| Biochar plays an important role in improving soil fertility and controling non-point source pollution of nitrogen and phosphorus. The three kinds of biochar named B250, B350 and B450 were produced by maize straw biomass materials at different temperatures of 250, 350 and 450 ℃, respectively, forthermore, the characteristics of structure and surface of the biochars were measured by the methods of SEM(scanning electron microscope) and FTIR(fourier transform infrared spectroscopy), and the adsorption characteristics of nitrogen and phosphorus on/in biochars were also investigated by laboratory simulation. Minewhile, the influence of the adsorption-liquid p H was on the adsorption characteristics of nitrogen and phosphorus on/in the biochars was also considered in the paper. The dark brown soil was mixed with B450-biochar according to the mass ratio of 0,0.5%,1% and 0.5%, respectively. After 30-days-incubation, the physical and chemical properties was measured and the adsorption characteristics of nitrogen and phosphorus on/in the soils was determinated. The results were as follows:(1) The properties of maize straw biochar were imparity under different carbonization temperature, with the increase of temperature, p H increased, at the same time, biochars showed similar content and different form for nitrogen and phosphorus. The results from SEM and FTIR showed that the pore deformation and the stalk roughness increased as the carbonization temperature rising, furthermore the pore canal can enhance the adsorption properties of biochar. Meanwhile, biochar showed a higher degree of stability enhancement with temperature rising.(2) The results from adsorption kinetics and thermodynamics of nitrogen and phosphorus on biochars showed that B250 released some phosphorus from itself during the adsorption process, so the adsorption of B250 on phosphorus was negative, while the adsorption kinetic of B350 and B450 could be fitted with the Lagergren pseudo-second order kinetic model, the adsorption rate of phosphorus and nitrogen on biochars was in descending order of B450> B350> B250. The adsorption isotherm process of nitrogen and phosphorus on three kinds of biochars agreed well with the Langmuir equation. Adsorption capacity was in descending order of B450> B350> B250, concrete numerical value were 15.04, 14.11, 13.11 mg/g and 2.33, 2.03 and 1.07×10-6 mg/g, respectively. The adsorption capacity of nitrogen on biochars was higher than that of phosphorus on biochars..(3) The results from the effect of adsorption-liquid p H on the adsorption kinetics and thermodynamics process of nitrogen and phosphorus on biochars showed that adsorption kinetic process of nitrogen and phosphorus on biochars were consistent with the Lagergren pseudo-first order kinetic model under different adsorption-liquid p H. The adsorption rate of phosphorus on the biochar was faster than nitrogen. The adsorption isotherm process of nitrogen and phosphorus on biochars agreed well with the Langmuir equation. The most adsorption capacity(5.30 mg/g) of phosphorus on biochar was obtained when the adsorption-liquid p H ranged from 8 to 10. And it has the most adsorption capacity of nitrogen when p H=4-6(9.90 mg/g)..(4) Adding maize straw biochar can darken the color of soils, improve the content of organic matter, total nitrogenand phosphorus, and available nitrogenand phosphorus in the soils., Compared with black soil, dark brown soil has a lower p H, the content of total nitrogen and phosphorus, available nitrogenand phosphorus were also very lower, consenquently, it was more obviously effected byr adding biochar.(5) The results from adsorption kinetics and thermodynamics process of nitrogen and phosphorus in soils showed that the adsorption kinetic process was consistent with the Lagergren pseudo-first order kinetic model, along with the increase of added quantity of maize straw biochar, the adsorption rate of nitrogen and phosphorus in dark brown soil increased obviouly. For black soil, adding maize straw biochar can increase the adsorption rate of nitrogen and phosphorus in soil, but, with the increase of the added amount of maize straw biochar, there is no obvious functions. The adsorption rate of nitrogen and phosphorus in black soil was faster than that in dark brown soil. The adsorption isotherm process agreed well with the Langmuir equation, moreover, the saturated adsorption capacity of nitrogen and phosphorus in dark brown soil increased with the maize straw biochar dosage increasing, concrete numerical value were 3.34, 3.83, 5.25, 5.28 mg/g and 3.09, 3.19, 3.53 and 3.61 mg/g, respectively. The saturated adsorption capacity of nitrogen and phosphorus in black soil increased slowly with the maize straw biochar dosage increasing,. concrete numerical value were 4.14, 8.94, 10.23, 10.27 mg/g and 6.30, 7.11, 7.38 and 7.45 mg/g, respectively. Meanwhile, enhance the fixing ability with nitrogen and phosphorus. On the whole, the adsorption capacity of nitrogen and phosphorus in black soil is higher than in dark brown soil. Besides, the adsorption capacity of nitrogen in soils is higher than phosphorus. |
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