Producers can take steps to mitigate extreme weather, and nutrient applications and timings – for both fertiliser spreading and grass cutting – are key to optimising crop growth and yields.
TEXT EMMA WALLER
The 2023 season saw another year of extreme weather and 2024 could be much the same. “But, although producers can’t control the weather, it is possible to adapt grass management to achieve optimal growth in grazing and silage swards,” says Yara’s Philip Cosgrave.
“Many producers experienced an extremely dry early summer in 2023, followed by a period where there was a lot of rain that, for some areas, continued into October. This made silage making and grazing a real challenge,” he adds.
So what can producers do when faced with this ‘unpredictability’. “One possible change may be to look at when first cuts are taken. The past couple of years have seen dry periods in early summer, which impacted secondcut silages,” he says. “To help mitigate the impact of this dry weather on second cut, harvesting first cut earlier can give second cut a head start before drier conditions really start to bite.”
Above-average rainfall in autumn 2023 means producers may also need to consider the impact on soils in the coming spring.
“When autumn and winter are wetter than usual, there will be lower levels of nitrogen and sulphur in the soil because above-average winter rainfall results in more of these nutrients being leached,” explains Mr Cosgrave.
Soil testing
Producers looking to optimise grass production and nutrient use should carry out soil testing and use the results to inform application decisions.
“Some producers may soil test the whole farm every few years while others test 25% of their farm every year in rotation. What’s important is that they use the results,” he says. “Producers should prioritise correcting soil pH and allocate resources to apply lime on those fields or leys that need it.”
He adds that for healthy soils and optimal yields, nutrient management planning is essential. “Producers should have a plan for each field, or group a number of fields together. If there are paddocks or fields with the same soil fertility and producers plan to cut the same number of silage crops from them, or graze them in the same way, they can be grouped together and producers can plan what the nutrient requirements are to grow that crop,” he explains.
“They can decide how to allocate organic manures to supply the nutrient requirements of silage crops or grazing. Typically manures fail to meet the full requirements of the crop and it is important that producers buy the fertiliser product they actually need to make up the shortfall in requirements rather than buying the same product year in, year out.”
For first-cut silage, which required fertiliser application this spring, producers should apply slurry in February if field conditions allow.
Home-grown forage: making silage using slurry and fertiliser is more cost effective than buying in feed
Apply early
There is no shortage of slurry on dairy units come February, with the closed period finishing for most soil types on January 31 in nitrate vulnerable zones (NVZs).
“The hope is that February 2024 will be similar to February 2023, which offered excellent field conditions to apply slurry early,” says Mr Cosgrave.
“It’s worth maximising slurry use in the spring, and first cut is an excellent ‘home’ for this slurry. Applying slurry to silage fields recycles nutrients extremely efficiently. Spreading on grazing paddocks would, preferably, only be carried out if soil potassium was low, or if a silage crop was taken from a paddock during 2023.
“Cooler conditions in spring, compared to summer, also mean that less of the available nitrogen in the slurry is lost as ammonia to the atmosphere. This, in turn, lowers the nitrogen fertiliser requirement,” he adds.
The availability of the total nitrogen in slurry applied in spring is 40%, while in summer it is 30%. A first cut removes upwards of 30kg of potash (K) per tonne of dry matter: “And, without balancing offtakes with inputs, soil K fertility can fall quickly.
“To safeguard against a nutrient shortfall, slurry applications can be supplemented with a NPKS or a nitrogen and sulphur product, applied around three weeks after the slurry and ideally by mid-March,” says Mr Cosgrave.
Producers can expect a yield-benefit response of between 10% and 20% with sulphur applications on first-cut silage crops. Sufficient nitrogen is also essential and should be applied at the recommended rate of 120kg per hectare. Typically between 20kg and 30kg of available nitrogen would be contributed from slurry and between 90kg and 100kg of nitrogen would be supplied by bought-in fertiliser. “To minimise losses, producers should, preferably, use a nitrate-based product,” adds Mr Cosgrave. “Optimal nutrient rates equal a better return on investment for producers.”
Cost effective
“First cut is the most cost-effective cut because a high proportion of the cost of making first-cut silage is not based on how many tonnes are produced. It’s a fixed cost per hectare,” he adds.
“If producers have a fixed cost per hectare, regardless of whether they grow an average or good crop, the cost of producing either silage hardly varies. To minimise the cost on a per-tonne basis, producers should do all they can to maximise first-cut quality and yield.”
Producers who prioritise early turn out, particularly spring-block calving herds, will need to ensure there is sufficient plant-available nitrogen in the soil ready for when soil temperatures and weather conditions are favourable for growth.
Applications of nitrogen and sulphur in February will be vital after the above-average levels of rainfall during autumn 2023.
“The application rate is always hotly debated among producers, but around 20kg of nitrogen per hectare in February is appropriate followed by 40kg in mid-March on units that have a high demand for grazed grass,” says Mr Cosgrave.
“By applying a smaller amount in February, producers can top up the nitrogen and sulphur levels in the soil to promote grass growth. Going into March, grass growth picks up, so that higher application is warranted.” In terms of costings and yield benefits, from growing grass, using manures and fertiliser, it is a more costeffective option than purchasing feed.
“We know that 1kg of nitrogen fertiliser costs around about £1 and it produces between 12kg and 15kg of dry matter. Compared to purchased feed, at around £300 per tonne, the cost to produce the same amount of dry matter is between £4.20 and £5.25. This underlines why there should be a strong emphasis on growing grass to feed cows,” he adds.`
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