Early summer advisory bulletin 2009
Managing grassland in May
After a wet and very cold winter, the productivity of grassland may be suffering due to compaction, poaching and/or winter kill. Now is a good time to inspect fields and assess what actions are needed to improve the soil structure, and the sward density and content – check weed levels too.
Once the first cut of silage has been taken, replenish soil nutrient content with appropriate applications of slurry and fertiliser.
Check for compaction and remove it
Last year’s wet summer coupled with a wet winter has increased the likelihood of compaction – both from livestock and machinery. Take a spade out into the field and dig out a square clod of earth. Drop this onto the ground and vertical fissures should appear. In compacted ground, only horizontal fissures will be seen.
Also, on examining the clod, look out for areas of rusty-coloured soil which smell of iron and sulphur. This denotes iron oxidation, where compaction has starved the soil of oxygen, another limit to grass growth.
Sub-soiling grassland (sward-lifting) will break the mineral pan, oxygenate the soil and grass roots, and improve nutrient uptake from the soil. It is best carried out when the soil is dry enough to crack a bit, but not so dry it collapses. Early Autumn is the ideal time for sward-lifting per se, as wet weather will follow and support grass growth again. Alternatively, results can be good after first cut provided the soil surface is not baked out and dry and there is rain forecast to help the sward recover.
More information on the different types of compaction can be found in the Grassright Group’s booklet on Best Practice Grassland Management which can be downloaded here {or wherever} …..or request a ready printed A5 copy by emailing info@grassright.co.uk.
Check swards for winterkill and reseed or overseed
Following the hardest winter for 20 years, plant death from winter kill has been very evident and some pastures are now looking very thin and open. Walk through your fields and see if the sward has become thinner, and/or if weeds and weed grass are newly taking hold in thin areas. A blank Field Inspection Report can be downloaded [here] in which sward status can be recorded.
Where winterkill has thinned out swards, then overseeding is recommended to ensure these gaps are filled with productive grasses and clovers rather than weeds.
For best results, either overseed straight after a silage cut when the sward is still short, or graze it down hard. Then harrow aggressively to create a fine tilth and open up the surface. Broadcast seed can then fall onto bare areas of ground and germinate. Always roll after seeding ensure good soil-seed contact to maximise germination percentage. Using ley mixtures treated with the biological seed treatments Headstart and Integral, can also boost establishment significantly.
Simply harrowing grassland has benefits too
The harrowing of pastures and silage leys per se opens up the soil surface aerating the sward and stimulating tillering and spring growth. It will also make available the small amounts of nitrogen that are locked up in the surface after the winter rainfall. Chickweed and other creeping weeds can also be pulled out and reduced in population to allow the grass a competitive edge. [picture of harrowing to right: Harrowing stimulates grass growth and removes shallow rooted weeds like chickweed]
Remove weeds to improve sward energy and yields
When should one aim to remove weeds such as docks, nettles and thistles? The simple answer is when they are at the correct growth stage (rosette) and in a healthy condition to take up chemical and translocate it to their roots. [picture of dock rosette to right: This dock is healthy and at the rosette stage, so now is the time to apply herbicide]
- Ideally, this should be done before first cut to increase the quality of what is the most important cut. But not if weeds are in poor condition, in which case it is better to wait until after first cut, for best long term control. Bear in mind that herbicides such as Doxstar and Pastor require a minimum period of 3 weeks for translocation to the root, before a cut should be taken.
Different weeds require different treatment dates, for instance creeping thistles tend to be fit mid May to mid June depending on where the farm is located, and this does not usually coincide with docks, unless the field has been cut first.
Having removed weeds from the sward, then fill the gaps by overseeding with productive grasses to prevent further weed ingress. If using a non clover safe treatment, there needs to be a minimum 6 week gap between treatment and stitching in of clover.
Plan to boost second cut silage
Grassland should be starting to look good for first cut silage now, particularly where slurry and fertiliser nutrients have been applied in response, not just to N requirements, but also to soil P and K indices too. The cutting date is often a compromise between holding off for more yield and cutting earlier to maximise D-value, and this may particularly be the case if the chilly start to the spring meant that fertiliser applications were delayed. If this is the case, there may be some advantage to cutting for D value rather than a bigger yield, as not only will the herbage quality be better, but the recovery after cutting should be quicker, meaning that second cut will not be compromised. However, make sure that you have left enough time for the applied nitrogen to be used by the sward – as a rule of thumb, the grass can use 2.5 kg/ha (2 units) per day.
Once first cut has been taken, then prepare for second cut. Useful amounts of nutrients can be supplied by spreading slurry on the aftermaths. Tailor applications of bagged fertiliser to supply the remainder of the nutrient requirement, taking into account those already spread in slurry. Many areas will benefit from using a sulphur-containing fertiliser at this time, and give improvements in both yield and quality.
If you are applying both slurry and bagged fertiliser leave a gap of 4 or 5 days between applying the two different materials, as the combination can provide ideal conditions for denitrification to occur, losing nitrogen from the soil and releasing a greenhouse gas to the atmosphere – a real double whammy.