Absorption of Nutrients from Subsoil in Relation to Crop Yield

1. This investigation was undertaken to determine the effects of absorption of nitrates and phosphates from the subsoil on quantity and quality of yield of barley. Eighteen containers, 22 inches in diameter and 30 inches deep, were filled with soil and subsoil and placed in trenches in the field. Thirty barley plants were grown in each container; they were surrounded by a crop of barley, growing partly in the refilled trenches. The soil, except in the controls, was fertilized at various levels to 30 inches in depth, and in some cases at two levels, with either NaNO3 or CaH4(PO4)2. Wax seals, through which the roots easily penetrated, were used to prevent the movement of water and nutrient salts from the fertilized layer to the soil above or below. 2. The roots in the controls reached a depth of 30 inches, but nitrate fertilizer at any level tended to lessen root depth and greatly increased branching. Phosphates did not noticeably increase root development. 3. Nutrients were absorbed in large quantities at every level to 30 inches. Although the plants used the largest amount of salts from the surface foot, they also took large additional quantities from the deeper levels when it was available. 4. Absorption of nutrients at levels below the surface foot affects materially the quantity and quality of the yield. It does not lose its additive effect even when the surface foot is abundantly supplied with a similar nutrient. Thus the chemical composition of the subsoil and the soil solution is very important. 5. Nitrates increased total dry weight when applied to the surface foot early in the life of the plant. This results from its effectiveness in promoting heavier tillering. It increased dry weight and also quality of grain still more when available at lower levels as well as in the surface foot. Phosphorus depressed yield, particularly that of the straw, somewhat in proportion to the amount absorbed. 6. Time of absorption is an important factor. The effects of the nutritive salts are most marked on both quantity and quality of yield early and late in the development of the plant, that is, when absorption is confined largely to the first foot of soil and the crop is tillering, and again when the younger portions of the longer roots are absorbing from the deeper levels at the time of heading. Thus an ample distribution of the deeper portion of the root system in a rich subsoil solution at the later critical period of growth is exceedingly important. Consequently, a knowledge of the development and extent of the roots of crop plants is of primary interest. 7. These experiments show the importance of the subsoil as a source of nutrients for crops, and the effects upon plant development. They emphasize the values to be gained by fertilizer practices which take the composition of the subsoil into account.