Drainage Management Systems
Waterlogging and drainage
By Greg Gibson
A Nuffield Scholar shares lessons learned.
By Greg Gibson
The importance of good water management is sometimes lost in the busy world of farming. As an Australian Nuffield Scholar, travelling to the United Kingdom, the Netherlands, the United States and Canada to gain knowledge on ways to reduce waterlogging, I soon realized the importance of looking at multiple ways to combat this issue.
My study topic is finding ways to reduce waterlogging in high value cropping programs. Controlling water from rainfall and irrigation is an important part of any modern farming business. Crop stress, either by being too dry or too wet, limits plant growth.
My wife Sarah and I run a mixed cropping farm in the Northern Midlands of Tasmania, Australia. Tasmania, being an island with a moderate climate, lends itself well to niche crops such as poppies, vegetables, cereals, and seed crops such as grass seed, carrot, etc. On the property we also run a prime lamb trading operation. As crops are harvested in summer, wheat and grass seed crops are planted and used as a cover or fodder crop to fatten lambs. Most of the property is irrigated using pivot irrigation. The soil is a red clay loam with very heavy clay subsoil. Crops suffer badly through the winter and early spring from losses attributed to waterlogging. Because of the heavy clay content, water infiltration is very slow and most crops suffer after prolonged periods of wet weather. Tile is used in conjunction with raised beds, surface drains and mole drains. All tile is put in by local contractor Tas Land Drainage, using a Mastenbroek trenchless plow with the aid of a laser. The company has been experimenting with GPS grade control and will hopefully take this technology on in the future. Gravel aggregate is placed around and on top of the tile up to 300 mm (one foot) of the surface to broaden the tile profile. In addition to this, mole draining at a depth of 600 mm (two feet) and two metres (approximately six to seven feet) apart is installed adjacent to the tile lines to allow water infiltration. The mole drainer is simply a vertical leg 600 mm (two foot) long with a cylindrical torpedo attached. Following this is an expander, to help compact the mole wall. Mole draining needs to be done when the clay is damp enough to hold the shape of the expander, but not too wet to be compacting the surface with machinery. The mole will stay there for four or five years and must then be reinstalled.
My goal was to find out what causes waterlogging and how to reduce its effects. I studied monitoring soil, plant health, irrigation management using variable rate application, drainage and nutrient loss. Drainage was a large part of my investigation. During my travels I met with many contractors, manufacturers, researchers and farmers. It seems drainage itself hasn’t changed a lot over the years, but many things that surround it have. There is no doubt the addition of GPS technology has made a big difference to the way fields are drained. The design work takes minimal time using the latest watershed modelling programs. Utilizing these programs enables contractors to quote when looking into a new job. For the farmer or grower, this technology means they have a complete plan laying out the costing, tile size, tile placement and how much water can be drained off the field. Upon completion of the job, a record can be kept for reference in future extensions or repair work. GPS is also used to control tile grade and placement in regards to the field topography. This technology is a giant leap forward. Controlled drainage systems, utilizing control structures, have been well highlighted to show benefits in the reduction of nutrient loss. Tile control structures have become very popular. By placing these structures just before the out fall, the water table can be raised to hold water in field and let the rain soak in and filter through the soil profile. This also holds nutrients in the field longer and doesn’t allow them to flow straight through the drainage tile into the waterways as a pollutant. It is a very simple structure that drastically reduces the amount of nutrient loss, keeping nutrients in the field to aid in crop growth.
I also met with researchers working on some very interesting programs. Richard Cooke, at Illinois State University, explained research is being done on saturated buffer zones and woodchip de-nitrification bioreactors to reduce nutrient loss. Hopefully, by using these methods in the future, nutrient loss will be vastly reduced.
Another relatively new idea is the use of in-line water gates to raise water levels. Using these for subsurface irrigation was another idea that was really pushing the thinking of water management. As Chin Tan, with the Greenhouse and Processing Crops Research Centre in Harrow, Ont. explained, the tile is already there and if it can be utilised as an irrigation option from beneath the plant it will promote deeper “searching” roots. Of course a close monitoring program needs to be in place in case of a major rainfall event. This can be done by lowering the water profile before rainfall through the use of stop logs in the control structure.
I was very impressed with the professionalism of the contractors that gave up some time to talk with me. They showed great precision and care when installing tile pipe. I am grateful for their honesty and openness when questioned on certain ideas and customs.
On returning home, after meeting so many great people with an array of ideas, I am focusing my time on a full system approach to waterlogging. The plan is to use the technology available to monitor as many factors as I can, and use drainage technique, design and technology, nutrient loss management, controlled tillage practices and variable rate irrigation to try to reduce crop loss from waterlogging.
Greg Gibson is a Nuffield Australia 2014 Scholarship winner.