Grassland improvement and weed controlThursday 21 June 2012
Despite the subject of grassland and soil improvement being covered in many previous meetings, the fact it lies at the root of any productive grass-based system makes it a top priority - as shown by the level of interest seen at this latest on-farm demo event at Lancaster.
Organised by Myerscough College and hosted by Richard Rhodes and family at Low Moorhead Farm, Quernmore, and attended by 33 farmers, the event focussed on improving grassland on upland farms where there are often more restrictions in terms of geography and the environment than on lowland holdings.
There were several areas of interest on the day:
- Soil - the most valuable resource on your farm!
- Compaction - a machinery pan has the potential to reduce grass growth by 10%
- Sward assessment
- Weed Control - docks, thistles, rushes
Soil - the most valuable resource on your farm!
Charlie Morgan, Grassmaster, started with the basics of soil and how it is the most valuable resource on your farm.
Soil should be tested on a regular basis (every 4 years for grassland) to determine the nutrient indices and whether or not these have improved since the last test. The host farm had carried out some soil sampling and the pH of the field we were working in was 5.8. As the soil is peaty this is adequate as the soil will be difficult to work if the pH is any higher. For other types of soil the optimum pH for grass growth is 6 - 6.5. The pH of the soil will determine the availability of nutrients to the growing crop.
P and K indices
Next to pH, potash (K) is the most important nutrient in the soil – it is effectively the soil’s blood supply and is involved in the movement of water, nutrients and enzymes around the plant from the roots to the growing leaves. Although the target for K is 2-, high levels of potash in the soil have no detrimental effect. In comparison phosphate (P) target levels are 2 and levels higher than this can lead to pollution of water courses and subsequent environmental damage.
Having adequate potash and phosphate in the soil will improve the response to applied nitrogen – if P and K are wrong then N utilisation will be greatly reduced and hence expensive fertiliser will be wasted!
Each hectare of soil contains between 5 and 15 tonnes of nitrogen. If soil is in the correct condition 1-2% of this nitrogen will be released each year to the plants which means that less nitrogen needs to be applied in fertiliser form.
Soil condition - compaction
Charlie then dug a hole to allow the group to examine the soil condition in more detail. The soil looked in good condition with no obvious areas of compaction. However when Charlie dropped a clod of soil on the floor it didn’t break up as would be expected with an open, airy soil.
The soil was very hard further down in the profile which could point towards a machinery pan. A sub-soiler would be needed to break this up as an aerator will only work on the top few inches to break up livestock pans. A machinery pan in soil has the potential to reduce crop yields by up to 10% as it prevents the plant roots from permeating the ground and so the only nutrients available to them are those in the top layer. In addition to this a pan in the soil will prevent water percolating down through the soil profile and the top layers will become waterlogged in wet weather which will negatively affect grass growth.
Machinery demonstration - grass harrow and over seeder / aerator
Local fabricator Robert Fox brought along one of his own aerators to demonstrate to the group. This type of machine is most suitable for breaking up any livestock pans which may be present in the top few inches of the soil profile.
For any deeper compaction issues a sub-soiler should be used. The best time of year for aerating depends on the farm and the land but it should ideally be done when the land is dry enough to travel on but not so dry that the soil shatters. Hence there is often only a small window of opportunity in the year when conditions are ideal for aerating.
Local contracting company Ashcon brought a tine harrow with seed box which can be used to rejuvenate a sward by overseeding with more productive varieties of grass and clover.
Helen Mathieu from British Seed Houses looked in more detail at the composition of the sward and the different varieties of grass which can be used.
Perennial ryegrass (PRG) can be identified by the red colouring at the base of the plant stem. As PRG utilises 100% of the nitrogen applied to the sward the greater the quantity in the sward the better. In addition to this PRG is at least 5 units higher in D value than other varieties such as Timothy.
The group were then all given a sward stick to measure the height of the grass in the sward in order to determine the DM availability to the grazing stock. With the level of stocking in the host farm Helen calculated that the total forage DM requirements would be 600t/year, which equates to 2.3t DM/acre. By working out your forage requirements and then measuring what grass is actually available this will give you a good idea of how you can allocate the grazing accordingly to ensure that you make the most out of it.
The optimum time for grazing grass is at the stage when the third leaf emerges. A grass plant only ever has 3 live leaves and so if the plant is not grazed at the right time the plant will go to head and the first leaf will die off leaving a layer of dead material in the base of the sward.
Weed control - docks, thistles, rushes
Brent Gibbon from DowAgro Sciences spoke to the group about the most common weeds that are found in grass leys and how they can be controlled.
All weeds thrive in bare soils where there is little or no competition from other plants. Soils can be bared due to either ploughing when reseeding, poaching by stock in wet weather or overgrazing.
Dock seeds will lie dormant but viable in the soil for up to 80 years and will then grow when the seeds are disturbed and brought up to the surface. Docks should be sprayed at the rosette stage when the chemical will be translocated down in to the root
Thistles - spear and creeping
Creeping thistles are very difficult to kill as they have a complex root network, whereas the spear thistle only has one large root and is also a biennial plant so it will only live for 2 years. Thistles can cause mouth lesions in grazing sheep, increasing the risk of highly contagious infection.
These are a particular problem on many farms in upland areas which may have more wet areas where rushes will thrive. The general opinion amongst the farmers at the meeting was that rushes should be mown first and then treated with a weed wiper.
Brent described how it is possible to work out the level of weed infestation in a field by measuring out a 5m x 7m block and counting the number of weeds within it. Each weed equates to 1% infestation in the sward. If the level of infestation is less than 5% then spot treatment with a knapsack sprayer is sufficient control. However if there are more than 5 weeds in the square then a broadacre treatment of the whole field will be more cost effective.
Click here to access the Dowagro website for further information on weed control:
Clover and weed control
Unfortunately many sprays will also often kill clover in a sward, although some treatments are clover-safe. As weeds are often a problem in newly-sown leys due to the level of soil exposure Brent recommended that a grass only sward is sown initially and then this can be sprayed when weed infestation becomes a problem. Once the weeds have been killed then clover can be stitched into the sward at a later stage.
Charlie concluded that as grass-based systems of animal production are usually the most profitable, then any investment in improving the productivity of your grassland is always worthwhile.