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Table 4. Circulation of nutrients in the above-ground portion of a 20-year-old Loblolly Pine (Pinus taeda) plantation in Mississippi (*). Among the major nutrients, retranslocation is greatest for nitrogen, phosphorus, and potassium. This results from their high mobility. The leaching losses of potassium are very high because K is not a structural component of organic compounds but rather exists in ionic form (K+) and participates in charge balance regulation.

Process	N	K	Ca	Mg	P
	kg/ha/yr
Uptake	59.5	27.4	7.4	4.6	5.0
Canopy Leaching	3.3	16.0	3.0	1.0	0.5
Retranslocation from senescing foliage	26.9	3.3	6.9	0	1.5
Litterfall	27.9	1.3	5.2	6.9	2.4

(*) Data from Switzer and Nelson (1972)

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