Nutrient Cycling in a Stand of Acacia holosericea A. Cunn. Ex G. Don. III. Calcium, Magnesium, Sodium and Potassium.

Abstract

Nutrient cycling by a 3-year-old Acacia holosericea plantation (1111 trees ha^-1) was studied over a 13-month period. The gross accumulation of each nutrient in the various above-ground organs was calculated from the net increase over the study period plus the amounts lost by leaching and litterfall. Gross accumulation was greatest for calcium (22.4 kg ha^-1), and potassium (18.8 kg ha^-1), sodium (6.8 kg ha^-1), followed by magnesium (5.2 kg ha^-1). Biochemical recycling was greatest for calcium (10%) magnesium (8%), sodium (3%) and potassium (2%); however, this may be an overestimate as some of the apparent mobilization was undoubtedly due to leaching. Litter return accounted for 14% of the gross accumulation for potassium, 11% of magnesium, 10% of sodium and 9% of calcium. Litterfall accounted for 90% of the return of calcium to the soil and 75% of the return of magnesium. On the other hand, transfer in solution (leaching, surface wash) accounted for 88% of the return of sodium from the canopy to the soil and 59% of the return of potassium.

Over the period 1 January 1979 to 28 February 1980 (total rainfall 2261 mm), the addition of nutrients in area precipitation was greatest for sodium (23.6 kg ha^-1), followed by potassium (11.2 kg ha^-1), calcium (6.8 kg ha^-1) and magnesium (1.8 kg ha^-1). Throughfall and stemflow increased the concentration of nutrients, such that the total nutrient addition to the soil was greatest for sodium (28.8 kg ha^-1) followed by potassium (15.0 kg ha^-1), calcium (7.0 kg ha^-1) and magnesium (2.0 kg ha^-1). These additions to the soil are significant in relation to the gross accumulation of these elements by Acacia holosericea.