Root growth of alfalfa, medium red clover, bromegrass, and timothy under various soil conditions

Studies were conducted under field and greenhouse conditions on the effect of various soil conditions on root growth of smooth bromegrass of Canadian origin (Bromus inermis L.), timothy (Phleum pratense L.), Grimm alfalfa (Medicago sativa L.), and medium red clover (Trifolium pratense L.) when grown in stands containing one species only. The results obtained under greenhouse conditions may be summarized as follows: 1. Root growth of all species was less in silt loam than in sandy soil. 2. Alfalfa and bromegrass produced about the same weight of roots per pot in sandy and silt loam soil, but each produced significantly more roots than timothy or medium red clover. 3. The gains in weight of roots were greater during the period the plants increased in age from 61 to 68 days than during the period from 45 to 60 days. 4. Root growth of both alfalfa and bromegrass was increased significantly by artificial aeration of Spencer silt loam. 5. The greatest benefit from aeration occurred when plants were grown in subsurface soil only, and the least when they were grown in surface soil only. 6. Root growth of bromegrass was significantly greater than that of alfalfa in both aerated and nonaerated Spencer silt loam. The following results were obtained in field studies: 1. The average weight of the roots of all four species increased steadily during the year of seeding, but much more rapidly the year following seeding. 2. Either alfalfa or bromegrass produced more root growth than medium red clover or timothy. 3. The average weight of the roots was largest in Miami silt loam, intermediate in Spencer silt loam, and lowest in Plainfield sand for all species. 4. Roots of alfalfa penetrated most deeply and those of timothy penetrated least deeply during both the first and second growing seasons. 5. In Miami silt loam, root growth of all species decreased progressively with increasing depth. More than half of the total root growth of each of the four species was found in the surface 8-inch layer. 6. The linear length of roots per gram of dry matter increased considerably in each successive 8-inch layer of Miami silt loam. It was greatest in all soil layers studied for timothy, intermediate for bromegrass, and least for medium red clover and alfalfa.