Studies on the Effects of Soil Physical Conditions on the Growth and Yield of Crop Plants : II. Effects of the bulk density and moisture content of soil on the growth and yield of crop plants.

Abstract

Using upland rice, soybean, sweet potato, soiling corn and cucumber as specimens, the authors studied the effects of the soils of different bulk densities and moisture contents (in this experiment, brown-colored volcanic ash soil was used) would have on the growth and yield of crop plants. The result was that the effects of the varying soil physical conditions due to the difference in its bulk density and moisture content were different depending on the kind of the crop plants used. But in all the kinds, conditions were largely influenced by the magnitude of the soil air capacity. In fact, the yield was lowered when the capacity in question was extremely small (or when the soil bulk density or moisture content was relatively high). In this case, the rate of decrease in the yield differed according to the kind of crop plants-the rate was high in the case of sweet potato plants (weight of tuberous roots), cucumber plants (number of fruits) and soybean plants (weight of grains), and was relatively low in the case of upland rice (weight of grains) and soiling corn (weight of parts protruding above the ground). In the authors' experiment, the yield of crop plants increased with the rise of the soil air capacity. When this capacity rose beyond a certain level, however, the moisture content of the soil decreased correspondingly, and as a result, the yield was lowered. This phenomenon was especially evident in the case of upland rice, and was least noticeable in soiling corn. Thus, the soil air capacity favorably affecting the yield of crop plants differed according to their kinds. The influence of the soil air capacity at various levels on the total weight of crop plants was, generally speaking, similar to such influence on their yield. In the case of sweet potato plants, however, the soil air capacity required for the growth of their upper parts was different from that required for the growth of their tuberous roots. That is to say, the soil air capacity, when decreased, had less unfavorable effects on the growth of the upper parts than on the growth of the tuberous roots. This goes to show that the effects of diffects of different soil air capacities differ from one part of the crop plant to another.