content
Claying Water Repellent Soils
The hydrophobic compounds (waxes, alkanes, long chained fatty acids) that are left behind in the breakdown of organic matter are a major cause of water repellence in non-wetting soils.
Most of the water-repellent soils have clay contents of less than 1%. Sands that have 3 - 4% clay contents do not appear to have these water-repellent characteristics. The clay particles are less than 2-micron in size and have such a great wettable surface area that water will contact the soil and infiltrate. The clay particles surround the sand and organic matter.
Water repellence generally exists only in the top 100mm cultivated layer as the soil below this wets up easily because of the lack of organic matter, therefore hydrophobic compounds.
The increase in farming systems which increase soil carbon such as stubble retention and no till farming are contributing to the increase in water repellency.
Past Research carried out by Agriculture Western Australia looked at the application of a clay subsoil to increase the ability of these soils to accept water. An amount of 100t/ha subsoil with a 30% clay content, mixed into the top 100mm increases the clay content of the cultivated layer to the 3 - 4%. This ameliorant is continuing to produce positive results even 8 years after the first application.
The Benefits of Clay Application
- Increased production -- Yields of Barley from clay treated trial are averaging 1.2 tonne /ha extra barley each year for the last 8 years compared to no clay treatment. Lupin yield increase was 700kgs. Pasture seed production increase of 100%.
- Increased moisture infiltration -- Infiltration rates increased by 3 times with the addition of the clay and the water repellency rating of the soil was reduced from high severity to zero in the second year after application. This has allowed earlier seeding operations than would have been contemplated on these soils.
- Even wetting of the soil --- The soil wets up evenly and even light rains are able to penetrate over the whole surface.
- Weeds germinate evenly --- The even wetting of the soil allows the majority of the weed seeds to germinate and not the staggered germination associated with water repellent soils. This allows better herbicide activity and weed kill.
- Wind erosion control --- the sand develops a crust after rainfall and enough strength to prevents wind erosion when undisturbed.
- Nutrient retention --- Retention of Phosphorus and Potassium which is made available to the plants.
- Increased microbial activity --- Longer period of soil wetness encourages longer soil microbial activity.
More information
Incorporatiing soil spread on water repellent soils
The subsoil spread on the surface should be incorporated soon after it is applied. If it is not and it rains, it will slake and form a solid mass, which will have to dry out before you can smudge and or incorporate. This mass of subsoil will also shed water and restrict plant growth ... read more
Location of suitable subsoil for claying water repellent soils
The greatest cost in clay spreading is the transport cost. If you can find suitable clay in the centre of the paddock you intend to treat, then that is the cheapest option ... read more
Spreading the subsoil for Water Repellent Soils
It is best to aim for an even cover of clay/subsoil as this will require only one incorporation and then left until seeding time ... read more
What are suitable clay subsoils for controlling water repellence?
The clay content of the subsoil is the most important thing you are looking for and doing a texture or ribboning test can assess this ... read more
Timing of clay spreading on water repellent soils
The optimum time for clay spreading exist usually from after harvest through to the break of the season ... read more
Further reading ...read more
View images of clay spreading machines for water repellent soils
Incorporatiing soil spread on water repellent soils
The subsoil spread on the surface should be incorporated soon after it is applied. If it is not and it rains, it will slake and form a solid mass, which will have to dry out before you can smudge and or incorporate. This mass of subsoil will also shed water and restrict plant growth.
Incorporation of 100t/ha should be to a depth of about 50mm to 75mm initially, so that half of the material is still on the surface and the other half is just below. The material on the surface gets rained on and slakes but is not in a high enough concentration to seal the surface and shed water. Being in contact with the spread clay that is on the surface will also wet the material just below the surface.
|
|
100t/ha after one incorporation |
If the whole amount of subsoil is buried in the water-repellent layer then whole layer has to get wet to slake the clay and the process of wetting will take longer.
The incorporation can be achieved with tynes, offset discs and heavy harrows.
50% of the 100t/ha-application rate, left on the surface, is enough to minimize wind erosion if your stubble or pasture levels were low.
Higher rates of subsoil application should be cultivated deeper to 100mm-150mm to dilute the clay concentration at the surface.
The applied subsoil does not move in the profile and it is only the rain at the surface and cultivation that breaks the subsoil up into its individual particles.
Seeding. The seeding operation is the next incorporation and this will bring up the lumps just below the surface. It will also incorporate the material that was on the surface which has already reacted with the water-repellent sand. Several seeding operations will distribute the clay material throughout the top 100mm.
