Forage Focus: January 2015

Exploring the world of high quality forage production and utilisation with specialist agricultural merchant Morton’s

To get the most from your fertiliser this year and to maximise forage for winter 2015, now is the best time to check your swards and soils for health, nutrient levels and productivity.

Soil Analysis

Regular soil analysis is required under phosphate regulations and should be carried out every four years across the farm.  In practice it can be more manageable to test a quarter of the farm each year. One soil sample per field (made up of 25 sub samples) up to 10 acres is sufficient.  For larger fields a second sample is required.  Areas within a field which have been identified as problematic in previous years should be sampled on their own. It not uncommon to have areas within fields which show lower pH or nutrient status figures: this can lead to a reduction in overall production of the sward or crop.

Once soil levels for phosphorous (P) and potassium (K) have been determined, fertiliser levels can be adjusted to meet individual field requirements. This means that savings can be made on fertiliser application while maintaining crop yields at higher levels. The optimum phosphorus level in soil for arable crops, intensive grassland and silage is an index 2. The optimum soil potash level is 2 – but always check RB209 or the nutrient calculator on the DARD web site, as additional applications may be required, particularly for arable crops.

pH is the other key soil analysis figure and one which can often be overlooked.  The target figure should be a minimum of 6.2 for grass and 6.5 for arable crops to improve the efficiency of fertiliser and slurry applied. At a pH of 6 - 89% of nitrogen is available, 52% of phosphate and 100% of potash. As an approximate guide 1 kg of CACO3 is required to counteract each kg of nitrogen applied (this varies with the type of nitrogen) or 12kgs of CACO3 for every 1000 gallons of slurry. The best approach is to bring your pH up to the correct level and then apply a high quality liming product like Granucal each year to maintain pH at the optimum level.

Grass Sward Assessment

You should plan to walk swards over the next month and identify those which need attention come spring. In particular you should check the level of perennial ryegrass in the sward. As a general guide, perennial ryegrasses have a red colouration at the base of the stem and a shiny underside to the leaf; weed grasses do not have these characteristics. 50% of your sward should be made up of ryegrass as a minimum. This should give 75% groundcover.  If groundcover is less this allows weed grasses to invade which reduces sward yields and slows regrowth. Modern grasses’ response to nitrogen will be five times higher than that of weed grasses, so reseeding pays.

You should tolerate no more than a maximum of 10% for broad-leaved weeds including docks, chickweed, thistles and creeping buttercup.  A four year study at IGER North Wyke found that where docks covered 20% of the field area, a control programme saw the treated plots yield 3.4t/ha more per year on average. A single dock plant can produce up to 60,000 seeds per year which can remain viable for 80 years. It may be that the sward has reached a level of weeds where it no longer makes economic sense to control them; in this case a full reseed is the only solution.

Soil Compaction

If possible take a spade out and dig to a depth of 40cms to check for soil compaction. Signs include rusty grey mottled colour, foul smell, poor root penetration (should be 30cms), lack of earthworms (normally 10-15 in each spade) and no vertical cracks. Plan to tackle these problems in the spring if the weather allows. For shallow compaction up to 10cms use a soil aerator with knives or spikes.  For compaction at 10-15cms use a sub-soiler or sward lifter.


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