Soil is made fertile in Andhra Pradesh by alluvium deposition, whereby fine soil particles collect in riverbeds as currents gradually slow, losing their ability to carry larger particles. These fine particles collect in river deltas in the eastern coastal plains -- Mahanadi River, Godavari River, Krishna River and Kaveri River -- where they are used to farm crops. Alluvial soils consist of optimal ratios of silt, sand and clay and carry potash, lime and phosphoric acid. According to the journal "Agricultural Water Management," alluvial soil covers 40 percent of India's total land mass
Like the prairie soil found in the United States, black soil contains a high concentration of calcium and magnesium carbonates and is relatively abundant in iron, lime magnesia and alumina. However, black soils are poor in phosphorous and nitrogen and contain little organic matter. Black soil is dark and fine-grained.
Red soils are composed of weathered crystalline and metamorphic rock and get their color from a high diffusion of iron. Red soils are poor in nitrogen, phosphorous and humus; they are poorer still in lime, potash, iron oxide and phosphorous. Red soils are often found in Southern India beside yellow soil high in ferric oxide, from which it gets its color.
Lateritic soils consist primarily of hydrated oxides of aluminum and iron formed during humid monsoon season, when siliceous (silica) rock matter is weathered from its source. Like red soils, lateritic soils appear red. Lateritic soils are typically more acidic than soils used for farming.
