5: Water Inputs
- Page ID
- 38736
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The diagram in Fig. 5-1 will help to guide our systematic study of the processes involved in the soil water balance and subsequently our examination of land surface energy balance process.We will begin with consideration of the process of precipitation, the primary water input to the soil water balance in most environments. We will also briefly consider water inputs through irrigation. From there we will follow the water as it moves through the soil water balance processes, considering in turn:
• interception of water by plant canopies and residue,
• impact of water drops on the soil surface,
• infiltration of water into the soil,
• the processes of runoff and erosion by water,
• then redistribution of water within the soil profile,
• drainage of water from the bottom of the soil profile,
• the associated processes of groundwater pollution and soil salinization,
• then evaporation of water from bare soil surfaces and erosion by wind,
• then root water uptake and transpiration by plants.
When we have completed this overview of the soil water balance processes, we will then consider the closely related processes of the land surface energy balance as shown on the right-hand side of Fig. 5-1. The soil water balance can be represented mathematically as:
P + I - RO - D - E - T = ∆S (Equation 5.1)
where P is precipitation, I is irrigation, RO is runoff, D is drainage, E is evaporation, Tis transpiration, and Mis change in soil water storage. The audio overview for Chapter 5 is available here (link).
- 5.1: Precipitation
- As we saw in the previous chapter, one of the earliest cornerstones of soil physics was laid in 1856 by the French engineer, Henry Darcy, whose work focused on water filters and groundwater aquifers. Shortly thereafter a German, Ewald Wollny, became perhaps the first scientist whose published work focused squarely on soil physics
- 5.2: Irrigation
- The amount or seasonal distribution of precipitation is inadequate for reliable crop production in many locations around the world, and people in those locations must either migrate or import food or irrigate in this context is the water which has fallen as precipitation on agricultural land and has infiltrated the soil. Crop production in parts of Asia, the Middle East, and the western US relies heavily on blue water, while much of Africa, Europe, and South America rely primarily on green water
- 5.3: Rainfall interception
- In many terrestrial environments, before water inputs from rainfall or irrigation ever reach the soil surface, the vegetative canopy and plant residue alter both the amount and spatial distribution of those inputs.When rainfall is prevented from reaching the soil because of interception by plant canopies or plant residue and subsequent evaporation, that process is called rainfall interception.
- 5.4: Raindrop impact
- Raindrops whose fall is not interrupted by vegetation or plant residues can strike the soil surface like miniscule bombs going off. The greater the speed and mass of the drop, the greater the force of the impact. The maximum speed a given drop can reach during its all, its terminal velocity, increases as the drop size increases
- 5.5: Crust formation
- primary mechanisms of soil crust formation are physical dispersion and chemical dispersion of soil aggregates. Chemical dispersion and the factors contributing to chemical dispersion have been discussed in section 4.5. Physical dispersion is the breakdown of soil aggregates caused by raindrop impact, by rapid rewetting of initially dry aggregates
- 5.6: Problem set
- The state of Oklahoma, USA, receives approximately 34 inches of annual precipitation on average. The land area of the state is 44.7 million acres. How many cubic kilometers of annual precipitation does Oklahoma receive on average?
- 5.7: References
- Baver, L., Ewald Wollny—A pioneer in soil and water conservation research. Soil Science Society of America Journal, 1938. 3: p. 330-333. Molden, D., ed.Water for food, Water for life: A comprehensive assessment of water management in agriculture. 2007, Earthscan and International Water Management Institute: London, UK. 688.