Studies on factors affecting the infiltration capacity of agricultural soils

Abstract

The purpose of this work was to identify factors influencing the infiltration capacity of agricultural lands in order to evaluate “infiltration” as an indicator of soil protection against degradation or water erosion. Long-term field experiments and fields on experimental farms with different land use systems and agricultural management practices were investigated for soil physical, chemical and biological characteristics and their effects on the infiltration capacity. The most important factors affecting infiltration were selected on the basis of the single regression analysis. The different impacts of the selected parameters on infiltration have been identified based on the multiple regression analysis. The soil protection indicator “infiltration” was described according to adequate model algorithms.
1 The investigation of soil infiltration rate under different land use systems produced the following findings:
- The infiltration rate of soil was found to be highest in the forest followed by the natural succession and lowest in the arable land.
- The high infiltration rates in the forest were attributed to higher macropores resulting from the great root activity, which leads also to high lateral fluxes into the soil resulting in higher infiltration rates.
- The higher infiltration rate in the natural succession was due to a higher soil structural stability produced by a higher aggregate stability, which in turn was generated by a greater soil organic matter content. In addition, the natural succession soil had less subsoil compaction and a lower bulk density, besides a higher fraction of biopores mostly produced by larger earthworm abundance, which contributed to increased soil infiltration rates.
2 The investigation of soil infiltration rate under different farming systems yielded the following results:
- Organic farming resulted in higher soil infiltration rates in comparison to conventional farming.
- The higher infiltration rate in the organically managed field ( Field O3), as contrasted with the conventionally managed field ( Field C1), was traced back to a higher soil mechanical stability, a higher fraction of macro- or biopores (soil pores with a diameter > 50μm) related to the earthworm activity. The earthworm population in Field O3 was twice as greater than in Field C1. 3 The investigation of soil infiltration rate under different soil tillage treatments reported the following consequences:
- The soil infiltration rate was found to be higher under shallow tillage as compared to deep tillage. Also, conservation tillage yielded a higher infiltration rate in comparison to conventional tillage.
- Conservation tillage resulted in a higher aggregate stability, which contributed to a higher soil infiltration rate in comparison to conventional tillage.
- Shallow tillage produced a higher soil biological activity indicated by a larger earthworm population, especially a greater number of deep earthworms “anecic”, and a higher dehydrogenase activity, as well as a higher soil structural stability, which promoted higher infiltration rates compared to deep tillage.
4 The investigation of soil infiltration rate under different fertilization treatments revealed the following effects:
- The infiltration rate was higher under the organic (fym) and the combined (NPK+fym) fertilization than under the mineral fertilization (NPK).
- The organic (fym) and the combined (NPK+fym) fertilization resulted in a higher soil stability, a lower subsoil compaction, a greater organic matter content, a larger earthworm biomass and number particularly a greater number of deep “anecic” earthworms which supported higher soil infiltration rates in comparison to the mineral fertilization (NPK).
5 The multiple regression analysis for the most important factors affecting the water infiltration of soil resulted in the following findings:
- At the site Braunschweig, the carbon stock had the highest influences on the infiltration rate followed by the soil dry bulk density and earthworm abundance.
- At the sites Trenthorst and Mariensee together, the greatest effects on the infiltration rate emerged from the soil textural classes (silt and clay content of the topsoil) followed by the soil dry bulk density and the earthworm abundance per carbon stock, as well as the aggregate stability of the topsoil.
6 The evaluation of the soil infiltration measurements revealed that the infiltration capacity is an adequate integrating measure for soil quality. The improved soil properties produce a high soil protection against water erosion and simultaneously a high soil infiltration capacity. Hence, the soil infiltration capacity can reflect the level of soil degradation and subsequently it can be used as a fundamental basis for measures of soil protection.