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AIR TANAH
LENGAS TANAH
Soil Water
SOIL MOISTURE
The importance of soil water :
1. Effect on soil formation,erosion, and structure stability
2. It is the major constituent of plant protoplasm.
3. It is essential for photosynthesis and conversion of starches to sugar .
4. It is the solvent in which nutrients move into and through plant parts.
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
The types and available of soil moisture Classification of soil water
• Adsorbed water• Membranous water• Capillary water• Gravitational water
• Numerical method
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Soil adsorbed water :
1. held by strong electrical forces - low energy
2. little movement- held tight by soil
3. exists as a film
4. unavailable to plants
5. removed from soil by drying in an oven
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Soil Membranous water :
1. held by hydrogen bonding
2. liquid state in water film
3. major source of water for plants
4. greater energy than adhesion water
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Sketch map of membranous water
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Air Kapiler = Soil capillary water :
Capillary water-The water held in the “capillary” or small pores of a soil, usually with a tension >60 cm
of water.
Capillary water includes capillary hanging water and capillary rise water.
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Capillarity : 0.1-1mm
Capillarity obvious
0.05-0.1mm
Capillarity strong
0.05-0.005mm
Capillarity very strong
〈 0.001mm
Capillarity disappears
Air ditarik “naik” ke dalam tabung kapiler
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Soil particle
Air kapiler dalam pori
tanah
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Field capacity:The amount of water remaining in a soil after the free water has been allowed to drain away (a day or two) after the root zone had been previously saturated;
expressed as a percentage.
Kapasitas Lapang (KL) = Field capacity:
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Soil particle
Air kapiler naik ke
atas melalui
pori kapiler dalam tanah
Groundwater Table
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Ketinggian naiknya air kapiler :
h ( cm): the hight of capillary water rise , d: the diameter of the capillary tube ( mm )
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Air Gravitasi = Gravitational water
Gravitational water Water which moves into, through, or out of the soil under the influence of
gravity.
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
二、 The express methods of soil water content
(二) The volume water content ( v ) Volume water content = volume of water/bulk volume of soil=(weight of water/ρW)/(weight of dry soil/ ρb)
V=m·
(一) The mass water content ( m)
Percntage water = {[(wet soil weight)-(oven dry soil weight)]/
(oven dry soil weight)} ×100
( 三) Relative water content ( % )
Relative water content= soil water content/ field capacity
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
(三) Soil water-storage capcity
2 、 Water fang( 方 ) ( m3 )
whaFang DV 10/
VFang/mu( 亩 ) = 2/3Dw
1 、 Water
deepth ( DW ) DW=V·h or D hw
i
n
i,100 1
1
mm
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
三、 Estimating water contents
• Gravimetric method: The soil sample is dried in an oven at 105°C and the mass of dry soil recorded.
• Neutron scattering method• Time Domain Reflectometry (TDR)
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Soil Water Potential
Total soil water potential and
individual potentials
Soil A:Sand Soil10%
Soil B:
Clay Soil15%
Where does water flow?SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Water moves from areas of high potential (wet soil : -2 or -4) to areas of low
potential (dry soil -8)
SoilSoilRoot
-7
-2
-3-.4
-8
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Soil water potential- The amount of work that must be done per unit of a specified quantity of pure water in order to transport reversibly and isothermally an infinitesimal quantity of water from a specified source to a specified destination.
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
The matric potential ( m )
This work is less than zero or negative work, thus reported in negative values.
The pressure potential ( p )
In saturated soil, the pressure potential is always positive. In an unsatrated field soil the pressure potential is always zero.
p=wgh
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
The solute (osmotic) potential ( S )The amount of work an infinitesmal quantity of water will do in moving from a pool of free water the same composition as the soil water to a pool of pure water at the same location. The solute potential is usually very small and negative values.
The gravitational potential ( g )The amount of work an infinitesmal amount of pure free water can do at the site of the soil solution as a result of the force of gravity.
g =±MgZ
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Since soil matric and osmotic potentials are always negative they are often onsidered as ‘suction’ or ‘tensions’. Suction and tensions are however always expressed as positive values.
T= -m
How do you use suction and potentials to decide the direction of soil water movement?
Absolute positive valueSoil moisture suction
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Soil water potential measurement
The popular unite of the soil water potential is : Pa
1 Pa=0.0102-cm column of water
1 atmospheres=1033-cm column of
water=1.0133bar
1 bar=0.9896atm=1020-cm column of water
1 bar=105 Pa
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Kurva Karakteristik Air Tanah
The relationship between the soil-water content (by mass or volume) and the soil-water matric potential.
S=ab
S=a(/s)b
S=A(s-)n/m
S: suction, Pa; θ:water content; a,b,A,n,m: experience constant.
