Farm Ireland

Thursday 26 April 2018

Getting the most out of fertilisers

Some simple steps will help maximise the value of your fertiliser expenditure this spring

Reduce costs by watching the weather before application.
Reduce costs by watching the weather before application.

Richard Hackett

Nature dictates that spring is a very busy time on Irish farms and one of the most crucial factors for all production systems is nutrient application. Spring is also the time that most expenditure is incurred on fertiliser programmes, so it is imperative that this expenditure is put to maximum effect.

While the costs are significant, fertiliser programmes are not complicated. There are basically three layers to a fertiliser programme cake, in order of importance: the soil pH level; the phosphorus (P) and potassium (K) status of the soil; and appropriate nitrogen (N) rates.

Unless the soil pH level is at a workable level, growth response to any nutrient applied, whether that is N, P or K will always be disappointing. If the soil P or soil K levels are deficient, response to applied N will also be dampened.

In the same way that there is no point in treating a bacterial calf scour with a fluke drench, there is no point applying more nitrogen on a soil that is deficient in lime.

The crop, be it grass, cereal, potato or vegetable, just won't respond.

Once the soil pH has been addressed, the next layer is to build up soil phosphorus (P) and potassium (K) levels.

There are two main sources of P and K: either granular application or the recycling of organic nutrients. For a well-run livestock farm, the recycling of nutrients is normally a simple process.

The slurry or farmyard manure is spread back onto the land after the silage or hay has been harvested. Where soil P and K levels are already high in a highly stocked holding, it may not always be the best way to maximise the value of these nutrients.

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For example, it makes complete sense to export these nutrients to more deficient soils somewhere else. This is where a well-designed nutrient management plan can determine where the excesses are and where more nutrients can usefully be applied.

For cereal farms, it can be a bit more complicated. It has been well established that low P and K soil reserves cannot produce maximum yields. However, it is often just not economically possible to build up soil reserves using granular fertiliser.

That is where organic manures come into play.

There are plenty of highly stocked dairy and beef farms with too much slurry to efficiently manage, not to mention pig, poultry and mushroom units, where management of slurries and composts is a perennial headache.

Compound fertilisers

Given the price of compound fertiliser, the biggest problem these producers should have is crowd control of enthusiastic cereal farmers lining up at the gate waving nutrient export forms at them.

Unfortunately this is often not the case. Management of organic manure is time consuming, messy and with significant transport, machinery and labour costs.

Some cereal farmers approach OCD levels of cleanliness around their yards and the thought of such messy products is enough to send them into a tizzy.

However, application of pig slurry, poultry manure and mushroom compost is recycling at its best.

The grain is fed to pigs, poultry, dairy and beef cattle who produce the manure, and the straw is used to make mushroom compost. Applying it back onto the soils from which it came from makes complete sense.

This form of nutrient use should not be the headache of one or other party. Instead, it should be for the benefit of all, and systems should be established to make this process as efficient as possible.

For growers that want to improve soil fertility levels, initial communications with local producers of excess organic manures should be made now to examine the feasibility and tease out transport and spreading issues well in advance.

This brings us to the third layer of the cake: nitrogen application.

For crops like cereals or silage, there are well established application rates. Nitrogen can be applied to grazing situations over the course of the season according to stocking rate.

Ireland as a country is unusual in that the predominant form of nitrogen applied is as calcium ammonium nitrate (CAN).

The other main form of nitrogen, urea is often side-lined to initial spring grazing use, and has almost disappeared from cropping programmes altogether. Urea can often provide a significantly cheaper source of nitrogen than CAN.

Lower soil temperatures and damp weather can result in very effective use of urea fertiliser, conditions that are not unknown to farmers here.

There is an opportunity to reduce our fertiliser costs by putting more thought into the form of fertiliser used and by watching the weather before application.

A number of protected urea fertilisers have been developed recently, which have the potential to overcome the risk of urea loss, but these are only viable if the fertilisers are significantly cheaper per unit of nitrogen compared to CAN.

Dr Richard Hackett is an agronomist based in North County Dublin and is a member of the ITCA and ACA

Conacre and lime

The biggest problem I see in Irish agriculture is land tenure, and the issue with soil pH is a case in point.

If you have land on short term rent, the cost of applying lime will not be recouped within one season. Equally, if there is a deficiency in lime, every other expenditure on a crop will have limited effect as the ability of a soil to grow the crop will be severely impacted.

There is no excuse for having the soil pH not up to scratch on more secure land, whether owned or on a long-term lease. A soil sample costing €20 will determine the soil pH level.

One tonne of lime costs slightly more than one 50kg bag of compound fertiliser. If the soil is lime deficient, that bag of compound won't work the way it should.

If a soil is seriously lime deficient, it is better to spend all the available money on rectifying the soil pH first and spend little or nothing on any other fertiliser.

The application of lime can often have an added benefit of releasing previously applied nutrients that couldn't be 'activated' due to the soil pH.

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