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Soil & Soil Fertility

The health of our soil is a key component to the efficient utilisation of soil nutrients in the production of food in an environmental and sustainable manner.

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Soils are the medium / raw material that we work with every day in the production of meat, milk, grain and fibre for both local and world markets. The health of our soils is a key component to the efficient utilisation of soil nutrients in the production of food in an environmental and sustainable manner.

To maximise the productivity of our soils it’s important that we understand there chemical, physical and biological properties. Soil testing is the starting point and the foundation to delivering the correct balance of both for major and minor nutrients.

We tend to look above ground at either the growing crop or the animals grazing on a particular part of our farms. Its however important to take out a spade and examine the soils structure / biological activity which can reveal a lot about the health of our soils.

Soil management is an important skill for maximising farm profitability plus it’s an important part of cross compliance which requires the maintenance of a farm fertiliser plan on an annual basis. This is a critical component of farming as the basic farm payment (BFP) now forms a significant income stream on many farms.

The information on this website aims to deliver useful crop nutrient advice from taking soil samples to correctly tailoring and formulating field and farm N, P & K advice.


Current Questions & Answers

Nitrogen (N)

What is the difference between CAN (27% N) & Urea (46%N)?

CAN is a straight 27% N source which contains calcium. 50% of the N is in the nitrate form and 50% in the ammonium N form. Urea contains 46% N and all the N is in the ammonium form.

How long should one leave between spreading fertiliser N and slurry?

Slurry applied on fertiliser N creates ideal conditions for dentifrication, i.e., anaerobic conditions and high carbon compounds. It is recommended to leave 4 to 7 days before or after slurry spreading for application.

How long should one leave between spreading lime and urea?

Lime increases soil pH which increases rate of volatilisation of ammonia. Do not spread urea for 3-6 months after lime application.

How long should one leave between spreading urea/ slurry and lime?

Where urea is spread in advance of lime it will eliminate the risk of N loss through volatilization. It is recommended to leave 10 days between applying urea and lime.

How long should one leave between spreading slurry and fertiliser N?

Slurry is a carbon source and where fertiliser is spread directly after slurry application it will result in a loss in N. It is recommended to leave 4 to 7 days between the application of fertiliser N and slurry

Q. When should I start applying my 1st Nitrogen to my dairy grazing paddocks?

A. When soil temperatures reach 4 to 5 ̊C and weather is forecast to be mild then it would be suitable to apply 20 to 25 units N/ac (½ urea). Soil temperatures will vary depending on location so check soil temperatures with Met Eireann. Consider spreading slurry on bare paddock and apply fertilizer N in the next couple of weeks.

Phosphorus(P)

Is the soil test for phosphorus a test of plant available phosphorus or total phosphorus?

The Morgans soil P test measures plant available P.

Where a soil test shows a P index 4 for either grassland or tillage what is the advice in this situation?

Omit P applications for 2 to 3 years and re test the soil at that stage to monitor soil P levels.

What effect has soil sampling depth on soil P levels?

Soil P levels decrease with soil sampling depth as P is immobile it tends to remain in the top few centimetres of soil. 

Potassium (K)

What is the % of K in Muriate of Potash (MOP)?

50% K

What is the % of K in Sulphate of Potash (SOP) and what % sulphur is in it?

42% K & 18% S

What is the maximum application of potassium on a grazing sward in the spring and why?

90kg/ha maximum application.  Reason why is to prevent grass tetany in grazing livestock

Where a soil test shows soil K levels are high (above 151 mg/L) what is the advice for grassland in this situation?

Omit K for one year and revert back to advice for K at soil Index 3 until the soil is tested again.

On light sandy soils should one aim to build soil K levels?

 Sandy soils have little ability to hold soil K.  Therefore apply maintenance applications of K annually.

Where a soil test is showing very low (Index 1) soil K levels. What is the best way to build soil K levels?

Apply organic manures such as cattle slurry / mushroom compost to build soil K levels.  Alternatively apply 50% K (MOP) depending on crop requirements.  It is good practice to apply fertiliser compounds containing K during the growing season for example 18-6-12 / 24-2.5-10 to replenish soil K levels over time.

Can lime and potassium be applied at the same time for example in the Autumn?

Yes

Sulphur

Q. What is the recommended rate of sulphur for grazing ground?

A. 20 kg S/ha/year

Q. What is the recommended rate of sulphur for grass silage ground?

A. 20 kg S/ha/cut

Q. When is the best time to apply S to grazing swards?

A. Apply in peak grass growing season. For example apply 4 to 5 units S /ac with each round of N applications from the 1st April.

Q. Will sulphur affect trace elements?

A. Excess sulphur on soils not deficient may reduce the uptake of copper and selenium in herbage.

Q. Which soils are most prone to S deficiency?

A. Light soils with low soil organic matter are generally more prone to S deficiency.

Q. Will slurry / FYM supply S?

A. Yes an application of 11m³/ha (1,000gal/ac) will supply approximately 4.5kg available S. An application of 10ton/ha FYM will supply approximately 9kg of available S.

Q. What is the best way to apply S?

A. Generally in fertilizer form. For example a compound (18-6-12+S) / straight N product (CAN +S) that contains between 3 to 5% S.

Q. Is it best to apply sulphur in a single application or in a little and often approach?

A. It can be applied as a single application for example ASN (26% N & 14%S). But where possible apply little and often.


Liming

Q. What effect will lime have on soil P levels on acidic soils (pH 5.0 to 6.0)?

A. Liming acidic soils will increase the availability of P for plant uptake.

Q. How do I determine the quantity of lime required to correct soil pH?

A. A recent soil report will show the rate of lime required depending on the soil type, soil pH and crop type.

Q. How long will it take lime to work?

A. The fine ground limestone (35%) will work relatively fast, and the course lime particles will react more slowly and help maintain soil pH for a number of years.

Q. What is the maximum rate of lime in a single application?

A. Apply a maximum of 7.5t/ha (3.0t/ac). Where more lime is recommended apply 50% now and the balance after 2 years.

Q. Can slurry and lime be applied at the same time?

A. Where slurry is applied first, lime can be applied in 10 days. Where lime is applied first, one must wait 3 months before applying slurry.  This is to reduce the risk of N loss from slurry as lime will accelerate the loss of N.

Q. How long should one leave between spreading 10-10-20 or CAN and lime?

A. There is no need to leave a gap with CAN or N P K compounds.

Q. What is the target pH for grassland where my land is in a high molybdenum (Mo) area?

A. Maintain a soil pH 6.2 on these soils.

Q. When is the best time to apply lime to grassland soils?

A. Now is a good time (summer / autumn) of the year as it allows time for the lime to work and reduces issues in early spring with slurry / urea applications.

Q. When is the best time to apply lime to tillage soils?

A. Ideally apply lime to the ploughed / pressed soils and incorporate into the top 7.5 to 10cm of soil.

Q. When is the best time to apply lime to fields target for reseeding?

A. Ideally apply lime as recommended on the soil test report one year in advance of reseeding. Alternatively apply lime at time of reseeding and incorporate (5 to 10cm) into the seedbed before sowing.