Agronomy advice

How to lower grassland fertiliser requirement by using manures more effectively

Using manures more effectively is one way to mitigate increases in the cost of fertiliser. This will allow a lowering of the fertiliser requirements on livestock farms without risking a reduction in grass production The distribution of manures around the farm, how and when they are spread will be key


 Using manures more effectively
 Using manures more effectively

Organic manures are valuable sources of plant nutrients and using these more effectively can result in significant savings in fertiliser requirements. A planned approach using a nutrient management plan will allow as much as possible of the nutrient content of the manures to be utilised by swards.

Testing of soils and manures or slurries allows better planning of applications

The first step to any good nutrient management plan is the testing of both soil and manures or slurries.

Before February comes around, you should aim to have up-to-date soil test results to hand and use them to put a nutrient plan in place for your farm. You should have a fair idea how much manure you have, so it’s a matter of allocating this manure to make the best use of the nutrients in them.  This can best be done using soil test results to identify which fields or areas have the lowest soil indices.

If there was ever a good time to test slurry, then it would be when fertiliser prices are high. The nutrient content of slurry is variable and book values are averages and may differ quite considerably from farm to farm based on feeding differences.  This means that for many farms, the nutrient content or fertiliser replacement value of slurries is being underestimated leading to moire nitrogen that can be used being applied.  Or it may be an underestimate, meaning grass growth is limited and forage production is reduced.

Better timing of manure applications reduces nitrogen losses

Can more slurry be applied in the spring? To make best use of slurry nitrogen applications should be made in late winter to spring.  Slurry applications in summer are less efficiently utilised because of higher losses due to ammonia volatilisation. Spreading slurry in the spring compared to the summer increases the nitrogen availability from 30% to 40%, this would increase the available nitrogen by 0.26 kg per cubic metre or 2.5 units per 1,000 gallons.

Using low emission equipment also reduces nitrogen losses

Can slurry be spread more efficiently? Where possible, spread slurry using low-emission equipment.  The use of band spreading and/or shallow injection (5-7cm) techniques reduces ammonia N losses, typically by 30-70% compared to surface broadcast applications.

These are just a few options to achieve marginal gains which will not fully offset an increase in fertiliser prices, but they can help.

Find more information on grassland nutrition

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