'Nitrates rules are forcing farmers to use chemical fertilisers instead of organics'

Farmer spreading slurry in a field
Farmer spreading slurry in a field
PJ Phelan

PJ Phelan

Reports on crop growth and yields over the years, and particularly last year, frequently comment on the advantages of organic manure (OM) applications.

While most commentators advise a nutrient valuation of around €25/t due to nitrogen, phosphorus and potassium, the value is much greater.

The secret may well lie in the content of the actual organic material which:

  • helps to maintain and improve soul structure;
  • provides bacteria which improves the soil biology;
  • provides a food source for existing soil organisms;
  • provides trace elements.

Claims for manufactured bio-stimulants may well be trying to achieve what is available from slatted tanks and manure heaps in farmyards throughout the country. Likewise, the trace element content can replenish depleted soils.

Our current NPK chemical fertilisers only contain what they state and do not contain the full range of trace elements that plants require.

Findings here and in Britain suggest that there are a lot more trace elements being applied to crops than is necessary - insurance treatments. No doubt insurance is expensive but pays well when it is needed.

Tillage lands that have received slurry, farmyard manure or compost in recent years may not have the same needs as lands which have not.

You should review all field histories and prioritise older tillage soils which have not received OM applications this year. It should also be very valuable to do crop foliage analysis for trace elements this year on crops grown on fields which have received OM - and compare it to crops on similar soils which have not received OM.

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Better still if you put a note with the soil sample requesting the laboratory to forward a copy of the results to me. Given a reasonable response rate, I will publish the results of the "mini survey".

The only data I need from the laboratory are the county and a description to state if OM had been applied to the land, from which the sample had been taken, within the past three years.

At farm level the biggest issue is to know what the nutrient value of the OM is. A thousand gallons of cattle slurry/ac at 6-8pc dry matter is likely to supply five units of Nitrogen (N), five units of Phosphate (P) and 30 units of Potash (K) when applied in spring.

The same slurry at 3-4pc dry matter will supply five units of N, three units of P and 15 units of K. Poorly agitated slurry will give even greater than that range of dry matter from one tank. A survey by Teagasc (2012) on 75 dairy and beef farms gave a range of dry matter contents from 1.7 to 10.3pc.

Laboratory analysis will be the most precise, but sampling must be done at least three weeks before the anticipated spread date so as to get back the results on time.

You may take your sample after agitating the tanks and adjust subsequent fertiliser applications in accordance with the results. Alternatively you may do a simple dry matter assessment on farm.

Sampling slurry

Sampling of unagitated slurry requires a tube sampler, a plastic pipe with a rubber ball attached to a rope that runs through the centre of the pipe, which is pushed vertically from the top of the tank to the base.

When the tube is near to the bottom, the rope is pulled so that the ball seals the end of the tube and the intact vertical sample is then removed, placed in a sealed container and sent for analysis.

Sample from the return flow on the agitator should give a very representative sample.

Sample collection on the day of spreading by placing buckets (weighted) in the field before spread and pouring from them into a container that can be sealed is very effective.

It will also make the driver very conscious that you know exactly what you are getting.

Assessment for dry matter

This can be done by taking a jug of well-agitated slurry, dropping a hydrometer into it and reading the dry matter percentage from the gauge - like reading the measurement on a standard ruler.

At regulatory level (Nitrate Regulations), standard nutrient concentrations must be used when doing and reporting on nutrient management plans.

There is no allowance for importation of more dilute slurry. Worse still we are bound by the organic nitrate limit of 170kg/ha N with every cubic metre of cattle slurry imported deemed to contain 5kg N.

Pig slurry contains 4.2kg N even though it may come from a fattening unit (high dry matter) or a weaning unit (low dry matter).

While I can understand the limit of 170 kg/ha N for livestock farms, where increasing stock numbers will result in increased nitrogen fertiliser imports, I fail to understand why farmers with either low or no livestock should not be allowed to import enough slurry to meet their N, P and K requirements.

The nitrate regulations are forcing those farms to avoid local slurry and purchase environmentally expensive chemical fertiliser.

PJ Phelan is a tillage advisor based in Tipperary and is a member of the ACA and ITCA

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