The most complete soil knowledge

(B) soil fertility and its factors


1, soil fertility types: soil fertility refers to the ability of the soil to meet the crop growth and development of water, nutrients, air, heat and so called. Soil fertility is divided into natural and artificial fertility; potential fertility and effective fertility. The so-called natural fertility, refers to the natural soil before reclamation and utilization of fertility; artificial fertility refers to the people of the soil cultivation, fertilization, irrigation and other agricultural technical measures to create a new fertility.


Therefore, the longer agricultural and cultivated crops can be harvested in any soil, the better the technical measures that can be taken, and the greater the proportion of man-made fertility. So, soil is the object of labor, but also the product of labor. The so-called effective fertility, refers to the cultivation of crops, the crop is absorbed by the utilization of that part of the fertility; potential fertility refers to those existing in the soil, can not immediately be utilized by those crops that fertility. Potential fertility and effective fertility are mutually transformable with the proper implementation of agricultural technologies.


2, soil fertility factors: soil moisture, nutrients, air and temperature, known as the four major factors of soil fertility. Soil fertility level, not only by the number of each fertility factor appropriate or not, but mainly depends on the degree of coordination between water, fertilizer, gas, heat under certain conditions. Therefore, we must study and master the status of soil fertility factors and their relationship.


(1) soil moisture status. "Water conservancy is the lifeblood of agriculture." First, the growth and development of crops require large amounts of water. This is because, for a typical crop to have a single crop, it must consume 500-1,000 points of water, which is supplied from the soil; the nutrients absorbed by crops also need to be dissolved in water before they can be used; the activity of soil microorganisms and the soil Nutrient decomposition and conversion require water.


Second, moisture directly affects the soil air and heat conditions, but also affects the soil's properties such as swelling, cohesion, cohesion and tillage. This shows that soil moisture is not only necessary for crop growth and development, but also can control the relationship between soil moisture to make the relationship between fertilizer, gas and heat.


① soil moisture type: soil moisture by its different forces, generally divided into three types:


A, irreducible water: This is the gravitational effect of the soil surface, tightly bound to the water around the soil particles and called. This water moves very slowly in the soil, and some do not move on the soil surface, it is difficult to be absorbed by crops. When the soil moisture reached only the bound water, the crop wilted. As the soil particles finer, absorb more water, so the bound water of clay is greater than the sand.


B, capillary water: This is called capillary water in the soil under the capillary gravity to maintain the tiny pores in the soil water. This water can move along the capillary pores in all directions up, down, left and right. The law of its movement from the humidity of the soil to move to a small soil moisture. It is the most suitable soil for water absorption and utilization of crops. As water is soluble in various crops, it provides nutrients for the crop.


Oil sand, tidal sand, the emergence of "resurgence" or "return Run" phenomenon, is the capillary water rise movement, the introduction of groundwater into the ground because of the reason. However, the capillary water movement will cause surface evaporation to occur constantly, resulting in the loss of soil moisture. Therefore, it is often used in production to cultivate loose soil, which has the effect of cutting off the soil capillary and reducing soil water evaporation.


C, gravity water: This is in the soil moisture content exceeds the soil capillary force range, excessive water leakage under the influence of gravity down, this seepage water is called gravity water. It is the most effective water for rice. Although the leakage may cause leaking and leaking, proper leakage is necessary both for paddy field and dry land. It is conducive to the renewal of soil air and the downward movement and leaching of harmful reducing substances.


② Paddy soil moisture status: Paddy soil during flooded period, tillage layer of water saturated with state, due to gravity, continuous vertical leakage. According to the vertical leakage characteristics of water, paddy soil is divided into three types.


A, groundwater type: this type of paddy soil, groundwater level is high (groundwater level within 60 cm from the surface), poor drainage, irrigation water and groundwater connected, poor permeability, low mud temperature, such as cold dip fields, mud fields And deep duck feces soil belongs to it.


B, surface water: This type of paddy soil, deep water table (more than 150 cm), irrigation infiltration can not reach the groundwater layer, drainage is good, but not resistant to drought. Such as Kaohtian, Tianshui and most of the terraces.


C, good water type: This type of paddy soil, groundwater level between 60-150 cm, the irrigation water layer and the groundwater level is not connected, but the soil capillary water can flow up and down, these fields are generally distributed in the field above or Row, two rows of fields belong.


Three types of paddy soils, with good water-based soil fertility is best, generally high and stable yield paddy fields. Appropriate seepage is necessary for paddy soils, which help to renew the air in the soil and eliminate toxic substances. Of course, not too large, so as to avoid nutrient leaching. Generally 1-inch water can be stored in irrigation for three days, that leakage is 0.5-1.0 cm / 24 hours the most appropriate.


(2) Soil air condition: Soil air is closely related to soil microbial activity and nutrient conversion, and also affects crop root development. Crop growth and development of the various stages of the soil air have certain requirements.


