Why soil fertility is all about getting the pH right first

Lime is one of the most important nutrients any farmer can spread on their land to address soil pH issues, according to Teagasc’s Vincent O’Connor.

“The first thing farmers should do is get the soil pH right. This will release Phosphorous (P) that is already present in the soil,” he said.

The Teagasc Advisor spoke at a recent farm walk, where he discussed the benefits of maintaining pH in terms of soil fertility.

Of the major nutrients, P is the one most affected by having a low soil pH, he said, as it becomes unavailable for use by grass below a pH 5.5.

He said that an application of 2t of lime is capable of releasing 40-50 units of P/ha on an annual basis, which is a huge return in value terms.

Along with increased P release, O’Connor also said that there can be as much as a 7:1 return on investment over a five year period in terms of the extra grass grown on farm.

Soil test every five years

The Teagasc Advisor also said that every farmer should soil test their land every five years to get a true understanding of soil fertility levels.

Farmers should put a plan in place, he said, to address any of the soil fertility issues that are presented in the results.

He advised farmers to correct soil pH first, and this should take priority over spreading chemical fertilisers which will not work effectively in acidic soils.

teagasc soil fertility

Applying any form of fertiliser is an inefficient use of resources if the soil pH is incorrect, he said, so addressing the soil pH needs to be a priority.

The latest Teagasc research shows that correcting soil pH from 5.5 to 6.3 will increase grass production by 1t of Dry Matter (DM) produced annually.

Once the pH issue has been addressed, the best and most effective method of restoring soil deficiencies in Phosphorous (P) and Potassium (K) is to target problem fields with farm-yard manure or slurry, he said.

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Lime spreading rates fall

However, despite the benefits of spreading lime and maintaining soil pH, O’Connor said the amount of lime spread in Ireland has reduced from 2m tonnes to 600,000t on an annual basis over the past 40 years.

He also said that national P levels reached low levels in 2013, with over half of all soils tested being in Index 1 or 2 for the nutrient.

The same data showed that K reached similarly low levels in they same year with over 40% being in Index 1 or 2.