Full cut tillage will speed up the mixing, no till methods may take longer.
Cropping the paddock for 2 years helps the incorporation and the use of covering harrows in those 2 years is recommended. Following the 2 years of cropping the incorporation will be almost complete. Seeding pasture or lucerne in the year of clay application is not recommended, as this will be the only year of cultivation. With no second year of cultivation the mixing process will not be completed.
Location of suitable subsoil for claying water repellent soils
The greatest cost in clay spreading is the transport cost. If you can find suitable clay in the centre of the paddock you intend to treat, then that is the cheapest option. This is however not always possible and the clays have been carted from up to 800 metres away and greatly increase the cost per hectare. The optimum distance would be 300 metres.
In large rectangular paddocks the use of 2 pits, depending on their location, could be cheaper than using 1 large pit. Other options include increasing the catchment on an existing dam, building a new dam and using the excavated subsoil, digging a silage pit, or if the sub-soil is close to the surface several shallow pits can be excavated and then filled in with overburden and cropped over.
- First thing is to auger in your desired locations for suitable clay. This drilling can be done with a post hole borer on the tractor as this is a quick way to get around your paddock. You only need to check the holes where you strike some promising material before going to the full depth of the auger. Suitable subsoil that is covered by more than 1m of sand overburden can be expensive to open. The less material that has to be removed, the cheaper the cost. At any promising site a texture test and slaking test should be carried out to see if it has suitable clay.
Where you have gravel overlying suitable subsoil, this material can be used for roads and could offset some of the cost of overburden removal. Remember that gravel is rock and not clay and can make up a large percentage of a subsoil weight. Better to go a bit deeper and get out of the gravel before you start extracting spreading clay.
Once possible site location / texture / slaking / pH / dispersion / overburden/depth and gravel content examinations are satisfied, the actual amount of subsoil at the site should be determined. The paddock size will determine the pit size. (100ha paddock spread with 100t/ha subsoil requires a pit 50m *36m *4m =7200cubic m * 1.4(bulk density clay) =10,000 tonnes of sub soil)
Most clay/spreading machines require 50 metres of pit length to fill the bowl in one pass. Examine the area to make sure there is depth of subsoil and no sand seams or large rocks.
Subsoils with a clay content higher than 30% can be spread at lower rates per hectare. This assumes they slaked well and were highly dispersive . Knowing the actual clay content can assist you in decreasing the amount of subsoil that needs to be spread and also the cost of spreading.
Changes in the subsoil as the pit is excavated should be checked to make sure you are not spreading sub standard material.
Spreading the subsoil for water repellent soils
It is best to aim for an even cover of clay/subsoil as this will require only one incorporation and then left until seeding time. This is however not possible with all the machines that are out there at the moment.
The "Claymate", "RoadScraper", "Multi Spreader", "Lehmann" and "Landplaner" have all been used to spread clay and can all do the job.
The amount of ripping that is done in the pit prior to loading the machines determines the quality of the spreading job. The finer and drier that the material goes into the machine the better it will come out.
The spreading rate of the subsoil is determined by the clay content and should be verified on the ground with the use of catching trays or small tarp. The fully loaded machine whether Scraper/ Claymate / Landplaner / Multi spreader should be run over the trays at a speed that will deliver the correct amount of clay for the size of the catching tray. (e.g. 1sq m tray = 10kgs if rate is 100t/ha, 20kgs for 200t/ha). Once the required speed and settings to deliver the correct amount are achieved, the distance to empty the bowl at that speed of travel should be noted and used for each load. This will ensure the same rate of application.
If gaps are left between the clayed strips, that distance should be no more than 1.5metres. This is about the maximum distance that can be comfortably smudged in two runs. Larger gaps between the clay/subsoil strips requires increased cultivation increasing the chance of burying all the clay.The extra cultivations all add to the cost of the clay spreading.
|
|
Subsoil laid in strips requires smudging |
Smudging is performed by dragging a frame made from two railway irons across the trails of subsoil. The frame is pulled at speed diagonally across the trails twice, in opposite directions at 45 degrees to the strips to give an even spread. This operation will also incorporate the clay.
What are suitable clay subsoils for controlling water repellence?
The clay content of the subsoil is the most important thing you are looking for and doing a texture or ribboning test can assess this.
Texturing requires a palm full of sub soil excluding stones, moistened with water and kneaded for 2 minutes to form a bolus that just fails to stick to your fingers.
