Is soil fertility becoming the new quota?

The shackles of production were lifted on Irish dairy farms in 2015, with the EU-wide abolition of milk quotas.

In the intervening period a number of factors have been dubbed the ‘new quota’. These include land availability and labour – to name just two.

But an area that warrants serious consideration, and not just for dairy farmers, is the fertility of Irish soils.

On an acreage basis, grass is the dominant crop grown on Irish farms. And so, the value of nutrients available in the soil and to the grass plant cannot be underestimated.

Soil fertility is the backbone of Irish agriculture, but it appears that the majority of Irish farmers have forgotten this in recent years.

It’s OK to blame a lack of land or labour as a limiting factor. But unless the right nutrients are made available, Irish grasslands can never reach their full potential.

This was galvanised by Teagasc’s Dr. David Wall at a recent Fertiliser Association of Ireland conference.

The leader of the Soil Fertility Research Programme at Teagasc, Johnstown Castle, presented startling figures on the fertility of Irish soils.

According to Wall, there has been a massive decline in soil fertility levels nationally with phosphorous and potassium levels being worst hit.

Wall said that approximately 35,000t of phosphorous and 90,000t of potassium fertilisers are used on Irish farms each year – not even half of the quantity required for maintenance.

When we go back to the start of the period (2005), we had roughly 40% of the soils in index 1 and 2 for phosphorous.

“Today, we have about 65% in index 1 and 2. We have totally changed the soil fertility picture in the country,” he said.

On a more positive note, he said, the number of index 4 soils have dropped – reducing some of the risks associated with P leaching into waterways.

But, he stressed, low P levels are a big negative in terms of lower efficiency of nitrogen use from both fertiliser and slurry applications.

This does compromise our ability to grow more grass and produce higher crop yields.

“But in terms of the sustainability credentials of our agriculture, we do need optimum soil fertility,” he said.

In addition, he said: “We have very low lime use on farms. Given that we have about 65% of soils that are sub-optimum for pH there is a job to be done there.”

Maintenance levels

When Wall compared fertiliser usage rates with the maintenance level required on a farm stocked at 2 cows/ha (170kg of nitrogen/ha/year), he said that P and K usage are at lower than desirable levels.

He said dairy farmers are meeting only about 25% of P maintenance levels and just 33% of the K requirements for grazing.

He added that fields growing silage only receive about 50% of their P requirement and 25% of the maintenance K requirement.

“Fertiliser usage seems to be dominated by straight nitrogen in the form of Calcium Ammonium Nitrate (CAN) or urea. CAN accounted for about 30% of the market last year, with urea back down at 6.6%.

“High nitrogen and low P/K compounds dominate the market, with very little high P and K compounds being used on Irish grassland,” he said.

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