AbstractQuality tobacco leaf comes from plants grown with balanced mineral nutrition. The “structural nutrients” (carbon, hydrogen and oxygen) are approximately 90 % of the dry weight of cured leaf but are of little economic concern. The macronutrients (nitrogen, phosphorus, potassium, calcium, magnesium and sulfur) and the micronutrients (boron, chlorine, copper, iron, manganese, molybdenum and zinc) are of great economic concern and adequate amounts in the soil are essential for production of quality tobacco leaf. Nitrogen, phosphorus, potassium and magnesium are mobile within the plant and deficiency symptoms are observed first in the lower leaves and later in the upper leaves. Deficiency symptoms of the immobile nutrients calcium, boron, manganese, sulfur and iron are observed first on the upper leaves or terminal bud. Of all the mineral nutrients nitrogen has the greatest effect on shoot and root weight. As available nitrogen increases leaf nicotine increases and reducing sugars decrease; thus the sugar:nicotine ratio decreases dramatically. There is a positive relationship between amount of reduced nitrogen and reduced sulfur in the plant and this interaction is important as most of the reduced nitrogen and sulfur are utilized in protein synthesis. Total uptake of potassium is greater than for any other mineral. Because of the immobility of calcium and boron, deficiency of these nutrients results in physiological decapitation (topping) and consequently increased nicotine content of leaves. Excessive amounts of nutrients can also produce some problems. Excessive nitrogen increases yield but it also increases the incidence of disease, delays flowering and leaf ripening, and lowers leaf quality. Excessive addition of lime causes a basic soil pH which increases disease incidence and limits availability of phosphorus, iron, manganese and zinc. Excessive chlorine increases the hygroscopic property of the leaf and reduces burn rate. Soil applied magnesium oxide may reduce potassium absorption and therefore reduce burn rate.
Studies on the boron deficiency in field crops (Part I) boron deficiency symptoms in rape plants
