According to vastu shastra, soil testing is a very important part of planning. Through soil testing, it is possible to know the constitution of a land in-depth. Nowadays more importance is given to whether or not a particular plot can support the weight of the proposed structure. But according to vastu shastra, the outer as well as inner characteristics of soil should be taken into account. The soil should be soft, fragrant and delicious according to the aacharyas.
During sunrise, dig a hole without throwing the dug earth too far away. The hole should be a cubical hole of 1 cubit (muzham) side length. Next day, during sunrise, fill the hole with the dug earth. If after filling the hole, there is still some soil left, then the land is fit for housing. If the dug earth does not suffice to fill the hole, then the land is deemed unfit for occupation.
In another method, dig a hole like in the previous technique. Fill this hole with water. If by sunrise the next day, water remains in this hole, then the land is auspicious for constructions. If the hole becomes dry and parched, not only is the land unsuited for housing, but the occupants will face frequent conflicts and illnesses.
Moving on to another procedure, a hole is dug and filled with water, similar to the previous technique. After this, move a hundred feet away from the hole, come back and inspect the water. If only less than one-fourth of the water remains, then the plot should not be used for construction works. The more water there is left, the better the land.
All these practices will also help determine the land characteristics. In an age where natural calamities including earthquakes are becoming common, one should not purchase land without proper testing and analysis. Even though the above mentioned techniques are great DIYs, it is always better to consult a vastu expert on this.