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
0 10 20 30 40 50 60 70
Clay
SiltSand
Soil moisture content%
Affect the factors
• Texture
• Structure
• Temperature
• Phenomenon of hysteresis
Soil m
oisture su
ction
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
SUMBER: http://www.tankonyvtar.hu/en/tartalom/tamop425/0032_talajtan/ch07s05.html
. Jumlah air dalam zona akar di antara FC dan WP , dan yang dapat digunakan oleh tanaman disebut “Air Tersedia”. (FC-WP = air tersedia). Untuk tanah-tanah pasir, lempung dan liat ,
nilai-nilai (air tersedia) adalah 6, 20 dan 17 persen volume.
Pergerakan Air dalam Tanah
1. The principle of water movement in soil2. Evaporation3. Infiltration4. Water redistribution
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Pergerakan Jenuh Air tanah
The rate of water flow through soil can be described by Darcy’s Law which states that the flux of water q is proportional to the hydraulic gradient (the gravitational potential and the pressure potential )multiplied by the conductivity or permeability of the soil.
q KH
Ls
Saturated flow-The movement of water though a soil that is temporarily saturated. Most of the water moves downwards, and some move more slowly laterally.
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
The rate of flow through a given amount of soil in a given time equals the water quantity collected (Qw) divided by both the cross-sectional area of soil
used (A) and the time (t) of measurement.
Konduktivitas Hidraulik Jenuh (Ks)
The characteristics of the saturated hydraulic conductivity:
①The saturated hydraulic conductivity is a constant
② It is maximum in hydraulic conductivity
③ It is decided by the soil texture and the soil structure
The factors of affect the saturated hydraulic conductivity:
• The soil texture
• The soil structure
• The amount of organic matter
• The clay mineral
At
QK w
s
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Pergerakan Tidak-Jenuh Air tanah
The movement of water in soil in which the pores are not filled to capacity with water.
The unsaturted soil water flow is decided by the matric potential and the gravitational potential.
q Kd
dxm ( )
Darcy’s Law can be extended to describe unsaturated flow:
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Konduktivitas Hydraulik Konduktivitas hidrolik merupakan fungsi dari
potensial air tanah.
Konduktivitas ini mengukur kemudahan air untuk
bergerak melalui massa tanah.
Penurunan konduktivitas kalau tanah mengering
terutama disebabkan oleh pergerakan udara ke dalam tanah untuk menggantikan
air tanah.
SUMBER: http://5e.plantphys.net/article.php?id=39
K(m) :unsaturated hydraulic conductivity
d/dx: water potential gradient
The unsaturated hydraulic conductivity is a function of soil matric potential.
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Pergerakan uap air dalam tanah
Bentuk-bentuk gerapan uap air dalam tanah:
1. Difusi uap air dalam tanah
2. Koagolasi uap air
Vapor flow can be considered as a diffusion mechanism in which the driving force is the vapor
pressure gradient.
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Infiltration , water redistribution and evaporation of soil surface
Soil water infiltration
The entry of water into soil.
Affect the factors :Velocity of Supply water
Infiltration rate
SUMBER: http://croptechnology.unl.edu/pages/informationmodule.php?idinformationmodule=1130447123&topicorder=3&maxto=13&minto=1
The stable infiltration rate in several different texture soils ( millimeter/ hour)
Soil SandSandy loam Silt Clay Alkalized
clay
Final infiltration
rate>20 10-20 5-10 1-5 <1
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Redistribusi Air-Tanah
Redistribution of soil water
The process of soil-water movement to achieve an equilibrium energy state of
water throughout the soil.
Soil water redistribution is unsaturated flow of soil water.
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Evaporasi (Penguapan) di permukaan tanah
Evaporation: Water lose as vapor from a soil or open water surface.
1.The keeping the stable stage of evaporation in soil surface
2.The stage of evaporate change with moisture content in soil surface
3.The stage of water vapor diffusion
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Neraca Air Tanah di Lapangan
Soil water balance in the field can be written as: W=P+I+U-E-T-R-In-D
P: precipitation; I: irrigation;
E: evaporation; T: transpiration; R: runoff
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Soil-plant-atmosphere continuum (SPAC)
Water moves from a relatively high potential energy level in the soil (-100 kPa) and flows down a potential gradient into the plant root (-500 kPa), plant stem (-800 kPa), and leaves (-1500 kPa), where it is eventually evaporated into the atmosphere (-10000 kPa).
Desert plants can live in -2×106 to -8×106 Pa.
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
Kontrol Air-Tanah
Air Tersedia:
The amount of water released between in situ field capacity and the permanent
wilting point (usually estimated by water content at soil matric potential of -1.5
MPa).
Ketersediaan Air Tanah
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt
SUMBER: http://www.tankonyvtar.hu/en/tartalom/tamop425/0032_talajtan/ch07s05.html
.Kurva Retensi Air Tanah
Kontrol Air Tanah
1.Olah tanah : plow depth, intertillage, roll etc.
2.Mulsa: straw, plastic sheeting etc.
3.Irigasi: drip irrigation, sprinkler irrigation etc.
4.Biological save water .
SUMBER: jpkc.njau.edu.cn/land/ppt/5.soil%20water.ppt