Development Of Large-Grained Activated Humic Acid Slow-Release Fertilizer And Its Application On Apple

Long-term excessive and unscientific application of chemical fertilizers not only reduces fertilizer utilization and increases farmers'costs,but also produces a series of problems such as waste of resources and environmental pollution.The fertilization method used by fruit farmers is still trenching fertilization,which not only has a large amount of labor and high cost,but also easily led to high risk to apple tree roots.In addition,most of the traditional fertilizers are still small particles or powder,which not only increase the contact area with the soil and cause nutrient loss,but also are not convenient for mechanized fertilization in orchards.In order to solve the above problems,it is urgent to develop a new fertilizer with high efficiency,low cost,environment friendly and mechanized application.Activated humic acid fertilizer is widely used in orchards because of its effect of improving fertilizer utilization,improving soil quality and promoting crop growth.However,the activation method of humic acid from lignite is mainly activated by strong acid and strong base in liquid state,which not only has high energy consumption and long reaction time,but also easily produces harmful gases and pollutes the environment.Although most catalysts can be used to oxidize lignite to increase the humic acid yield,their actual applications are limited because of their single structure,high toxicity and poor catalytic effect.In view of the above problems,we designed and prepared new three-dimensional nanocatalysts based on the beneficial elements needed for plant growth,such as N,P,S,Mo and Fe.Then,the activated humic acid from lignite was obtained using the three-dimensional nano-catalyst combined with solid-state ball milling.Next,the effect of solid phase activation of humic acid,molecular structure of humic acid activation and mechanism of humic acid were further evaluated and discussed.After that,activated humic acid of lignite,polymeric slow-release fertilizer and some common fertilizers were mixed and processed into a multifunctional large-grained activated humic acid slow-release fertilizer(LAF,cylinder,diameter:4.5cm,high:5cm,mass:100g).The LAF was evaluated for its leaching properties,the slow-release behaviors and water-retention capacity of in soil by laboratory tests.Finally,the effects of LAF on apple growth characteristics,nutrient utilization,soil fertility and soil microbiology were revaluated through two-year pot experiment and four-year field experiment using the drilling fertilization around an apple tree trunk.The main results are as follows:(1)3D molybdate-phosphorus hollow nanosphere(Mo-P-HH)catalyst on solid phase activation of humic acid.Firstly,the Mo-P-HH catalyst was synthesized under conditions of optimum ratios of dopamine hydrochloride with ammonium molybdate(1:1,m/m)and water with ethanol(1:2,v/v).Then,Mo-P-HH catalyst was mixed with raw lignite(RL)to obtain activated humic acid(AML)by solid-phase ball mill.The results show that the water-soluble humic acid content of AML was 60.12%and 30.28%higher than RL and alkali-activated humic acid from lignite(AL),respectively;Compared with the RL,the relative abundance of condensed aromatic and tannins in the AML decreased by 39.58%and 18.19%,respectively,but the relative abundance of lipids,proteins and amino acids and carbohydrates in AML increased by 484.31%,108.67%and 15.61%,respectively.(2)The effect of 3D molybdate-sulfur hollow nanosphere(3D-Mo S₂-HN)catalyst on solid phase activation of humic acid.Firstly,the 3D-Mo S₂-HN catalyst was synthesized through simple vulcanization.The 3D-Mo S₂-HN catalyst was mixed with RL to obtain activated humic acid(ASL)by solid-phase ball mill.The results show that the water-soluble humic acid content of ASL was 64.16%and 32.28%higher than RL and AL,respectively;Compared with the RL,the relative abundance of condensed aromatic,lipids,tannins and carbohydrates in the ASL decreased by 41.95%,63.02%,24.21%and 43.62%,respectively,but the relative abundance of lignin,proteins and amino acids in ASL increased by 23.56%and 139.15%,respectively.(3)The effect of double-shelled Fe-N hollow microspheres(DS-Fe-N-HC)catalyst on solid phase activation of humic acid.Firstly,the DS-Fe-N-HC catalyst was synthesized through a novel pyrolysis method with porous Fe₃O₄ microspheres(0.15g)as the template and pyrrole monomers as C and N precursors.DS-Fe-N-HC catalyst was mixed with RL to obtain activated humic acid(AFL)by solid-phase ball mill.The results indicate that the water-soluble humic acid content of AFL was 76.55%and 25.31%higher than RL and AL,respectively;Compared with RL and AL,AFL effectively increased the water-soluble humic acid content and the proportion of small molecules in humic acid;Compared with the RL,the relative abundance of tannins in the AFL decreased by 24.31%,but the relative abundance of proteins and amino acids in AFL increased by 25.23%.(4)Preparation,slow-release behavior and water-retention capacity the LAF.The results show that when the water content of the mixture is 7%,the ratio of humic acid and fertilizer is1:1,and the fertilizer quality is 100g,the spheroidization rate and the hardness of LAF is the highest;Compared with the powder activated humic acid slow-release fertilizer(PAF)and powder conventional fertilizer(PF),soil column leaching experiments confirmed LAF can significantly reduce leaching of available nutrients,indicating LAF had a preferable slow-release property in soil.In addition,the water content of LAF is 7.85 times that of PF and the absolute water content of 33%is still maintained after 15d of water retention test.(5)The pot experiment of LAF on apple seedlings.Eight treatments were set up:no fertilization(CK),customary fertilization(CCF),three different application rates of LAF(LAF1:LAF at 100%application rate;LAF2:LAF at 80%application rate and LAF3:LAF at50%application rate)and three different application rates of PAF(PAF1:PAF at 100%application rate;PAF2:PAF at 80%application rate and PAF3:PAF at 50%application rate).A two-year of apple seedling pot experiment with 8 fertilizer treatments was conducted.The results showed that compared with CCF,the application of 100%and 80%LAF treatment can significantly promote the growth of fruit tree seedlings,improvement of the photosynthesis properties and increase the available nutrients in soil.Meanwhile,the average utilization ratio of nitrogen,phosphorus and potassium in LAF treatment was significantly higher than that of CCF.(6)The field apples experiment of LAF.Eight treatments were set up:no fertilization(CK),customary fertilization(CCF),three different application rates of LAF(LAF1:LAF at 100%application rate;LAF2:LAF at 80%application rate and LAF3:LAF at 50%application rate)and three different application rates of PAF(PAF1:PAF at 100%application rate;PAF2:PAF at 80%application rate and PAF3:PAF at 50%application rate).A four-year field experiment with 8 fertilizer treatments was conducted.The results showed that compared with CCF,100%and 80%LAF treatment could effectively increase the available nutrient content of soil,photosynthetic index of apple leaves,SPAD value and apple yield.At the same time,long-term application of activated humic acid slow-release fertilizer can significantly increase the content of soil organic matter.The total number of fungal OTU and unique OTU of PAF and LAF were not different,but they were significantly higher than those of CCF and CK treatment.However,the total number of fungal OTU and unique OTU in PAF and LAF is lower than that in CCF and CK treatment.It is shown that activated humic acid slow-release fertilizer can increase the total number of soil bacteria and its unique bacterial species,but reduce the number of fungi and unique fungal communities.