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10. Subsurface Drainage Pros and Cons

A drainage system should be able to lower the water table from the soil surface to 1-ft depth in less than 48 hours following a heavy rainfall (Ghane, 2022b). Draining the excess water from the soil profile provides the necessary aeration needed for proper crop root development (Figure 9). Drainage promotes deep root development and prevents the crop roots from drowning in too much water. Drainage improves soil aeration, thereby increasing biological activity, which leads to better soil structure by increasing soil aggregation.

Crop root development for undrained and drained conditions. Not to scale.
Figure 9. Crop root development for undrained and drained conditions.

Drainage helps the soil dry sooner, which provides timely field operations (planting, harvesting and other processes) and trafficability. Earlier drying of the soil provides earlier seed germination because the soil warms faster in spring. Drainage reduces surface runoffs by allowing water to infiltrate the soil and flow into the perforated drain pipes rather than flowing over the land. Crop yield is less variable from year to year with subsurface drainage. The overall impact of subsurface drainage is a healthier, more productive soil with more stable crop yields (Table 1).

A disadvantage of drainage is that it provides less opportunity for groundwater recharge due to less deep percolation, which may be important in locations where the aquifer is in decline.

Furthermore, when soil aeration is increased with water removal, oxidation of soil organic matter increases, and thereby loss of soil organic matter is accelerated. Thus, it is important to improve soil health to build carbon in the soil.

Table 1. Pros and Cons of Subsurface Drainage in Humid Regions.



Increases crop yield

Excess phosphorus transport

Less year-to-year crop yield variability

Excess nitrate transport

Increases soil aeration

Less groundwater recharge

Improves soil structure

Accelerates loss of soil organic matter

Decreases surface runoff


Provides timely field operations and trafficability