328 EXPERIMENT STATION RECORD. 



iu pot experiments to determine the influence of fertility, moisture content, and 

 soil compactness on the development of the root system and on the weight of 

 the underground and aboveground portions of the plants. A clay and a sandy 

 soil were used. The fertilized pots received a complete fertilizer application, 

 in addition to which the sandy soil of the fertilized series was treated with 

 calcium carbonate. The soil moisture content, based on the water-holding 

 capacity of the soil, dried at 100° C, was held in the dry series of the clay soil 

 at 11.25 per cent and in the moist series at 19 per cent, the corresponding figures 

 for the sandy soil being 5.4 and 9 per cent, respectively. The soil, sifted to 

 remove lumps and coarse particles, was placed loosely in the one series of pots, 

 while in the other it was tamped by layers to insure uniform compactness up 

 to the upper 2 or 3 cm., which remained loose and friable. 



In the experiments with barley a comparison of the fertilized and unfertilized 

 series of pots showed that the unfertilized sandy soil produced the highest 

 absolute weight of root material. This was also true of the clay soil with high 

 moisture content, but in the dry series the fertilized soil produced the larger 

 absolute weight. Determinations of the weight per unit length of the roots 

 indicated that the fertilized soil produced, to some extent, stronger and thicker 

 roots than the soil which had received no fertilizer treatment. It was further 

 found that in most cases a unit weight of root material in the fertilized soil 

 produced a slightly larger amount of substance above ground than the same unit 

 weight in the unfertilized pots. The conclusion is drawn that during the early 

 vegetative period, when the plants used the nutriment stored in the seed, the 

 fertilization of the soil had but little effect upon the production of organic 

 substances. 



The clay soil in every instance produced a higher absolute weight of root 

 material in the dry series than in the moist series of tests. The sandy soil in 

 general yielded the largest amount of root material by weight when supplied 

 with the larger quantity of moisture. The roots in themselves developed 

 stronger or denser in the dry than in the moist sandy soil, but this was not 

 so evident as in the clay soil. The results also demonstrated that the plants 

 required less water for their development and maximum production on the 

 sandy soil than on the clay soil when other conditions were the same. 



The compactness of the soil apparently had no influence on the number of 

 main roots, but the lateral roots were most numerous in both clay and sand in 

 the compact series with high moisture content and in the pulverized or loftse 

 series with low moisture content. The length of the roots in general was but 

 little affected by the degree of soil compactness. It was found, however, that 

 the roots were longer in the dry and pulverized series of the clay soil than in 

 the dry and compacted series. The area of root surface produced was found 

 to be largest in the loose or untamped soil, but the highest absolute weight of 

 root substance was obtained in the pots in which the soil had been tamped. 

 With both clay and sand the compacted series yielded in every case the largest 

 quantity of substance above ground. This result is regarded as due to the 

 greater capillarity of the compacted soil and to the greater area of root surface 

 in contact with soil particles under this condition. The conclusion is drawn 

 that a compact soil adequately provided with moisture and containing sufficient 

 plant food in readily available form favors the development of the parts of the 

 plant above ground during the earlier stages of growth to a greater degree 

 than does a loose soil. In general a unit weight of root substance in the com- 

 pacted soil yielded a larger quantity of substance above ground than the same 

 unit weight in the loose soil. The low moisture series yielded less substance 

 above ground than under ground in the clay soil and slightly more in the sandy 