① The composition of soil air: the air in the soil, part of which is entered by the atmosphere; and partly by the biochemical processes in the soil. Due to the influence of the life activities of organisms in the soil (crop roots and microbes) and the decomposition of organic matter, the continuous depletion of oxygen and the production of carbon dioxide and other gases causes a significant difference between the composition of air in the atmosphere and the atmosphere: the oxygen content of soil air is below Air, and carbon dioxide content is higher than the atmosphere; In addition the soil air is often saturated with water vapor, atmospheric humidity is generally only 50-90%; soil air sometimes contain a small amount of reducing gas, such as methane, hydrogen, ammonia and hydrogen sulfide .


The characteristics of paddy soil air conditions: paddy soil seasonal or perennial flooding, soil air and atmospheric gas exchange between the water layer isolated, often in the restored state. Oxygen consumed by the life activities of crops can only be supplied to the roots by the oxygen supply tissues of the stems and leaves of the crops, and the oxygen is then secreted from the roots to cause the oxidative environment of the rhizosphere micro-areas to prevent the rice roots from being reduced by the surrounding reducing substances Poisoning. This is the secret that rice can grow in anoxic environments.


Therefore, the characteristics of paddy soil air conditions have obvious hierarchy and micro-area. In the tillage layer surface a few millimeters to 1 cm at the oxide layer, due to the state of iron compounds into high prices, soil color yellowish brown or yellow brown. In the oxide layer below the tillage layer for the reduction of the iron into the state of cheap compounds, soil color was gray or blue gray. However, near the rhizosphere of soil around, often due to the role of oxygen in rice root groups appear rust and rust.


③ soil air in the soil fertility status: soil air supply crop root respiration required oxygen. Such as hypoxia, root development is affected, water absorption and absorption of weakening function, and even death. In particular, seed germination and seedling more so. Although rice has aeration tissue, the soil should also have some aeration performance, to facilitate the growth of rice roots.


In addition, soil air conditions affect soil microbial activity and nutrient conversion. Anoxic microorganisms mainly dominate anaerobic activity, which decomposes organic matter slowly, resulting in insufficient nutrients and even nitrogen losses. In the meantime, reducing toxic substances such as acetic acid, butyric acid and hydrogen sulfide are also produced. In addition, poor soil aeration is conducive to the growth of germs, causing crop infections, affecting crop growth and reducing production. Therefore, rice fields are often drained fields and sunning to regulate.


(3) soil warm conditions: soil temperature on crop growth and microbial activity in the soil and a variety of nutrients conversion, soil moisture evaporation and exercise have a great impact. Crops from sowing to maturity require certain temperature conditions, such as barley, wheat germinate at 1-2 ℃, while rice, cotton germination at 10-12 ℃. So timely sowing of different crops, is determined by the soil temperature. General soil microbial life, soil temperature 25 ℃ -37 ℃ suitable, the lowest is 5 ℃, the highest does not exceed 45 ℃ -50 ℃. Soil temperature is too low, microbial activity weakened, or even completely stopped, difficult to decompose organic matter, the lack of effective nutrients. Cold soaked field is the case, so to exclude cold water, additional pigs barn dung, lime, ash and fire ash to improve soil temperature.


① factors affecting the soil temperature: temperature is the performance of heat. Soil heat mainly comes from solar radiation heat, followed by microbial decomposition of organic matter, emit a certain amount of heat, soil temperature increased.


There are many factors affecting soil temperature changes, latitude, altitude, topography and aspect. But mainly soil thermal properties of the soil itself, such as soil heat capacity, thermal conductivity, endothermic and heat dissipation. In particular, heat capacity and thermal conductivity are the most important internal factors that determine soil temperature.


A. Soil heat capacity: The number of calories (calories / cm3 / degree) required for warming 1 ℃ per 1 cm3 of dry soil is called soil heat capacity. Water has a heat capacity of 1; air is 0.0003; soil particles are between about 0.5-0.6. As the soil solid part of the change is very small, so the size of the soil heat capacity is mainly determined by the amount of soil moisture and air, where less water and gas less heat capacity is large, slow warming, cooling is slow, small changes in temperature; the other hand, Soil temperature changes on the big. Therefore, management of paddy fields, early spring daytime drainage warming, night irrigation insulation; summer use of deep-fed cooling.


B, soil thermal conductivity: soil thermal conductivity refers to the performance of heat transfer from the higher temperature soil to the lower temperature soil. Its size and soil solid, liquid and gas phase ratio of the three components. The thermal conductivity of soil minerals is 100 times that of air; the water is 25 times that of air; the organic matter is 5 times that of air; and the air hardly transfers heat. This shows that the size of soil thermal conductivity depends on the relative proportions of air and moisture. Therefore, cultivating loose soil has reduced the thermal conductivity of the soil, so that the top soil temperature is not easy to pass down, deep soil temperature is not easy to lose.


The adjustment of soil temperature changes: the soil temperature changes with the meteorological factors, in order to meet the needs of crop growth and development, we must focus on increasing soil temperature in early spring, reducing soil temperature in summer, autumn and winter to maintain soil temperature goals, to take effective Measures.


