The correct answer is option 2 - 2 and 3 only.

Option 1: Low per capita income - This is not responsible for the decrease of per capita holding of cultivated land. The income level of individuals does not directly affect the availability of land for cultivation.

Option 2: Rapid rate of increase of population - This is one of the factors responsible for the decrease in per capita holding of cultivated land in India. As the population increases, the amount of available land per person decreases, leading to smaller land holdings.

Option 3: Practice of dividing land equally among the heirs - This is another factor responsible for the decrease in per capita holding of cultivated land. In India, it is common for land to be divided equally among heirs, leading to fragmentation of land holdings over time.

Option 4: Use of traditional techniques of ploughing - This is not directly responsible for the decrease in per capita holding of cultivated land. The techniques used for ploughing do not necessarily affect the amount of land available for cultivation.

Therefore, options 2 and 3, which are the rapid rate of increase of population and the practice of dividing land equally among the heirs, are responsible for the decrease in per capita holding of cultivated land in India.