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Spreading season starts as closed period ends

Last updated: 16 Feb 2016

The spreading season has started with the end of the closed periods. Fertiliser nitrogen and all types of manure can be spread if conditions are right but there are NVZ restrictions on manures in February - no more than 30m3 or slurry or 8 t of poultry manure per hectare at one time with at least three weeks between applications. Updated NVZ guidance was published by Defra on 1st January and it's at www.gov.uk/guidance/nutrient-management-nitrate-vulnerable-zones .

There are two sides to fertiliser use - deciding how much to use and then using it. The first of these gets a lot of attention and, quite rightly so, with new or updated recommendation systems, decision support tools, mapping and so on. It is vital to get things right here as nitrogen use alone supports around half of crop output. However, all the effort put into deciding how much and when can be wasted if what's decided is not what's accurately applied. That means maintaining, setting and operating spreaders properly yet the annual British Survey of Fertiliser Practice shows that 40-45% of farms with spreaders don't tray test their machines at least annually. 25% never check their machines, a percentage that hasn't changed for some ten years. There's scope here for getting better value from fertiliser use.

Fertiliser spreaders are now high technology machines but the basic job hasn't changed - a Slurry injector_13258particle weighing about 10mg must be accelerated from a spinning disc moving over uneven ground to fall accurately on the ground anything up to 50m away. The technical challenge has increased as bout widths have widened at an average rate of 7m per decade for the past sixty years. The spreader needs all the help it can get and annual tray testing (along with good maintenance and operation) is a must. It's a horrible job to get right and best left to professionals - the cost of less than £250 per machine can be recouped in just a few hectares.

Manures too are high value nutrient sources and should be spread as accurately as possible to make sure this value is achieved. As fertiliser spreaders have become more expensive, manure spreaders have taken their place as the 'Cinderella' of farm equipment. They deserve better - an application of cattle slurry at 30m3/ha applies nutrients worth around £80/ha and one of pig FYM at 35 t/ha applies nutrients worth £260/ha. This is what the nutrients are worth in the spreader, what they're worth to the crop depends on how the manure is applied. Main requirements are to spread the manure as evenly as possible at the required rate and then to prevent nitrogen loss to the air as ammonia.

'Required rate' is the real problem, much easier to say than to achieve.

Firstly, the nutrient content of the manure must be known. Standard tables are in RB209 but batches of manure can vary and analysis can give a more representative value. Cost of around £50 is easily recouped but everything depends on getting a representative sample. Then the nutrient application rate decided on must be applied which means checking the amount of manure the spreader holds and the number of loads spread per hectare.

Nitrogen is lost as ammonia during and after manure spreading. It's been estimated that around 67,000 t of ammonia is lost in this way every year in the UK from cattle manure alone. That's equivalent to 55,000 t N worth around £37 million. Incorporating or injecting manure soon after application can reduce this loss. NVZ rules say incorporate within 24 hours at the latest but much of the ammonia is lost in a few hours after application so immediate incorporation will save money.

The end of the closed period can mean impatience to get started. Resist it, it's more important at this time to make sure all spreading equipment is in good condition and set up properly. more fertiliser has been wasted by too early an application than too late.