A comparison of methods to assess susceptibility to soil sealing

Abstract

Many methods and indices have been developed for assessing seal formation. However, difficulties persist in selecting a suitable method because of the effect of the procedure on the results. The present study aims to evaluate appropriate soil sealing assessment methods that enable to distinguish the surface condition of soils with contrasting characteristics. A comparative study was conducted among the most frequently used methods, viz: wet sieving tests, raindrop impact tests under field and laboratory conditions, penetration resistance (PR), consistency index (C5–10), soil stability index (StI), and crusting index (CI). Different agricultural Venezuelan ‘tropical’ soils were ranked according to their susceptibility to soil sealing. The ranking and the correlation between the parameters were used to assess and compare soil sealing formation measured by the different methods. According to multiple and single wet sieving tests the soils were classified into two groups as stable (kaolinitic-rich) and unstable (smectitic-rich) soils. The ranking of the soils and correlation analysis (p<0.05) indicated that aggregate stability as determined by wet sieving, infiltration rate, runoff and soil loss under laboratory and field conditions was effective in predicting seal formation among smectitic-rich loam to kaolinitic-rich clayey soils. C5–10 and PR were not comparable tests for sealing formation (p>0.05). The StI that considers soil organic matter (SOM) as the most important factor to maintain soil structure did not reflect the high stability of the kaolinitic-rich soil that lacks SOM. The CI, which indicates the risk for soil crusting formation in the function of silt fractions, is a more capable indicator for evaluating susceptibility to sealing of our soils. This study further proposes that when topsoil aggregates are characterized by high silt and smectite contents the use of wet sieving and raindrop impact tests or simple indices such as StI and CI can satisfactorily assess the susceptibility to seal formation. Differences obtained in seal formation ranking indicated that method selection impacts the measured value. It can therefore be recommended to take the effect of the method into account when interpreting the results obtained.