Artificial subsurface drainage continues to be a common practice in Minnesota, as well as in other states and countries around the world.
Subsurface drainage is the practice of placing perforated pipe at a specified grade (slope) at some depth below the soil surface. Excess water from the crop root zone can enter the pipe through the perforations and flow away from the field to a ditch or other outlet.
This Pritish Kumar Halder guidance will help you to know about Drainage Systems In Agriculture.
Until the 1970s, most subsurface drainage pipes were made from short, cylindrical sections of concrete or clay called a tile. That’s why terms like tile, tile drainage, and tiling are still used, even though most drainage pipe today is perforated polyethylene tubing.
Subsurface drainage pipes
How pipes are placed
When installing a subsurface drainage system, either strategically place pipes in a field to remove water from isolated wet areas or install it in a pattern to drain an entire field. In some areas, surface inlets or intakes (riser extended from underground pipes to the surface) remove excess surface water from low spots in the field.
Benefits
Subsurface drainage improves the productivity of poorly drained soils by:
- Providing greater soil aeration.
- Enabling faster soil drying and warming in the spring.
This may allow producers to plant fields earlier, and for other field operations to take place in a timely fashion.
It also provides a better environment for crop emergence and early growth and can reduce soil compaction. Once a crop has been established, subsurface drainage greatly reduces the risk of crop water stress from ill-timed or excessive rainfall. For these reasons, subsurface-drained soils represent some of the world’s most productive soils.
Glacial processes in the Upper Midwest created an abundance of highly productive but poorly drained soils. While it improved agricultural production, drainage also affects hydrology, water quality, and wetland habitats.
Improved agricultural production
Poorly drained soils increase risks to agricultural production from excess water and high water tables. Proper soil drainage improves agricultural production by:
- Ensuring timely planting and field operations.
- Minimizing soil compaction and salt buildup.
- Promoting conditions for good seedbed establishment and germination.
- Reducing high water table stresses to growing crops.
- Out yielding poorly drained soils
- Offering less year-to-year yield variability.
- Improving the opportunity to employ other conservation practices such as minimum tillage.
Other effects
Both artificial drainage and land-use change (prairie to agriculture) affect hydrology, water quality, and habitat. It’s difficult to separate the individual effects of drainage and land-use change.
Hydrology
- Surface and subsurface drainage have very different hydrologic impacts.
- drainage speeds flow from the landscape and increases peak flows.
Tile drainage promotes more infiltration, slowing water delivery from the landscape (compared to surface drainage). However, studies indicate the potential for overall water yield increases from 5 to 10 percent.
Local hydrologic effects are dampened at larger watershed scales.
Water quality
- Surface and subsurface drainage affect water quality differently:
- drainage may increase losses from surface runoff (primarily sediment and phosphorus).
- Tile drainage may reduce surface runoff pollutants, but may increase dissolved nutrients such as nitrate.
Wetland reductions
Drainage activities have reduced the number and extent of wetlands. In some areas, they’ve reduced by as much as 90 percent. However, wetlands are now protected by federal and state laws. In some areas, wetlands are being restored, usually on land that once was cultivated.
Types of subsurface drainage systems
There are several options available for draining excess subsurface water to a specific depth from the soil profile. The most suited drainage system is influenced by:
- soil type
- topography
- rainfall
- outfall type and location.
Drainage systems are expensive to install but, if they’re well maintained, their benefits outweigh their initial cost. For more information please visit Pritish Kumar Halder ‘s page
Make sure you have surface drainage
Most wet soil problems are the result of waterlogged soil profiles, not just surface water. Install surface drains to drain excess surface water off paddocks before installing your subsurface drains. This will reduce the load on the underground drainage system and allow you to install an effective subsurface system at a lower cost.
Benefits of a subsurface drainage system
The cost of drainage systems has shown that both increased pasture utilization and extra pasture growth from drainage can be competitive with other feed sources. But to take advantage of this extra growth, more cows and farm improvements (including a feed pad) may be necessary.
Environmental sustainability benefits
Subsurface drainage provides many long-term sustainability intangible benefits, such as:
- improvement in soil health due to the increased aeration of the soil
- increased responses to fertilizer use
- reduced mineral imbalances in the soil and sometimes in the plants as well
- prevention or reduction of salinity (if in its early stages).
Improved animal production
Drained soils enable fodder conservation of silage and hay to occur several weeks earlier than on undrained soils. The resultant fodder has the potential to be of much higher quality, improving animal production.
Better retention in desirable plant species
Drainage, by reducing pugging and creating favorable soil environments, results in the retention of the improved pasture species, instead of promoting the influx of plants suited to waterlogged conditions such as rushes, fog grass, Glycemia species, and water couch.
Personal benefits to the farmer
Most importantly, reduced stress in managing stock and pastures during the wetter months of winter or spring has very large benefits for the farm operator.
Types
There are 4 main types of subsurface drainage systems:
- corrugated and PVC slotted subsurface pipes
- mole drainage (including mole drains, mole drains over collector pipe systems, and gravel mole drains)
- interceptor drains
- ground
- waterer pumps.
Subsurface pipes
Such pipes are best suited in deep permeable soils where their depth allows wider spacing and minimizes cost. Subsurface pipes can also successfully drain heavy (clay), poorly drained soils but have to be installed so close together that they are uneconomic in extensive farmland systems.
