Why farmers use fertilisers

Plants absorb as many nutrients from the soil as necessary for their normal development. After the end of their life cycle plants decompose, and all the elements go back into the soil.

When using the land for agricultural purposes, humans interfere in the cycle of elements in nature.

Together with the harvest, they take the nutrients that plants have absorbed from the ground, thus breaking the ecosystem balance. With each harvest, humans remove 60 to 70% more nutrients from the soil than plant residues give back. Over time, the concentration of the most important macronutrients in the soil decreases. This process is called soil depletion.

To retain soil fertility it is necessary to replenish nutrients by returning to the soil at least the same amount. Therefore the modern cycle of agricultural production invariably involves application of mineral fertiliser.
SCHEMATIC OF THE POTASSIUM CYCLE IN SOIL AND AGRICULTURE
Schematics base on International Potash Institute sources
INGESTION
CROP OFFTAKE
EROSION
FERTILIZATION
RELEASE
RELEASE
DESORPTION
RELEASE
SORPTION
FIXATION
RELEASE
FIXATION
WEATHERING
LEACHING
FERTILIZER
PLANT K
ORGANIC
FERTILIZER
CROP
RESIDUES
IRRIGATION
SOLI SOLUTION K
IMMEDIATELY
AVAILABLE
0,1-0,2% OF TOTAL
MICROBIAL
BIOMASS K
0,25-0,5%
OF TOTAL
EXCHANGEABLE K
READILY AVAILBLE
0,1-3%
OF TOTAL
FIXED K
(NON EXCH.)
SLOWLY AVAILABLE
1-10%
OF TOTAL
PARENTS MINERALS
VERY SLOWLY AVAILABLE
90-98%
OF TOTAL