Tech Talk: Benefits of organic manure

By BPEX - The benefits of organic manures are not taken into account by Nitrate Vulnerable Zone (NVZ) rules because the intention is to reduce nitrate leaching.

10 December 2005

4 minute read

Tech Talk: Benefits of organic manure - By BPEX - The benefits of organic manures are not taken into account by Nitrate Vulnerable Zone (NVZ) rules because the intention is to reduce nitrate leaching.

Tech Talk
is brought to you by the MLC on behalf of BPEX.

Of course organic manures and slurries not only provide organic matter but also a blend of nutrients including trace elements essential for good crop growth, and most bagged manufactured products do not offer this added value.

While the legislation is due to be reviewed shortly, for now the NVZ rules can be summarised as follows:

Up to 250kg/ha (200 units per acre) of Total Nitrogen in the form of organic manures and slurries can be applied to land falling within a NVZ (excluding grazing deposition - a Defra term).

Typical pig FYM both fresh and old contains 7kg/t of total nitrogen according to Defra research. So, to stay within the 250kg/ha limit it is possible during a 12 month period to spread up to 36t/ha (14.5t/acre) of pig muck.
If your muck heap has composted and reduced by 40% then what started as 24 tons can be spread on one acre, provided the N content is 7kg/t.
Remember, 7kgN/t is a typical value for pig FYM, so if you know otherwise and can show proof (e.g. lab test results) you can base your applications on specific values - for anyone faced with having to transport the stuff a long way, a lab test could turn out to be cost effective.

Within the NVZ you are allowed to apply nitrogen according to crop requirement.

This is determined by soil type, rainfall, cropping history, crop being grown, market and yield potential.

So, if your crop requires 220kg/ha (176 units/acre) of nitrogen, and you have applied 36t/ha of fresh FYM providing 30kg/ha of available N after leaching and atmospheric losses, then you can also apply up to 190kg/ha (152units/acre) as manufactured fertiliser.

It is worth remembering that not all of the nitrogen in manure will be available in a growing season (for fresh budget on 20 - 25% and 10% for well-rotted) and the length of time FYM is left on the soil surface also affects availability, so incorporate it quickly to retain value.

Whole farm limits for organic nitrogen (250kg/ha on non-arable land and either 210 or 170kg/ha for arable cropped land, depending on when the Zone was designated) apply to both ‘applied’ and ‘grazing deposited’ manure.

There is no limit per hectare for grazing deposited manure, provided the whole farm average is not exceeded. This, for example, allows for rotational grazing by outdoor pigs.

Look out for reviewed NVZ legislation, due early 2006.

Source: British Pig Executive - November 2005