The Relation of Corn Yields to Leaf Nitrogen, Phosphorus, and Potassium Content

PLANT performance and its relation to internal nutrient concentrations during periods of active growth as revealed by plant and foliar analysis studies is receiving increasing attention. Plant analysis was employed by early workers to establish many of the principles of plant nutrition. It also received considerable early attention as a method of approach to the practical problem of determining the availability of soil nutrients. In contrast to present methods of expressing nutrient concentration in terms of drymatter weight, earlier workers (6) usually expressed concentration in terms of ash weight. Diagnosis based on ash analysis failed largely because it rested on two hypotheses, since disproved, that the plant ash for a particular species was nearly constant and that soil nutrients were of equal availability to all species. The majority of the early studies, moreover, were made either on mature plants, storage organs, or entire plants rather than, as at present, on some functioning plant part which is known to assess nutrient status accurately. Thus, while the idea of plant analysis is not new, the modern approach is different, and when used with the best soil information provides a logical approach to many plant nutrition problems. The literature on the present status of plant analysis is reviewed in recent publications by Scarseth (17), Ulrich (23), Boynton and Compton (i) , and .Thomas (21). The plant-nutrient composition of corn has received the attention of many workers. The early work of Schweitzer (18), Smith (19), and Jones and Huston (10) is noteworthy. This deals primarily with the variation and distribution of plant nutrients in the leaves, stalks, or ears with advancing maturity. More recent work includes that of Lucus, Scarseth, and Sieling (n) on the influence of soil fertility levels on nutrient composition and consumption. Little is known concerning the actual nutrient concentrations present in actively growing corn and their relation to ultimate yield. The Purdue tissue tests (8) are being used extensively in diagnosing nutrient deficiencies in corn. These tests are semi-quantitative in nature and are based on the principle of "critical concentrations". Scarseth (17), Drake (4), and others have used these tests in fertility investigations. The reports of Thomas (20) on foliar diagnosis and of Tyner and Webb (22) on the relation of corn yields to nutrient balance make possible some comparisons of the leaf contents of N, P, and K associated