DIMORIAN REVIEW: RELATIONSHIP OF SOIL WATER AND PLANT WITH ATMOSPHERE
The soil will release water to the atmosphere and the soil spaces not occupied by water are Rete~1\on, movement and availability of soil water to plants. The growth of any plant depends on two important natural resources namely soil and water. Beside all the inputs used in agriculture, water is an important factor. Dec 8, A basic understanding of soil/water/plant interactions will help irrigators Soil surveys of every county in North Dakota have been completed by the . from the soil surface or transpired through the plants to the atmosphere.
Water movement through the SPAC is driven by the passive movement of water generated by an energy gradient. The energy gradient is created by a difference in water potential from high potential in the soil, to a gradually lower potential in the plant and the atmosphere. Factors affecting Soil-Water-Plant Relationship There are three major factors that affect the soil water plant relations 1. Weather factors Soil Factors: Any soil factor which affects root density or depth can be expected to influence the response of the crop to irrigation.
Mechanical impedance, slow water penetration and poor internal drainage, and deficient aeration frequently are responsible for sparse and shallow roots.
Soil structure, texture, and depth determine the total capacity of the soil for storing available water for plant growth. The total available moisture capacity within the root zone and the moisture-release characteristics of the soil are both important factors determining the rate of change in soil moisture tension or stress.
Deep-rooted crops on deep soils usually show smaller responses to irrigations than shallower-rooted crops on the same soil. The rate at which water can move to the absorbing root surface may play an important part in water-soil-plant relations.
Several different aspects of plant growth-such as elongation of plant organs, increase in fresh or dry weight, and vegetative versus reproductive development are easily recognized. These processes are resultants of intricate combinations of many physiological processes which are probably not all equally affected by increasing soil moisture stress and an accompanying change in the internal balance of cells and tissues.
Thus, it is not surprising that various measurable aspects of growth do not respond in the same manner to moisture stress. Weather conditions particularly light and temperature may influence the growth characteristics of the shoot and root as to affect soil moisture-growth relations.
The length of the crop season before fall rains or frost may at least partially determine whether harvestable yields will be affected by imposing different soil moisture stress levels during the growing period.
Meteorological factors like light, temperature, humidity and wind control the rate of water loss by transpiration from plant leaves and evaporation from the soil surface. Plant growth is probably dependent upon plant turgor pressure, whose relation to soil moisture stress for different rates of transpiration needs to be explored.
It can be reasoned that an increased rate of transpiration would lower the plant turgor corresponding to any given soil moisture stress. Conclusion Soil-water-plant relationships play an important role in determining input use efficiency. Models should be developed for better understanding of soil-water-tillage-nutrient-plant interaction with respect to input use efficiency.
Optimal application of fertilizers according to soil type and crop requirement can help in proper utilization of fertilizers and minimize the wastage. Similar to that fertilizers and water fertigation also keeps the equal importance. Can be used for irrigation on almost all soils with little danger of the development of harmful levels of exchangeable sodium. S2 - Medium-sodium water: Will present an appreciable sodium hazard in fine-textured soils, especially under low leaching conditions.
This water may be used on coarse-textured soils with moderately rapid to very rapid permeability. S3 - High-sodium water: Will produce harmful levels of exchangeable sodium in most soils and requires special soil management, good drainage, high leaching and high organic matter additions.
Plant and Soil Sciences eLibrary
S4 - Very high sodium water: Generally is unsatisfactory for irrigation purposes except at low and perhaps medium salinity. Carbonates Carbonate and bicarbonate ions in the water combine with calcium and magnesium to form compounds that precipitate out of solution.
The removal of calcium and magnesium increases the sodium hazard to the soil due to the irrigation water. The increased sodium hazard often is expressed as "adjusted SAR.SOIL MOISTURE PLANT RELATIONSHIP
Nozzles of sprinkler systems have been plugged by carbonate minerals in some states but this has not been observed in North Dakota. However, carbonate minerals have plugged the emitters in drip irrigation systems in North Dakota. To control this problem, add a mild acid to lower the pH of the irrigation water.
Boron Boron is essential for the normal growth of all plants, and the quantity required is low compared with other minerals. However, some plants are sensitive to even low boron concentrations. Dry beans are very sensitive to small amounts of boron, but corn, potatoes and alfalfa are more tolerant. In fact, the concentration of boron that will injure the sensitive plants often is close to that required for normal growth of tolerant plants.
Although no problems with boron in water used for irrigation in North Dakota have been documented, testing for this element in irrigation water is a precautionary practice. Boron does occur in some North Dakota ground water at concentrations that are theoretically toxic to some crops.
