Soil Fertility

Soil Testing | Soil pH | P & K Index | Slurry | Compound Balancing

Good productive soils are the foundation of any successful farming system and key for growing sufficient high quality grass to feed the herd. Therefore, the management of soil fertility levels should be a primary objective of every farm. To measure soil fertility we test soil to identify the pH level, Phosphorus (P) level, and Potassium (K) level. A recent review of soils tested at Teagasc indicates that the majority of soils in Ireland are below the target levels for pH (pH 6.3), P and K (i.e. Index 3) and will be very responsive to application of lime to increase pH, and also P & K. On many farms sub-optimal soil fertility is leading to a drop in output and income if allowed to continue.

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John Maher, of the Grass10 campaign, highlights 5 steps for effective soil fertility management in the video below.

Soil Testing

How to Take a Soil Sample

Soil testing is the first step in correcting any soil fertility issues on your farm and to get accurate soil test results you need to get a soil sample which is representative of the area you’re testing. To understand how to take a soil sample, the soil index system and interpreting your soil sample results click on Soil Analysis.

Specialist Mark Plunkett (Teagasc, Johnstown) speaks with Declan McArdle (Teagasc Equine Specialist) on the best way to get a true reading of your soil fertility so you know what paddocks are below target and can be improved.

Soil pH

Applying Lime

If the soil pH is below target pH 6.3, there is potential locked up in the soil waiting to get out. When lime is applied to soils below target pH there is an immediate realise of nutrients which unlocks this potential and drives grass production on the farm. Our wet climate in Ireland means that a lot of calcium and lime is naturally washed out of our soils making our soils very acidic. For this reason it is important that we apply lime regularly to control soil acidity and keep soil pH as close as possible to the optimum range. For more information click on Soil pH & Liming and for advice for grasslands click Liming Grassland Soils.

In the video below Mark Plunkett, Soil Nutrition specialist talks to Declan McArdle about the importance of looking after our soils. Remember Grow More – Graze More – Earn More!

P & K Index

Target Index 3

The aim is to have optimum soil P and K (Index 3) fertility levels in all paddocks. At optimum fertility levels, nutrients being removed in products as meat or milk need to be replaced. Low fertility (Index 1 & 2) soils need to be fertilised correctly to achieve soil index 3.

For soils in Index 3 the fertiliser program should be designed to replace the nutrients being removed, thus maintaining the soil fertility levels.

Index 1 and 2 soils have a very low to low nutrient supply, and require additional nutrients to increase the fertility levels on an annual basis.

Index 4 soils have a high nutrient supply. These soils present an opportunity to save money on fertiliser inputs by harvesting the P and K soil reserves for a number of years depending on the soil test reading.

If you’re looking for fertiliser advice for your dairy, beef or sheep farm please click Grassland Fertiliser Advice Also check your Nutrient Management Plan to ensure you don’t exceed your maximum limits.

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Slurry

Make the most of what you’ve got!

Slurry is a valuable resource when used effectively by targetting the paddocks which need it most and applying in the right conditions. The nutrient value of cattle and pig slurry are in the following table: 

Type	N(units/1000gals)	P (units/1000gals)	K(units/1000gal)
Cattle Slurry	5	5	30
Pig Slurry	19	7	20

This table should only be used as a guideline as values can differ. For the values of other organic manures click Value of Organic Manures. Patrick Forrestal, soil nutrient researcher explains how to get the most from your slurry, which will help save you money on chemical fertilisers.

Balancing

Balance with Compound Fertilisers

After making the best use of slurry and other organic manures the farm will likely need to be topped up with chemical fertilisers to reach the soil fertility targets. The time it takes to balance soil nutrients can vary depending on the nutrient. K can usually be fixed relatively quickly (move up 1 index per annum) whilst P generally takes longer especially on heavier soils. The amount of P & K needed for optimum soil fertility will also vary depending on farm stocking rate (higher stocking rates will require more P & K to replace higher offtakes), soil indexes (lower indexes require higher P & K to build fertility) and whether the field is being grazed or used for grass silage/hay making (silage/hay production has high K offtakes whereas grazing is usually harder on P index). It is important to remember that getting the soil pH right is foremost as this can in itself raise the P and K soil index.

If you’re looking for fertiliser advice for your dairy, beef or sheep farm please click Grassland Fertiliser Advice. Also check your farms Nutrient Management Plan to ensure you don’t exceed your maximum limits.

Other Useful Information:

Trace Elements For Grassland

Soil Fertility Frequently Asked Questions

Soil Quality

Along with soil fertility the quality of the soil is also an important factor wich can limit the functionality of the soil in terms of production, nutrient cycling, carbon sequestration, water purification and biodiversity. Of the physical indicators which influence soil function, soil structure is considered a key factor. Decline in soil structural quality can lead to soil degradation and compaction. Click on the link below for advice to avoid this happening on your farm.

Soil Quality