Absorption of Nutrients from Subsoil in Relation to Crop Yield
Investigations of the development of root systems of native and crop plants have been pursued for a number of years at the University of Nebraska. The gradual intensification of this work has led to a type of experimentation designed to discover the nature of the activities of roots at great depths in relation to absorption of water and nutrients. In the present investigation the effects of absorption of nutrients from deep levels upon quantity and quality of yield were determined. Studies on
... e amounts of water and nitrates removed by crops from various soil levels were begun in i919, but little attention was then given to yield. Since the results of these earlier experiments have a direct bearing upon the present problem, however, the methods employed being essentially the same, the more important results will be briefly summarized (cf. WEAVER, JEAN, and CRIST 20). Containers I.5-3 feet in diameter and 2.5-5 feet deep were employed. They were placed in trenches, which were then refilled with soil, and crops planted around the containers in such a manner that the experimental crops in the containers were grown under field conditions. The containers were filled with well mixed soil of known water content and physical and chemical composition, to which, at certain levels, NaNO3 had been added at the rate of I21 I22 BOTANICAL GAZETTE [APRIL 400 parts per million. The containers were filled in such a manner that the well compacted soil at any level occupied the same relative position as regards depth that it had occupied before removal from the field. The fertilized layers, and in some cases every 6-inch layer, were separated from the rest of the soil by wax seals which prevented the movement of water or solutes, but through which the roots readily penetrated. To prevent water intake, each container was furnished with an appropriate wooden roof. Crops of Manchuria barley, early Ohio potatoes, and maize were grown. In order to study the activities of the roots at various stages in their development, enough containers were used so that some could be examined at each of the several periods of growth. In fig. I , containers i and 2 illustrate diagrammatically the development of the roots of barley when 55 days old and in the 6 or 7 leaf stage. In containers 3, 4, and 5 the crop was in blossom (74 days old), while in 6 and 7 it had reached maturity. The horizontal lines indicate the positions of the wax seals, and the double vertical lines the positions of the 6-inch levels to which the nutrient was added. The numbers at the bottoms of the containers give the nitrates in parts per million, based on the dry weight of the soil, absorbed from the fertilized layers. The gains by nitrification at the several levels were determined from the control container (no. 8), without a crop. The amount of water absorbed by barley from the deeper soil (to 3.5 feet) was in direct relation to the growth of the root system into these deeper layers. The total amounts absorbed to depths of 2.5 feet in general were practically the same from the several 6-inch levels. Corn is an extravagant user of water, absorbing large quantities from the third and fourth foot of soil, and smaller amounts from the fifth foot. Potatoes absorbed water to depths of 2.5 feet. Potatoes used the nitrates in smaller amounts than barley. When beginning to blossom (74 days old) they had removed I43 and 70 parts per million of nitrates from the I-I.5 and I .5-2 foot layers respectively, and when beginning to ripen (ioo days old) they had removed 228 parts per million at a depth of I.5-2 feet, and 76 to i65 parts per million at the 2-2.5 foot level. From these experiments we may conclude that (i) the roots of crop plants are active in the absorption of both water and nitrate salts, even at the maximum depth of their penetration; (2) both water and nitrates are taken up from these lower portions of the soil in considerable quantities, although to a less extent than from 1 2 3 4 168 145 286 135 5 6 7 8 168 139 186 FIG. i.-Diagrammatic representation of root development of barley at three different stages in growth; NaNO3 occurred at several levels delimited by double vertical lines and horizontal lines, latter represent wax seals.