Correct option (a) excessive use of fertilisers
Explanation :
Unfavourable reiteration of soil by addition or removal of substances and factors which decrease soil productivity, quality of plants and ground water is called soil pollution. It is of two main types : negative and positive. Negative soil pollution includes over use of soil and erosion.
Positive pollution is a pollution caused by (i) pesticides, herbicides and fumigants (ii) chemical fertilizers and (iii) air pollutants washed down from atmosphere through rain. Excessive use of chemical fertilisers causes soil deterioration through the decrease in natural bacterial population and destruction of crumb structure. The salt content of the soil is also bound to increase with continuous use of fertilisers. Addition of industrial wastes come under positive pollution.
