Lime – the forgotten fertiliser

Improving soil fertility, especially soil pH, leads to increased Nitrogen use efficiency and an increase the availability of soil phosphorus (P) and potassium (K) for plant uptake. James Dunne, Teagasc Dairy Specialist sums up why it is so important to apply lime and why it makes financial sense

Optimised soil fertility, especially soil pH, leads to increased N use efficiency and an increase the availability of soil phosphorus (P) and potassium (K).

A recent study across 15 intensive dairy farms in Ireland showed that where soil fertility was less than optimum (i.e. soil pH <6.3, and P & K <Index 3) N fertiliser use efficiency was only 35%. Correcting soil pH alone increased N fertiliser use efficiency to 53%, with further gains from optimising soil P and K.

Research has shown an average grass production response of ~1.5 t DM/ha from lime alone which is worth €271 per hectare. This represents a return of €6 for every €1 invested in lime

Have a liming plan

Based on the most recent soil test reports identify where lime is required on the farm, and when and at what rate lime should be applied. Having a liming plan in place will open up opportunities to get lime applied over the year when conditions are suitable and land is available. You should not exceed 7.5t /Ha (3 ton / acre) in one application with the remainder applied on very acidic soils in two years’ time.

With a large proportion of first cut silage now made or to be cut over the next week there is an excellent opportunity to get lime spread on any of these silage fields that may need it. Land that is to be closed for second cut silage should be left until the subsequent crop has been harvested before applying lime.  

Lime interaction with slurry and urea

One question that always comes up with regard the spreading of lime is its interaction with the N applied in slurry and urea based fertilisers. The type of N in slurry and urea is ammonical N and prone to loss if applied to freshly limed soils. To avoid N loss the following is recommended:

• Leave seven days between applying urea or slurry before applying lime
• Leave three months between applying lime and following with urea or slurry application
• No interval is required between liming and using protected urea

You might also like to read New Lime Factsheet - The Facts on Applying Lime | Also check out: www.teagasc.ie/crops/soil--soil-fertility/

The Teagasc Dairy Specialists issue an article on a topic of interest to dairy farmers every Monday here on Teagasc Daily. Find more on Teagasc Dairy here