Soil Testing with ARL
The first step in designing a fertiliser programme is to test your soil.
Why soil test?
Soil testing helps you establish the nutrient status i.e. “the reservoir” of your soil. It also means you are able to:
- More accurately assess fertiliser and lime requirements and maximise your fertiliser dollar
- Make better informed management decisions
- Monitor the effectiveness of previous fertiliser applications
- Keep track of fertility trends over time
- Establish a starting point for looking at sustainability and designing fertiliser programmes
Getting the best from your soil sample
The greater the variation in a sample area the more difficult it is to manage and fertilise it correctly. The key to taking a representative sample is to choose sample areas that have a similar soil type, fertiliser history, productivity, topography (slope) and land use. Sample numbers should increase with greater variation in these factors.
You will get the most value from your sample when the area it represents varies the least.
How do I sample for soil analysis?
- Select sites to take soil samples from. The samples should be representative of the whole area taken in a transect (line) or grid pattern and should be taken in a way which can be repeated from year to year. Painting fence posts, use of GPS or placing pegs under fences can permanently identify sampling lines. Avoid areas that are not typical of the block/paddock that you are looking to sample from, such as, gateways, troughs, fence lines, unusually high or low fertility “spots” and manure or waste spots.
Soil sampling for your block
- Make sure the core is taken at the appropriate depth. Core depth should be 7.5cm for pastoral soils and 15cm for cropping and horticultural soils. A soil auger can be borrowed or purchased from ARL or your local Ravensdown store. Alternatively a clean spade can be used but it is essential to maintain core width i.e. not sample in a wedge shape and that the core is sampled to the correct depth. Take a minimum of 20 individual cores at 10m intervals.
- These 20 cores make up one sample and can be placed in one ARL sample bag.
- Securely close the sample bags and label them clearly.
- Fill in the soil submission form and put the samples plus the submission form in the pre-paid courier bag and send them to ARL immediately or store in the refrigerator (any delay exposes the sample to excess heat and moisture and can affect the analysis).
- Standard soil test results will be available 5 working days after they are received at ARL. From there your Ravensdown agri manager or one of the Customer Centre regional agri support agents will be in touch to go over your test results and look at the next steps.
Samples can be sent or dropped off to the lab:
890 Waitangi Road
How many soil samples and how often?
We recommend sampling as much of your farm as possible to assist in long-term planning and providing for the overall sustainability of your operation. It’s a small investment to add science to your land management practices.
Maximum advantage from soil testing is best achieved by repeated testing on a regular and planned basis, rather than relying on a “snap shot” in time. For most situations an annual soil test, coupled with plant tissue testing during the growing season is recommended.
Do I need to do a plant analysis as well as a soil test?
Soil testing cannot tell you if your plants are capturing all the nutrients available, and if the nutrients needed are in the correct proportions. So it’s best practice to soil test in conjunction with plant analysis to give you the most accurate picture of your block and crop. This will enable you to make better informed decisions.
Soil analysis suites
Basic soil analysis
Pasture soil analysis
Soil nutrient status suitable for pastoral, cropping and horticulture enterprises with sulphate and organic sulphur included. The recommended soil fertility suite for nutrient budget analysis.
(Basic soil + SO4-S + Organic S)
Cropping soil analysis
Soil nutrient status suitable for pastoral, cropping and horticulture enterprises includes sulphate and Anerobically Mineralisable Nitrogen (AMN) analysis that is a measure of the soils capacity to supply nitrogen to crops.
(Pasture soil analysis + Anaerobic Mineralisable N)
A measure of the readily plant available nitrogen (Ammonium-N and Nitrate-N) at the time of sampling, allows application decisions to take into account existing soil nitrogen.
(Deep Nitrogen Tests)
Potentially Mineralisable Nitrogen (PMN)
Estimates the contribution to plant available nitrogen from mineralisation of organic matter and is correlated with long term aerobic incubation studies. This test replace the AMN test since it is a better predictor of mineralisable nitrogen in cropping soils.
Additional tests available
Anion storage capacity - (also referred to as the phosphate retention test) - Measures the ability of the soil to store phosphate and sulphate. Soils with higher anion storage capacities will require. Larger amounts of fertiliser phosphate and sulphate to raise soil test levels or to overcome deficiencies. Recommended once for each block or paddock.
Reserve Potassium (TBK) - Measures the amount of reserve potassium available in some soils. Recommended every three to five years on sedimentary soils only.
Anaerobic mineralisable nitrogen (also referred to as the available nitrogen test) - Estimates the likely mineralisation of organic nitrogen providing an estimate of soil nitrogen supply. Recommended where land is to be cultivated and cropped.
Organic matter - Organic matter in soil has an important role in the supply of nutrients, improving soil structure, reducing the risk of erosion, increasing the water holding capacity of soils and providing a food source for earthworms and microbes. It generally declines under cropping and increases under pasture. Recommended once every 4 – 5 years.
Exchangeable aluminium - One reason for poor plant growth in New Zealand on acid soils (those soils where pH< 5.6) can be aluminium toxicity. This test measures the exchangeable aluminium and confirms toxicity problems.
Hot water soluble boron - Provides a measure of available boron in the soil. Recommended where crops have a high boron requirement such as avocados and olives or when changing to crops which are sensitive to boron toxicity.
Trace Element Testing - We offer a number of options for soil trace element testing. We recommend plant tissue testing in conjunction with animal liver/blood tests for determining trace element deficiencies in pasture.