Test soil pH now for good spring growth

12 October 2001

Test soil pH now for good spring growth

By Hannah Velten

GRASS soils typically require lime applications every four years and, with late autumn a good time for spreading, soil pH should be tested now to ensure good spring growth.

According to ADAS Gleadthorpe fertiliser researcher Brian Chambers, although pH 6 is recommended for grassland, about a third of UK soil is slightly acidic and an eighth is below pH 5.5.

"Productive grass growth and quality is lost when soils are acidic, clover disappears below pH 5.5 and nitrogen and phosphorous fertiliser efficiency decreases.

Adjusting acidic soil will keep bio-activity levels up, so soil nutrients are released from organic matter and maintain plant diversity."

The main reason for acidic soil is failing to put on enough lime to match natural soil losses, says Dr Chambers. "Although losses are very slow and insidious, soil testing and liming should be a routine preventative measure to maintain soils at pH 6.

"To achieve this, about 3-5t of lime/ha should be applied every four years." It will take a year for the lime to react fully in the soil, but an initial neutralisation will occur within three to four months, he adds.

The highest application rate suggested will be needed on grassland which receives a high rate of nitrogen fertiliser, which is itself an acidifier of soils.

However, Dr Chambers warns that over-application of lime is a waste of money and will inhibit the availability of certain trace elements, such as cobalt and copper. "Soil pH can be as low as 4-4.5, but no more than 7t of lime/ha must be applied at one time. After one or two years, soil should be tested again to see whether additional lime is needed."

He advises asking lime merchants or contractors to test soil pH. "They will be able to take accurate readings across the whole field and map out exactly where soil is acidic, so lime can be applied where it is needed most and not wasted." These measurements can also be backed up by lab analysis.

Ground limestone and chalk have 50% neutralising capacity and are the most cost-effective liming options, particularly when supplies are local. "These limes can be delivered and spread for about £12/t, whereas quicklime is more expensive, even though it has a 100% neutralising capacity." Magnesium limestone is useful when soil is also magnesium deficient, he adds. &#42


* Test soil pH.

* Apply every four years.

* Excess limits trace elements.

If youre aiming for good spring grass yields a pH test this autumn could easily prove worthwhile, says Brian Chambers.


&#8226 Test soil pH.

&#8226 Apply every four years.

&#8226 Excess limits trace elements.

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