Farm Ireland

Friday 19 January 2018

Tillage: Organic fertilisers are the only way to rejuvenate old soils

Contractor Nicholas Brennan Leighlinbridge about to start sowing 50 acres of Wheat (JD DIAGIO) at 9.5 stone/Acre for Milford Farms near Clogrennene Co Carlow. Photo: Roger Jones.
Contractor Nicholas Brennan Leighlinbridge about to start sowing 50 acres of Wheat (JD DIAGIO) at 9.5 stone/Acre for Milford Farms near Clogrennene Co Carlow. Photo: Roger Jones.
PJ Phelan

PJ Phelan

The closed period for organic fertilisers starts on October 15 for slurry spreading, and on November 1 for farmyard manure (FYM). So the next few weeks are the final opportunity this year to spread.

Organic fertilisers are really the only way to rejuvenate old tillage soils. Not alone will they provide the major nutrients but they also provide a wide range of trace elements and organic matter.

We normally put a economic value on slurry of €25 per 1,000 gals (slurry) and €10 per tonne (FYM) based on the units of nitrogen (N), phosphorus (P) and potash (K). Pig slurry has a higher P and lower K concentration than cattle slurry, so it should be prioritised to land with the lower soil P levels.

Poultry manures are worth at least €30/t and spent mushroom compost €10-15/t. Treated biosolids (the organic byproduct of urban waste water treatment) vary widely in value depending on the type of treatment and nutrient content.

Yield improvements following a few years of organic manure application cannot be explained by the nitrogen, phosphorus and potash content of the slurry/farmyard manure, which muddies the guideline economic values of the materials.

The additional yield is probably attributable to the increased organic matter, improved biological activity and additional trace elements.

Current cereal prices are making us more and more cost conscious, but the risk is that savings will be attempted that put the economic yield at risk. A classic example is the on-going fall in both soil P and K levels on many farms.

This year's higher yields have resulted in greater nutrient removal. The standard advice is that for every tonne of winter wheat or barley harvested, and the straw taken off, 3.8kg P and 9.8kg K is removed. Oats will also have removed 3.8kg/t of P, and even more K at 14.4kg/t.

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Since it is now past September 15 you are not allowed to apply chemical fertiliser P until next January/February. Chemical potash can, and should, be applied this autumn if your soil is at index 1 or 2. Combine drilling is preferable for low soil fertility situations. Organic manures are now the only option if soil fertility is low. The rate of availability of P and K from them is relatively slow and, as soil temperatures drop biological activity is reduced, resulting in even slower access to the nutrients by plants.


Biosolids have a high P content but little, if any, K. Unfortunately, Bord Bia have determined that crops treated with biosolids, regardless of treatment standard, will not be accepted for the grain quality assurance scheme.

In addition, farms on which biosolids were applied to tillage soils have had their grassland-reared lambs rejected for quality assurance.

The same Bord Bia has no issue with imported cereals from other parts of the world which do not have a standard for the treatment of biosolids and may even accept untreated sewage sludge on agricultural lands.

This year the Irish harvest is in the order of 2.5m tonnes and we will still import approximately 1.2m tonnes of maize. Most of that maize will be the produce of genetically modified seeds, which we are also not allowed to use.

If the risk is too high to allow the use of GMOs on our land why do we assume that there is no risk to man or beast from consuming GMO products?

Does Board Bia consider that it is not safe to use GMOs and biosolids on land but that it is safe for animals and humans to consume imported GMOs and possibly products that have come from land fertilised with untreated sewage sludge.

In order to maintain some semblance of being cost effective farmers need every possible source of nutrients. Regardless of the risk presented by GMOs to our food and our environment, GMOs have the potential to destroy our industry as Irish farmers cannot survive green grain prices of €130-140/t.

Remember 5pc of an over supply can result in a 50pc decrease in price, while the opposite is also true.

Imported GMO maize is the major determinant of our current grain prices. It fits well into least-cost ration formulations competing with our grain that is produced to much more exacting standards.

In order to compete for market share we must be allowed to have the same technologies and resources as our competitors. If we are to be excluded from the use of such technologies and resources, products produced by using them should be excluded from our marketplace.

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

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