First of all, it is necessary for us to correctly understand the concept of soil fertility. Soil fertility is the ability of soil to meet and adjust the living conditions such as water, nutrients, air and heat required for plant growth and development. This shows that soil fertility is a comprehensive concept of soil aeration, water permeability, water retention, mineral content, humus content, pH value and many other factors, rather than any one or several of them. \x0d\ In soil science, "glutinous rice and yellow mud" is not yellow soil, but red soil in mountainous areas. Because it is rich in iron ions, the soil color is red and the soil PH value is acidic. This kind of soil is low in humus content, sticky, easy to harden and impermeable to water and air. Therefore, according to its physical and chemical characteristics, it is not difficult to see that for most flowers and trees, "glutinous rice and yellow mud" is not fertile and is not worthy of preference. It can be seen that in the process of greening planting, the practice of "catching up with the trend" is very blind. \x0d\ Of course, this habit has its roots. Urban greening has learned from and inherited some experiences of forestry afforestation in technology. Pine trees are widely used for afforestation. Pine trees have a characteristic that their roots can form mycorrhiza with fungi in the soil in the form of * * * *. Mycorrhiza expands the ability of root system to absorb and transfer nutrients. In the process of transplanting pine trees, mycorrhizal fungi, that is, exotic soil, are usually inoculated, that is, the soil of old forest land is selected and moved to the planting hole, and mycorrhiza is quickly formed after inoculation to improve the survival rate of afforestation. The soil exchanged by the guests is mountain red soil. Therefore, for barren pine trees, "glutinous rice and yellow mud" is of course the best choice. Perhaps this is the cause and effect of people's preference for "glutinous rice and yellow mud". Secondly, we should also recognize the relative meaning of soil fertility. Each plant has its own biological characteristics and needs certain ecological and environmental conditions to grow and develop normally. Therefore, plants also need certain soil ecological conditions. Therefore, whether a soil is fertile or not can only be meaningful to specific plants in theory. Therefore, it is really not advisable to treat "glutinous rice and yellow mud" as "universal soil" to deal with practical problems. \x0d\ So, what kind of soil is suitable for planting? I think loam rich in humus is ideal. For example: fluvo-aquic soil, alluvial soil, forest topsoil, cultivated soil (farmland soil, vegetable soil), etc. The soil conditions of urban greening sites are generally complex, and the soil that is completely suitable for flowers and trees is rare. Soil replacement is an indispensable link in greening and planting construction. \x0d\\x0d\ The concept of soil \x0d\\x0d\ What is soil? This is a complicated problem. We already know that soil is closely related to everyone, but it is not easy to really define the concept of soil. There are different concepts of soil in soil science in history. This is because people have different starting points to study soil and different angles to summarize the concept of soil, so they have different concepts of soil. \ x0d \ x0d \ Chinese working people had a simple understanding of soil thousands of years ago. 12 1 years ago, it was recorded in China's ancient book "Shuo Wen Jie Zi": "Everything is born when the earth spits." "Soil, soft soil, no soil." . In ancient times, soil spit together, and the soil was like the moon, and the moon was like fat, that is, fertile soil was called soil. \ x0d \ x0d \ Geologists understand soil from the geological point of view of rock weathering and think that soil is a broken old rock. Or think that soil is the surface weathering layer of solid crust. Understand soil only as the transformation of rocks. \x0d\\x0d\ Plant nutritionists believe that soil is the repository of plant nutrients. People think that soil is the part of the earth's crust where plants can grow. Or the soil is just the natural medium for the growth of land plants. \ x0d \ x0d \ 65438+Kukayev, a Russian scholar and founder of the school of soil genetics in 1970s and 1980s, regarded soil as an independent natural body, which was regarded as five great achievements. This is to understand soil from the viewpoint of soil genesis, which has been widely recognized in soil science. \x0d\\x0d\ The definition of soil in modern America and Western Europe is reflected in some representative works, such as the view of American scholar N.C.Brady: "Different mixtures containing weathered and broken minerals and decomposed organic matter form an aggregate of natural bodies in profile, and the land is covered with a thin layer of material, which can provide mechanical support and nutrition for plants when it contains appropriate air and moisture." The American definition of soil terms is: (1) The surface is a dynamic natural body composed of minerals, organic matter and organisms that can grow plants. ⑵ The collection of natural bodies occupying a part of the earth's surface can support plants, and it has the characteristics of being influenced by certain topography, climate and biology through the comprehensive action on parent materials in different periods. Or it can be seen that they attach great importance to linking soil with other natural factors, emphasizing that soil can grow plants and produce their fundamental characteristics. \x0d\\x0d\ The definition of soil published by the National Committee for the Examination and Approval of Scientific and Technical Terminology 1998 is that soil is an unconsolidated layer on the land surface, which is composed of minerals, organic matter, water, air and organisms, and has fertility and can grow plants. \ x0d \ x0d \ forest soil: it is the soil developed under the condition of forest vegetation, which is the basis of developing forestry production, and has its particularity compared with other soils. There will be a chapter devoted to forest soil later. \ x0d \ x0d \ Composition of soil \ x0d \ x0d \ Soil consists of solid, liquid and gas. The solid part includes mineral soil particles and soil organic matter, as well as microorganisms and animals living in the soil. Soil minerals account for more than 95% of the solid part, and the mass percentage of organic matter is generally less than 5%. Organic matter is usually wrapped around mineral soil particles. The solid part contains all kinds of nutrients needed by plants, forming a skeleton to support plants. Soil liquid and gas coexist in soil pores. Soil liquid is soil moisture, which is actually a thin soil solution because it dissolves many nutrients. Gas is soil air. The volume ratio of three-phase substances in