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A Guide to Agricultural Drainage

Agricultural drainage is a necessity for anyone who owns land with crops, however it can be confusing to get your head around. There are many aspects to agricultural drainage so in this blog we will try and break it down to give a basic technical knowledge.

Image of Agricultural Drainage

What is agricultural drainage?

There are two types of agricultural drainage systems:

1. Surface drainage
2. Sub Surface Drainage (Underground).

There is no actual definition for agricultural drainage however the purpose of the systems is to control the surface water level using underground drains or other above ground systems to enhance agricultural crop production. Rainwater lands on soil and soon gets to a point where no more water can be absorbed.

What is Surface Water?

Surface water is another way of saying rainwater that falls on the land surface. In fields, surface water often creates puddles due to uneven land often referred to as ‘low spots’ or ‘depressions’. There are a few techniques that can be used to decrease the amount of low spots and cease water collecting in the same place for a long period of time. Land levelling are two options or the construction of a waterway to allow water to drain out of the field, however you can also build surface inlets to connect into underground drains.

Surface Water Drainage Design

These regular drainage systems begin to work once there is an excess of rainfall and consist of reshaped or reformed land surfaces. They can be segmented into bedded systems which are used on flat land for all crops excluding rice, or graded systems which are used on sloping land for any crops other than rice.

Before you begin designing a surface drainage system you must ensure you issue a topographic survey and create a contour map of the area to come back to if you ever need to adapt or fix the drainage.

Surface water drainage generally comes in three types:

Open Ditch Drains: As the simplest option, open ditch drains follow the contours of the land. Depending on the amount of space available you can either have a V-shaped or U-shaped channel.

Field Ditches: These are deep V shaped or vertically sided with narrow tops and can be crossed by large, heavy farm machinery.

Narrow Ditches: These are used in areas where farm machinery isn’t in use.

For more information on surface water drainage visit the RSPB website: https://www.rspb.org.uk/Images/land_drainage_systems_tcm9-254843.pdf

Below-Ground Drainage

In well drained land you may find perforated pipes 3 to 4 feet below the surface of the ground which remove puddles of water from the land. Water drains into the soil and through into the perforated pipes which allow water to drain along the length of the pipe and out into the soil through the many perforations. The water travelling through the pipe may end up in a local water course, a much larger soakaway system or could be recycled for cattle drinking water. It can also be stored within a culvert system for use as land irrigation during dry periods.

Subsurface Drainage Design

This is where things become more complex so we will only give you a basic technical understanding of subsurface drainage design. When dealing with subsurface drainage there are a few things you have to think about first, one being permission. Have you got permission to dig into the land and place drains under it? You will need to plan before you start and think about how long it will take, the costs, and who you may need to help you.

As previously mentioned, subsurface pipes are there to remove any excess water from the soil, and are installed 2 to 4 foot below the surface of the soil. Older systems have clay tiles however more recent systems are comprised of perforated plastic pipes. Once the rain water begins to fall and backlog on the ground it flows into the perforated pipes therefore lowering the water table.

There are numerous different design layouts for subsurface drainage depending on the specific requirements and conditions of the site. Some of the requirement factors are: soil type and condition, hydrology, crop requirements and site topography. All of these factors will help decide on the type and layout of your drainage.
For more information on subsurface drainage design visit the RSPB website: https://www.rspb.org.uk/Images/land_drainage_systems_tcm9-254843.pdf

The importance of agricultural drainage

1) Increase Yield Potential: Most importantly, agricultural drainage looks after your crops and maximises their growth and development. The puddles or wet soil make it hard for the crops to breathe meaning they aren’t able to grow, this affects the yield potential.

2) Reduced Costs: If the soil becomes damp or wet it could drastically affect the fertiliser, seed and chemicals that are applied to the yield. For these to help with growth they need stable conditions to maximise their potential therefore wet conditions will decrease chances of them reaching this potential or may even eliminate it. It also reduces costs for machinery, as wet weather can hinder the way agricultural machinery works as they tend to get stuck in wet soil. This means machinery can work more efficiently, reducing the cost of diesel or expensive rescue operations.

3) Increase the value of your land: Arable and rural land are both in high demand therefore it is worth keeping your land in good condition. If your land is well looked after it will be easier to sell or rent and are more likely to get the money you expect for it.

4) Boosted Timeliness: Having agricultural land drainage means your timing and precision can work well at optimum levels. The task of harvesting, drilling, spraying and fertilising all need to happen within a small time frame to increase the potential of the crop. Drainage allows the soil to dry out quicker after heavy rainfall meaning any tasks can be carried out within a short time period.

Can you recycle and re-use agricultural drainage water?

Put simply, yes you can and it is a very beneficial process which is becoming increasingly popular and is an important source for irrigation water. Due to the growing demand for food and water in urban communities, the agricultural sector must expand its food production but still with water preservation in mind.

Before you think about how you are going to re-use waste water you must consider a few things:

• What are the water requirements of the community?
• What is the waste water being used for?
• Is it economical?
• Is the content harmful?

For irrigation and other outdoor water uses, rain barrels can be used to collect rain water. You have the option of either getting a commercial rooftop collection system or you could also connect your downpipe into a covered barrel which is a cheaper way of going about it.

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