July 2013

VIEWPOINT

with John Barnes, Managing Director – July 2013

Soil Testing and the Results

Traveling around the South Island recently gave me time to listen and reflect on what is happening in the field. Some of this is about applying nitrogen. The industry standard is only apply nitrogen if the soil temperature is over 8°C. Of course this makes sense, as to apply any sort of nitrogen, especially urea (which is a synthetic water soluble growth promotant), will only be lost into the soil or into the atmosphere if the conditions are not correct. Some advisers are saying it will be there for when the plant conditions come right – seems to me to be stretching the truth. The only way this could be partially true would be if the correct amount of a coating was applied to the urea.

What I am most concerned about is the waste of money. Farmers spend hard-earned cash on product with no or very little return.

It is interesting that so much emphasis is put on the two most common tests. Farms are valued on those tests and tens of thousands of dollars are spent on fertiliser programmes based on both the pH and the Olsen Phosphorus test. The Olsen P test is an indication of how much available phosphate your soil holds. Reports on its accuracy vary but it seems fair to say the margin of error is plus or minus 40 percent. It is worthy of mention here that the Olsen P test is not a good measure of RPR, as most good natural phosphate products release P at about the same speed that the plant takes it up. So often there is not a lot spare to measure. This is unlike “Super” which is 100% water soluble and 100% available. Because of this the Olsen P measures all the phosphate. There are good reserve phosphate tests available with no need to send samples overseas at a huge expense.

pH measures the alkaline or acid of soils. The range varies from zero being very acid, to fourteen being alkaline. Seven is neutral. Our soil should be slightly acid, with an ideal range of 6 to 6.5. Remember there is no such thing as a typical soil. Once a pH of 6.0 to 6.5 is achieved it will need to be maintained. The amount of lime that is required depends on your choice of fertiliser. Super, with a pH of 2 to 3 will need more lime as this product is very acidic, while RPR has a pH of 7 and may hold the pH. Nitrogen will also lower the pH. And by the way, some nitrogen can also lower the soil temperature if enough is used.

Soils are very complex and the more I learn the less I know. One thing I do know, they aren’t making any more and we must look after what we have. The very first aspect to look out for in any soil test is what type of soil are we looking at? To find this out, look for bulk density (or volume weight), CEC and Base Saturation, and understand the type of soil we are about to deal with. Then and only then will we make sense of the other parts of the test.

For more clarification, email your tests through to us for our recommendations.

Lime is an all important part of any farmers fertiliser programme. In our company we have a saying that “Calcium is King”! First get the calcium level sorted, then many other problems can be easily sorted.

Take a look at this diagram:

At the top the numbers go from left to right, 4.0 being acid and 10.0 being alkaline. The various elements become available at various stages of the pH range. For example, we don’t want aluminium available so by applying lime we shut down this element. At the same time we allow phosphorus to become available.

You will notice that at a pH of 6.5, most fertilisers become plant available and the two unwanted ones become less available – aluminium and iron. This is why calcium is king. For calcium to work effectively, boron is required. In short, boron mobilises calcium.

Dr Jim Bruce-Smith, whom I have a high regard for, has written extensively regarding this subject. Here is an extract from his collection of articles written in December 1980 by Rex Newman B.Sc., Dip.Ed., Dip.R.E., Dip.Ed.Admin., N.D. published in the Soil and Health Journal, and describes how soil, plant, animal and human health is interrelated.

“It is well documented in the literature that when superphosphate is added to soil the uptake of copper, boron and zinc are all inhibited. Potash fertilisers have a similar effect. Most of us get more than enough copper from modern plumbing systems. All human remains do contain traces of boron and plants cannot grow without it, yet some plants are very sensitive to an excess of boron. We have been using superphosphate on our agricultural soils since last century and since 1950 its use has greatly increased, more potash and nitrogen fertilisers are also being used. This all means that the acidity of the soil is increasing and the availability of both boron and magnesium, zinc and copper are all decreasing. Many soil scientists tend to emphasise the minerals that can be measured, but there are other factors in the soil that cannot be measured so easily.”

The table below summarises the reductions in the average mineral content of 27 vegetables and 17 fruits, between 1940 and 1991 in the US and UK as originally published in the Journal of Complementary Medicine.

Ultimately we are growing food for human consumption. The Governments stated aim is to lift production. The market our primary producers have been asked to focus on is the middle class and up. These people have disposable discretionary income and want the best.

To meet these targets it is proposed by some fertiliser companies in New Zealand to use more nitrogen. While nitrogen is important for plant growth, excessive use of nitrogen, which is what I believe is happening now, will deplete even further the nutrient value of our foods. It is our belief that we need to change this so that once again our food source has a better nutrient value. By lifting the trace elements in our fresh foods we will also lift the energy levels and taste of our food.

At Fertilizer New Zealand we strive not only for a better soil structure and better plants, but also for better human health. If you are already working with us, thank you for the support – you are part of the solution. Please feel free to pass this email on to others who may wish to join us.