Check swards for forage potential
Grassland may not look its best in February but now is an ideal time to assess its quality.
Grass diseases such as rust can limit production dramatically, while ryegrass can be identified by the maroon colouring of the leaf sheath.
Grassland may be looking its worst at this time of year, but this is also a good time to inspect swards and evaluate what actions are needed to ensure fields can provide sufficient forage supplies for the coming year.
Maximising grassland productivity is not just all about grass an integrated approach to management needs to be in place. This includes annual soil sampling, to confirm whether the right levels of nutrients, phosphorus and potassium are present, and also a pH check.
Grass needs a pH of 6.0-6.5 for successful establishment and to maximise productivity. So pH testing kits, which can be bought very cheaply, are a worthwhile investment. Extremes of pH can favour invasive weed grasses, such as creeping bent, which thrives in acidic conditions, or meadowgrasses, which are sadly more tolerant of both extremes of soil pH than ryegrass. None of these weed grasses are productive, ranging from a miserable 7% to a maximum of about only 28% of the production potential of perennial ryegrass.
A well-drained surface is another prerequisite for long-term grass health. Compaction not only harbours water, but prevents the natural exchanges of nutrients, inhibits roots and, again, yield potential.
Assuming, then, that soil structure and nutrient content are sound, follow the steps below to carry out a spring health check and ensure you are geared for maximum production from forage this coming year.
Step 1: Create a field inspection report
All grazing and cutting fields will be contributing to total dry matter yield, so it is important to assess all of them. Yes, even the paddock outside the parlour.
First, create an inspection report sheet for each field and include the following: Field name and size, type of ley sown – eg, long-term, short-term – cutting and also the date it was sown. Also record the date of the inspection you make.
Step 2: Field inspection – ground cover assessment
Ideally, you want a field with 100% ground cover of productive grasses and clovers. So cast your eye around the field and estimate how much ground cover there is, versus bare areas. Typically, bare areas will arise from poaching or where herbicide application has killed off weeds and left an open space, or where winterkill or flooding has killed off grass. Record this percentage on each field report.
Step 3: Field inspection – assessment of productive species
Next, look at the content of the sward. How much is weed? Broad-leaved weeds – docks, chickweed, buttercup – should be easily identified. But much harder to assess are the grassweed species. These include meadowgrass, Yorkshire fog, fescue, brome, foxtail and bents.
Weed grasses do not use nitrogen that well, so are not as productive as ryegrass species, nor do they have the nutritional quality. Some weed grass species, like Yorkshire fog, are also unpalatable.
To tackle this part of the assessment, it is easier to identify plants that definitely should be in the sward – ryegrasses, timothy and clovers – and then assume every other green plant is a weed.
Ryegrass has the following unique features: A maroon pigmentation on the leaf sheath just above the growing point at ground level. A ryegrass leaf is clearly folded, not flat or rolled, and is matt on the inside and shiny on the back.
Timothy is unique in having leaves with a blue-green appearance and a mild twist. The growing point is also bulbous, like a mini-onion. Unlike many similarly coloured weed grasses, the leaves are soft to the touch. As for clover, its obvious unique feature is the trifoliate leaf plus its low spreading habit.
To make an overall field assessment of productive species, take a trowel and carefully remove 10-15 small patches of grass, about 10cm in diameter, from different parts of the field. Bag these up field by field, and take somewhere warm and dry to make your assessments.
Then for each field, calculate the percentage of weeds to the identifiable non-weed grasses and record this on the field report.
Step 4: Calculate field production potential
Grass is such an essential crop, yet the difficulties in measuring productivity mean calculations of dry matter yields from single fields or farm grassland are rarely done.
So base your calculation on NIAB figures, which cite a ley in its first year is capable of producing 16t/ha of DM. But by the third year, its productivity will have fallen to 12t/ha. So, for example, an inspection of a 15ha field with a three-year-old ley reveals a ground cover of 80% and a sward with 10% weed content.
The field’s maximum DM yield potential is 180t/ha (15ha x 12t DM). But with only 80% ground cover, its yield would be 144t/ha, and since only 90% of the sward is productive species, the actual potential DM yield is 130t/ha.
This means missing out on 50t/ha, or a loss from that one field of 750t of DM. So, if this field contained a modern high tetraploid ryegrass sward with an ME value of 11MJ/kg DM or higher which was then cut and ensiled at a DM of 27%, this 50t/ha loss would equate to at least 150t of silage.
Step 5: Consider quality potential
It is not possible to measure sward quality at this time of year. But the following factors should be included in decisions on field improvements.
The quality of grazing or silage from a ley will fall as the sward gets older. Typically, an old pasture might give an average D value at silaging of 65D. But a new pasture should provide up to 72D. Tetraploid ryegrasses will also have higher D values than diploids and tend to be more palatable.
For every one unit increase in D value, it has been shown that liveweight gain improves by 20g a day in lambs and 38g a day in beef cattle.
Disease, like crown rust, will reduce sward palatability. You may notice some residual symptoms of last autumn’s crown rust. The disease itself should have long cleared up, but the plants will often still exhibit yellowing. Thanks to the warming climate, this disease can now be found as far north as Blackpool. The best long-term strategy is prevention, sowing mixtures with a high proportion of resistant varieties.
Step 6: Plan remedial action
Depending on your usage plans and anticipated forage needs, you must now decide what remedial action is needed. You may decide to leave the field as it is, carry out a full reseed, or rejuvenate it by slot seeding or overseeding.
There is no substitute for a full reseed for the maximum potential of a ley to be realised. A total reseed is the most expensive option, costing £160-£350/ha depending on inputs such as herbicide and fertiliser. But the full cost including inputs is easily repaid in the first year. Even an average grass mixture is capable of delivering 25% more forage than an old pasture and with a top specification mixture this could rise to more than 35%.
A new grass ley will also deliver improvements in ME, palatability and digestibility, even at today’s milk prices a dairy enterprise can expect an extra return of more than £600/ha, with equivalent benefits for beef and sheep units.
However, a full reseed is not always a viable option. The field might be difficult to plough, or have an undesirable substrate, or quite simply stocking rates may not allow a field to be taken out of production for long enough to establish a new ley. But there are a number of methods in which existing pasture can be substantially improved and topped up with productive grasses and clovers.
The most reliable is slot seeding with a purpose-built drill. The likely cost of this is £100-£200/ha depending on other inputs and whether you do the job yourself or use a contractor.
Another option is to overseed using a grass harrow with a seed box. The grass harrow will remove moss, annual meadowgrass and some weeds, creating some bare earth in which seed can land and germinate. Cost is about £40-£70/ha.
Clovers fix worthwhile quantities of atmospheric nitrogen and lend themselves well to reintroduction to pastures. In addition to the methods mentioned above, clovers can be spun on to a field with a fertiliser spreader during periods of low grass growth between spring and autumn. Due to the seed’s small size and low weight, it can be difficult to distribute. Pelleted blends are now available, which not only make distribution less haphazard, but contain the biological growth stimulant Headstart, to aid establishment.
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