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Soil Moisture Regime
Soil Moisture Regime (SMR)：According to the groundwater level and water control strata in each period of the year the water determination with or without < 15*105 surface tension. It can be assumed that soil moisture can sustain the growth of plant that can survive. In other words, exclude artificial irrigation to increase the water content of plant, but as depend on the soil itself of water status of crops, forages or natural vegetation's moisture level. The processes of soil and water degradation, leading to desertification, are strongly linked to unfavorable changes in the hydrological processes responsible for the soil water balance and for the soil moisture regime.

Descriptions
Soil moisture status is used to classify soil criterion because they affect the origin (formation), use and management of soils, and can be used to classify soils with similar properties and morphology.

The soil moisture regime classes are :


 * 1) Aridic (or     torric) : Arid climate, generally dull, need artificial watering. This     condition usually will keep 3 months.
 * 2) Udic:      Humid or subhumid climate, usually moist, usually not required irrigation     for crop production. SMC drying time < 3 months and continuous drying     time in summer < 45 days.
 * 3) Ustic:     Semiarid climate, usually keep raining for 3 months,
 * 4) Aquic (or     Perudic):  Saturated with water to cause oxygen depletion, not used     as a standard to measure others.Ustic
 * 5) Xeric:      Special Mediterranean climate region (pleasantly     cool in spring, arid during summer, damp in winter ) It is unsuitable for 1/2 to 3/4 time of high     temperature or equal strength SMCS humidity. It is wet in winter > 45     consecutive days, dry in summer > 45 consecutive days.  Perudic: The amount of precipitation is greater than the amount of evaporate, soil keep unsaturated for a long period. [3]

Temperature, air, sunshine, water and soil are the main factors which can determining the yield of crop. For many reasons, it is a hard issue for human to control. Among them, soil and water are the most important factors can affect crop’s growth. In a sense, the success of the farming system depends on the scientific management of water because water in the soil play an important role that must be able to effectively supplement. The evaporation of water and the water’s consumed by crop transpiration throughout the growing season. The water contain in the soil has all kinds of nutrients needed for crop’s growth, will have a great impact on soil permeability and temperature change. For crops if want to achieve high yields, soil moisture regime have to get a high level.

Water is the primary component of plants. In general, moisture content reached 60%-80% of a plant. Those water evaporate through crop’s leaver to the around environment, this process will consume a huge amount of moisture content of the plant, the consumption of this behavior called transpiration.

Soil humidity grow, thus dry matter accumulate, leaves area increase. Soil moisture for crops also has effect on the physiological characteristics, when soil humidity minor, because of the stomatal closure, stomatal resistance will get bigger. When soil humidity increase, the pore will open, there is a sharp drop of the resistance. Soil humidity to a unique degree, pore will completely open, the resistance will be fixed on a specific value.

Assessment of SMR
In many cases, the assessment of degraded soil quality mostly adopts subjective views and soil quality index, which are scored on the basis of empirical judgments. Often, the scope is narrow and there are classification deviations. It is not allowed to link the assessment with the overall sustainability of alternative land use systems (production, environmental control). Influences, etc.

Only define hydrology theory, measure or reckon hydrology data under clear and definite condition can solve the question.

== Soil Water == Water supply through soil is essential for plants and soil organisms that need water to survive. Soil water contains nutrients that enter the roots of plants when they absorb water. Water enters the soil through macropore (macropore) and is stored in many micropore (micropore). Porous soil has a balance between macropore and micro pore.

=== Specific terms === In order to understand the water content in soil, the following terms are important:

Field water holding capacity:                    Water content in soil after complete wetting and stop of free drainage. Water above this limit will saturate the soil, but water will quickly run off or run off

with runoff.

Permanent Wilting Point:                         The condition of soil moisture in which plants cannot obtain water and die of wilting. Crops can't be restored by artificial watering or raining.

Plant Available Water Capacity (PAWC) : The amount of water between field capacity and plant available permanent wilting point. This requires careful management and depends on the texture, structure and organic matter in the soil.

Soil Moisture Control Section
Purpose of defining the soil moisture control part is to facilitate the estimation of soil moisture status based on climate data. When the top margin of the center is 2.5cm depth of wet-dry soil (tension greater than 1500 kpa, but not air-dried) in twenty-four  hours. The border-bottom refers to the depth at when the arid soil will be moisten by 7.5 cm of water in forty-eight hours. the moisten depth toward to the cave do not belong to the depth.

