Porosity the soil’s respiratory and circulatory system White zones are pores > 1mm No-till soil Tilled soil (Young and Ritz, 2000)
Soil pores come in many sizes and shapes http://www.mtm.kuleuven.ac.be/Research/NDT/IDO_SHerman_final.ppt
Intensive tillage Long term no-till well connected network of biopores plow pan AgriCanada
Effect of previous 20 years of rotations on SOM and corn growth on Beltsville silt loam in Maryland Continuous bluegrass sod Continuous corn with tillage
20 yrs of bluegrass, then 5 yrs CT corn 25 yrs of CT corn
After adding water After adding water 25 yrs of conventional corn 20 yrs of bluegrass, then 5 yrs conventional corn
Not enough O2 for root respiration Soil too hard for roots to penetrate Least Limiting Water Range LLWR for loose well-aggregated soil LLWR for compacted soil Root growth rate 20 25 30 35 40 45 50 55 dry Soil water content, cm3/cm3 *100 wet From Weil, 2003 Ray Weil
How does compaction affect a soil’s least limiting water range? 100 75 LLWR Soil Moisture (% of saturation) 50 8” 25 16” June July August Uncompacted soil Compacted soil
Compacting effects of wheel traffic Bulk density Cone resistance Number of wheel passes Chapter 7 in Ross (1989)
AgriCanada Without restricted traffic, most field surfaces receive traffic each year
Tillage and traffic damages wet soils !!! Soils with more OM are weaker when dry and stronger when wet ! Compaction (Watts and Dexter, 1997)
Why are soils more compactible at field capacity than at saturation? Soil will flow before water filled pores collapse
Prenetrometer pressure Moisture strongly affects penetration resistance!! > 3 MPa 1 - 3 MPa < 1 MPa The same soil can be hard when dry and weak when wet. 1 MPa = 145 psi http://www.bettersoils.com.au/module6/6_3.htm
Understanding bulk density Soil structure must be intact and soil must be oven dry
It is often said that bulk densities > 1.6 g / cm3 are root restrictive… Is this true ??
So how does compaction impact soil water relationships ? Loss of drainage pores Gain in small pores
Soil circulatory system Field Capacity Saturation Drainage pores Most available 10-30 μm Wilting point Plant available water less available ~0.2 μm Unavailable water Adapted from Buol (2000)
Impact of texture on soil water 35 - 14 Available water 21% 21% of 12” ~ 2.5” Brady and Weil, 2002
SOM increases plant available H20 Adapted from Brady and Weil (2002)
Visualizing water in a 1 foot layer of soil Macropores 50% porosity saturation 6” Plant available H2O 2.5” Total water at field capacity 3.5” 50% plant available H2O 1.25” 12” 50% solids 6”
What will happen if more than 1.25” of water infiltrates into this soil ? How much water is need to bring the soil to field capacity ? 1.25” 50% plant available H2O Water will percolate deeper than 1’
How fast does water move through soil ? Darcy’s Law Hydraulic conductivity Flow rate = Area*Ksat *pressure head/length Brady and Weil, 2002
Permeability = Hydraulic conductivity Flow rate ~ pore radius4
How does the presence of a coarse textured layer under a fine textured layer affect percolation ? Fine textured layer Coarse textured layer
Water will not enter the coarse textured layer until the upper layer is near saturation Coarse textured layer After water enters the coarse textured layer, it will percolate more quickly. http://www.personal.psu.edu/asm4/water/drain.html
Does a thin layer of coarse material improve drainage ? Thin layer with coarser texture NO !
Systems for rapidly draining surface water should be open to the surface Soil capped slit Slit filled with coarse material
Slit trenching equipment Outlets are needed !!
The current guide reflects recent developments in drainage science and technology. Most of these are related to new equipment and materials, widespread use of computers, and water quality considerations. It includes information not in the previous edition on pipeline crossings, water and sediment control basins, drain fields for septic systems, design of drainage water management systems, and design charts for smooth-walled pipes.
In Illinois, soil drainage is rated using a number (1 to 4) and letter (A or B) system. The number indicates the degree of soil permeability. The letter indicates the natural drainage. IL Permeability classes
Bioreactor vs. standard tile outlet
One calorie is the amount of thermal energy required to raise the temperature of one gram of water by one Celsius degree. 3000 calories of thermalenergy enters each cup.The temperature of thewater on the left rises by30 Celsius degrees.By how much does thetemperature of thewater in the cup on theright rise ??
Why does soil heat up faster than water ? The heat capacity of water is ~ 5 times higher than the heat capacity dry soil. As a result, moist soils heat up and cool down more slowly than dry soils.
Water has a high thermal conductivity Air has a low thermal conductivity What can be done to maximize geothermal heat transfer ? compacted vs. loose ? moist vs. dry ?