Crop production and environmental benefits of tile drainage

One thing the 2011 crop season in the Northeast will be remembered for is moisture. In a year like this it"s hard not to think about the benefits of tile drainage. Without tile drainage many fields in our area may not have produced a crop that was worth harvesting. 

The practice of land drainage was essential to civilization and dates back thousands of years. England claims to have laid the first cylindrical clay tiles around 1810 (Fraser and Fleming, 2001). Tile drainage was used in Ontario beginning in the early 1800s and in the U.S. soon after this.  William Miner made extensive use of tile drainage on Heart"s Delight Farm in the early 1900s and advocated grid-based installation (tiles spaced at regular intervals across a field to improve drainage efficiency).   

Drainage affects a host of biophysical soil properties and strongly influences crop growth and quality.   The objective of proper tile drainage is to remove excess gravitational water (water in larger pores not considered plant-available) from the crop rooting zone. This water consists of shallow groundwater flow and water draining from upper soil horizons. Artificial tile drainage increases aeration because water is more rapidly removed from the soil profile- this promotes root health and microbial activity (important for maximizing nutrient availability). 

Extending the field season with tile drains is critical to farms in northern NY and other regions with short growing seasons. Tile drainage permits earlier planting, which increases the yield potential for many crops. Research has shown that tile drainage drastically improves workability while reducing the potential for soil compaction. Studies show that tile-drained fields can have a month or more of additional workability (time when fields are dry enough to work with field equipment) compared to undrained fields. The yield increases associated with tile drainage often pay for the cost of the drainage installation in just a few years.   

There are several environmental benefits of properly installed and managed tile drainage systems. Tile drainage tends to increase water storage capacity and decreases peak and total surface runoff flow compared to undrained land. Irwin and Whitely (1983) summarized results from the U.S., UK, Europe, and Canada and reported that water tables in tile-drained fields fell to tile depths in three to four days whereas undrained fields needed up to several weeks for profile drainage to occur. Many studies have reported a significant reduction in surface runoff from tile drainage (Fraser and Fleming, 2001). Istok and Kling (1983) found that tile drainage reduced surface runoff and sediment yields in a silt loam watershed in western Oregon by 65 and 55%, respectively.  Skaggs and Broadhead (1982) reported that tile drainage reduced soil loss by tenfold on a sandy loam in North Carolina, while Bengston et al. (1992) showed that tile drained fields had a 31% lower P loss in overland flow over a 10-year period. While the amount of overland flow reduction and sediment loss expected from tile drainage installation will vary by site (e.g., due to differences in hydrology, soils, weather, and management), studies show that tile drainage reduces surface runoff yield compared to undrained conditions.    

Some loss of N and P in tile drainage water is inevitable, but the large potential reduction in surface runoff and associated P loading from tile installation must also be recognized and requires further study. This is especially important in watersheds where sediment and P loss are major concerns. In addition, sediment and P concentrations in surface water runoff are generally greater than levels in subsurface drainage water. Another benefit of tile drainage is that runoff can be managed more precisely than surface runoff.  For example, research has shown that drainage water management technology (e.g., controlling water table levels in a field at certain times of the year) can reduce N loading from drainage by as much as 50% compared to free-flowing tiles. 

Tile drainage of cropland is a critical practice for dairy and crop farms in northern climates, and without it many farms would not be economically sustainable. It"s important to recognize that tile drainage is just one part of the complicated nonpoint source pollution story. Implementing integrated nutrient management strategies requires a systems approach and farms should consider all of the latest technology to maximize nutrient use efficiency in the cow and in the field (precision feeding, soil and manure testing, nutrient management, nutrient simulation models, cover crops, riparian buffers). Improving nutrient use efficiency on the farm and reducing losses always makes economic and environmental sense.

Editor's note: This article first appeared in the October 2011 issue of the Miner Institute's Farm Report.



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