The Effects of Inorganic Fertilization on Soil Shrinkage in Wetting-drying Cycles

Abstract

【Objective】 Swelling and shrinkage are important process reshaping soil structure. It is impacted by many factors, and the objective of this paper is to investigate how fertilization impacts this process. 【Method】 We used a silty loam in the experiment. The soil was fertilized using different inorganic N and K fertilizers at concentrations ranging from 1 g/L to 3 g/L. The emergence and development of the shrinkage during and following multiple wetting-drying cycles were measured in each treatment. 【Result】 ① The shrinkage in the transverse and longitudinal directions both decreased asymptotically with the increase in the number of drying-wetting cycles. Adding inorganic fertilizer reduced the shrinkage in both transverse and longitudinal directions, and the reduction became more significant as the wetting-dying cycles increased. ② The VG-Peng model can fit the effects of the fertilization on soil shrinkage, and the shrinkages in each treatment can be classified into four types: structural shrinkage, proportional shrinkage, residual shrinkage and zero shrinkage. Increasing drying-wetting cycles increased the structural shrinkage at the expense of proportional shrinkage and residual shrinkage. The addition of the inorganic fertilizers reduced the void ratio of the soil in the shrunk region. ③ Soil shrinkage experienced three stages: complete longitudinal shrinkage, longitudinal-dominant shrinkage, and transverse-dominant shrinkage, with the anisotropy of the shrinkages decreasing after several drying-wetting cycles. 【Conclusion】 Applying inorganic fertilizers reduced soil shrinkage due to wetting-drying cycles, and the inorganic fertilizers accumulated after multiple wetting-drying cycles due to the decline in soil shrinkage.

Keywords

• wetting-drying cycle
• inorganic fertilization
• soil
• contraction curve
• geometric factors