We made a trial production of a simple form of driving typed soil penetrometer suitable for the investigations of the agricultural machines-soils relation. The view of the apparatus is shown in Fig. 1. It has so simple structure that it is very handy and portable, and the measuring values are accurate and reliable respectively.
The dropping height H and the weight W are adjusted in accordance with the soil conditions so that the applicable range for the various soil conditions are enlarged remarkably. Then, we had many experiments in laboratory to verify the characteristics of the apparatus when it had various combinations of H and W, and tried also some measurements of soil hardness in actual fields. The results are as following:
D=kD0, k=W0⋅H0/W⋅H
Where, D0=standard driving index number at H=300mm and W=250g, D=driving index number at H and W, k=const.
5 times D0 is nearly equal with the soil hardness (kg) by Kanto- Tozan type soil penetrometer.
