Water and nitrogen dynamics in rotational woodlots of five tree species in western Tanzania |
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Authors: | GI Nyadzi BH Janssen RM Otsyina HWG Booltink CK Ong O Oenema |
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Institution: | (1) Tumbi Agricultural Research Institute, P.O. Box 306, Tabora, Tanzania;(2) Department of Environmental Sciences, Wageningen University, P.O. Box 8005, 6700 EC Wageningen, The Netherlands;(3) HASHI–ICRAF Agroforestry Project, P.O. Box 797, Shinyanga, Tanzania;(4) The Netherlands Organization for Energy and the Environment, P.O. 8242, 3503 RE Utrecht, The Netherlands;(5) International Centre for Research in Agroforestry (ICRAF), P.O. Box 30677, Nairobi, Kenya |
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Abstract: | The objective of this study was to compare the effects of woodlots of five tree species, continuous maize (Zea mays L.) and natural fallow on soil water and nitrogen dynamics in western Tanzania. The tree species evaluated were Acacia crassicarpa (A. Cunn. ex Benth.), Acacia julifera (Berth.), Acacia leptocarpa (A. Cunn. ex Benth), Leucaena pallida (Britton and Rose), and Senna siamea (Lamarck) Irwin & Barneby). The field experiment was established in November 1996 in a completely randomized block design
replicated three times. Maize was intercropped between the trees during the first three years after planting and thereafter
the trees were allowed to grow as pure woodlots for another two years. Transpiration by the trees was monitored when they
were 3 years old using sap flow gauges. Soil water content was measured using the neutron probe approach between November
1999 and March 2001. Soil inorganic N profiles were measured when the trees were four years old in all treatments. The results
indicated that the trees transpired more water than natural fallow vegetation during the dry season. The difference was apparent
at a depth of 35 cm soil, but was more pronounced in deeper horizons. The water content in the entire soil profile under woodlots
and natural fallow during the dry period was 0.01 to 0.06 cm3 cm−3 lower than in the annual cropped plots. This pattern was reversed after rainfall, when woodlots of A. crassicarpa, A. leptocarpa, A. julifera, S. siamea and L. pallida contained greater quantity of stored water than natural fallow or continuous maize by as much as 0.00 to 0.02, 0.01 to 0.04,
0.01 to 0.04, 0.01 to 0.03 and 0.00 to 0.02 cm3 cm−3, respectively. Natural fallow plots contained the lowest quantity of stored water within the entire profile during this period.
Transpiration was greatest in A. crassicarpa and lowest in L. pallida. All tree species examined were `scavengers' of N and retrieved inorganic N from soil horizons up to 2-m depth and increased
its concentration close to their trunks. This study has provided evidence in semi-arid environments that woodlots can effectively
retrieve subsoil N and store more soil water after rains than natural fallow and bare soil.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | Acacia Leucaena Senna Soil nitrogen Soil water Transpiration |
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