A testing programme to analyse composts and growing medias for their nutrient content is available. Additional tests for organic growers are also offered.
About this Testing
What are Composts and Medias
Soil-less growing media are used directly as a complete growing media for the plants to grow in. Likely ingredients of soil-less growing medias are fine bark or peat with pumice or untreated sawdust with slow release fertilisers. At Hill Laboratories, materials other than growing media will be regarded as composts.
Compost is a material added to a soil as a mulch or soil conditioner to add valuable soil organic matter. Composts are often dug into the soil to improve soil drainage, aeration and nutrient holding ability.
Please Note: Other than dairy effluents, raw manures are not accepted by the lab.
Basic Media Testing
Almost all of the growing media received at Hill Laboratories are analysed for the Basic Media Test. This test includes pH, Electrical Conductivity and the immediately plant available nutrients ammonium-nitrogen, nitrate nitrogen, phosphorus, potassium, calcium, magnesium and sodium.
Additional Media Tests
The trace elements iron, managanese, zinc, copper and boron are analysed. As with soil trace element testing, there are limitations to the reliability of testing trace elements in media samples. In most instances, suspected trace element problems should be confirmed with plant tissue analysis.
- Nitrogen Drawdown Index (NDI)
The nitrogen drawdown index (NDI) test measures how ‘stabilised’ the potting media is after composting. If a potting media has not ‘stabilised’, microbes will compete with the plant for nitrogen supply and nitrogen deficiency symptoms may appear in the crop. If the media has ‘stabilised’, the nitrogen drawdown by the microbes has reduced to the point where the supply of nitrogen to the crop is relatively unaffected.
The NDI test should be performed on media before the addition of slow release fertilisers as these additional nitrogen sources will interfere with the test.
Taking a sample
- Take at least 15 to 20 representative sub-samples from different areas of the potting media.
- Approximately 0.5 litre of media should be submitted for analysis. If trace elements and NDI are also required, please submit 2 litres of potting media.
- Avoid contamination of samples by using clean sampling equipment and bags.
- Send samples to the laboratory as soon as possible. Do not allow mixes to incubate in moist conditions for long periods prior to submission.
- Where intensive cropping is involved, it may be advisable to monitor nutrient levels by sending samples for analysis every 3 to 6 weeks.
- If a nutritional problem is suspected, plant tissue samples should be taken in combination with media samples.
- If diagnosing a specific problem, select a representative sample from pots showing the most prominent symptoms.
- Media & Compost Request Form
- Soil, Plant and Media Analysis Request Form.
How to Order a Test
Complimentary Soil and Plant Test Kits for submitting media samples are available from the laboratory. These sample kits contain instructions, an analysis request form, sampling bags and courier bag to send in the samples.
Guides and Supporting Information
Call us on 07 858 2000 or 03 377 7176 (South Island) or click below for the contact details of a Client Service Manager: