The main building blocks of plants are:
If one of these essential nutrients is missing, all the other nutrients present are useless. This is the law of the minimum, or the law of limiting factors of Justus Liebig.
Crop yields are proportional to the amount of nutrient that is lowest in the soil. The lack of an assimilable element in the soil reduces the effectiveness of the other elements, and consequently, decreases the yield of crops. This law of the minimum of Justus Von Liebig is commonly illustrated by the image of the barrel whose shortest stave determines the maximum level of filling of the barrel.