1. Soil latentization (1) Process, necessary conditions and formation stages of soil latentization 1) Soil latentization process Agriculturally speaking, it is a complex soil formation consisting of biochemical and chemical processes that are interconnected and influence each other.

process; from the perspective of agricultural geology, it is an agricultural geochemical soil formation process.

In short, it makes the soil latent and becomes latent soil.

2) The necessary conditions for soil cultivation are sufficient water and rich organic matter.

3) The formation process can be roughly divided into four stages.

First, the anaerobic decomposition of the easily decomposed part of organic matter under flooded conditions consumes a large amount of oxygen in the soil. The redox potential drops sharply, forming strong reducing conditions in the soil, producing organic and inorganic reducing substances and a series of intermediate products; secondly, the intermediate products (

Including acids, low molecular weight carbohydrates, sulfides and phenolic compounds, etc.) affect the dissolution and activation of iron and manganese minerals in the soil, and can also form water-soluble combinations with iron and manganese to generate organic and inorganic reducing substances, such as

CH4, H2S, H2 and NH4, etc., and reduce iron oxide, manganese oxide, etc. to form different forms of ferrous iron, manganese, etc.; thirdly, while iron and manganese are activated, there is dissolution and migration of SiO2, Al2O3, and there are

Changes in basic ions such as Ca, Mg and K will eventually lead to changes in clay particles and possible alteration of clay minerals, which will worsen the soil texture and even make the soil heavy and reduce permeability.

The above four stages make the soil become latent soil, and there are five main changes to the soil: First, the bluish-gray color displayed by ferrous iron and manganese becomes the typical color of latent soil, which is the so-called "latent color"

; The second is that some trace elements are activated and increase the soluble state; the third is that toxic gases and compounds are produced; the fourth is that the changes in clay particles and base ions increase the viscosity of the soil and the permeability becomes worse; the fifth is that it changes

Soil structure.

(2) Characteristics of latent soil and its relationship with groundwater levels. The understanding of the characteristics of latent soil and its impact on agricultural production has been concluded in the agricultural field. Therefore, we only quote the previous work in the Dongting Lake area.

research material.

Predecessors have systematically studied the soil potential of Dongting Lake Yueyang Junshan Farm, Huarong Xinhe Township and Honghu Xiaogang in Jianghan area. The relevant characteristic indicators are listed in Tables 4-17 and 4-18, according to information from the Hunan Academy of Agricultural Sciences

, the yield of latent cultivation rice fields in Dongting Lake area is 7024kg/hm2, and the yield of retention rice fields is 8524~10024kg/hm2.

Therefore, the number of submerged rice fields decreased by 17% to 30%.

Table 4-17 Nutrients of latent soil and retention (delatency) soil There are two points in latent soil that need to be pointed out in particular: First, the active manganese and organic matter are higher than those of retention soil, and only the available P is lower.

Therefore, from the perspective of nutrient composition, latent soil is no worse than retention soil, so the reason for its yield reduction is not nutrient factors, but may be mainly due to the deterioration of soil texture and the increase of toxic reducing substances; the second is the degree of latent soil, redox

The electrical potential and active reducing species increase as the water table rises.

Therefore, the degree of potential incubation is closely related to the groundwater level.

This is clearly reflected in the changes in groundwater level and soil structure (Figure 4-4; Photos 4-8, 4-9).

Table 4-18 Characteristics of pointers for latent and fertile (depotted) soil Figure 4-4 Relationship between groundwater level and soil structure in the Dongting Lake-Jianghan area A—cultivation layer; P—plough bottom layer; W—cultivation

layer; G - latent layer (the dotted line between the sections is the groundwater level) (3) The development trend of soil latent soil erosion after the opening of the Three Gorges Reservoir is relatively serious in the Dongting Lake area.

According to the second soil census in 1970, there were 181,800 hm2 of latent rice field soil in the Dongting Lake area, accounting for 36.8% of the province's latent rice field soil area.

Among them, Changde City has 80,000 hm2, Yueyang City has 52,800 hm2, and Yiyang City has 49,000 hm2. Since the 1980s, the Yangtze River Commission has carried out a series of studies on the construction of the Three Gorges Project. Among them, Cai Shuming [4] published a monograph in 1997 on the Dongting Lake and River Network.

For the latent soil in the plain area, a wetland distribution map was created by superimposing the soil type map and land use map on the 1989 Landsat-Tin false color composite photo (scale 1:250,000); then through analysis, and in typical areas

Conduct on-site investigation and verification, and classify the soil into swamp soil, potential paddy soil, retention paddy soil, and infiltration paddy soil according to soil moisture conditions and wetland characteristics. Calculated based on the area, the potential paddy soil is 20.94

million hectares, an increase of nearly 30,000 hectares compared with the second soil census.

The argument before the opening of the Three Gorges Reservoir has been mentioned before. It is believed that the water level of Dongting Lake will rise, and the groundwater level will also rise. Therefore, the potential paddy soil will increase to 426,000 hectares.

In fact, after the opening of the Three Gorges Reservoir, the water level and groundwater level in the Dongting Lake area dropped significantly during the dry season, which will be very conducive to the de-potentialization of soil, so the amount of latent soil will be reduced.

However, after the opening of the Three Gorges Reservoir, the sedimentation rate of Dongting Lake was lower than the tectonic subsidence rate and it evolved in the direction of expansion. Since Dongting Lake has been surrounded by levees and cannot expand, only by increasing the water depth or raising the water level will it naturally expand.

This will cause the groundwater level to rise, which in turn will aggravate the degree of soil erosion.