amide group of urea to form an artificial humic acid-urea complex with a secondary amide structure.Urea-N is loaded into the structure of artificial humic acid mainly by intermolecular for ces and chemical bonds and forms a urea film on its surface.（3）The application of artificial humic acid urea fertilizer has different effects on soil N utilization,greenhouse gas emissions and microbial community abundance.A-HAU_3-4fractions were able to provide higher levels of ammonium and nitrate nitrogen on days 3-14and maintained higher contents of soil total nitrogen on day 70.The increase in soil ammonium and nitrate nitrogen content depends on the rapid release of small molecule loaded nitrogen from artificial humic acid urea,while the increase in soil total nitrogen content depends on changes caused by the difficulty of degradation of nitrogen loaded into the artificial humic acid structure in the soil.At the same time,the application of humic acid urea fertilizer increased the relative abundance of Proteobacteria and Actinobacteriota in the soil and decreased the relative abundance of Acidobacteriota prompting humic acid urea to further regulate the soil nitrogen transformation through biological mechanisms.（4）The application of artificial humic acid urea fertilizer has different effects on crop growth.Under the fertilizer of the same nitrogen content,the physical hybrid application of artificial humic acids and urea and artificial humic acid urea fertilizer under the melting conditions have promoted the growth of corn crops.The physical mixing of artificial hum ic acid and urea is mainly through reducing the activity of urease,promoting urea nitrogen to slowly release the absorption and use of nitrogen in crops.The artificial humic acid urea fertilizer prepared under the melting conditions reduces its inhibitory effect on the urease activity under the action of plants,which is more conducive to the rapid decomposition o f microorganisms and release more ammonium nitrogen and nitrate nitrogen supply to the growth of crops growth.In the rhizosphere soil,the physical mixture of artificial humic acid and urea and artificial humic acid urea prepared under molten conditions i ncreased the relative abundance of the Actinobacteriota and decreased the relative abundance of the Proteobacteria compared to urea applied alone.Actinobacteriota and Proteobacteria are two major phylum involved in the decomposition of soil organic matter and the transformation of soil nitrogen,helping to maintain the nitrogen balance in the soil.Therefore,the physical mixture of artificial humic acid and urea applied and artificial humic acid urea prepared under molten conditions influences soil nutrient content and community structure of soil bacteria,which affects the nitrogen cycle process in the fertilizer-soil-plant.