It can also be used in soils that might have an impeding layer (for example, clay) at some depth but, if the clay type and content are suitable, mole drains can be installed above these in mole drainage over a collector pipe system (skip to this section).
Correctly installed and maintained, these systems can last many years. Regular inspection of outfalls is necessary, as this is the weak link in all drainage systems.
PVC pipes replaced clay pipes
Subsurface pipe drainage was referred to as ’tile drainage’ in the past due to the use of short clay pipes. Clay was expensive and difficult to lay and has now been replaced by slotted PVC or flexible corrugated plastic pipes of variable diameters.
How subsurface pipes are laid
Specifically designed drainage trenchers, usually fitted with laser guidance equipment, dig the trench, lay the slotted pipe, and place permeable backfill into the trench on top of the laid pipe. This backfill is delivered by trucks or trailers fitted with conveyor belts that feed the backfill into the hopper. The forward speed, hopper channel opening size, and material size determine the depth and amount of material laid on top of the pipe.
Although trenches can be dug with a typical builder’s type trencher, producing a flat even trench base of the constant slope is very difficult. Laying pipes manually, without knocking soil into the trench before the pipe is laid, is also very difficult. The specific drainage machine uses lasers to maintain constant depth and fall regardless of ground surface conditions.
Backfilling the trenches
Is a major cost of a drainage system but is crucial to the drain’s effectiveness so the quality and price of backfill should not be compromised.
In very permeable soils, very little backfill is needed, but in less permeable soils, or where moles are to be pulled through above a pipe, the backfill depth reaches near the ground surface.
Mole drainage
Can be classified as:
- mole drains
- drains over a collector pipe system
- gravel mole drains.
The suitability of each type will depend on the:
- clay content and type
- sand and stone in the profile
- gradient
- outfall location.
The action of the mole plow forms a mole channel in the area of the soil profile with specific clay content. The plow also cracks the soil profile immediately above the mole channel, allowing water to flow into it.
A mole plow is used to form mole drains. Simply, a mole plow contains a leg (or blade) with a torpedo (or foot) attached to its bottom. Sometimes a plug (or expander) with a slightly larger diameter is attached to the rear of the torpedo, to ensure the mole channel is left with the correct shape.
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Mole drains
Are used in heavy soils where clay subsoil near molting depth (400mm to 600mm) prevents the downward movement of groundwater.
The success and longevity of mole drains are dependent on soils having a high clay content so that once a mole channel is formed, it will maintain the channel for many years. Mole drains are not suited to:
- soils with clay types that have dispersive or slaking characteristics
- permeable soils due to their high sand or loam contents.
- Mole drains over collector pipe systems
This system is used in soils where it is not possible to form moles that reach the outfall. This includes the presence of stones, sandy pockets, uneven surfaces, or excessive distances to the outfall.
In heavy soils where mole drains would need to be very long (over 80m) before they reach an outfall, it can be very successful to install subsurface pipes at approximately 60m to 100m, over which mole drains are pulled. Washed sand or small-diameter gravel is backfilled into the pipe trench near the ground surface at installation.
Mole drains are then installed at or close to a right angle to the direction of the pipes. Excess ground water flows into and along the mole drains, then drains into the porous backfill above the pipes, and then is quickly removed to outfalls via the subsurface collector pipes. A mole plow demonstrates how a mole channel is created, in this case with a slotted drain pipe underneath. The mole channel should be between 400 mm to 600 mm below the ground surface.
Gravel mole drains
Gravel mole drains are best suited to soils and situations:
- where subsurface pipes are unsuitable
- mole drains have a very short life span, or
- in slaking soils so the mole channel will maintain its shape at or soon after moving.
A gravel mole drain is an unlined channel or leg slot filled with small-diameter gravel or washed sand.
Gravel mole drains are also expensive because of the:
- amount of backfill
- close spacing.
But they do offer an alternative in some ‘difficult to drain’ situations. They might be useful in slaking and dispersive soil types, but get an expert opinion if you’re considering a gravel mole drain in these situations.
Interceptor drains
These drains are installed at the base of slopes at the change of gradient, usually where a steeper slope meets the flats to intercept the downhill flow of subsurface water. Often the soil type on the slope is more permeable than those of the flats and this forces the water to come to the surface, usually at the change of slope.
Interceptor drains can also be installed below springs and spring lines to intercept spring water. Grazing animals severely pug the areas around springs and damage is usually more concentrated downslope as the soil is very wet and has little structural strength. This affected area usually spreads unless fenced off.
Groundwater pumps
These remove water from aquifers so the water table will fall or be maintained at a suitable level below the ground surface.
The act of pumping causes a drawdown of groundwater leading out from the pump’s location — its effect will be much less at depth.
The extent of effect will depend on factors such as:
- aquifer depth
- soil type
- height of water table.
You must discuss with your regional rural water authority the cost, benefits, disadvantages, whether these pumps can be used and if you need a permit.
Choosing a drainage system
To decide which drainage system to install, you must first determine:
- the soil’s characteristics
- its permeability (the speed at which water can move through the soil)
- suitability for mole drainage (clay type and content).
Farmers and drainage contractors can often decide which subsurface drainage system to use based on some simple on-farm tests. But if there is any indecision, have your soil tested or consult a subsurface drainage expert.
Water Act
The Water Act 1989 guides the management of waterways and swamps. Before considering draining a wet area, contact your local catchment management authority for advice and to check if you need a permit.
