Grassland management: healthy soil = healthy stockMonday 06 June 2011
THERE should be the equivalent in weight to nine cows in worms and micro organisms in a hectare of healthy, well-aerated soil.
That was grassland specialist Charlie Morgan's most thought-provoking point at a recent Lancashire demo event highlighting how important it is to get the most out of your soils and grassland.
Despite it being the best day of the week as far as the weather was concerned, 17 farmers were able to attend the grassland demo event at Low Meadows Farm, Hoscar, Nr Ormskirk courtesy of the Scarisbrick family.
Speakers for the day were Charlie Morgan, independent grassland specialist, and Liz Genever, livestock scientist with EBLEX, and the focus of the meeting was grazing management and improving soil condition for optimum results.
Liz took one group of farmers out into the field to look at how well the grass in that field was being utilised by grazing sheep and lambs, and began by discussing the quality of grass as a feedstuff in comparison to barley.
Grass has a very similar ME content (Metabolisable Energy) but a higher protein content than barley, but only costs 6p/kg DM (dry matter) to grow compared to barley at 18p/kg. When the cost is taken into consideration it certainly shows that it makes good business sense to make the most of what you can grow easily (particularly in the wet conditions of the North West).
Each farmer was given a sward stick and asked to measure the height of the grass in the pasture. This gives a good indication of the quantity of grass available. One member of the group was then sent off with a rising plate meter to measure more accurately the kg of grass dry matter (DM) in the field.
The measurements showed that there was 1,746kg DM/ha. As sheep can effectively graze down to 1,200kg DM that leaves a total of 546kg DM/ha available to be utilised. By multiplying the DM available/ha by the size of the field at 1.5ha, Liz calculated there to be 819 kg DM available on the field that day.
Liz then calculated the daily dry matter requirements of the 30 ewes and lambs currently grazing that field:
30 ewes and twins @ 70kg each
Daily dry matter intake @ 4% of liveweight (70kg) = 2.8 kg DM/day/ewe
2.8 kg DM x 30 ewes = 84 kg DM/day
Optimising grassland utilisation
In order for optimum utilisation of the grass, the daily requirements of the livestock should be balanced with the grass available, and measured to allow planning for deficits and surpluses throughout the season.
The rate of grass growth per day over the growing season, at approximately 70 kg DM/day, must also be taken in to consideration. In this example the sheep require an additional 14 kg DM/day, so the 819 kg DM grass available in the field will be sufficient to keep the sheep for at least a further 58 days (819/14 = 58). Liz recommended stocking the field more heavily to utilise the grass more quickly before it started to reduce in quality.
If the field was to be grazed rotationally as opposed to being set-stocked there would be 20-30% more grass grown. This is due to the fact that the grass plant is given time to rest between grazings so it is healthier and thus grows more, and grazing the plant hard helps to prevent the grass going to seed which promotes further tillering.
Rotational grazing is practiced widely in the dairy industry as it is much easier to move the cows onto a new pasture after each milking. However Liz agreed that this may not be as easy to achieve in practice with beef and sheep due to the nature of many farm set-ups.
Strip grazing is another option to help improve utilisation by forcing the stock to graze more effectively. However there is more risk with this that the grass which is shut up will go to head before the sheep are able to graze it, thus reducing the quality.
Liz concluded her piece with a discussion of the grass growth curve over the growing season. Whilst animal requirements remain fairly constant throughout the year, grass growth alters according to season, weather etc.
To optimise utilisation grass should be conserved when supply exceeds demand ie. May when grass is at peak growth, and then use this conserved forage at times when demand is greater than supply ie. Winter. This will help to maintain the quality of the grass and prevent it going to seed and being wasted.
If other feeds, such as barley, are offered when there is sufficient grass available, there will be a substituting effect and the stock will tend to consume less grass. Creep feeding is most cost-effective and beneficial when grass is in short supply.
The importance of soil testing
In the other field Charlie was discussing soil health, the importance of soil testing and how soils can be improved. He began with the basics – correct soil pH is crucial to enable the grass to utilise the soil nutrients. Soil pH for grassland should be 6-6.5; any higher or lower than this and vital trace elements will be locked up thus depressing grass yield.
Charlie pointed out that unless farmers are testing their soils they have no idea what the pH is and therefore what is needed to correct it - and getting pH to around this level is the key ingredient.
What lime to use?
- Prilled lime is a quick-fix solution as it breaks down very quickly in the soil and so will only be effective for 12-18 months.
- Ground limestone is broken down much more slowly so the effects will last for 6-7 years.
- Basic slag contains high levels of metals such as iron which actually lock up all the phosphate and trace elements - something that is not recommened.
- The level of grinding of the limestone will determine how quickly it is broken down and hence the length of time it will be effective. The smaller the particles the more rapid the breakdown, so a mix of powder and larger particles is the ideal.
As well as the correct pH being vital in determining nutrient availability to plants, the physical condition of the soil is also important. Soil needs to have the ability to retain sufficient water for plant growth, but not to retain too much water.
"For every 2 cows on the surface of the soil there is the equivalent in weight to another 9 cows below in soil bugs, worms and organisms nourishing the soil" - Charlie Morgan
The activity of these organisms will be greater in healthier soil which has plenty of air and sufficient water. Charlie advised to get the best out of your "two cows" you've got to feed the "nine cows below" by freeing up movement in the soil to draw down, water, air and nutrients from manures and fertilisers that would otherwise sit on the top few inches of the land and possibly be lost to run off.
Dig a hole
Charlie illustrated his point by getting one of the farmers to dig him a hole in the soil so that everyone could look at the soil profile. The soil was quite solid with very little give and there was also quite an obvious line where a compaction pan was present.
Above this line there were very few worms in the profile indicating that the soil was perhaps not quite as healthy as it could be due to compaction preventing water and air from penetrating the pan - discouraging worm movement and stopping nutrients from manures and fertilisers from being drawn deeper in to the soil from the surface and possibly being lost to surface run off.
Grass roots will also struggle to penetrate past the pan, which was demonstrated when the turf broke away too easily from the soil, "farm all the land not just the top few inches".
A pan will lead to waterlogging in the top of the soil profile and the soil will not heat up as quickly in the spring. This in turn will mean that grass and clover will be slower to start growing in the spring which means that cows will have to be housed for longer before turn-out. With housing costing at least £1.70/day/cow it makes good business sense to turn-out as early as possible.
Mike Burley from Opico (working in conjunction with local dealers Clarke & Pulman) demonstrated a sward lifter and explained how this would be best used where the compaction was relatively deep, such as that caused by running machinery over the soil regularly. In cases where the compaction was shallow eg. due to livestock poaching, then other equipment such as an aerator would be more effective.
Mike stressed the importance of digging a hole to determine what sort of compaction is there before investing a lot of money in a machine that would not be suitable for the job. Mike also emphasised that the timing of carrying out such operations is a critical determinant of the success – autumn and spring are the best times as the soil is damp rather than too wet or dry.
Following lunch there was the opportunity to see further machinery demonstrations by Clarke & Pulman, including a grass harrow with seed box for reseeding.