SOIL WATER BUDGET
INTRODUCTION
Soil is the most crucial factors for life on Earth. Soil is linked to everything around us and performs many important roles in sustaining life on Earth. One of those is for providing the basis for food and biomass production. However, this role is being affected by the degradation of soil. Hence, an understanding of soil is needed for finding an optimal measure for soil management. As a matter of facts, numerous factors are needed for the soil formation. Water is one of the most important constituents in any soil. Without water, soil formation would not be possible. Moreover, water availability in soil is a significant factor that affecting the crop growth. However, in many area crops, soil water is not properly managed which will lead to a poor yield. Therefore, an understanding of the hydrological cycle is essential for the effective management of soil water.
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Especially, in the hydrological cycle, the water budget is used as an approach to reflect the relationship between the input and output of water through a region. In particular, the balance between precipitation and evapotranspiration potential will help us to directly compare the water supply and the natural demand for water as well as to determine the time when there is much rain and when there is not enough.
Studying soil water budget makes it possible to determine if there is a water shortage that can reduce yields or if there is excessive water application that can result in water logging or leaching of nitrates below the root zone. Moreover, it can build knowledge of the soil and water storage and supplying capacity of each irrigated.
II.
WATER BUDGET
Water budgets are used for accounting the inputs, outputs, and changes in the amount of water by breaking the hydrological cycle down into components. Basic components of water budgets are precipitation (rainfall), evapotranspiration (the upward flux of water from the land surface to the atmosphere, a combination of evaporation from the soil and transpiration by plants), surface-water (such as streams and lakes) and groundwater flow (aquifers) into and out of the watershed, change in surface-water and groundwater storage, change in snow and ice storage, and human withdrawals and inter-basin transfers.
The water budget affects how much water is stored in a system. And the stored water is calculated by the following formula:
Stored Water = (Rain + Irr.) – (Runoff + ET + Drainage)
Where Irr is abbreviated for irrigated water, ET is abbreviated for evapotranspiration.
For instance, in wet seasons, precipitation is greater than evapotranspiration, it means (Rain + Irr.) > (Runoff + ET + Drainage), which creates a water surplus. Ground stores fill with water, which results in increased surface runoff, higher discharge and higher river levels. This means there is a positive water balance. Contrastly, in drier seasons, evapotranspiration exceeds precipitation ((Rain + Irr.) < (Runoff + ET + Drainage)). As plants absorb, water ground stores are depleted. There is a water deficit at the end of a dry season.
The storage ability depends on depth and texture of the soil. Drainage and runoff only happen when the bucket is full.
III.
THE IMPORTANCE OF WATER BUDGET
They provide scientific measurements and estimates of the amount of water in each component and calculate the movement of water among the different components – the flux or flow of water. The result is a budget that is a hydrologic record comparable to deposits, withdrawals, and changes in the balance of a checking account.
Soil water budget is the balance of water in the soil; this is the net result of the combined effects of precipitation (P) and potential evapotranspiration (PE). . The storage ability of the water budget is greatly influenced by the depth and the texture of the soil. The drainage and runoff of water in the soil occur when the budget is full and they are considered as recoverable losses while evaporation and transpiration are considered as non-recoverable losses. Water budget can be used to help manage water supply and predict where there may be water shortages. Likewise, it is also used in irrigation, runoff assessment, flood control and pollution control. Further it is used in the design of subsurface drainage systems which may be horizontal (i.e. using pipes, tile drains or ditches) or vertical (drainage by wells). To estimate the drainage requirement, the use of a hydrogeological water balance and a groundwater model may be instrumental.
