(a) Soil erosion caused by running water can be controlled by following methods : (i) By planting trees. (ii) Terrace farming. (b) Alluvial soil of the northern plains are coarse in texture and light in colour whereas the alluvial soil on the coastal plains are dark and fine in texture. (c) Three characteristics of black soil which make the soil fertile are : (i) It is rich in iron, potash, lime, calcium, alumina, magnesium, carbonates and humus. (ii) It is moisture retentive. (iii) It is fine grained in texture. (d) Geographical reasons: (i) Laterite soil is not suitable for cultivation because it is acidic in nature and does not retain moisture. (ii) Red soil is red in colour because it is rich in iron. (iii) Khadar soil is preferred to Bangar because it is more fertile as it is replished every year by floods.