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Land is the most limiting resource on any livestock or arable unit and soil fertility ultimately determines stocking rates, grass growth and crop yields.
As 2023 draws to a close, the restrictions preventing slurry spreading on farmland will be lifted in phases, starting on 13 January for counties in zone A.
With little sign that prices for chemical fertilisers are likely to fall this spring, slurry and farmyard manures remain a valuable source of soil nutrients to be used wisely.
Therefore, if weather windows and ground conditions allow, spring 2024 may be the year to look at drawing up a targeted fertiliser plan for the farm.
The nitrogen availability in slurry is highest in early spring compared to any other point in the season.
Phosphate (P) and potassium (K) availability remains fairly consistent across the year and key to increasing nitrogen uptake for early season growth.
When it comes to drawing up a fertiliser plan, it doesn’t need to be over-complicated.
The more straightforward it is, the easier it is to stick to it. Outlined are some tips to consider.
1 Soil testing
The starting point for any fertiliser plan is a soil sample. If fields have not been sampled in the past four years, it is worth doing this before any slurry or chemical nitrogen is applied.
On cattle farms, sampling at the year end should give a good reflection of soil fertility as fields are unlikely to have been grazed for several weeks.
Slurry and chemical nitrogen applied back in autumn will be long used up, avoiding any distorting of samples.
Soil samples should reflect around 10 acres of ground and smaller fields managed in a similar manner can be grouped together.
2 What are the sample results telling me?
Soil samples will give a pH reading and indicate if lime is needed. Grassland fields perform best at pH levels around 6.5, although for soils with a higher peat content, aim for pH 6.
Soils below these levels will benefit from lime and it is probably the cheapest form of fertiliser that can be applied.
When pH levels drop below 6.0, soil nutrients are locked up and unavailable for growth.
At pH5.5, around 25% of nitrogen is unavailable for plant growth. If 46 units/acre of urea is applied, almost 12 units are being wasted.
Aim for index 2 on P and K levels for grazing and silage swards. Most cattle slurry is capable of maintaining these levels.
Soils below index 2 are deficient in P and K and if fertiliser requirements for a growing crop are not met, yields will be impaired.
3 Target fields with low grass covers
Target slurry to dry fields with low grass covers, as they are unlikely to be grazed until late spring, giving plenty of time for slurry to be washed in.
If heavy covers have accumulated over winter, graze these swards first with sheep, calves or light weanlings.
Grazing will stimulate regrowth, which in turn will make better use of slurry nutrients.
4 Target silage ground
Silage removes a lot of P and K from soils, which can be returned to land through slurry.
Target silage ground with as much slurry as possible this spring to drive first-cut yields.
Cattle will recycle nutrients on grazing fields over the growing season, so the requirement for slurry on these areas will generally be lower.
5 Spreading rates
Grass growth will struggle to hit double figures during January and February, so there is little point in spreading heavy applications of slurry during these months.
Light and watery dressings around 1,500 to 2,000 gallons per acre will make greater use of slurry nutrients.
Heavy spreading rates will over-supply nutrients and increase the risk of runoff into water courses or atmospheric losses.
Low emissions slurry spreading equipment should also be used to increase nitrogen availability and reduce the risk of runoff.
6 Not all slurry has the same fertiliser value
Slurry differs in nutrient content depending on the animals producing it. Cattle, poultry and pigs on high meal levels produce slurry with a superior nutrient content than dry cows on a silage-only diet.
There can be an enzyme reaction that increases nitrogen losses if chemical fertiliser is applied too soon after slurry
On farms with multiple tanks, target the higher-value slurries to silage swards or fields with lower P and K levels. Tanks with lower-value slurry can be used to maintain fields with higher P and K levels.
7 Be wary of tetany risks with slurry
Slurry is high in potash, so avoid spreading on paddocks within three to four weeks of turning lactating cows out to grass this spring.
Potash inhibits magnesium uptake. When combined with changeable,spring weather and lush low dry matter grass, the risk of tetany will be extremely high.
8 Leave a week’s gap between slurry and chemical fertiliser applications
If spreading a combination of slurry and chemical nitrogen on the same fields this spring, leave a gap of around one week between applications.
There can be an enzyme reaction that increases nitrogen losses if chemical fertiliser is applied too soon after slurry.
There is also a risk of overloading soils with nitrogen at a time of low grass growth. Again, that increase the risk of nutrient runoff. If lime spreading is planned, leave a three- to four-week window after applying slurry.
9 Weather
If weather windows and ground conditions permit, spreading slurry on dry, overcast days with no frost usually increases the nitrogen availability in slurry.
Bright, frosty days increase atmospheric nitrogen losses from early season slurry. Slurry spreading should also be avoided within 24 hours of heavy rain being forecast.
10 Safety
Working with slurry has it dangers. When mixing tanks, stay out of sheds and remove animals directly above slurry being agitated.
Never leave mixing points uncovered. Keep children and pets away from mixing points.
Make sure your tractor is fit for purpose, has sufficient weight to safely handle the tanker, particularly when braking under full load.
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