A. Reasonable Irrigation: In the early spring, more irrigation and deep irrigation of cold water are needed to avoid the sudden drop of soil temperature and enhance the ability of seedlings to resist low temperature. During normal weather, shallow irrigation, warm ventilation and crop growth are used. Summer to enhance the soil heat dissipation mainly to take short-term irrigation of deep water and combined irrigation of open fields to achieve the purpose of cooling, ventilation, water supply, and promote crop growth and development. Autumn and winter season, the general combination of fertilization, the implementation of frost before irrigation, to reduce crop frost damage.


B, reasonable fertilization: Under the premise of guaranteeing adequate fertilizer, increase the application of organic fertilizer, such as fire ash, matured pig bulldozers and so on, to improve the soil temperature. First, deepen the soil color, increase soil heat absorption; Second, organic fertilizer decomposition in the release of heat; Third, the soil loose, increase air capacity and reduce soil heat capacity. In addition, the nutrition of the crop is directly increased.


C, the implementation of coverage: early spring and autumn and winter low season, the use of ash, chopped grass (aspen), dry (wet) cow dung, moss, plastic film covering the ground, can increase soil heat, reduce heat, insulation Antifreeze; summer and autumn during high temperature and drought, the straw or other crop straw covering the ground, shading sunscreen, reducing soil temperature role, while reducing evaporation and elimination of weeds.


D, cultivating loose soil: This is conducive to the increase of soil air capacity, reduce the surface soil heat conduction down and the role of soil temperature rise below. Therefore, in early spring, sticky compacted soil soil cultivation of loose soil to improve soil temperature and speed up the seed germination; cultivate loose soil in summer to ease the root activity layer soil temperature is too high, and promote crop root growth.


In addition, the use of wind barriers, windbreaks, fumigation and the use of chemical warming agent, can adjust the soil temperature, can be applied according to local conditions.

(4) Soil nutrient status: Most of the nutrients needed by crops come from the soil. However, most of the nutrients in the soil are found in the insoluble minerals and organic matter, which are delayed and can not be absorbed by crops. However, the fast-acting nutrient in ionic form, which can be absorbed and utilized by the crop, accounts for only 0.005-0.1% of the soil weight. It exists in aqueous solution and is adsorbed on the surface of soil colloids. However, this delayed-acting nutrient and fast-acting nutrient can be transformed into each other under certain conditions.

① conversion of organic carbon compounds: soil cellulose, starch, disaccharides, monosaccharides and fats and other organic matter, do not contain nitrogen. There are two cases of their transformation in soil:

First, good ventilation, by aerobic bacteria and fungi, rapid decomposition, the final generation of CO2 and H2O, and release a lot of heat. This heat is the source of energy required for the biodynamic activities of soil and the life activities of soil microbes. CO2 is an important raw material for crop photosynthesis.

Second, poor ventilation, by the role of anaerobic bacteria, slow decomposition, just release a small amount of heat and CO2, while the accumulation of large amounts of organic acids (acetic acid, butyric acid), methane, hydrogen and other reducing substances, obstacles crop growth and development. Such as rice, "turning the autumn" or "dissolution 蔸" phenomenon, is butyric acid damage. Therefore, paddy green pressure fertilizer, combined with lime, is to neutralize organic acids, eliminate rice poisoning.

Soil nitrogen conversion: organic nitrogen in soil accounts for more than 99%, inorganic nitrogen is less than 1%; paddy field total nitrogen content of about 0.1-0.2%, less inorganic nitrogen. Nitrogen absorbed by crops from the soil is largely converted from organic nitrogen. The formation of its conversion there are four main types:

A, ammonification: nitrogenous organic matter in the soil, such as protein, urea and chitin (chitin) in the role of ammoniated bacteria, the gradual decomposition of the release of ammonia, called the ammoniation. This process can be done regardless of ventilation. Ammonia and the acid in the soil combined into ammonium salt, for crop absorption and utilization, or adsorption by soil colloids.

B, nitrification: ammonia or ammonium salt in well-ventilated conditions, the nitrite bacteria, nitric acid bacteria, the role of conversion to nitric acid process, known as nitrification. Since this effect is carried out under well-aerated conditions, NO3-N is found in dry land and rare in paddy fields. NO3-N is a good crop nutrients, but can not be adsorbed by soil colloids, easy to lose with the water, so deep plowing loose soil, keep the soil moist, nitrification and prevent the loss of ammonia in the soil.

C, denitrification: When the soil is poorly aerated, and contains large amounts of fresh organic matter and nitrate in the soil, under the action of denitrifying bacteria, the reduction of nitrate to nitrogen can not be used by crops to lose, this process is called denitrification effect. This effect has adverse effects on crop nutrient uptake and growth and must be discouraged. Paddy fields with shallow irrigation, open field ventilation and application of ammonium nitrogen fertilizer, dry soil after cultivating loose soil, can prevent the occurrence of denitrification.

D, biological nitrogen-deprived effect: inorganic nitrogen in the soil (such as ammonium, nitrate) by microorganisms, weeds, soil animals to absorb the use of synthetic biological body