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4. Impeded infiltration and percolation due to soil and installation problems
Impeded infiltration and percolation occur due to soil management and installation problems, causing slower water removal from the field than needed. Thus, the performance of the drainage system is reduced. Also, this problem could lead to increased surface runoff. One sign of this problem is when surface ponding lasts for extended periods with little to no drainage discharge, indicating that water cannot reach the drain pipes.
In impeded infiltration, water cannot infiltrate the soil surface fast enough because of surface sealing, and ponding usually occurs on the surface. In the case of impeded percolation, water in the soil cannot move downward to the drain pipes and causes a perched water table due to a plow-pan or compacted layer below the surface. In both cases, soil auguring and consultation with a soil scientist can identify this problem.
4.1. Impeded infiltration and percolation caused by compaction
The most common cause of impeded infiltration and percolation is field operations (planting, spraying, harvesting, and drain pipe installation) during wet soil surface conditions that lead to soil compaction. Tillage can also create a compacted layer just below the tillage depth that limits percolation. The following are some guidelines to address the compaction issue:
- If a plow-pan or compacted layer is the problem, break it up with subsoiling or moling. Mole drains result in soil cracks, leading to increased infiltration. For more information about mole drains, see Ghane (2022). Caution is advised when subsoiling or moling under wet surface conditions as these can worsen the compaction issue.
- Improve soil health with reduced tillage, cover crops, manure or compost, and diverse rotations, thereby improving infiltration and percolation.
- If the impeded infiltration is in a depressional area, a blind inlet can be installed to increase infiltration. For more information about blind inlets, see Ghane (2022).
- Surface drainage can be used to prevent surface ponding. For more information about surface drainage, see Ghane (2022).
4.2. Impeded infiltration caused by soil dispersion
Another reason for impeded infiltration is soil dispersion on the soil surface, which causes soil structure degradation, sealing of the soil surface, reduced infiltration, and increased surface runoff. Soil dispersion can be caused by mineral imbalance and raindrop impact.
4.2.1. Mineral imbalance causes soil dispersion on the soil surface and around the drain pipes
Generally, soils are more susceptible to dispersion when the mineral concentration of the soil solution is low. One method of increasing the soil mineral concentration is to add calcium to enhance the soil’s physical properties and improve infiltration. Soil dispersion can also occur when the ratio of soil calcium to magnesium is too low, that is low calcium and high magnesium. Soil dispersion can also occur if the soil has high sodium and low calcium (sodic soil). The high sodium causes clay particles to disperse and seal the soil surface, thereby reducing infiltration. In Michigan, most soils are rich with calcium, so the risk of impeded infiltration due to excess magnesium or sodium is generally low. Nevertheless, soil test and consult a soil scientist to identify soil dispersion.
In parts of the Red River Valley in the Upper Midwest U.S.A., sodic or saline-sodic soil may cause under-performance of the drainage system due to soil dispersion on the soil surface. Before installing drain pipes in those soils, evaluate the suitability for subsurface drainage as described in the Extension bulletin by Cihacek et al. (2012).
4.2.2. Raindrop impact causes soil dispersion
The impact force of raindrops on bare soil can break soil aggregates, disperse soil particles, and reduce infiltration (Figure 6). To reduce soil dispersion, protect the soil from raindrops with cover crops, crop residue, or mulch. The cover absorbs the raindrop impact force and reduces soil dispersion.
Figure 6- Top: A soil surface with a failed germination. Bottom: A close-up of the same soil surface showing soil dispersion and crusting caused by mineral imbalance and raindrop impact (photo credit: Zouheir Massri).
