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Secondary Succession Following Slash and Burn Agriculture in North- Eastern India: II. Nutrient Cycling
O. P. Toky and P. S. Ramakrishnan
Journal of Ecology
Vol. 71, No. 3 (Nov., 1983), pp. 747-757
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2259590
Page Count: 11
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(1) The accumulation of elements by vegetation and their rate of uptake and release through litterfall were determined in stands developed during 20 years after shifting agriculture. The concentrations of nitrogen, phosphorus and potassium were higher in the living aerial biomass than in the litter. Trees were found to have a high concentration of calcium, a bamboo of potassium, and herbaceous species of phosphorus. (2) The elements in the above-ground living biomass increased linearly with increase in the age of the fallow until, in the 20-year old fallow, the densities were (g m-2): 49, nitrogen; 6, phosphorus; 138, potassium; 44, calcium; and 23, magnesium. In fallows 10-20 years old, bamboo alone contained 40-45% of the nitrogen, 44-49% of the phosphorus, 54-60% of the potassium, 17-20% of the calcium and 35-40% of the magnesium in the total vegetation. (3) The annual rate of accumulation was maximal after 15-20 years for nitrogen (2.5 g m-2 year-1), 10-15 years for potassium (8.1 g m-2 year-1), and during the first year for phosphorus (0.4 g m-2 year-1). Potassium showed the highest rate of accumulation in different fallows and was 2.5- to 4.5-fold higher than calcium and 3- to 14-fold higher than magnesium. (4) The enrichment quotient (the weight of an element in the vegetation divided by its rate of uptake) was higher for phosphorus and potassium than for nitrogen, calcium and magnesium, indicating the rapid rate of accumulation of phosphorus and potassium in the standing biomass. The density of elements in the soil was minimal in 5-10 year old fallows. The annual return of elements through litterfall increased with the age of the fallow during the 20 years of study.
Journal of Ecology © 1983 British Ecological Society