A quantitative study has been made of the root systems of two varieties of barley (Hordeum vulgare L. vars. Maris Badger and Proctor) grown in water culture under three nutrient regimes—complete nutrient supply and deficiencies of potassium and phosphorus. The weight of the root systems, and the number, length and diameter of the seminal and nodal axes and laterals were measured. From these measurements, surface area and volume were calculated, and to show changes in the relationships between these quantities an expression of the fineness of the root systems, termed the average diameter, was derived. This paper describes the root systems after 4 weeks growth.
Maris Badger was more affected than Proctor by nutrient deficiency, but in both varieties the main effect was on the size of the nodal, as opposed to the seminal, root system. The number of axes and the length of the primary laterals were greatly reduced by both potassium and phosphorus deficiency but, by comparison, the mean length of the axes, the number of primary laterals per axis and the diameter of all types of root member were little affected.
Deficiency of potassium reduced the length of the primary laterals to a greater extent than that of phosphorus; in addition, it completely inhibited the formation of secondary laterals. Consequently, the average diameter of the root systems of the potassium-deficient plants was greater than that of the phosphorus-deficient plants.
Interactions between variety and nutrition were highly significant statistically, especially with respect to the development of laterals.