Plant Nutrition Diagnostics

the determination of the extent to which plants are supplied with nutrients during their period of growth. Plant nutrition diagnostics makes it possible to determine a deficiency of a given nutrient in a plant and to provide supplementary feeding promptly. Two methods are widely used—visual and chemical diagnostics. Other methods are based on the introduction of nutrients into the vegetative parts of plants (for example, foliar nutrition).

Visual diagnostics is the determination of a deficiency of mineral nutrients based on the color, shape, and size of the leaves and spots on dead tissues, as well as other external signs. If there is a nitrogen deficiency (nitrogen starvation), the leaves take on a pale green color that changes in some plants to orange and red, or the leaf tissues begin to die from the apex to the base (in corn, for example). A phosphorus deficiency may be manifested by dark greenish blue, violet (corn, sorghum, and tomato), or purple (cabbage) leaves and the appearance of brown or black spots along the edges of the lower leaves. Potassium deficiency causes shriveling of the leaf blades, shortening of the internodes, and loss of turgor. The leaves become dark green with a bluish or bronze tint (in potatoes and tomatoes, for example), and the edges of the tissues turn yellow and brown and die. When there is a magnesium deficiency, the leaves become pale because of the decrease in chlorophyll. Spots of different shades appear between the veins, and the leaves become brittle. Iron deficiency results in chlorosis of the top young leaves, the death of tissues along the edges of these leaves, and the shriveling of the shoots. A boron deficiency causes weak flowering and fruiting, death of the apical buds, and chlorosis of the leaves, and a copper deficiency causes chlorosis of young leaves, loss of turgor, and retarded seed formation. Markings and small spots of dead tissue appear on the leaves when there is a manganese deficiency, and a zinc deficiency causes yellowing, spottiness, and asymmetry of leaves, formation of rosettes, and shortening of the internodes. A molybdenum deficiency results in yellowing of the leaves and in legumes, weak development of nodules on the roots.

Visual diagnostics is simple and does not require special equipment. However, it is not completely accurate because the external signs of deficiencies in different nutrients are sometimes alike. Moreover, pests, diseases, and unfavorable weather conditions may cause changes in the external appearance of plants that are similar to symptoms of a deficiency. In such cases the diagnosis must be confirmed by chemical analysis.

Chemical diagnostics is the determination of a deficiency of plant nutrients from the results of chemical analysis of a leaf or juice, a slice, or extract from petioles, veins, and stems. The results of chemical analysis on individual elements establish the content and deficiencies of elements in a plant. The simplest method of chemical diagnosis involves analyzing a drop of juice from the petiole or vein, using Magnitskii’s field laboratory, or directly analyzing plant slices with a Tserling OP-2 instrument. The color of the juice or slices obtained by these analytic methods is compared with standards.

A disturbance of normal plant nutrition and metabolism may cause not only a deficiency but also an excess of certain elements. To determine more completely the conditions of plant nutrition and to increase the efficiency of fertilizer use, it is very important to have the results of diagnostics in the various phases of plant development as well as the results of soil analysis.