It is then made into a sausage and sheared ("ribboned") through thumb and forefinger. A ribbon of 75mm in length will indicate you have approx. 30% clay content. The longer the ribbon the higher the clay content.
The other important thing in the subsoil is its ability to slake (spontaneous aggregate collapse in water).
Slaking requires 2 pieces of subsoil the size of a thumbnail placed into a glass jar full of rainwater. The lumps should be dry when placing in the water so you get a proper representation of the subsoils slaking ability. The lumps should start to disintegrate almost immediately on being placed in the water. The quicker the lumps break down the quicker the clay can be released into the sand to start its work.
(If the subsoil does not slake it is not suitable)
Dispersion If the lumps are left for 24hrs the dispersive character of the subsoil can be seen. The more dispersive the subsoil the greater the halo or "milkiness" around the collapsed pieces of subsoil. Subsoils that slake well and are not dispersive are still suitable but should not be spread at reduced levels from the 100t/ha recommended. Subsoils that have high clay content (>50%), slake quickly and are highly dispersive could be spread at lower rates.
pH of the subsoil should also be taken into account in determining the rate of subsoil to be spread. Most subsoil in Western Australia are slightly less acid than the top soils and will not affect the pH of the topsoil markedly. However old lakebed subsoils do have high pH (pH 8.0 - 10) and should be used at rates 100t/ha to 150t/ha. If applied at rates of 200t/ha 300t/ha they could induce problems with nutrient deficiencies due to the dramatic change in topsoil pH. Also there is evidence that calcium carbonate nodules will hold atrizine or sulphonylureas (e.g. glean®, logran® ) that can affect successive crops. If these chemicals have been used on the soils, there might be some accumulation on alkaline subsoils. This needs to be tested.
The amount of subsoil that is applied will determine the clay content in the top 100mm of topsoil. If you are spreading larger quantities than 100t/ha you need to incorporate these to a greater depth so you don't get hard setting problem in your topsoil. Some machines have difficulty spreading at lower rates but are large in capacity. These can spread more subsoil for a cheaper or equivalent cost including the extra smudging cost. These high rates of application can dramatically increase the clay concentration in the water-repellent layer and need deeper incorporation.
Timing of clay spreading on water repellent soils
The optimum time for clay spreading exist usually from after harvest through to the break of the season. This can be extended as long as the subsoil is not too wet to spread and heavy rain during the spreading and incorporation operations isn't likely.
The earlier the subsoil is spread and incorporated the quicker the weathering from sun and rain to start the breakdown of the lumps. If it rains on subsoil that has been spread but unincorporated, it will slake and form a solid mass, which will have to dry out before you can smudge and or incorporate. This mass of subsoil will also shed water and restrict plant growth. All the effort in breaking up the material prior to spreading has been lost. The number of workings required to break up this material could lead to some of it being buried and therefore lengthening the time for the process to work. Also the possibility of wind erosion due to the number of soil workings could be greatly increased.
Spreading on stubbles after harvest is quite common. Large amounts of standing stubble or windrows of canola stubble could present a problem in that poor sand /clay contact is achieved due to the large amounts of vegetable material. In this situation raking stubble into windrows to burn or using secondary cutters on the header to reduce stubble length might be a consideration.
Pastures also need to be grazed to reduce the amount of vegetable material. Pasture topping to reduce the amount of material prior to spreading, could be used to increase the access period enabling subsoil to be spread in Oct/Dec.
Reading Material
For copies of these articles and other information contact R.E. Hetherington or Dr D.J. Carter at Department of Agriculture Western Australia, 444 Albany Hwy, Albany 6330. Phone 98928444, Fax 98412707.
- Carter, D.J., Gilkes, R.J. and Walker E. (1998). Claying of water repellent soils: Effects on hydrophobicity, organic matter and nutrient uptake. Proc. 16th World Congress of Soil Science 1998, Montpellier, France.
- Carter, D.J. (1990) Water repellence in soils and its effect on wind erodibility. Proc. National Workshop "Water Repellency in Soils" Adelaide 1990.
- Spadek, T. Scrase G.and Carter, D.J. (1994). Extraction of hydrophobic materials from sandplain soils: A case study of Esperance. Proc. 2nd National Workshop "Water Repellency in Soils", Perth 1994.
