Recent developments in plant physiology suggest possible new techniques for rapidly determining how well a crop is growing at various times in the season. Measurements of physiological activities of growing plants such as photosynthetic CO₂ uptake by leaves might be used to detect whether a crop was growing below its maximum potential rate, enabling the farmer to correct an agronomically controllable problem before crop losses were incurred. This report discusses the feasibility of such an approach and presents experimental data on the effects of deficiencies of phosphorus, potassium, magnesium, calcium, and manganese on various physiological attributes of sugar beets.