Relationship Of Pf, Corresponding Air Pressure, Type And Constant Of Soil Water And Measurement Method

From (2) to (7) we get: Bp = B - B 0 (9)

In which: Bp is the amount of heat change stored in the plant stem and in the air of the plant population.

Geographical distribution of heat balance:

Soviet climatologist Buduko used climatological methods to study the geographical distribution of heat balance: the amount of heat released by evaporation, the amount of heat exchange by diffusion. The study showed that, in terms of the amount of heat for the whole year, as shown in Figure 4.2

(a) shows that the net radiation on the continent and on the sea is clearly different, the boundary line shows a discontinuous value. This is because the albedo ratio of the sea surface is smaller than that of the continental surface at the same latitude. The largest value of the net radiation on the earth is seen in the northern part of the Arabian Sea, about 140kcal/cm 2 .year. At sea, the straight line forms bands extending from East to West; at high latitudes, the net radiation value decreases very quickly.

On the mainland, the largest net radiation value is found in the humid tropics, which is only 100 kcal/cm2 per year, very small compared to the sea. In addition, if comparing dry areas with humid areas, the value is smaller. This is because the reflectivity of shortwave radiation in dry areas is larger, the effective radiation of longwave is also larger (high surface temperature, few cloudy days, low humidity).

Figure 4.2 (b) shows the heat released by evaporation. The values ​​of the continent and the sea are clearly different, changing clearly at the boundary line. Here, it is similar to the situation of pure radiation mentioned above, but the distribution is more complicated, whether on the continent or on the sea, it does not form ice. On the sea, the value of the high pressure zone is slightly larger than near the equator. In the humid water current area and the cold water current area, even at the same latitude, the difference is 2 - 3 times. On the other hand, on the continent, if the amount of water in the soil is sufficient, the heat released by evaporation is mainly determined by pure radiation. In desert and semi-desert areas, where the soil lacks water, it is almost equal to the annual rainfall. The largest annual evaporation on the continent can reach 100 mm (water column height), on the sea it can reach 200 mm.

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(c) Annual eddy current heat exchange (kcal/cm 2. year)

Figure 4.2 a, b, c . Annual geographical distribution of heat balance (kcal/cm 2. year) (Buđuko, 1956), the hatched part is missing data.

7

The amount of heat exchange due to eddies (in figure 4.2c, the negative and positive signs are determined inversely), all land surfaces and most sea surfaces provide heat to the air, the annual value of desert and tropical regions is the largest, from 50 - 60 kcal/cm2 year or more.

Change in balance during the year a)

heat

Figure 5.2 shows the change over the year.

on the heat balance of some regions

points belonging to typical climate zones LE

(in the figure, in addition to pure radiation, the sign

of other terms determined inversely).

Figure 5.2a shows the situation of H.

Ho Chi Minh City climate zone

equatorial monsoon, net radiation in the dry season is high, and in the rainy season it is low (in the equatorial zone in general, except for the monsoon zone, the annual variation of net radiation is very small).

1 2 3 4 5 6 7 8 9 10 Month

5.2a. Equatorial monsoon region (Ho Chi Minh City 10 0 47' North latitude, 52 0 59' East longitude)

b) The heat released by evaporation is very high.

6 early dry season, much lower in

Kcal/ cm2year

5 end of dry season because the soil is dry (April), to

4 rainy seasons increased again.

3 Note that the lowest evaporation value is

2 later than the maximum net radiation value,

1 LE relationship between soil water content and

0 H evaporation can clarify this issue. The transformation

R change in year on eddy current heat exchange,

1 2 3 4 5 6 7 8 9 10 11 12 Months

5.2b . Subtropical continental climate zone (Krasnovosk, 40 0 ​​degrees N, 52 0 59'

Usually the opposite of evaporative heat exchange, the dry season is very high.

East

Take the continental climate zone of Kratnovsk in Central Asia as an example, as shown in Figure 5.2(b). Here, due to astronomical reasons, the net radiation changes relatively large during the year, and the winter value is negative. Because of little rain, the amount of evaporation is very small, and it is even lower in summer. Therefore, the eddy current heat exchange is especially high in summer, exceeding the net radiation in winter from the air to the ground.

