The fact that plants need various mineral elements had been recognized in the early 19th century. Yet, no method had been accepted for measuring the quantitative mineral nutrient requirements of plants. Working at Cornell University, Paul Macy in this elegant paper found a relationship between the percentage content of a nutrient in a plant and the sufficiency for the nutrient for growth. He didn’t really invent that concept, but he brought it forward hugely. Others before him had proposed that there is a certain ‘sufficiency’ for a nutrient, but they also found that responses to nutrients was dependent on several factors.
The central idea in Macy’s paper is that each kind of plant has a critical percentage of each nutrient. Above a certain threshold, there is luxury consumption and below it is poverty adjustment. The latter is almost proportional to a deficiency until a minimum percentage is reached.
He confirms this hypothesis using data from the literature and by conducting experiments with nitrogen in barley. Extreme effects of other factors on the yield and on the nitrogen content of the straw had no effect on that relationship. He concluded that the critical nutrient composition of a plant is an “ideal” but inherent characteristic of the plant. According to him, this concept could be used to determine fertilizer needs of particular crops on particular soils under particular local conditions. Discoveries such as this one have laid the foundation for what we nowadays call precision farming, or site-specific nutrient management.
