炭肥比和膨润土粘结剂对炭基肥颗粒理化及缓释特性的影响

为探究炭肥比和膨润土粘结剂对生物炭基肥理化及缓释特性的影响,以生物炭为基底,分别制备了炭肥比1:4,膨润土粘结剂质量分数为20%、15%、10%、5%和粘结剂质量分数10%,炭肥比为1:6、1:5、1:4、1:3的柱状尿素和氯化钾生物炭基肥颗粒,分析了生物炭基肥颗粒的理化及缓释特性。结果表明,在炭肥比为1:4条件下,膨润土粘结剂质量分数越高,生物炭基肥微观结构越紧密,力学和缓释特性越好,质量分数为20%时,氯化钾和尿素生物炭基肥平均抗压强度分别为286.78和281.27 N,前3天养分淋出率分别为45.53%和36.87%。在膨润土粘结剂质量分数为10%条件下,炭肥比越高,生物炭基肥缓释性能越好,炭肥比为1:3时,氯化钾和尿素生物炭基肥前3天养分淋出率分别为42.06%和40.32%。同时,氯化钾生物炭基肥表面孔隙先增后减,炭肥比为1:6和1:3的平均抗压强度分别为271.25和282.42 N。尿素生物炭基肥内部结构中孔隙变多,炭肥比为1:6时,平均抗压强度为最大值267.84 N。综合考虑,满足中等肥料浓度要求时,膨润土粘结剂质量分数为20%、炭肥比为1:4或膨润土粘结剂质量分数为10%、炭肥比为1:3的生物炭基肥成型配方较优。

Effects of biochar fertilizer ratio and bentonite binder on physicochemical properties and slow release properties of biochar fertilizer particles

Abstract: The blend ratio of biochar and fast-release fertilizer (urea and potassium chloride, respectively) and the content of bentonite binder may influence the physicochemical and slow-release properties of biochar-based fertilizers particles. Experiments were carried out under 2 conditions: 1) biochar fertilizer ratio of 1:4, bentonite binder mass ratio of 5%, 10 %, 15% and 20%, and 2) bentonite binder mass ratio of 10%, biochar fertilizer ratio of 1:6, 1:5, 1:4 and 1:3. Based on corn straw biochar, cylindrical biochar based fertilizer particles with urea and potassium chloride were prepared by flat mold extrusion device. Their mechanical properties, surface functional groups, surface topography, soil column leaching properties, pH value and conductivity of biochar-based fertilizers were analyzed. The results showed that the average compressive strength of biochar-based particles urea and potassium chloride were higher than 200 N, greater than that prepared by pan granulation technique. The nutrient leaching rates in the first 3 days were lower than that of pure urea and potassium chloride. It meant that they had good mechanical properties and certain slow-release effect. The average compressive strength of biochar-based fertilizer particles of potassium chloride biochar-based fertilizer particles and urea biochar-based fertilizer for the 4 different contents of bentonite were significantly different (P<0.05). The high content of bentonite binder and the low biochar and fertilizer content would lead to closer microstructure, more uniform composition distribution, and fewer surface pores. The mechanical properties and slow-release properties were better. When the mass fraction of bentonite binder was 20%, the average compressive strength of potassium chloride biochar-based fertilizer particles and urea biochar-based fertilizer were the maximum value of 286.78 and 281.27 N, respectively, the nutrient leaching rate of potassium chloride biochar-based fertilizer particles and urea biochar-based fertilizer in the first 3 days were the minimum value of 45.53% and 36.87%, respectively. The high biochar fertilizer ratios would result in the better slow-release performances. When the biochar fertilizer ratio was 1:3, the nutrient leaching rates of potassium chloride biochar-based fertilizer particles and urea biochar-based fertilizer particles in the first 3 days were the minimum values of 42.06% and 40.32%, respectively. The pores on the surface of potassium chloride biochar fertilizer particles increased first and then decreased. When the biochar fertilizer ratios were 1:6 and 1:3, the average compressive strength were 271.25 and 282.42 N, respectively, but the relative standard deviation of the average compressive strength at 1:3 was the maximum. The pores in the internal structure of urea biochar-based fertilizer particles gradually increased. When the biochar fertilizer ratio was 1:6, the average compressive strength was the minimum values of 267.84 N. At the same time, the electrical conductivity of potassium chloride biochar-based fertilizer leachate and the pH value of urea biochar-based fertilizer leachate were similar to their respective nutrient leaching rates in change rule, which could be used for prediction of their nutrient leachate trends. Thus, the formulation of biochar-based fertilizer with the mass fraction of bentonite binder and the ratio of carbon to fertilizer of 20% and 1:4 or 10% and 1:3 are suggested to meet medium fertilizer concentration.