Soil fertility series: pH and lime

Good soil fertility management for efficient grass production helps to reduce or at least stabilise feed costs and protect farm profitability, especially during periods of low dairy prices.

The next series of Dairylink articles will use information and results gathered on Dairylink farms to investigate the soil fertility challenge.

Has soil fertility improved thus far in the project – and what steps are project farmers implementing to deliver improvement?

Two key areas to increase the production efficiency of soils are the application of lime and nitrogen (N) fertiliser.

Soil test results on project farms show that the pH is below optimum for the group and all farmers would see an immediate benefit from spreading lime.

Advantage of lime

Lime is essentially a soil conditioner, which controls soil acidity by neutralising the acids generated from N fertiliser and slurry applications.

Soil pH has a large influence on soil nutrient availability, and we should be aiming to maintain mineral soil in the pH range 6.3 to 7.0 and peat soil in the pH range 5.5 to 5.8, to maximise nutrient supply. Soils below this target pH will have a poorer response to applied nutrients of N, P and K.

High annual rainfall leads to a large removal of lime each year, with Irish research showing typical maintenance lime requirements of 2.5 to 5.0t/ha once every five years, depending on regional location and rainfall (in other words, typically higher rates may be required in the west).

Numerous research projects have highlighted correcting soil pH from 5.2 to 6.3 increased grass production by at least 1.0t/ha. Lime increases the availability of both stored soil P and freshly applied fertiliser P.

Robin Clements Co Tyrone

Based on soil samples taken on the farm in 2015, our farm had 62% of the area at optimal pH. We focused our attention on getting lime spread on the low-pH fields during 2015 and 2016, with a total of 250t spread in 2016 alone on the grazing block (average 2.5t/acre).

Recent soil analysis taken in January this year highlighted a significant improvement in soil pH. Now over 88% of the total area is in the optimal range on pH.

There are still deficiencies in soil P and K on this block. However, starting with the quick win – the soil pH was part of the plan – the focus moves to P and K this year.

We applied lime throughout last year, with the majority of it spread on grazing area after cows had finished. Some of the grazing block was reseeded during 2016, with lime applied to the seed bed in these particular paddocks.

To help with maintaining soil pH on the grazing block, we plan to lime 20% of the farm each year. This will spread the cost and gives us a five-year plan for the grazing block.

Bill Brown Co Down

Increasing the amount of fresh grass in the cows’ diet has to start with growing as much grass as we can on the farm.

We started early this year on the grazing block, with excellent ground conditions in January and the first half of February.

Cows went out at the end of January, and to date 60 units of nitrogen per acre have been spread. I will be going again with urea this week, taking my total nitrogen applied to 82 units per acre by the end of the week.

I started with 25 units of urea in February and then 37 units of 25-5-5 compound on 10 March. Currently, growth has slowed on the farm, with cold nights holding ground temperature down.

From a grass-growth perspective, I have nine grass measurements completed this year and the grazing block has recorded 1.8tDM/ha grass growth so far.

So, in terms of nitrogen spread on the grazing block I have 104kg/ha of straight nitrogen applied.

Grass measurement is showing 1,850kgDM/ha grown to date this year – basically 18kg grass DM for each 1kg of nitrogen.

Read more

Soil fertility: where are we starting from?