8

c)

10

Kcal/ cm2year

4

2

LE

0

H

R

-2

1 2 3 4 5 6 7 8 9 10 11 12 Months

5.2c . Mid-latitude monsoon climate zone (Vladivostok 43 0 07' N latitude, 134 0 54' E longitude); R: net radiation,

LE: heat released by evaporation; H: Cyclonic heat exchange Figure 5.2a, b, c . Annual variation curve of heat balance in climate zones

typical (Buđuko, 1956)

Taking Vladivostok as an example of a mid-latitude monsoon climate zone (Figure 5.2c), the values ​​of the summer heat balance types here are inhibited by cloudy weather, so the curve is slightly flat.

In general, at sea, the eddy heat exchange is very small, and the annual variation is also very small. Net radiation and heat released by evaporation differ according to latitude and climate zone, because the amount of heat released by evaporation is much higher or much lower than net radiation, resulting in a shortage or surplus of heat; this shortage or surplus is compensated by the amount of convection heat between the deep and shallow layers of the sea or the amount of heat transported by ocean currents.

1.2. Water balance in the fields

Based on the law of conservation of energy, the heat balance formula can be used to express the redistribution of solar energy on the field. By the same reasoning, the water balance formula can be used to clearly state the redistribution of water on the field. The water balance formula of the field shows that in a certain period of time, the total amount of water in solid, liquid, and vapor forms that the surrounding space provides to the field and the amount of water lost must be zero. The formula is as follows (Buduko, 1956):

r + E + fw + m = 0 (10)

In this formula, r is the amount of rainwater, E is the difference in evaporation and condensation on the field surface; fw is the water lost on the ground surface; m is the water exchange between the ground surface and the lower layer of the field. The signs of the terms in formula (10) are the same as in the heat balance formula, the direction into the field has a positive value. The value of m is equal to the sum of the gravitational water flowing down from the ground to the deep layer, the water absorbed by plant roots and the vertical flow of all water in layers with different water contents. Formula 10 can also be used for the slightly modified case, that is, the vertical flow of water is equal to the total amount of water flowing out of the soil fp and the water content in the top layer b.

The sum of the surface water runoff fw and the soil water runoff fp is equal to the total water runoff f (f = fw + fp), which can be expressed as the following formula:

r + E + f + b = 0 (11)

This formula can be used to calculate the water balance of an entire lake, or the water balance of a certain area (e.g. a river basin). Here, f is the total amount of water redistributed horizontally during a given study period, both on the water surface and in the soil bottom. If the average value is taken, the term b is very small. Formula

(10) can be transformed into the following formula:

r + E + f = 0 (12)

For the whole earth, the horizontal redistribution of water is zero so: r + E = 0 (13)

The annual average of the undrained desert land will be as formula (13).

9

2. Soil environment

Land

Land with crops or higher plants growing and developing in the ecosystem is also called "soil" or "planting land". Along with crops, land is also a business object of humans. But giving land an exact definition is not that simple. The main components that make up land are of course inorganic substances in the parent rock, but if there are no countless microorganisms, animals living in the land and organic matter decomposing from dead plants and animals, it cannot be considered land. Up to now, the definition of land that is widely accepted is that of Dacutraiev. Kira (1959) considered soil as an inseparable combination of living and non-living things, composed of a system of actions and reactions, and pointed out that “What becomes a part of a certain ecosystem, stays for a long time in the same place, in interaction with living things, becomes something with a certain structure adapted to the characteristics of that ecosystem, that is soil”. Agricultural soil is greatly influenced by humans, resulting in the mutual interactions between living and non-living things being promoted or inhibited. For details on recent developments in soil science, the interaction between soil and plants, please refer to related documents, here we mainly clarify the issue of soil formation closely related to the physical environment.

Soil composition

Soil has three phases, first is the solid phase, that is, the solid part including rock fragments, inorganic components of parent rock weathering products and soil organic substances which are products of biological decomposition; then comes the gas phase and liquid phase located between the gaps of the solid phase. This is called the three-phase gap of soil. The ratio of the solid phase, liquid phase and gas phase, that is, the distribution of the three phases, even in the same type of soil, also changes, especially in different climatic conditions, the ratio of the liquid phase and the gas phase changes quite a lot. In the fields, due to plowing and farming methods, the three-phase distribution of soil is also different. In general, the three-phase distribution of soil is due to the difference in soil type and soil layer position, which forms the corresponding property value.

