6) Soil testing from a well-drained soil sample in 0-15cm depth of a farmers fie

Question

6) Soil testing from a well-drained soil sample in 0-15cm depth of a farmers field provides the following
information:

• Wet weight of a soil sample from a volume of 100 cm3: 200 g
• Moisture content: 20%
• Soil chemical properties (in cmol/kg):

Exchangeable K: 2
Exchangeable Ca : 10
Exchangeable Mg: 4
Exchangeable H: 8

• Molar mass of H+ = 1; Mg2+ = 24; K+ = 39; Ca2+ = 40

a) 2 marks. What is the bulk density of this soil?
b) 4 marks. How many kg ha-1 of exchangeable Mg2+ is there in the top 15cm of this field?
c) 1 mark. What is the percent base saturation?

Explanation / Answer

Volume of soil sample = 100 cm3

Weight of soil sample = 200 g

Then,

bulk density of soil sample = weight/volume

=200g / 100 cm3

= 2 g/cm3

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