Understanding Soil Infiltration


Infiltration is the downward movement/flow of water from aboveground into the subsurface. This process is important in irrigation, contaminant transport and groundwater recharge. A quantitative understanding of this process is critical in linking surface and subsurface processes in describing the hydrologic cycle.


Most of the world’s freshwater is soaked into the ground as rain and snow. Infiltration makes the water cycle complete.

Soil Characteristics

The physical characteristics of soil affect infiltration. These include the particle size of the aggregates and their arrangement, soil structure, and the presence of macropores. A soil’s texture, which is determined by the proportion of sand, silt and clay particles, is an important factor in its infiltration capacity. A coarse textured soil has large particles, between which are large pores. In contrast, a fine textured soil has small particles between which are smaller pores. A coarse textured soil will have faster infiltration rates than a fine textured one.

In addition, the presence or absence of macropores increases or decreases a soil’s permeability. A soil with many pore spaces and good connectivity between them has high permeability; water will flow easily through it. A clay-like soil with very small pores has low permeability.

The infiltration rate of a soil depends on its constant properties, such as the BD and the pore size, as well as its variable properties, such as the initial soil moisture content and management practices. Several studies have been performed to analyze the dependence of soil infiltration on its properties. The results of the research showed that BD, CC and IWC all had an indirect promoting effect on soil IR; however, BD was the main limiting factor for soil IR. The research further revealed that the plant community, soil BD and root structures all significantly affected soil infiltration.

Water Retention Capacity

Infiltration is an important hydrologic process that affects soil moisture availability for tree roots, microbial activities and chemical weathering. It can be difficult to determine, but knowledge of infiltration can help manage irrigation and water loss in orchards, especially in sloping areas where the potential for surface runoff is high.

Soil texture and organic matter content influence 흥신소 infiltration rates. The larger pore size of sandy soils allows for rapid movement of water while clay and silt textured soils can slow the water flow. Organic matter increases aggregation and improves the distribution of pores, making the soil more infiltration friendly.

The initial soil water content is also an important factor that influences the infiltration process. If the soil is already saturated then it cannot hold additional water and will only continue to shed rainfall at a much higher rate leading to surface runoff. Soil should be at field capacity prior to conducting infiltration tests. Dry soils will overestimate the infiltration rate while saturated soils will underestimate it.

Long-term vegetation restoration is a beneficial practice that can increase the infiltration capacity of orchard soils by improving the aggregation of the soil and enhancing its pore space. This is achieved through the use of livestock grazing, organic fertilizers and mulches. Organic matter enhances aggregation of the soil and provides good habitat for earthworms that improve pore space and link surface to subsurface soil layers, increasing the infiltration rate.

Soil Porosity

Soil porosity is the amount of space around soil particles that can be filled with air and water. The size of these spaces affects infiltration, plant available water, and soil structure. It is dependent on both the texture of the soil and its aggregation. For instance, finely textured soils have more pores and hold more water than coarse sandy soils.

Porosity is also affected by the permeability of the pores. Pores that are able to move rapidly through the soil allow for fast infiltration and evapotranspiration. Slower pore movements are associated with more resistance to infiltration.

Another factor that affects pore space is the number and size of mineral and organic particles in a given volume of soil. Larger sized particles have lower bulk density and less porosity than smaller particles. Generally, a finely textured soil has fewer larger particle sizes and therefore has more pores.

Soil porosity also depends on the presence of cracks and fractures in the soil. These play an important role in allowing water to percolate through the soil, influencing preferential flow patterns, hydraulic conductivity, and evapotranspiration. Using national data sets that span the mineral to organic continuum, research has shown that there is a strong dependence between soil porosity and soil organic matter (SOM). The more SOM in the soil the higher the soil porosity.

Infiltration Rate

The rate at which water infiltrates downward into soil is called the infiltration rate. Infiltration allows water to be stored in the soil, which is useful for a variety of reasons including root uptake and nutrient replenishment1.

The type, amount and duration of precipitation impact infiltration. Snow and sleet tend to have lower infiltration rates than rain. During the first few minutes of rainfall, infiltration rates are high as the soil is unsaturated but then slow down when the water reaches saturation. Eventually the infiltration rate reaches a steady state, after which no more water can infiltrate and surface runoff occurs.

Different tillage methods also impact infiltration, with no-till soils often having higher initial infiltration rates than tilled ones. However, once the soil reaches saturation, it doesn’t matter which tillage method was used because they all have similar infiltration rates.

A good infiltration rate indicates that the topsoil has stable aggregates around which water can percolate. A low infiltration rate, on the other hand, is an indication that the topsoil has poor structure and is compacted, preventing water from infiltrating downward. These types of soils can have a negative effect on irrigation because water is not absorbed and instead runs off the site, contaminating groundwater and causing erosion1. 1