The composition of the solid phase, according to the size of the particles, is divided into sand, limon and clay. The combination according to the diameter of these inorganic particles is called the mechanical composition. Classification based on this is called classification of soil according to mechanical composition. For example: sandy soil, light loam, medium loam, heavy loam, light clay, medium clay and heavy clay.

In nature, sand, lime and clay particles are rarely in the form of single particles, but they are often linked together by organic and inorganic glues to form larger particles. Soil aggregates have different shapes depending on the soil type: plate-shaped, column-shaped, ball-shaped, spherical and their variations. These aggregates can be seen as small “bricks” that structure the soil. Soils made up of aggregates are called “soil with aggregate structure” or “soil with aggregate structure”. These are soils with high natural fertility, such as temperate black soil or red basalt soil of Vietnam.

10

Water in the soil

Liquid water in the soil can be called soil solution, because it contains dissolved substances including many types of inorganic and organic substances. Based on the binding force of water in the soil with soil particles, it can be divided into: water tightly bound to mineral compounds, hygroscopic water, mushy water, capillary water and gravitational water. Of which, the water that plants can absorb is capillary water and gravitational water, called effective water. To express the intensity of water absorption in the soil on soil particles, Schofield (1935) suggested using the logarithm to express the height of the water column (cm) equivalent to the suction force called PF. Figure 6.2 clearly shows the relationship of PF with the type of water in the soil and the soil water constant.