- Carter, D.J., Hetherington, R.E., Morrow, G. and Nicholson, D. (1994). Trends in water repellency measurements from soils sampled at different soil moisture and land use. Proc. 2nd National Workshop "Water Repellency in Soils", Perth 1994.
- Carter, D.J. and Hetherington, R.E.(1994). Claying of water repellent soils in the Albany region of the South Coast of Western Australia. Proc. 2nd National Workshop "Water Repellency in Soils", Perth 1994.
- Blackwell, P.S., Morrow, G.F., Nicholson, D.F., Wiley, T., Webster, A., Carter, D.J. and Hetherington R.E. (1994). Improvements to crop yield and pasture production on water repellent sand by claying in Western Australia, 1992-93; including comparisons to surfactants and limesand. Proc. 2nd National Workshop "Water Repellency in Soils", Perth 1994.
- Blackwell, P.S., Carter, D.J., Hetherington, R.E., Webster, A. and Bunker G. (1994). Prototypes delvers for claying to correct water repellency of duplex soils. Proc. 2nd National Workshop "Water Repellency in Soils", Perth 1994.
- Dellar, G.A., Blackwell, P.S. and Carter, D.J. (1994) Physical and nutritional aspects of adding clay to water repellent soils. Proc. 2nd National Workshop "Water Repellency in Soils", Perth 1994.
- Carter,D.J. and Hetherington, R.E., (1997) Claying for Profit. Proc. Workshop "Farming Systems Developments 1997" held at University of Adelaide March 18-20, 1997, p153-154.
- Carter, D.J. and Hetherington, R.E.(1994). Claying of water repellent soils of the South Coast of Western Australia. Proc. WA Branch of Aust. Soil Science Soc., Conf., Busselton 1994, p 193-198.
- McKissock, I., Gilkes, R.J., Harper, R., and Carter, D.J. (1997) Relationships of water repellence to soil properties for soils of southwestern Australia. Proc. WA Branch of Aust. Soil Science Soc., Conf., Geraldton 1997, p 64-69.
- Carter, D.J. and Hetherington, R.E.(1994). Claying of water repellent soils of the South Coast of Western Australia for profit. Proc. WA Branch of Aust. Soil Science Soc., Conf., Geraldton 1997, p 70-77.
- Walker, E.L, Gilkes, R.J. and Carter, D.J. (1997) An evaluation of clays for combatting water repellency of sandy soils. Proc. WA Branch of Aust. Soil Science Soc., Conf., Geraldton 1997, p 78-85.
- Findlater, P.A., Carter, D.J., Hetherington, R.E. and McTainsh, G.H. (1997) Replace soil removed by wind and increase production? Proc. WA State Landcare Conference, Geraldton, Sept 1997.
- Carter, D.J. and Hetherington, R.E., (1997) Claying for Profit. Proc. Workshop "Crop Update" GRDC and University of Western Australia, compiled W. Anderson and J. Blake Ag WA, Feb 1997.
- McIssock, I., Gilkes, R.J., Harper, R.J. and Carter, D.J. (1998). Relationships of water repellency to soil properties for different spatial scales of study. Aust. J. Soil Res. 36, 495-507.
- Harper, R.J and Gilkes, R.J. (1994). Soil attributes affecting water repellency and the utility of soil survey in predicting its occurrence. Aust. J. Soil Res. 32, 1109-24.
- Harper, R.J and Gilkes, R.J. (1994). Hardsetting in the surface horizons of sandy soils and its implications for soil classification and management. Aust. J. Soil Res. 32, 603-19.
- Carter, D.J., Findlater, P.A. and McTainsh, G.H. (1999) An economic solution to water repellency and wind erosion on light textured soils. In Proc. "Comland 99" International Geographers Conf. (Comm. For Land Degradation and Desertification) University of Western Australia, Perth Sept.1999.
Further information can be obtained by contacting
Dr Dan Carter or Rob Hetherington
Department of Agriculture and Food
444 Albany Hwy, Albany, W.A.
Phone +61 8 9892 8444.
Page reviewed : October 2006
Events
| 07/08/2012 | |
| Plant Disease Identification Course... | |
| 06/08/2012 | |
| Insect Pest Identification Course... | |
| 26/06/2012 | |
| Sheep Updates 2012 "More Sheep - It... | |
| 09/06/2012 | |
| Marketing and Business Plan worksho... | |
| 08/06/2012 | |
| DAFWA and the Beef CRC present...Br... | |
| 05/06/2012 | |
| DAFWA and the Beef CRC presents...B... | |
| view all... | |