Nutrient test strips

Fertiliser and nutrients should be strategically applied to pastures to ensure the most cost-effective result is achieved.

The major plant nutrients, phosphorus (P) and sulfur (S) are key drivers of pasture productivity. It is common for landholders to regularly apply fertilisers containing P and S to maintain or build pasture and livestock production levels.

There may also be other nutrients that are limiting pasture growth.

Nutrient test strips are a practical, low‑cost tool that allows you to compare the pasture yield response of your current practice against applications of a given product at various rates. Test results can then be used to support decision making for whole‑paddock applications. 

Soil testing vs nutrient testing

Soil tests are a good place to start for assessing major nutrients in pasture paddocks, such as phosphorus (P), sulfur (S) and potassium (K).

Soil tests are less useful in determining deficiencies or toxicities of the minor nutrients required in much smaller quantities by plants (such as molybdenum, copper, boron, zinc). 

Nutrient test strips provide a way to directly observe pasture yield responses in the paddock to determine whether particular nutrients may be limiting production. 

The key nutrients to examine are usually phosphorus, sulphur, nitrogen, potassium and micronutrients. 

When to use nutrient test strips

Nutrient test strips are best set up in autumn, ideally around the break of the season, when fertiliser would normally be applied.

If you are relying on your pasture legume to supply soil nitrogen, it is important to ensure there is good legume content in the pasture at the time of setting up nutrient test strips. 

Spring is the time of year to determine if there is a pasture response to applied nutrients. This is because moisture and temperature are less likely to constrain growth at this time.

If you have concerns about your pastures and other possible nutrient constraints, or reason to question the pasture growth response to a particular soil nutrient or fertiliser type, you should plan ahead.

How to set up nutrient test strips

Test strips are simple to establish. 

1. Determine how many test areas are needed to compare different products and different application rates. It is preferable to replicate test strips to improve confidence in the results.
2. Select locations for the test strips that are representative of the paddock. 
   Always avoid stock camp areas, around trees, near gates or fence lines, old fertiliser dump sites or hay/silage storage sites, poorly drained areas and rocky outcrops. 
   Pasture should be reasonably uniform and based on perennial grasses with an adequate legume content, to ensure nitrogen is being supplied and is not limiting growth.
3. For each treatment plot, mark out an area 5 m x 2 m with star pickets or similar. 
   This area makes it easy to convert kg/ha of product applied to grams/10 m² of product to test. For example, if you are trialling a rate of 300 kg/ha of a product, then this equates to applying 300 grams over the 10 m² test area.
4. Weigh out the product and place it in a small bucket before you begin.
5. Spread out as evenly as possible over each 10 m² treatment plot.
6. Clearly mark or label each area with the date and treatment applied.
7. Make a record of the location and layout of all nutrient test strips. Use both a photo and map so you can refer to tests over time.
8. Once established, plots can be grazed normally until late winter.
9. In late August or early September, ensure the pasture on the test strips is evenly grazed down or mow using a standard lawn mower.
10. Exclude stock for a period of 6-8 weeks to allow any pasture response to become evident.
11. In spring, visually assess and compare pasture growth in each test strip. 
    It is difficult to visually asses a growth response of less than 20%. Smaller responses are better measured using pasture cut techniques or pasture probe measuring devices.   

Examples of use

To test response to a specific fertiliser

To set up fertiliser test strips to test Product X, which has a recommended application rate of 300 kg/ha.

In this case, the treatments to test would be Product X as well as your standard current practice treatment (for example, single super applied at 125 kg/ha). 

It would be useful to know the percent phosphorus in Product X as you could then also apply a rate of your standard practice fertiliser at a rate that delivers equivalent amounts of phosphorus per hectare.  

Set up 2 test strips for each of the following:

• Product X at recommended rate.
• Current product at your current rate.
• Current product at a rate that matches the % of phosphorus in Product X. 

To test response to rates of fertiliser

To test if a less commonly applied nutrient is limiting pasture production, you could test the same product at various rates of application. For example, if your soil P and S are at optimum levels, however your soil K levels are reading low on your soil test reports over time. 

Set up 2 test strips for each of the following:

• Current product at your current rate.
• Product X at 50% of recommended rate.
• Product X at 100% of recommended rate.

If there is a visual response in pasture yield from the added nutrient at a particular rate, you can assess the benefits of broadacre application.   

If you need advice on soil testing or fertiliser use, speak to your local Ag Advisor.