Effects Of Fulvic Acid And Polyaspartic Acid On Nitrogen Uptake Of Vegetables And Transformation Of Fertilizer Nitrogen

In recent years, fulvic acid （FA） and polyaspartic acid （PASP） as fertilizer additives has developedrapidly in the process of production and application. In order to investigate the effects and possiblemechanisms of combined application of FA, PASP and nitrogen fertilizer in alkaline soil, fourexperiments were conducted. Field experiment and hydroponic experiment were conducted to study onthe effects of FA and PASP on the growth and nitrogen uptake of cabbage, radish and water spinach.Thermostatic incubation experiment was conducted to explore the effects of combined application of FA,PASP and urea on nitrogen transformation, while pot trial with15N tracer technique was conducted toclarify nitrogen uptake and fate of nitrogen fertilizer in water spinach. The main conclusions are showedas follows:1. There were different productions and nitrogen uptake rates of cabbage and radish undertreatments of different application rats of FA and PASP. When the amount of FA was72kg·hm-2, theproduction and nitrogen uptake rates of cabbage was increased by13.25%and16.06%, which wasincreased by10.50%and14.10%respectively when the amount of PASP was15kg·hm-2. After theapplication of FA and PASP, the yield of radish was increased significantly, but the nitrogen uptake rateof radish had no obvious change.2. The root morphology, biomass and nitrogen uptake rates of water spinach changed significantlyat the suitable concentration of FA and PASP. When the concentration of FA was400times diluting, thefresh weight of water spinach was increased significantly, total root length and root surface area wasincreased by25.76%and22.61%respectively，but nitrogen uptake rates of plant had no obvious change.When the concentrations of PASP were2000and1200times diluting, the biomass, nitrogen uptake rates,total root length, root surface area and root volume of water spinach increased significantly and nitrogenuptake rates of water spinach had high positive correlation with its root morphology.3. Compared with urea treatment, the transformation rule of nitrogen in soil was different undervarious application rates of FA and PASP.（1） The NH₄⁺-N content of soil was decreased by7.54%³8.15%after FA was applied, which verified the absorption of FA on NH₄⁺in soil. Duringincubating, nitrogen production rate of FA treatments was basically the same with urea treatment, butthe potential nitrification rate was increased by16.74%and37.55%respectively when the amount of FAwas1.5g·kg^-1and3.0g·kg^-1, which was related to the mineralization of organic nitrogen in FA.（2）Under the treatments of combined application of PASP and urea, the NH₄⁺-N content in soil wasdecreased by9.29%³0.74%, because the H+of carboxylic groups in PASP with NH₄⁺in soil took placeion exchange. The production rate of NO-3-N was different with the application rates of PASP. Thenitrification rate constant was decreased by15.73%when the amount of PASP was900mg·kg^-1, whichdecreased the release rate of NO-3-N during incubating.4. The uptake rates of nitrogen of water spinach from different origins and fate of nitrogen fertilizerchanged after combined application of FA, PASP and15N labeled urea. Nitrogen uptake rates of water spinach was increased by10.84%¹8.25%when it had grown for60days, and the uptake rates ofno-labeled nitrogen of water spinach was increased significantly with the increase of FA and PASPapplied. Compared with urea treatment, the15N use efficiency was decreased significantly only whenthe amount of FA was3.0g·kg^-1. The15N loss ratio of FA and PASP treatments was decreased by5.41¹4.58percentage points, and the residual15N ratio was increased by5.08²0.02percentage pointswhich showed significant contribution for the nitrogen pool of soil.To sum up, after combined application of FA and urea, FA could quickly absorb NH₄⁺in soil,which is good for reducing losses of ammonia volatilization in the alkaline soil. Then FA could bemineralized to inorganic nitrogen with incubation time. After combined application of PASP and urea,PASP could decrease the release rate of NH₄⁺-N, and the production rate of nitrate decreases with theincrease of the application of PASP. In soil-plant system, combined application of nitrogen fertilizer andcertain amount of FA and PASP could increase production of vegetable and improve root growth andtotal nitrogen uptake rates of plant. In addition, the combined application treatments could reduce lossrates of nitrogen fertilizer and increase total recovery ratio of nitrogen fertilizer.