A boron concentration greater than 2 parts per million ppm may be a problem for certain sensitive crops, especially in years that require large quantities of irrigation water. If a cubic foot of a typical silt loam topsoil were separated into its component parts, about 45 percent of the volume would be mineral matter soil particlesorganic residue would occupy about 5 percent of the volume and the rest would be pore space.
The pore space is the voids between soil particles and is occupied by air or water. The quantity and size of the pore spaces are determined by the soil's texture, bulk density and structure.
Water is held in soil in two ways: Soil water in the pore spaces can be divided into two different forms: The two primary ways that water is held in the soil for plants to use are capillary and gravitational forces. Gravitational water generally moves quickly downward in the soil due to the force of gravity. Capillary water is the most important for crop production because it is held by soil particles against the force of gravity.
As water infiltrates into a soil, the pore spaces fill with water. As the pores are filled, water moves through the soil by gravity and capillary forces. Water movement continues downward until a balance is reached between the capillary forces and the force of gravity. Water is pulled around soil particles and through small pore spaces in any direction by capillary forces. When capillary forces move water from a shallow water table upward, salts may precipitate and concentrate in the soil as water is removed by plants and evaporation.
Water Holding Capacity of Soils The four important levels of soil moisture content reflect the availability of water in the soil.
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These levels commonly are referred to as 1 saturation, 2 field capacity, 3 wilting point and 4 oven dry. When a soil is saturated, the soil pores are filled with water and nearly all of the air in the soil has been displaced by water. The water held in the soil between saturation and field capacity is gravitational water. Frequently, gravitational water will take a few days to drain through the soil profile and, thus, some can be absorbed by roots of plants.
Field capacity is defined as the level of soil moisture left in the soil after drainage of the gravitational water Figure 7. Water held between field capacity and the wilting point is available for plant use. The water available to plants is exhausted. Soil moisture available to plants is the amount held between field capacity and wilting point. The wilting point is defined as the soil moisture content at which most plants cannot exert enough force to remove water from small pores in the soil.
Most crops will be damaged permanently if the soil moisture content is allowed to reach the wilting point. In many cases, yield reductions may occur long before this point is reached. Capillary water held in the soil beyond the wilting point can be removed only by evaporation. When dried in an oven, nearly all water is removed from the soil.
When discussing the water-holding capacity associated with a particular soil series, the water available for plant use in the root zone commonly is given Table 3. Available soil water content commonly is expressed as inches per foot of soil. For example, the water available can be calculated for a soil with fine sandy loam in the first foot, loamy sand in the second foot and sand in the third foot.
The top foot would have about 2 inches, the second foot would have about 1 inch and the third foot would have about 0. Soil Moisture Tension The degree to which water clings to the soil is the most important soil water characteristic to a growing plant. This concept often is expressed as soil moisture tension. Soil moisture tension is negative pressure and commonly expressed in units of bars. During this discussion, when soil moisture tension becomes more negative, it will be referred to as "increasing" in value.
Thus, as soil moisture tension increases the soil water pressure becomes more negativethe amount of energy exerted by a plant to remove the water from the soil also must increase. One bar of soil moisture tension is nearly equivalent to -1 atmosphere of pressure 1 atmosphere of pressure is equal to A soil that is saturated has a soil moisture tension of about At field capacity, most soils have a soil moisture tension between Soils classified as sandy may have field capacity tensions around At field capacity, removing water from the soil is relatively easy for a plant.
The wilting point is reached when the maximum energy exerted by a plant is equal to the tension with which the soil holds the water. For most agronomic crops, this is about bars of soil moisture tension. To put this in perspective, the wilting point of some desert plants has been measured to be between and bars of soil moisture tension. The presence of high amounts of soluble salts in the soil reduces the amount of water available to plants.
As dissolved salts increase in soil water, the energy expended by a plant to extract water also must increase even though the soil moisture tension remains the same. In essence, dissolved salts decrease the total available water in the soil profile. Without enough water, normal plant functions are disturbed, and the plant gradually wilts, stops growing and dies.
Plants are most susceptible to damage from water deficiency during the vegetative and reproductive stages of growth.
Transpiration - Water Movement through Plants
Also, many plants are very sensitive to salinity during germination and early growth stages. Most of the water that enters the plant roots does not stay in the plant. Less than 1 percent of the water withdrawn by the plant actually is used in photosynthesis assimilated by the plant.
The rest of the water moves to the leaf surfaces, where it transpires evaporates to the atmosphere. The rate at which a plant takes up water is controlled by its physical characteristics, the atmosphere and soil environment. As water moves from the soil into the roots, through the stem, into the leaves and through the leaf stomata to the air, it moves from a low water tension to a high water tension Figure 8.
The water tension of the air is determined in large part by the relative humidity and always is greater than the water tension in the soil.