Improving Structure of Dark Loessial Soil by Addition of Potassium Fulvic Acid

Abstract

【Objective】 The productivity of dark loessial soils is generally low due to their poor structure. We studied how to improve their structure using potassium fulvic acid. 【Method】 The experiment was conducted using pots. Soil in the pots were amended with potassium fulvate at mass ratio from 0 to 1%. For each pot, we measured its water transport ability, soil porosity and aggregate formation and distribution. 【Result】 ① Potassium fulvate amendment at 1% ratio was optimal for improving soil properties, increasing cumulative water infiltration, infiltration rate, stable infiltration rate and wetting front distance by 43.96%, 182.5%, 47.06% and 28.41%, respectively, compared to CK (without amendment). ② Fitting the measured infiltration data to different models showed that, depending on the amending ratio, the empirical coefficient in the Kostiakov formula decreased from 1.648 7 to 0.901 3 and the empirical index increased from 0.478 1 to 0.537 5. For the Philip model, the stable infiltration rate and the imbibition rate varied from 0.002 0 to 0.003 2, and 0.956 2 to 1.004 2, respectively, depending on the amendment ratio. For the improved Kostiakov model, the stable infiltration rate increased from 0.012 6 to 0.084 6. ③ Compared with CK, the amendment at ratio 1% improved soil porosity most, with the total soil porosity and soil aeration porosity increasing by 2.65% and 64.29% respectively, and the capillary porosity decreasing by 17.00%. With the increase in the amendment ratio, the bulk density decreased by up to 2.99%. ④ With the increase in incubation time, aggregates (>0.25 mm) increased significantly at the expense of aggregate (<0.045 mm). The geometric diameter of aggregates and the amendment ratio were positively correlated, while the unstable aggregate index and soil erodibility were negatively correlated, with the correlation decreasing with the increase in the amendment ratio. We found that the fractal dimension decreased with the increase in incubation time and the amendment ratio. 【Conclusion】 Amending the dark loessial soil with potassium fulvic acid at mass ratio 1% was optimal for improving soil structure and its physical and biochemical properties.

Keywords

• potassium fulvic acid
• moisture transport
• soil porosity
• water-stable soil aggregate
• soil structure