Law of the minimum:The availability of the most abundant nutrient in the soil is only as good as the availability of the least abundant nutrient in the soil. Only by increasing the amount of the limiting nutrient (the one most scarce in relation to "need") is the growth of a plant or crop improved(formulated byGerman scientist Justus von Liebig).
Law of return:nutrients removed must be returned in the quantities taken away, in order to maintain a balanced ecological state and fertile soil.
Law of diminishing returns: a small quantity of fertilizers leads to a big increase in output, meaning that when a nutrient which is deficient in the soil added, the crop yield will increase to a certain extent. This increase is not proportional to the amount of the nutrient that is added.