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How to make the most of slurry

How to make the most of slurry

With the spiralling costs of fertiliser this year, more dairy farmers are looking at ways of increasing slurry or manure utilisation and growing more forage from less. Most farms appreciate the value of slurry and use it efficiently, but it is possible to further improve utilisation whilst increasing your farm's forage utilisation or milk from forage figure – which is where the true value lies.

Read more: Maximising potential milk from forage

Importance of soil health and testing

Testing your slurry for nutrient levels for a start is important, as most nutrient management plans use standard RB209 values, which your slurry may vary significantly. Sampling kits are available through Wynnstay. Slurry versus dirty water for example has a big difference in the amount of N, P and K, with both having very low levels of sulphur. Sulphur is essential for grass nitrogen metabolism and protein production, so additional supplementation may be needed. Soil testing prior to application is equally as important, as the soil is the storage of all nutrients that grass needs, and sets the foundation for good growth rates. If soil is below optimum pH 6.5, liming will be needed prior to slurry or fertiliser so the soil can release these nutrients for the grass. (Table 1- From RB209, shows the typical difference in nutrients).

Read more: Grassland Soil Health

Phosphate, potash, magnesium and sulphur content of cattle slurry and dirty waterPhosphate, potash, magnesium and sulphur content of cattle slurry and dirty water
Table 1: Phosphate, potash, magnesium and sulphur content of cattle slurry and dirty water (fresh weight basis).

Application method to grazing ground

During the grazing months, artificial fertiliser is typically spread at a low level between rotations, to keep up that dry matter growth through the season and even-out nutrient levels across the pasture. This year fertiliser prices may impact the commonality of this practice, and some dairy farmers may look to using slurry or dirty water between rotations instead. The application method of slurry will play a big part in the nutrient capture and utilisation by the grass, and considering moving from splash plate to dribble bar or injection is highly recommended to improve soil availability.

This will not only ensure less waste in the form of ammonia gas but also less contamination of the leaf which would affect the palatability and intake of the cows on the next rotation. If slurry remains on the grass by the time the cows are on the next rotation (3-4 weeks in peak), then dry matter intakes may be affected, and supplementary feed may be needed to maintain milk yields. Application timing is also important to consider, to maximise utilisation and soil uptake and avoid waste, especially during a year where manure and slurry are becoming a valuable commodity!

Maximise silage quality and ME yield

Losses can still be incurred after all the hard work of retaining nutrients in the soil and then the plant, with the silage-making practices from field to clamp. Dry Matter Loss from silage does not just mean the visible losses we see in a clamp, such as visible mould or wastage, it is mostly made up of losses of CO2 and water (effluent) and the loss of digestibility (D-Value), which is energy for the cow.

The less energy and Nitrogen we end up with at the end of reaching the cow's rumen, the more purchased feed we need to fill this gap. Improving efficiencies here in the final step of silage making, and driving the dry matter yields from forage, can dramatically improve a herd’s ‘milk from forage’ figure and ultimately drive profitability. Another potential risk this year, if the 6–8 week window between spreading and cutting is squeezed, is the risk of clostridial and enterobacteria contamination, and poor fermentation with higher dry matter losses.

Using an appropriate silage additive such as Ecosyl 100 or Ecocool for drier silages would be highly recommended, to avoid losses in D-Value but also to limit the risk of poor fermentation and unpalatable silage following heavier slurry usage (Figure 1 – Volac research). It is well worth retaining as much value as possible in the last step of silage making.


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