Lab 4 Flashcards
What is bulk density?
mass of dry soil solids per unit total volume of soil
What does bulk density take into account?
pore space and weight of solid particles
characteristics of low bulk density?
- granulated, loose, fluffy
- good pore space for oxygen and water
- OM is present
- good drainage
- encourages root elongation
characteristics of high bulk density?
compacted - particles close together
Calculate % moisture on the basis of the oven dried soil
% soil moisture content = [(Loss in weight upon drying)/(Oven dry weight of soil)] x 100
Calculate the % moisture (% water content) of your soil
% water content by volume = [(Volume of water from soil in the core)/(Volume of soil)] x 100
What is particle density?
mass per unit volume of the dry soil solids
What does not affect particle density?
Size and arrangement of the soil particles
What influences particle density?
OM - calculated particle density includes organic particles and mineral particles
How to determine volume of water displaced (need this to calculate what?)
Add 50 mL to a 100 mL graduated cylinder, then add 20 g of sieved, oven dry topsoil. The new recording minus 50 g is the volume of water displaced.
Needed to calculate particle density
Particle density equation
Particle density = (weight of soil [20 g])/(Volume of water displaced)
What is an important conversion rate to remember during these labs?
1 g or water = 1 ml of water = 1 cm^3 of water
What are we supposed to assume particle density of our soil to be in this lab?
2.65 g/cm^3
What is porosity?
proportion of a soil volume that is not composed of solids
What happens in terms of water flow if pore spaces are too large?
water drains away faster than plants can utilize it
What happens in terms of water flow if pore spaces are too small?
poor drainage and build up of water –> lack of O2 in rooting zone & poor root development
What do you need in order to calculate porosity of a soil in its dry state?
bulk density and particle density
Bulk density equation + units
(mass of dry soil)/(Total volume of soil)
unit - (g/cm^3)
Particle density equation + units
(mass of dry soil)/((Volume of soil solids)
unit - (g/cm^3)
Porosity (%) =
100 - % solid space
or
[1-(bulk density/particle density)] x 100
% solid space =
(Bulk density)/(Particle density) x 100
What 3 things can one measure related to soil moisture?
- % water content by weight
- % water content by volume
- % saturation
% water content by weight =
(mass of water from soil in the core)/(mass of dry soil) x 100
% water content by volume =
(volume of water from soil in the core)/(volume of soil) x 100
% saturation =
% pore space occupied by water = (volume of water from soil in the core)/(volume of pore space) x 100
must calculate volume pore space 1st
Volume pore space =
(% porosity)/100 x Volume of core