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Are you making the best of slurries and manures?

As the closed period for the spreading of slurry has now ended, Chloe Palmer finds out the best advice for making the most of slurries and manures.


Making the best use of slurries and manures makes sense on all livestock farms, whether or not they are located within a Nitrate Vulnerable Zone (NVZ).

A source of valuable nutrients, slurries and manures, if stored and spread wisely, can contribute to greatly reduced fertiliser bills and improved soil biology and structure.

Joe Winstanley, an independent FACTS qualified farm consultant, recommends farmers establish a baseline regarding the nutrient status of their soils before applying any manures.

Soil analysis

He says: “The first thing to do before applying manures is to find out which fields need it the most and how much they need. Soil analysis of the fields considered for the application of slurry and manures is the starting point.

“Now is the ideal time to sample, providing soils are not waterlogged and no manures or phosphate [P] and potassium [K] fertilisers have been applied during the previous four months. Analysis will usually indicate that grazing fields rarely need manure or slurry because P and K levels tend to hold up well.”

Mr Winstanley says the phosphate offtake from an intensively grazed field on a dairy farm will be about 20kg/hectare over the grazing season and potash offtake will be considerably less because nutrients are constantly recycled.

On silage fields, the situation is very different as in a typical three-cut regime yielding 45-50 tonnes/ha (18-20t/acre) of 25 per cent dry matter silage, the potash offtake will be about 270-300kg/ha and phosphate offtake about 75-85kg/ha.

Mr Winstanley points to these mowing fields as the ones which will benefit from muck and slurry applications.

“On many livestock farms soil sampling will often show P and K indices as excessively high on fields closest to the farmstead. On outlying fields, P and K levels tend to be lower due to the past history of manure applications and grass use.”

trailing shoe pic

Joe Winstanley favours the use of a trailing shoe application system.

trailing shoe pic

Trailing shoe

Mr Winstanley favours the use of a trailing shoe application system on grassland over other methods.

“The trailing shoe is more flexible on grassland because of the wider window of opportunity for spreading, particularly for second and third cuts as slurry can be successfully applied up to three to four weeks after cutting.

“Research shows slurry can be applied by trailing shoe six weeks before cutting without any adverse effects on silage quality. This increased window of opportunity allows farmers to reduce the risk of damage to soil structure by avoiding spreading at times when soil conditions are sub-optimal.

Joe Winstanley’s top tips for applying manures and slurries

  • Test your soil to identify which fields and crops should be prioritised for manure and slurry spreading
  • Draw up a plan at the start of each year and calculate how much slurry and manure will be produced and how much should be spread across each field and when
  • Invest in at least five months slurry storage to enable slurry to be applied when it will be used most effectively by the growing crop

Mr Winstanley adds: “Another key advantage of using a trailing shoe and shallow injection over a conventional splash is losses of nitrogen to the atmosphere are significantly reduced. Because grass leaves are not coated in slurry, the ability of the plant to photosynthesise is not impeded.”

Mr Winstanley believes the shallow injection systems are better suited to arable land because on applications to grassland following very dry weather, the slit created can sometimes cause sward damage by damaging the grass roots.

Farmers in NVZs must be aware of maximum field limits and Mr Winstanley finds many farmers are caught out by this rule.

“Farmers should apply no more than 250kg/ha of total nitrogen within a 365-day rolling period. As weather conditions vary markedly from year-to-year, if farmers are not referring back to spreading records on a regular basis, they may find they inadvertently exceed this limit within the rolling 12 months.”

Avoiding the application of too much slurry at any one time is also important.

Optimum rate

“When applying 6 per cent dry matter dairy slurry in spring to first cut silage the optimum application rate is 28cu.m/ha. On second cut, a maximum rate of 34cu.m/ha is recommended.

“Exceeding these rates can affect the ability of the soil to function aerobically because slurry is an anaerobic substance. If seagulls are following a slurry applicator, it is usually a sign earthworms have been drowned out by too much slurry so they have come to the soil surface,” Mr Winstanley says.

When NVZ regulations were introduced, some farmers looked at the option of installing a slurry separator as a means of reducing the volume of storage required. Mr Winstanley believes separators can be useful in certain situations.

“A farm where there is a need to take manure to outlying land at a distance from the buildings may benefit as transporting the solid fraction only can reduce transport costs,” she says.

“Similarly, the liquid fraction contains high readily available nitrogen levels and can be used efficiently by applying with a precision spreading method, such as trailing shoe or shallow injector. Up to 55 per cent of the total nitrogen will be available to the growing crop.

“Separators can achieve up to a 20 per cent reduction in slurry volumes so they can help farmers who have just less than the five months storage requirement.”

Muck and slurry good practice

An example of a risk-abased spreading map

  • Draw up a spreading risk map (see below) before spreading manure and slurry to identify features such as boreholes, springs and watercourses which require a buffer zone
  • Spread the manure and slurries according to the conditions and your risk map
  • Site manure heaps away from hedges and trees, also avoid easily-drained land such as sand or gravel
  • Maintain your spreader in good working order and ensure it is regularly calibrated and tested
  • Do not spread on wetlands, waterlogged land or frozen ground, within 10 metres (33ft) of a watercourse or within 50m (164ft) of a well or borehole
  • When spreading slurries, use a trailing shoe or shallow injection equipment because these will greatly reduce losses of nitrogen to the atmosphere and will reduce the period required prior to mowing or grazing
  • Manures with high ‘readily available’ nutrients such as slurries and pig and poultry manure are most vulnerable to losses through leaching, so apply these to the growing crop when crop nutrient demand is high
  • Keep records of manure applications including fields, dates, amounts and equipment used
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