Lime

It’s time to Lime

Why do farmers need to apply lime?

The most common reason for applying lime is to lift soil pH.  New Zealand soils often have a pH below optimum for growing grass.  You need to aim for a top soil pH of 6.  The amount of lime needed to lift a soils pH is approximately 1 tonne for every 0.1 pH unit e.g. to lift pH from 5.9 to 6.0 you need to apply 1 tonne of lime.  This rule of thumb can vary a little as the quality of lime varies.  Most New Zealand limes contain 60 – 95% Calcium Carbonate, and it is the Calcium Carbonate that increases a soils pH.

What about my Peat farm?

Organic soils are a little different to mineral soils, they tend to have a much larger buffer capacity so they take a lot more lime to lift the soil pH, the amount of lime you need will depend on the soil type, so a soil test is necessary.  Lime will not move through an organic soil to the sub soil therefore lime must be worked in as part of a cropping cycle or re-grassing.

When do I apply the lime?

The best time to apply lime is summer to mid Autumn.  The reason for this is lime can limit the up take of Magnesium in pasture and therefore cows blood Magnesium levels.  Cows Magnesium requirements are high prior to calving through to after their peak milk production, so avoid liming through this period.  Farmers that apply lime in winter, while the cows are dry, are more likely to see greater incidence of grass staggers and milk fever.  Lime needs to be applied to the farm in dry weather (or prior to a lot of rain) so the lime particles fall off the leaf, onto the ground.  It is important to avoid cows grazing pasture with lime on it.  Grass with lime on it will be unpalatable to the cows, and grazing it may cause mineral imbalances in the cow.    

How often should I lime the farm?

This will depend on several factors, generally areas with higher annual rain fall will need to apply lime more often, or will need to apply more lime in each application.  The amount of Nitrogen you apply will also affect the soil pH.  Nitrogen fertilisers have an acidification effect on soil, so the more Nitrogen you use, the more lime you need.  The response to relatively low lime application, one or two tonne per hectare, can last for 3-4 years.  You should soil test every year or two, so you will be able  to monitor the soil pH and apply lime as it is needed.

What will it cost?

This is of course the most important question, and once again it will depend on a number of different factors.  You can expect to pay approximately $12 – $18 per tonne (ex quarry), you will then have a cartage cost of approximately $10 - $15 per tonne (depending on where your farm is), you then need to spread it, or pay some one to spread it, which will cost $12 - $15 per tonne. 

What you need is value for money. Softer limes react faster, so you may see a quicker response to the softer limes.  Particle size is also important, smaller pieces break down and react faster then the larger pieces, so you need to purchase lime with a greater percentage of smaller particles.  You also need to consider the Calcium Carbonate content, as this is the part of the lime that lifts the pH.  Purchase a lime that is cheap, has a fine particle size, that is relatively soft, and has a high percentage of Calcium Carbonate.  By purchasing lime from a quarry close to your farm, you will save on the cartage cost.

David McGuire
Dairy Consultant
Intelact Nutrition Limited