Why need soil water budget:
– Optimize water use
– Determine irrigation needs
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How can ET be used to schedule irrigation? |
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A: |
With the use of a soil water balance or budget, daily evapotranspiration (ET) amounts are withdrawn from storage (or the balance of plant available water) in the soil profile. Rainfall or irrigation amounts are added to soil water storage. Should the water balance calculations project soil water to drop below some minimum level, irrigation is indicated. Weather forecasts enable prediction of ET rates and projection of soil water balance to indicate whether irrigation is needed in the near future(CSU Extension). |
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Q: |
Why is it important to measure and monitor soil moisture? |
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A: |
Measuring soil moisture makes it possible to determine if there is a water shortage that can reduce yields or if there is excessive water application that can result in water logging or leaching of nitrates below the root zone. Measuring soil moisture also can build knowledge of the soil and water storage and supplying capacity of each irrigated. Monitoring soil moisture levels is required for effective irrigation water management. Many tried and proven methods of estimating or measuring soil moisture are available. The method selected depends on a variety of factors such as accuracy, cost, and ease of use (South Dakota Cooperative Extension Service). |
Increased soil moisture will result in:
- higher yields, through maximised rainfall utilization
- recharge of groundwater and thus securing the water level in wells and the continuity of river and stream flows
- reduced risk of yield losses due to drought
A sound irrigation scheduling program can help an operator:
- prevent economic yield losses due to moisture stress.
- maximize efficiency of production inputs.
- minimize leaching potential of nitrates and other agrichemicals below the rooting zone.
- conserve the water resource and maximize its beneficial use.
This publication describes some “best” soil moisture management strategies and monitoring techniques that an irrigating farmer should consider in managing irrigation water and soil moisture for optimum crop production and least possible degradation of ground water quality.
Understanding the process of soil-water budget,
By calculating the Stored water in the soil, With the use of a soil water balance or budget, daily evapotranspiration (ET) amounts are withdrawn from storage (or the balance of plant available water) in the soil profile. Rainfall or irrigation amounts are added to soil water storage. Should the water balance calculations project soil water to drop below some minimum level, irrigation is indicated. Weather forecasts enable prediction of ET rates and projection of soil water balance to indicate whether irrigation is needed in the near future.
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Likewise, it is also used in irrigation, runoff assessment, flood control and pollution control. Further it is used in the design of subsurface drainage systems which may be horizontal (i.e. using pipes, tile drains or ditches) or vertical (drainage by wells). To estimate the drainage requirement, the use of a hydrogeological water balance and a groundwater model may be instrumental.
In the complete view of the panorama of the earth, all organisms live on or beneath the soil. Therefore, the systems of flows that are happening on Earth have consequences on nature. Mainly, the soil biota is greatly affected by the movement of water in the soil. Soil water affects both the temperature and its aeration activities so it affects the movement and predation of microorganisms in the soil. When the soil pores are so much filled with water, the organisms tend to be disoriented for the sudden change in their environment as well as for the lack of air. The oxygen needed by the organisms depletes that later on leads to anaerobic condition which is hardly a good condition for soil biota. Moreover, if the soil is very dry, plants takes too much energy in order to remove water from the small pores that is why the plants inhabiting the area tend to suffer from difficulty to extract sufficient amount of water through the roots—this phenomenon is called as the permanent wilting point—the condition which plant hardly recover.
In addition, irrigated soils contain significant amount of salt which develops osmotic pressure that slows down the uptake of water by the plants that doesn’t help them for good growth. Thus, significant increase in slow growth might also mean the slow production of food for all organisms in the ecosystem.
IV
SUMMARY AND CONCLUSION
The following are the summary of the main points of the report:
- Soil water budget, is a balance in a net result of hydrological cycle in nature in which the inputs, output
- Larger pores conduct water more rapidly in saturated soils than smaller pores while in unsaturated soil condition, smaller pores conduct water movement more rapidly.
- Coarse over Fine– Water build up over fine soil because water moves faster through coarse soil.
- Fine over Coarse– Water movement will temporarily stop until fine soil is nearly saturated.
There’s always flow in every system and those flows are very much necessary even the tiny little bits of details of it. Once subjected to changes, could lead to negative flaws.
BIBLIOGRAPHY
SAI Platform. (2010, June). Water Conservation Technical Briefs—The Importance of Soil to Water Use. From http://www.saiplatform.org/uploads/Modules/Library/SAI%20Technical%20Brief%205%20%20The%20Importance%20of%20Soil%20to%20Water%20Use.pdf
Irrigation Management—Chapter 3, Soil Water. From http://croptechnology.unl.edu/pages/informationmodule.php?idinformationmodule=1130447123&topicorder=3&maxto=13&minto=1
Food and Agriculture Organization. Physical Factors Affecting Soil Organisms. From http://www.fao.org/agriculture/crops/thematic-sitemap/theme/spi/soil-biodiversity/soil-organisms/physical-factors-affecting-soil-organisms/en/
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