In low-latitude regions (generally referring to areas between 30°N and 30°S), a type of brick-red soil is widely distributed. Southern China, including Guangdong, Guangxi, and Yunnan, is the main red soil region in China, while red soils are also found in southern Sichuan, southern Guizhou, and central and northern Hainan. So why is the soil there red? The subtropical climate with high temperatures and abundant rainfall, and pronounced seasonal changes between wet and dry periods, is an important condition and factor for the formation of red soils. Like all other soils, red soils are formed through the long-term weathering of rocks. Under the high-temperature and rainy climate of southern China, silicate minerals in the soil are decomposed and destroyed, and silicon, alkali metals, and alkaline earth metals are continuously released and lost with rainwater. Elements like iron, manganese, and aluminum often move in a hydrated oxidized state. However, when these hydrated oxides move, they dehydrate upon encountering drought and become fixed as red iron oxide and brown manganese and aluminum oxides. Due to the high content of iron oxide in the soil, red hues predominate. However, under the influence of other elements, the red color may also contain a slight gray tint, resulting in a brick-red hue. Interestingly, yellow soils also contain high iron levels, but under conditions with pronounced wet and dry seasons, red soils form, while under less distinct seasonal conditions, yellow soils develop.
Red soils are highly acidic, have low mineral nutrient content, poor fertilizer retention, and are prone to compaction. They are also susceptible to aluminum and manganese toxicity, making them generally unsuitable for directly growing food crops. However, people can appropriately modify red soils to meet farming needs, such as adding organic fertilizers to improve soil pH or using chemical reactions and spreading lime to increase alkaline elements and organic matter in the soil. Another effective method of utilizing red soils is planting crops or economic trees that are naturally adapted to acidic soils, such as tea trees and citrus, which have been widely cultivated in southern red soil regions. Not only do they generate direct economic benefits, but in some places, they have also become tourist attractions and cultural landmarks.