If 7.5 cm of water wets the soil to a dense, lithic, paralithic or iron interface, or a calcareous or gypsum or hard clay layer, the interface or top margin of the bonding layer constitutes the border-bottom of the SMR part. If the soil is wetted by 2.5 cm of water to one of the contact points or the horizontal plane, the soil moisture control part is the margin or the contact point itself. If there is a thin water film on the interface or upper boundary of the cementation layer, the part of control soil will be considered to be wet. If the top margin is dry, control section is considered dry.

If the soil particle size is fine loam, coarse silt, fine silt or clayey soil, the water control part of the soil extends from 10 cm below the soil surface to 30 cm; (2) if the particle size is coarse loam, it extends from 20 cm to 60 cm; (3) when the infinitesimal size of sand, it will extend from 30 cm to 90 cm. When soil embody rock and debris fragments that do not set free and soak up water, the boundary of the water control part is deeper. The boundary of soil water control area is not only affected by particle size, but also by the difference of soil structure between pore distribution and other factors influence the movement and maintenance of soil water.

== How to calculate moisture value == 1. Drying method: Drying method is the most common and standard method for determining soil moisture. Specifically: get a certain amount of soil from the field, and then put it in the oven at 105 C, waiting for drying. Among them, the standard of drying is that the weighing is constant before and after two times. The loss of moisture after drying is the soil moisture content. The formula is soil moisture = W/M*100%, M is the weight of soil before drying, W is the weight of soil moisture, that is, the difference between M and the weight of soil after drying.

2. Resistance method: Resistance method uses the resistance of gypsum, nylon, glass fiber and so on, which is related to their moisture content. When these intermediates are placed in moist soil with electrodes, the water content of these materials reaches equilibrium after a period of time. Because of the relationship between resistance and moisture content, we previously calibrated the corresponding relationship between resistance and percentage. Then we can get the moisture readings in the range of 1-15 atmospheric pressure suction through these components.

3. Neutron scattering method: Neutron scattering method is suitable for measuring soil moisture in the field. It is based on the principle that hydrogen sharply reduces the speed of fast neutrons and scatters them away. Now there are neutron moisture meters on the market for measuring soil moisture. Neutron moisture meter has many advantages, but it has considerable limitations on organic soil, and it is not suitable for the determination of 0-15 cm soil moisture content.

4. Gamma-ray method: Similar to neutron meter, gamma-ray transmission method uses 137Cs radiation source to emit gamma-ray, and uses probe to receive the energy of gamma-ray passing through soil, which is converted to soil moisture content.

5. Time Domain Reflectometry (TDR): TDR is a soil moisture measurement method developed in the 1980s. It is a time domain reflectometer in Chinese. This method is widely used in foreign countries. It has just been introduced in China. Every Department attaches great importance to it. TDR is a radar-like system with strong independence, and its results are basically independent of soil type, density and temperature. What's more, TDR can measure soil moisture under freezing conditions, which is incomparable with other methods. In addition, TDR can simultaneously monitor soil water and salt content, and the results of two measurements are almost the same. The accuracy of this method is evident.

== What effect SMR ==


 * 1) Growth Parameters and Phenology
 * 2) Biomass and Seed Production
 * 3) Biochemical Attributes
 * 4) Photosynthetic Parameters

Evaluation
To observe water balance, scientists built water balance station. It was used to survey groundwater table, precipitation, evaporation, temperature and moisture of soil. This project began at 20 century, at the end of 20 century there were 18 stations. Also, each station has three or four trail area to test drainage.

Degradation of soil and water is closely related to adverse changes in hydrological processes, which determine soil water balance and soil water status. They are also constrained by climate conditions and the use and management of soil and water resources.Therefore, using hydrological methods to assess and predict the degradation process of soil and water conservation is essential for an appropriate development section and the application of sustainable and effective management practices. The new approach is based on the assessment of hydrological processes under different conditions, such as climate change, soil properties, soil and crop management, and uses practical and flexible mechanisms and computer-based programs, such as Smoke. It will help to select or develop more appropriate technology packages to reduce soil and water degradation and to control its increasing negative impact on crop productivity, ecosystem degradation and global catastrophic events.