In which regions of China are yellow-brown soils distributed, and what crops are suitable for growing there?
In which regions of China are yellow-brown soils distributed? What are they suitable for growing? To understand these two questions, we first need to clarify what yellow-brown soil is.
Yellow-brown soil is a soil developed under subtropical evergreen broad-leaved and deciduous broad-leaved mixed forests. Its main characteristics are that the profile contains a brown or red-brown B horizon, that is, an argillic horizon with a relatively high clay content, and the soil body contains iron-manganese nodules. Chinese soil science literature once called yellow-brown soil gray-brown clay-pan soil, and after the 1950s it was given its current name. For similar soils, the Soviet Union called them yellow-brown forest soils, Japan named them yellow-brown soils, and the Food and Agriculture Organization of the United Nations and UNESCO named them luvisols.
The distribution regions of yellow-brown soil in China
The distribution range of yellow-brown soil in China is roughly as follows: it starts in the north from the Qinling Mountains and the Huai River, reaches south to the Daba Mountains and the Yangtze River, extends west from the southeastern edge of the Qinghai-Tibet Plateau, and reaches east to the lower reaches of the Yangtze River. Yellow-brown soil is distributed on the northern margin of the subtropics, where summers are hot and have subtropical characteristics; winters are cold and have warm temperate characteristics, with an annual average temperature of 15-18°C, an accumulated temperature above 10°C of 4500-5300°C, and a frost-free period of 210-250 days. The annual precipitation is 750-1000 mm, and in mountainous areas it is greater than 1000 mm. The zonal vegetation is deciduous broad-leaved forest, but evergreen broad-leaved tree species are also mixed in. The soil-forming parent material is mostly weathered granite, gneiss, phyllite and sandstone-shale.
From specific regions, yellow-brown soil is mainly distributed in the Shandong Peninsula and Liaodong Peninsula, and it also occurs in the vertical belt of the cinnamon soil zone. The climate conditions of the yellow-brown soil region are characterized by warm, hot and rainy summers and cold, dry winters, with an annual average temperature of 5-14°C, an accumulated temperature above 10°C of 3400-4500°C, a seasonal frozen layer reaching as deep as 50-100 cm, annual precipitation of about 500-1000 cm, and an aridity index between 0.5 and 1.0. The original forest here was long ago destroyed, and at present it is mostly secondary coniferous forest and broad-leaved mixed forest.
The terrain where yellow-brown soil occurs is mainly low hills and mountains, and the soil-forming parent material is mostly residual slope deposits of granite, gneiss and sandstone-shale, or thick proluvial deposits. In the brown soil region, because summer temperatures are high and rainfall is abundant, not only is the argillization in the soil strong, but relatively obvious leaching also occurs, causing easily soluble salts and free calcium carbonate to be leached away, and clay particles also move downward along the profile and become deposited. Because the ash content of deciduous broad-leaved forest litter is high, this prevents the development of soil podzolization, but bleached horizon formation often occurs and can be seen in both hills and mountains.
What yellow-brown soil is suitable for growing
The yellow-brown soil region has superior water and heat conditions and relatively high natural fertility. It is very suitable for the growth of many kinds of forest trees, is a concentrated production area of China's economic forests, and is also an important agricultural region, rich in many kinds of grain and cash crops.
Mountain yellow-brown soil should be restored and developed to suit local economic forestry production. When introducing economic forest trees, attention should be paid to its characteristic of being distributed in the north-south transitional zone, and afforestation should be carried out according to soil conditions and specific circumstances. In places with shallow soil layers, it is advisable to plant drought-tolerant and barren-tolerant Masson pine, black locust, poplar, etc. In places with deep soil layers and good fertility, oak species, Chinese fir, and economic forest trees such as oil tea, tung tree, lacquer tree, bamboo tea, and mulberry can be vigorously developed. In places with poor drainage, the Chinese tallow tree, which has relatively high economic value as an oil crop, can be planted.
On mountain slopes with relatively steep gradients, combined with past excessive logging and unreasonable reclamation, serious soil erosion has been caused, greatly reducing soil fertility in some areas, especially in the Dabie Mountains. Therefore, soil and water conservation work should be vigorously strengthened. First, small watershed planning should be done well. In those places where soil is exposed and gullies are numerous, fast-growing tree species with well-developed lateral roots should be selected to establish slope-protection forests (such as Masson pine and black locust) and gully-bottom erosion-control forests (such as Chinese tallow tree). For tea, mulberry and orchards on sloping land, methods such as contour planting and terrace construction should be adopted, combined with green manure cover, which can both prevent soil erosion and achieve a double harvest of forestry and animal husbandry.
For the clay-pan yellow-brown soil distributed over large areas in hill and mound positions, because its texture is heavy and its water-physical properties are poor, such as high bulk density, low porosity, water stagnation in the rainy season, and poor water retention and supply capacity in the dry season, it is a major obstacle to agricultural and forestry use. Generally, measures such as gradually deepening the plow layer, heavily applying organic fertilizer, and increasing phosphate fertilizer are adopted to gradually mature the soil, or coal cinder, stove ash, and the use of fallow-season soil heating and soil smoking are applied, thereby improving the soil's aeration and water permeability and its tillage performance.