Nitrogen is key in making the most of muck

Persuading farmers to regard muck and similar materials as fertiliser rather than waste is getting easier, as they look to slash soaring nutrient input costs.

The main reason is the rocketing price of manufactured fertiliser, explains Brian Chambers, ADAS head of soils and nutrients. “In the past 10 years the prices of manufactured N, P and K fertilisers have all just about tripled. Today nitrogen is about 90p/kg – only a few years ago it was only about 30p/kg. Clearly by using organic sources growers can reduce production costs.”

Many farms have access to manures that cost comparatively small sums and attract little more than storage and application charges, Prof Chambers points out.

Another key reason for growers’ greater interest is improved technology allowing them to assess the nutrient content of manures more quickly and apply them more precisely, he adds.

There are plenty of fertiliser substitutes.

 Annual application of organic fertilisers in England & Wales  
  tonnes (fresh weight) 
Livestock manures 90m
Biosolids such as sewage sludge 4m
Compost 1.9m
Paper crumble 0.7m
Food-based digestate 1m
Source: ADAS

“Farmyard manure and slurries are still the main sources, but the new kid on the block is digestate. We’re now seeing significant volumes coming through, and annual output could rise to 5m tonnes.”

At the recent relaunch of ADAS’s updated MANNER-NPK software, the value (at current fertiliser prices) of pig farmyard manure, cattle slurry and broiler litter were put at £10/t, £3.40/cu m, and £37/t, respectively.

Solid fertiliser substitutes, especially composts and sewage sludge cakes, have extra long-term value in that they help raise soil organic matter levels, adds Prof Chambers. “Most of the UK’s arable land needs more organic matter.”

As manufactured fertiliser prices have increased so has the value of organic materials, and suppliers have raised their prices in line, notes Hutchinsons’ Rob Jewers. “Even so, organic materials usually represent good value for money when imported on to farms,” he says.

As well as contributing nutrients, they improve the soil’s structure and water retention and benefit the organisms living within it, he adds. Ideally, to minimise nutrient losses, they should be applied in early spring.

“But this doesn’t suit all rotations, and growers with large areas of winter cropping may have to spread in summer. This can clash with the busy harvest and autumn cultivations period.”

The bottom line

  • Manufactured fertiliser prices have tripled in past decade
  • Fertiliser costs for the average wheat grower have risen annually by 21% over the past seven years
  • Current value of pig farmyard manure, cattle slurry and broiler litter are £10/t, £3.40/cu m, and £37/t, respectively

So to what extent may organic materials replace manufactured fertiliser? The Fertiliser Manual (RB209) provides detailed analyses of a wide range of them.

Where available in sufficient amounts, manures are really good for correcting low soil P and K indices, says Ecopt’s Ian Richards. “Treat manures as fertilisers – not wastes.”

The key driver is nitrogen content, he explains. “It’s best not to try to use manure to meet a crop’s full N requirements – the supply and rate of release is too uncertain.”

RB209 advises that no more than 50-60% of a crop’s N needs should come from manure, notes Prof Chambers. “It’s the nitrogen content of the manure that should dictate how far you can go with substitution. Get it wrong and you can easily end up with flat crops.”

That is where science, in the form of equipment such as the Agros and Quantofix meters, which measure the readily available N content of slurries/digestates, backed by the MANNER-NPK software, comes into the picture to help, he explains.

“Nobody uses manufactured fertiliser without knowing its analysis – it should be the same with manures.”

Manure application is mainly dictated by the nitrate vulnerable zone (NVZ) regulations, warns Mr Jewers. “The rules are complex and a FACTS-qualified adviser should be used to assist with planning manure use and writing a nutrient management plan. Regular soil testing should be carried out on one-third to one-quarter of the farm each year so that crop requirements can be accurately predicted.”

Mr Richards urges farmers outside NVZs to follow the advice in DEFRA’s publication Protecting our Water, Soil and Air.

Cutting fertiliser costs 
Philip Huxtable of the JSR Farming group in East Yorkshire calculates that using manure cut his 2011 fertiliser bill on 3,600ha of crops by £110,000.

“We began trying to make better use of manure 25 years ago when we realised that we couldn’t just keep dumping it on sacrificial areas,” he says.

The organic manures from six pig units (totalling 3,500 sows plus progeny) is handled as solid farmyard manure, which is spread on autumn stubbles, and separated pig slurry as liquid fraction, which is applied to growing crops in the spring.

“In the past 12 months we’ve applied 11,000t of farmyard manure – what I like to call ‘solid gold’ – on about 400ha at 27t/ha.

“In principle we could grow a crop of wheat with all the nutrients provided by muck or slurry, and we have done so on small areas,” says Mr Huxtable. “In practice we don’t because of the logistics, and even with our large number of pigs we still wouldn’t have enough.”

However, about 40% of the nitrogen need for the farms’ wheat and oilseed rape comes from “liquid gold” applied by tanker through a 24m tramline-matching dribble bar. “If we’re planning, say, to use a total of 220kg N/ha on wheat, we’d be looking at about 90kg from separated liquid.”

For use on barley stubbles ahead of oilseed rape the boom can be replaced by an injector. But his preferred, more “light-footed”, choice is a 24m tractor-mounted boom fed via an umbilical system.

Arable operations manager Neil Butler uses MANNER-NPK to determine application rates, says Mr Huxtable. “We see the latest version as an evolution of what was already a good programme and he tells me he’s very pleased with it.”

A Quantofix, costing only £250, is used frequently during work to check the liquid manures’ N contents and adjust application rates.

Although the application machinery is expensive, there are contractors in his area providing a similar precision service, he notes. “For smaller farms there’s always the option of sharing.”

The manure’s benefit extends beyond monetary savings. “We’ve seen a consistent yield improvement, presumably through the increased fertility it creates.”

Over the past eight years, JSR’s wheat fields, which had slurry in the spring as part of their nitrogen requirements, have averaged 0.6t/ha more than those given manufactured N fertiliser alone.

“In the drought year of 2011 the figure was 1.1t/ha, and last year it was 0.8t/ha. We think the ‘liquid gold’ gives the crops staying power.”

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