Does organic farming mine our soils?

The negative nutrient balance for phosphorus and potassium leads to a decrease in the easily available fraction of these elements. The nutrient reserves in soil, however, decreased less dramatically.

Even though soluble phosphorus was low in the organic systems, phosphorus deficiency has not yet been observed. This can be explained by the increased transfer of elements between the solid phase and the soil solution and by the higher microbial activity (An investigation carried out by the Institute of Plant Sciences, ETH-Zürich).

Potassium became rate-limiting relatively early after conversion to organic management when potatoes were cultivated. Fertilization with potassium is indicated where allowed according to the rules of organic farming.

Water soluble phosphorous

Water soluble phosphorus decreased markedly in all systems.

In the beginning of the field trial the conventional system was strongly fertilized to enhance the phosphorus and potassium concentration.

Towards the end of the third crop rotation, however, soluble phosphorus values decreased to those of the organic systems.

The phosporus soluble in 2% citric acid is less immediately available, and represents reserve nutrients.

Starting from similar phosphorus-loads at the beginning of the trial, no large changes were apparent, but total phosphorus-load was higher in the conventional system.

Water soluble potassium

The water soluble potassium in the organic soils has remained at the same level.

The increase after stock fertilization in the conventional system in the beginning of the field trial is obvious.

Potassium soluble in lactic acid

Potassium soluble in lactic acid, the reserve fraction, even increased in the organic systems and remained at a constant level in the conventional system.