Humic acids derived from Leonardite to improve enzymatic activities and bioavailability of nutrients in a calcareous soil

Understanding the role of humic substances in soils is important for developing and utilizing organic fertilizers or soil amendments for sustainable agriculture.The objective of this study was to determine the effects of different fractions of humic acids derived from Leonardite on enzymatic activities and bioavailability of nutrients in a soil.The experiment was carried out by mixing different factions of humic acids with a soil and incubated for 70 d.The treatments included five factions of humic acids(HS1(low molecular weight),HS2(medium molecular weight)),HS3(large molecular weight,SED(sediment of fractions),HS(mixture of HS1,HS2,and HS3)),raw Leonardite(IM)and a control(no addition of humic acid).Experimental results showed that application of humic acids significantly improved acid and alkaline phosphatase activities,especially with HS1.Humic substances with high molecular weights significantly inhibit urease activity,and the optimal application rate was 600 kg/hm2 of humic substances with the high molecular weights.Concentrations of NH4+-N were decreased with increasing humus applications.All treatments(HSmix,HS1,HS2,HS3,IM,SED)did not affect the soil contents of Ca,although soil concentrations of K,P,Cu,Zn were increase significantly when small molecular weight humus(HS1)was applied.

Theoretical Study on the Effects of Spatial Structure of P Complexation Sites on the Soil Phosphorus Activation in Leonardite Humic Acid Complexes

Humic acid is an important active component in soil environment. The spatial structures of P complexation sites in humic acid complexes play an important role in soil phosphorus activation and fertilizer efficiency. To explore the effects of spatial structure, the three different coordination modes of iron-carboxyl in models were calculated by the ONIOM method available in the Gaussian09 package. The(U)B3LYP hybrid density functional was employed to optimize the configuration for the QM region, and the UFF force field was used to calculate for the MM region. The results show that the different spatial structures influence the soil phosphorus activation by affecting the electronic structure, Gibbs free energy and interaction energy of the models. And the effects are as follows: the unidentate structure model ~6P-Fe-MHA-UD, the bidentate chelating structure model ~6P-Fe-MHA-BD>the bidentate bridging structure model ~5P-Fe-MHA-BD-BG. It can be known that, the fertilizer efficiency can be improved through increasing the proportion of the unidentate structure and the bidentate chelating structure in production engineering. The research provides a theoretical basis for further optimization of the production of humic acid phosphate fertilizer.

Isotherm and kinetic studies on the adsorption of humic acid molecular size fractions onto clay minerals

Humic acid(HA)can adsorb onto mineral surfaces,modifying the physicochemical properties of the mineral.Therefore,understanding the sorption behavior of HA onto mineral surfaces is of particular interest,since the fate and transport of many organic and inorganic contaminants are highly correlated to HA adsorbed onto clay surfaces.Due to the extreme heterogeneity of HA,the extracted IHSS Leonardite humic acid(LHA)used in this work was fractionated using an ultrafiltration technique(UF)into different molecular size fractions(Fr1,>0.2μm;Fr2,0.2 pm-300,000 daltons;Fr3,300,000-50,000 daltons;Fr4,50,000-10,000 daltons;Fr5,10,000-1000 daltons).Equilibrium and the kinetics of LHA and fraction adsorption onto kaolinite and montmorillonite were investigated.The results demonstrated that the maximum adsorption capacity of LHA,Frl,Fr2,Fr3,Fr4,and Fr5 was 5.99,13.69,10.29,7.02,5.9&and 5.09 on kaolinite while it was 8.29,22.62,13.17,8.91,8.62,and 5.69 on montmorillonite,respectively.The adsorption equilibrium data showed that the adsorption behavior of LHA and its fractions could be described more practically by the Langmuir model than the Freundlich model.The rate of humic acid fraction adsorption onto clays increased with decreasing molecular size fraction and increasing carboxylic group content.Pseudo-first-and second-order models were used to assess the kinetic data and the rate constants.The results explained that LHA and its fractions adsorption on clay minerals conformed more to pseudosecondo rder.

Characterization of Humic System in Fertilizer Raw Materials

The aim of the study was to characterize humus system of natural and artificial products. Humus systems from leonardite, lignite biotransformed with Trichoderma sp. （Plantagra）, plant materials after pyrolisis （charcoal） and composts are compared. Humus systems are characterized by Kononova-Belchikova＇s method, and heavy metals content was measured by atomic absorption spectroscopy （AAS）. Humic acids from the International Humic Substances Society （IHSS） collection are the standards for humus substances quality of compared products. Data obtained for leonardite indicate that the studied substances from factory, Izmir, Turkey contain humic acids over 94%. Compared to the standard, heavy metals content in these materials demonstrate high amounts. Organic carbon content in the composts is very low compared to the leonardite materials and IHSS collection, where the heavy metals content is lower. Biotransformed lignite is characterized with lower content of organic carbon, but humic acids are with high degree of humification. Results obtained show that the fourth studied humus systems may be used in agriculture on base of the high humic acids content. It is recommended to measure heavy metals content before applying the materials in agriculture.

New Method for the Production of Barium Humate from Turkish Coal

Metal humates have been generally produced from water soluble alkaline humates with the related metal salts. In this study, a new method for the production of barium humate (Ba-HA) from Turkish coal was developed. Insoluble Ba-HA was produced from the result of the extraction of coal directly with barium hydroxide at 120℃. The effect of the amount of raw materials on the solubility and on the content of barium metal was investigated. The pilot plant trial was performed by using 100 kg of coal in one batch based on laboratory results. Ba-HA was characterized by means of FTIR and TGA. The calcination of Ba-HA at the different temperatures and in atmosphere of nitrogen and air was realized to provide the increase in the surface area and the decrease in the chromatographic groups giving yellow color. In terms of the surface area and UV-absorbance values, the calcination condition was selected as the temperature of 350℃ and atmosphere of air. The calcinated Ba-HA was used in the adsorption of some heavy metals. The results show that Ba-HA may have potential to be used as a low cost, natural and eco-friendly adsorbent.