No abstract

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The present study deals with root architecture of 6-year-old trees of 9 indigenous and 3 exotic species growing in and climate of north-western India. Observations, made on excavated root systems (3 tree rephcates of each species) showed large variation in horizontal and vertical spread of roots. In Morus alba, Melia azedarach and Populus deltoides, the roots were confined to 80 cm, while m Prosopis cineraria, Acacia nilotica and Eucalwtus terettcornis, roots penetrated more deeply to 233 cm. The number of total roots ranged from 103 in Acacia catechu to 1932 in Eucalyptus teretwornis, and 62 to 80% of the roots were less than 2 mm in diameter. The primary roots were more horizontal than the secondary roots. The total root biomass varied from 2.2 kg in Acacia catechu to 30.6 kg -~ tree in Popuhts deltoides, and top 30 cm soil contained 42 to 78% of the total biomass. The imphcations of the results are discussed in the context of the ecological niche of the species, and its usefulness in agroforestry systems.

1 6 ' i. TABLE IV. Total Loss of Nutrients (kg/ha/yr) in Run-off Water from Agro-ecosystems under Various Jhum Cycles.M J J A S 0 M J J A S 0 MONTHS M J J A S 0 Fig. 5. Changes in concentration of potassium (A), calcium (B), and magnesium (C), in run-off water during the monsoon at time of cropping after bum on sites under 30-(•), 10-(o), and 5-(*•/, years'Jhum cycles. J J A S 0 M J J A S 0 MONTHS M J J A S 0

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Ecology. SUMMARY(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-'), 10-15 years for potassium (8. 1 g m-2 year-'), 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 2.5to 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.