PF

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For this type, the current supplying the turn signal lights is supplied directly from the turn signal relay to the lights. div.maincontent .p { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 14pt; margin:0pt; } div.maincontent p { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 14pt; margin:0pt; } div.maincontent .s1 { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 13pt; } div.maincontent .s2 { color: black; font-family:"Times New Roman", serif; font-style: italic; font-weight: normal; text-decoration: none; font-size: 14pt; } div.maincontent .s3 { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 14pt; } div.maincontent .s4 { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 13pt; } div.maincontent .s5 { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 13pt; vertical-align: 1pt; } div.maincontent .s6 { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 11pt; } div.maincontent .s7 { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 14pt; vertical-align: -9pt; } div.maincontent .s8 { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 11pt; } div.maincontent .s9 { color: #008000; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 14pt; } div.maincontent .s10 { color: black; font-family:"Times New Roman", serif; font-style: italic; font-weight: normal; te
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After those monopolized connections are temporarily suspended, Once the queue is cleared, it takes a considerable amount of time for TCP connections to return to their original speed. − Full Queue phenomenon: Data transmitted on the Internet often has an explosion, packets arriving at the router are often in clusters rather than in turn. Therefore, the operating mechanism of DropTail makes the queue easily full for a long period of time, leading to the average delay time of large packets. To avoid this phenomenon, with DropTail, the only way is to increase the router's buffer, this method is very expensive and ineffective. − No QoS guarantee: With the DropTail mechanism, there is no way to prioritize important packets to be transmitted through the router earlier when all are in the queue. Meanwhile, with multimedia communication, ensuring connection and stable speed is extremely important and the DropTail algorithm cannot satisfy. The problem of choosing the buffer size of the routers in the network is to “absorb” short bursts of traffic without causing too much queuing delay. This is necessary in bursty data transmission. The queue size determines the size of the packet bursts (traffic spikes) that we want to be able to transmit without being dropped at the routers. In IP-based application networks, packet dropping is an important mechanism for indirectly reporting congestion to end stations. A solution that prevents router queues from filling up while reducing the packet drop rate is called dynamic queue management. 3.2. Random elimination method – RED 3.2.1 Overview RED (Random Early Detection of congestion; Random Early Drop) is one of the first AQM algorithms proposed in 1993 by Sally Floyd and Van Jacobson, two scientists at the Lawrence Berkeley Laboratory of the University of California, USA. Due to its outstanding advantages compared to previous queue management algorithms, RED has been widely installed and deployed on the Internet. The most fundamental point of their work is that the most effective place to detect congestion and react to it is at the gateway or router. Source entities (senders) can also do this by estimating end-to-end delay, throughput variability, or the rate of packet retransmissions due to drop. However, the sender and receiver view of a particular connection cannot tell which gateways on the network are congested, and cannot distinguish between propagation delay and queuing delay. Only the gateway has a true view of the state of the queue, the link share of the connections passing through it at any given time, and the quality of service requirements of the traffic flows. The RED gateway monitors the average queue length, which detects early signs of impending congestion (average queue length exceeding a predetermined threshold) and reacts appropriately in one of two ways: − Drop incoming packets with a certain probability, to indirectly inform the source of congestion, the source needs to reduce the transmission rate to keep the queue from filling up, maintaining the ability to absorb incoming traffic spikes. − Mark “congestion” with a certain probability in the ECN field in the header of TCP packets to notify the source (the receiving entity will copy this bit into the acknowledgement packet). Figure 3. 1 RED algorithm The main goal of RED is to avoid congestion by keeping the average queue size within a sufficiently small and stable region, which also means keeping the queuing delay sufficiently small and stable. Achieving this goal also helps: avoid global synchronization, not resist bursty traffic flows (i.e. flows with low average throughput but high volatility), and maintain an upper bound on the average queue size even in the absence of cooperation from transport layer protocols. To achieve the above goals, RED gateways must do the following: − The first is to detect congestion early and react appropriately to keep the average queue size small enough to keep the network operating in the low latency, high throughput region, while still allowing the queue size to fluctuate within a certain range to absorb short-term fluctuations. As discussed above, the gateway is the most appropriate place to detect congestion and is also the most appropriate place to decide which specific connection to report congestion to. − The second thing is to notify the source of congestion. This is done by marking and notifying the source to reduce traffic. Normally the RED gateway will randomly drop packets. However, if congestion If congestion is detected before the queue is full, it should be combined with packet marking to signal congestion. The RED gateway has two options: drop or mark; where marking is done by marking the ECN field of the packet with a certain probability, to signal the source to reduce the traffic entering the network. − An important goal that RED gateways need to achieve is to avoid global synchronization and not to resist traffic flows that have a sudden characteristic. Global synchronization occurs when all connections simultaneously reduce their transmission window size, leading to a severe drop in throughput at the same time. On the other hand, Drop Tail or Random Drop strategies are very sensitive to sudden flows; that is, the gateway queue will often overflow when packets from these flows arrive. To avoid these two phenomena, gateways can use special algorithms to detect congestion and decide which connections will be notified of congestion at the gateway. The RED gateway randomly selects incoming packets to mark; with this method, the probability of marking a packet from a particular connection is proportional to the connection's shared bandwidth at the gateway. − Another goal is to control the average queue size even without cooperation from the source entities. This can be done by dropping packets when the average size exceeds an upper threshold (instead of marking it). This approach is necessary in cases where most connections have transmission times that are less than the round-trip time, or where the source entities are not able to reduce traffic in response to marking or dropping packets (such as UDP flows). 3.2.2 Algorithm This section describes the algorithm for RED gateways. RED gateways calculate the average queue size using a low-pass filter. This average queue size is compared with two thresholds: minth and maxth. When the average queue size is less than the lower threshold, no incoming packets are marked or dropped; when the average queue size is greater than the upper threshold, all incoming packets are dropped. When the average queue size is between minth and maxth, each incoming packet is marked or dropped with a probability pa, where pa is a function of the average queue size avg; the probability of marking or dropping a packet for a particular connection is proportional to the bandwidth share of that connection at the gateway. The general algorithm for a RED gateway is described as follows: [5] For each packet arrival Caculate the average queue size avg If minth ≤ avg < maxth div.maincontent .s1 { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 15pt; } div.maincontent .s2 { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: bold; text-decoration: none; font-size: 15pt; } div.maincontent .p { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 14pt; margin:0pt; } div.maincontent p { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 14pt; margin:0pt; } div.maincontent .s3 { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: bold; text-decoration: none; font-size: 14pt; } div.maincontent .s4 { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 14pt; } div.maincontent .s5 { color: black; font-family:"Times New Roman", serif; font-style: italic; font-weight: normal; text-decoration: none; font-size: 14pt; } div.maincontent .s6 { color: black; font-family:"Times New Roman", serif; font-style: italic; font-weight: bold; text-decoration: none; font-size: 14pt; } div.maincontent .s7 { color: black; font-family:Wingdings; font-style: normal; font-weight: normal; text-decoration: none; font-size: 14pt; } div.maincontent .s8 { color: black; font-family:Arial, sans-serif; font-style: italic; font-weight: bold; text-decoration: none; font-size: 15pt; } div.maincontent .s9 { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: bold; text-decoration: none; font-size: 14pt; } div.maincontent .s10 { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 9pt; vertical-align: 6pt; } div.maincontent .s11 { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 13pt; } div.maincontent .s12 { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-decoration: none; font-size: 10pt; } div.maincontent .s13 { color: black; font-family:"Times New Roman", serif; font-style: normal; font-weight: normal; text-d
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Figure 6.2 . Relationship of PF, corresponding air pressure, type and constant of soil water and measurement method

