MY MATE Ted rang the other morning as I was rushing out the door to a meeting.

"I've been reading about some of these new products to put on crop and pastures, a lot of blokes are using them. Harry reckons he'll try some. What do you think?" he asked.

Ted's question cannot be answered in five minutes but some guiding principles should be considered.

Science shows the relationship between major and minor elements and production levels.

In Australian conditions phosphorus is often the major limiting factor.

Other limiting factors include potassium, sulphur, molybdenum, sometimes copper, zinc and boron.

Before deciding to use any product there are five important questions which require answers.

What is the intended use of the paddock in terms of crop type or stocking rate?

What elements will be required to achieve the production aim?

What are the current levels of the required elements?

What products will ensure adequate levels of the required elements?

What is the cost-per-unit of the applied element? This is very important as many alternative products are promoted on the basis that they are cheaper than superphosphate.

To answer these questions it is essential to have detailed tests on the paddock or livestock and the product.

What does it contain, how much water is in it and how many grams or kilograms of active ingredient does it contain?

This information should be obtained by using accepted scientific methods from reliable testing laboratories.

Some labs conduct a range of tests that look very impressive but the results actually mean very little.

Once the five questions have been answered, products that supply the required elements at a competitive price should go on a short list for further consideration.

Before using a new product it is wise to look for independent trial data.

To be independent, a trial should be conducted by a person or entity who or which has no vested interest in the result.

Trials need to be conducted with several replications, over a number of seasons, preferably in a number of locations and always comparing the product with accepted practice and a "do nothing" test.

The input and output of each of the trial replications needs careful and independent measurement.

The results, including financials, need independent analysis.

Visual differences can be very misleading and measurement is essential.

Where there are claims that products need years to address a particular problem trials may need to be done over a longer period.

Many farmers are claiming significant improvement in productivity by the use of some of the newer products.

The question is at what cost and for what return?

Where independent assessments cannot be found do a test strip in a paddock with normal treatment and untreated strips alongside it.

So Ted, if Harry asks the questions above and uses the answers to make decisions based on evidence rather than emotion, he won't go far wrong.

If he does change suggest that he does a small trial himself.