soil varies with different environmental conditions. Generally speaking, soil solids account for 50%; Liquid and gas account for 50% respectively, and gas and liquid are unstable, and the gas ratio is 15% ~ 35%. \x0d\\x0d\ The concept of soil fertility \x0d\\x0d\ The most basic characteristic of soil is that it has soil fertility. Regarding the concept of fertility, different scholars and different times have different interpretations of soil fertility: \ x0d \ x0d \ In 1930s, the Soviet soil scientist Williams thought: "Soil fertility is the ability of soil to provide maximum effective nutrients and water for plants at the same time and continuously throughout their life". This ability is not available in other natural bodies. But now it seems that Williams' theory is not comprehensive and complete. The reason is that there are many factors affecting plant growth, not only water and nutrients, but also temperature and ventilation. \ x0d \ x0d \ Shenyang agricultural soil: Soil fertility is a concrete manifestation of the comprehensive characteristics of various factors. \ x0d \ x0d \ Nanjing Soil Research Institute: Soil fertility is the ability of soil to supply plants and coordinate nutrition and environmental conditions. \ x0d \ x0d \ Mr. Hou Guangjiong: Soil fertility is the composition and life of soil. \x0d\\x0d\ At present, the accepted concept of soil fertility in China is that the soil can supply and coordinate the nutrients needed by the normal growth and development of plants and the ability of water, gas and heat. \ x0d \ x0d \ Soil fertility can be divided into natural fertility and artificial fertility. \ x0d \ x0d \ 1。 Natural fertility is soil fertility formed by natural factors, such as forest soil and grassland soil. The level of natural fertility depends on the interaction of soil-forming factors, especially the role of biology. The vast forest areas in China mainly make full use of the natural fertility of soil to realize the fast growth and high yield of trees. \x0d\\x0d\2。 Artificial fertility is soil fertility formed by human factors such as farming, fertilization, irrigation and soil improvement. The level of artificial fertility is influenced by many factors. Developed soils such as cultivated soil and orchard soil have both natural fertility and artificial fertility, and the relationship between them is based on natural fertility and dominated by artificial fertility. The level of social science and technology directly affects the level of soil fertility. \x0d\\x0d\3。 Economic fertility, due to the limitation of environmental conditions and management level, soil fertility is often only partially manifested. This part of fertility is called "effective fertility", also known as "economic fertility", that is, the part that reflects the soil productivity under certain agricultural technical measures, also known as the sum of natural fertility and artificial fertility. In forestry production, the soil with economic fertility is mainly nursery land, mother tree woodland, seed orchard, economic forest orchard and soil that must be improved to form forest. Especially the soil of nursery, seed orchard and economic forest orchard, although its area is limited, it plays a huge role in the process of expanding the planting area in the national economy. \ x0d \ x0d \ 4。 Potential fertility, and the other part of fertility is not directly expressed as "potential fertility", which means that it cannot be used by plants due to environmental conditions and scientific and technological level, but can be transformed into effective fertility under certain production conditions. \x0d\\x0d\ Section 4 The role of soil in ecosystem and its relationship with forestry production \ x0d \ x0d \ 1. The role of soil in the ecosystem \ x0d \ x0d \ Soil is an important environmental factor and the interface between living and abiotic environments, whether in the global ecosystem, or in the small-scale forest ecosystem and farmland ecosystem. Many human impacts on the ecosystem are realized directly or indirectly through soil. Some of these influences are beneficial to human production and life. For example, the desert has become an oasis through comprehensive management; Through drainage and salt washing, planting green manure and applying organic fertilizer, the barren saline-alkali beach was altered to become a fertile field. However, some activities, such as deforestation, steep slope land reclamation, overgrazing and so on. , making soil erosion, floods and droughts frequent. It can be seen that human production measures should not only focus on short-term economic benefits, but also consider its long-term impact on the ecosystem. Soil is one of the important components of ecosystem. The development and utilization of soil can not destroy the ecological balance and natural environment, but should be conducive to maintaining and establishing a good ecological system and natural environment. According to the characteristics of soil and other natural factors, adapting measures to local conditions will not only help to develop production and improve economic benefits, but also prevent the imbalance of ecosystem and the destruction of unique environment. \ x0d \ x0d \ It is worth noting that the plant yield (biological yield) produced by soil is the result of the interaction between soil and environmental conditions. Because in addition to soil, factors such as atmosphere, temperature, precipitation, sunshine and pollution will also affect the growth and development of plants to varying degrees. In addition, even under the same environmental conditions, different plants have different abilities to absorb and utilize the conditions provided by soil. Soil with the same fertility can show two different effective fertility levels. For plants that are ecologically suitable for a certain soil, the effective fertility is high, while for plants that are not suitable, the effective fertility is low. For example, calcareous soil can make Platycladus orientalis grow well, but it will grow poorly if pine trees are planted. This is the ecological relativity of soil fertility. For another example, in some wet or even waterlogged peat swamp soil, alder grows well, but other tree species do not grow well. Therefore, only by combining the ecological requirements of tree species with the ecology of soil can we make full use of soil fertility, which is emphasized in production practice. \ x0d \ x0d \ In China's afforestation work, trees sometimes grow poorly or die because of improper tree species selection. The reason is not that there is no matter and energy in the soil or that it is absorbed by trees, but that there is no matter and energy necessary for this tree species in the soil. Therefore, when selecting tree species for afforestation, soil factor is one of the most important factors, and sometimes even the decisive factor.