- Moisture absorption coefficient: Water absorbed from humid air when spreading the soil thinly.

- Withering coefficient (plant wilting moisture): The amount of water in the soil that causes plants to begin to wilt is called the initial withering coefficient, the amount of water that cannot be restored to its original state after wilting is called the permanent withering coefficient.

- Water equivalent: Saturate soil with water, put into a centrifuge equivalent to 1000 times gravity, the remaining water in the soil is water equivalent, almost equivalent to capillary water.

- Field water retention: Rainwater and irrigation water become gravity water moving

moves downward, then upward by capillary action, when this water almost stops moving.

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The amount of water in the topsoil layer is called the field water capacity. The PF value is about 1.5-1.7. The range between this value and the initial drying coefficient is the effective water.

Figure 6.2 also shows the possible range of different methods for measuring water in

soil, based on the range of required PF values, select the appropriate measurement method.

Air in the soil

The composition of soil air is the same as that of air in the sky, including oxygen, nitrogen, carbon dioxide and other rare gases. The main difference between soil air and atmospheric air is the CO 2 content . In normal air, the CO 2 content is about 0.33% while in surface soil air it is usually 0.2 - 1%. In rice fields, air can dissolve into the surface water and then diffuse into the soil. In the soil, oxygen is consumed, producing CO 2 , H 2 and methane, forming bubbles that rise to the surface of the water and then into the air. The composition of soil air is different from that of normal air because the respiration of plant roots and microorganisms requires oxygen consumption and CO 2 release .

Table 1.2 shows the difference in oxygen consumption, in the presence and absence of plants. It is clear that the oxygen consumed by soil organisms is greater than that consumed by plants. In soils near the roots, the presence of roots stimulates microbial activity, so that in reality the oxygen consumed by plants is even smaller; the CO2 dynamics in soils will be discussed later.

3. Biological environment

Soil organisms

Many species of animals and plants live in the soil. The main plants are fungi, bacteria, actinomycetes, algae; animals include amoeba, dung beetles, large arthropods, worms, mollusks... These soil organisms in the process of energy conversion of the field ecosystem are consumers and decomposers of energy, connected to each other through the effects and reactions of the host-environment system (Figure 7.2). Regarding soil microorganisms, please refer to the Soil Microbiology textbook of the Agricultural University I.

Table 1.2 . Oxygen consumption in soil with and without plants

Land

Insects, pathogens

The presence of insects in crop production is often considered harmful, in stark contrast to the fixed, solar energy-transferring system of crops. Therefore, the focus of research is often on pest control. From the perspective of field ecosystems, much attention is paid to the ecology of animal populations, at least to clarify the energy and material circulation of these animal populations and pathogenic organisms.

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Weed

Weeds in the field ecosystem are the subject of great concern to crop researchers and plant ecologists. Weeds are competitors of crops, and are the objects that must be controlled. Recently, in the study of weeds, more and more people have applied ecological methods (perhaps the first person to follow this direction was Arai, 1961). About weeds in the field ecosystem, will be mentioned in the competition section.

Fertilizer Herbicides Fungicides Pesticides Acid Rain

Selection and breeding Cultivation

Parasitic species Carnivorous species

Saprophytes

Fish-eating species

Symbiotic species

Parasitic fungi, viruses

Worms, soil animals that decompose organic matter

Symbiotic species

Figure 7.2 . Relationships between crops, soil organisms, and insects under human control through field ecosystems ( Source : Shiyomi and Koizumi, 2001)

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