ABSTRACT
Crop plants typically are comprised of C, H, O, N, and then other elements, in that order, so it is obvious that nitrogen is required by plants in large amounts. The fact that nitrogen is taken up by plant roots was shown by de Saussure in 1804, who demonstrated that an inorganic nitrogen source such as nitrate is essential for plant growth (Hewitt, 1966). From these facts, it follows that as plants have a high nitrogen requirement there are many situations in which its supply could limit crop growth, and amending soils and growing media with additional nitrogen can increase yields.
