In soil science, particles that are less than ( ) microns in diameter are called soil colloids.
A. one
B. two
C. three
D. four
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For Inorganic nitrogen, ______ and nitrate nitrogen can be absorbed by plant directly.
Mineral potassium is the main forms of soil K.
There is a potassium deficiency in the Southeast of China.
Potassium is taken up by plants in quantities second only to nitrogen.