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Aug 31, 2016

Autumn application of potassium is worthwile

For basic fertilisation with potassium there are two main periods of application: autumn and spring, with the autumn fertilising season being the period from summer after harvesting (stubble fertilising) to the fertilising of already growing winter crops. A much asked question is whether it is more advantageous to apply potassium in the autumn or in the spring. The general recommendation is frequently made that spring application should be preferable on light soils. We will closely examine the optimal time for fertilising:

In several field tests carried out by K+S KALI GmbH, the comparison between spring and autumn application is one of the aspects considered. Here one can see that even on light soil the best option can be early application with potassium in the autumn. This is illustrated by the example of the Trüstedt site in Saxony-Anhalt, Germany, by means of the comparative yields of a five-year crop rotation period:

The results show that potassium fertiliser application after harvesting makes sense. Classical stubble fertilising generally guarantees both good traficability of the field and the application of high amounts, e.g. in the event of a necessary improvement or stock fertilisation for two or three years. Soil cultivation measures usually follow, ensuring that the fertiliser applied is well mixed in.

Losses due to translocation to deeper soil levels are not expected through the winter, apart from small inevitable amounts, on better soil with a significant proportion of clay minerals, even in the case soil that lays fallow. The clay minerals bind the potassium ions interchangeably to their surface. This limits the concentration of dissolved potassium ions in the soil water and prevents them from being washed out. One can assume such conditions as of approx. 35 ground points.

However, on lighter soil too, fertilising can and should be done in the autumn, when winter crops are grown and there is no optimal potassium soil content. To prevent translocation, the fertiliser amount can here be limited to 100 kg K2O in the autumn, and the further fertiliser requirement can be replenished in the spring. This amount can be accommodated by well developed crops before the dormancy period. In this way, the potassium in the crop assists optimal development already in the autumn and is immediately available for further growth at the beginning of the vegetation period in the spring.

Another argument for autumn application is that potassium has an important function in the frost resistance of winter crops. Potassium ions stored into the cells act as an antifreeze agent. They increase the osmotic pressure and effectively reduces the formation of ice crystals that destroy the cells. At the same time, potassium reduces unproductive water losses through its function in stomata regulation, and prevents winter desiccation.

The use of Korn-Kali meets the initial need for magnesium and sulphur. Precisely on light soil and with poorly developed stocks, sulfur provision can already become a problem in the fall, because sulfate-sulfur is discharged from the topsoil by extensive rainfall. Magnesium encourages root growth and thus ensures good starting conditions.

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