Better soils with Brett Petersen Kiwi Fertiliser & Golden Bay Dolomite

I recently found a very interesting scientific paper titled ‘The potassium paradox: Implications for soil fertility, crop production and human health’. It contains a list of 280 references. What it documented was not news to some of us. We’ve known that potassium chloride causes more harm than good for many years. We had serious discussions about KCl v potassium sulphate at kiwifruit field days in the 1980s. “If you do not want your children to eat vegetables or fruit, grow them with KCl.” Food grown with this substance tastes bland at best and sour at worst. So why is KCl the standard product for crops?

It comes down to highly qualified academic soil chemists telling farmers and growers that “N is N, P is P, K is K. Use the cheapest one. The plant doesn’t know the difference.” This garbage ignores the fact that plants can tell the difference via their health. They cannot run away. Insects and diseases can tell the difference. That invites more toxic sprays. Humans can tell the difference with the health of the plants and animals affected, by the keeping qualities and flavour of the food produced. But this is not what the paper above, is about.

Extensive survey

An extensive survey of more than 2100 yield response trials confirmed that KCl fertilisation is unlikely to increase crop yield. Contrary to the persistent instruction perception of KCl as a qualitative commodity, more than 1400 field trials predominately documented a detrimental effect of this fertiliser on the quality of major food, feed, and fibre crops, with serious implications for soil productivity and human health.

Here are some of the principles. Forty-seven per cent of KCl is chloride not required for crop production. And 100 per cent of potassium sulphate is beneficial for crop production. K2SO4 has a salt index of 46, while KCl’s is 116. The lower the better. The sulphate form does not overwhelm the soil with chloride and cause K to be blocked out by the chloride. Consequently, more potassium is taken up by the plant when in the correct form. Sulphates stimulate microbes.

Sulphur levels in soils are usually low, so any source of S is a valuable one. Plants need to make oils and amino acids such as cysteine and methionine that contain sulphur. Flavour and keeping qualities of food are negatively affected by chlorides. Sulphate enhances flavour. Flavour is quality. Quality is health. In most crops, 100kg/ha of K2SO4 will give a greater response than 200kg/ha of KCl. Chlorides suppress microbes. We need to nurture them. We do not advocate zero chlorides. If Cl is short, it must be applied.

Industrialised agriculture

Since the onset of industrialised agriculture, the view has been drummed in that inputs of KCl are indispensable for maximising crop yield and quality and for the long-term maintenance of soil productivity. This view is not reconciled with the large volume of scientific evidence presented in the above paper that encompasses soil testing for plant-available K and the consequences of KCl fertilisation for agricultural productivity, food safety and soil degradation. To avoid the adverse consequences of chloride, potassium sulphate is preferred as a fertiliser source.