Why the south land is red?

It’s well known to us that the foothills in south of the Yangtze River of China distribute with numerous red land. Why the south land is red? Do they contain the compositions such as ferrous sulfate heptahydrate in the soil?

South climate always keep on high temperature and plenty of rainfall thus less organic matter in soil, strong acid and sticky. The primary reason of showing red is that iron, aluminum are oxided in the soil. It’s especially suitable for planting acid plants, such as tea plant, camellia, fir, etc. If the soil need to be adjusted PH value, just increase organic fertilizer and supply slaked lime in it.

In saline-alkali land of the north as Shandong area, on the other hand, ferrous sulfate not only can solve iron deficiency symptoms but also adjust soil PH value.