Farm Ireland

Friday 28 October 2016

Grassroots issues

David Wall looks at what farmers can do to reverse declining soil fertility levels

Published 23/09/2015 | 02:30

'For what's in a name indeed, as a map of Ireland with literal English translations of Irish counties reminded me recently.'
'For what's in a name indeed, as a map of Ireland with literal English translations of Irish counties reminded me recently.'

Soil fertility levels have declined dramatically in recent years as a result of reductions in fertiliser usage, with farmers conscious of the cost of spreading their lands.

  • Go To

Currently, data from soil samples analysed by Teagasc, indicate that 90pc of soils or nine out of 10 farms have less than the optimum balance of phosphorus (P), potassium (K) and pH status.

These very low levels of soil fertility pose a significant threat to achieving increased productivity and profitability for those with cattle or sheep, or those with acres of cereals.

Yet grazed grass is the cheapest feed input on drystock and dairy farms and investing in soil fertility will pay dividends in terms of increasing the carrying capacity of the farm.

It will deliver increased grass production during especially during the shoulders of the growing season in the spring and autumn and help off-set more expensive feedstuffs that would otherwise need to be purchased.

The management of soil fertility levels should be a primary objective on any farm to deliver increased low-cost grass and increase profits.

It is something that all enterprises including dairy farmers looking to get more DM per ha out of their milking platform after the removal of quotas should be considering.

With fertiliser becoming more expensive, it is vital that nutrients, both chemical and organic, are managed as efficiently as possible to maximise returns in terms of grass or crop production.

Two equally important steps are required in order to achieve this.

Taking soil tests

Using the results to plan fertiliser and lime applications

Now is an ideal time to develop or update a fertiliser plan to guide lime and fertiliser applications that will begin next spring.

An up-to-date set of soil test results for the fields on the farm is required for this exercise.

Autumn is also a good time to consider lime applications on both grassland and tillage farms. Lime spread at this time of the year will have a good opportunity to work and adjust soil pH to the target before fertilisers and slurries are applied in the spring.

Soil testing and fertiliser planning during the autumn will help to identify fields that may benefit from extra P and K allowing enough time to plan farmyard manure/cattle or pig slurry applications early in the spring to help build-up soil P and K levels to the optimum level which is Index 3.

Unlock stored soil nutrients with lime

The majority of agricultural soils in Ireland are naturally acidic which means they have low soil pH.

Soil pH is a measure of acidity or alkalinity and this regulates nutrient availability in the soil and uptake into plants.

When soil pH is low with an acidic pH <6.0, crops may give reduced yield or fail due to high levels of aluminium (Al) and manganese (Mn) interfering with root growth and nutrient uptake.

These soils require regular applications of lime to maintain more neutral pH conditions which are more favourable for nutrient release and grass and crop production.

Lime is a soil conditioner and corrects soil acidity by neutralising the acids present and allowing the micro-organisms and earthworms to thrive and break down plant residues, animal manures and organic matter.

This helps to release stored soil nutrients such as nitrogen (N), P, K, sulphur (S) and micro-nutrients for plant uptake.

On mineral soil types a target soil pH of 6.3 is recommended for grassland, while slightly higher target soil pH levels are recommended for more sensitive tillage crops such as cereals (pH 6.5) and beet, peas and beans (pH 6.8).

Lime should always be applied on the basis of a recent soil test report as it recommends the rate of lime based on the soil pH and the soil type.

Aim to put a three to five year liming programme in place and target lime applications to fields with the lowest soil pH levels over multiple years.

Recent research from Johnstown Castle clearly shows the importance of lime in relation to the availability of soil P and the improved efficiency from applied chemical P fertiliser.

Correcting soil pH levels is the first step to consider when setting out to build-up soil P and K levels.

The graphic shows the grass yield response to lime and P fertiliser in grassland.

The application of 5t/ha ground limestone produced similar grass yields compared to the application of 40 kg/ha P fertiliser alone.

However, the addition of lime plus P fertiliser in combination produced the largest grass yield response delivering 1.5 t/ha more grass than the control.

These results show how effective lime is for increasing the availability of both stored soil P, from previous fertiliser and manure applications, and freshly applied fertiliser P.

Dr David Wall, Teagasc, Johnstown Castle, Co Wexford

Discounted  soil sampling from Teagasc

Teagasc is offering its  clients six soil samples for the price of five for early delivery to the soil testing laboratory during September.

This will ensure that up to date results are available to plan lime applications, make best use of valuable manures and ensure money is well spent on the correct type and rate of fertilisers.

A soil sample is a relatively small cost of €0.50c/ac/year and will provide specific information on a field by field basis on your farm to maximise both grass and grain production annually.

Divide the farm into fields or areas of around two to four/ha.

Walk across the field in the shape of a 'W' taking samples as you go and place 20 cores of soil in each individual soil box and write a number or the name of the field on it.

Indo Farming