Journal of Animal and Plant Sciences
J. Anim. Plant Sci. [ISSN 2071 - 7024]
Volume 4 (3): 384 - 398. Published October 18, 2009.
Native soil N mineralization in major rice based cropping systems
Jean-Pierre Bognonkpe*^and Mathias Becker**
*UFR SN - University of Abobo-Adjame – Abidjan, 02 BP 801 Abidjan 02, Cote d’Ivoire ; ** Institute for Plant Nutrition, University of Bonn, Karlrobert-kreitenstr 13, 53115 Bonn, Germany
*Corresponding author Email: j.bognonkpe@gmx.de
SUMMARY
A laboratory and field study was conducted in Côte d’Ivoire during the dry-to-wet season transition period (DWT) of 1996 and 1997 with the objective of quantifying native soil nitrogen (N) mineralization dynamics in the major rice based system. It comprised of (1) an incubation study under controlled conditions in the laboratory in 1996 to determine soil N mineralization potential using soil samples from the 10 major rice based systems of Côte d’Ivoire, (2) a detail soil survey in 1997 to quantify in situ soil N dynamics in 6 rice based systems of Gagnoa (bimodal forest zone) with weekly soil samples being analyzed for ammonium and nitrate. Results indicated that the amounts of the mineral soil N (Nmin) strongly varied by system as well as in space and time. Nitrogen mineralization trends in time were similar for both ammonium and nitrate. Extensive systems showed higher N mineralization than intensive systems. Peak levels of soil Nmin were observed under upland conditions, reaching up to 42 kg N ha-1 in the humid forest zone. The dry-to-wet season transition period was composed of successive increases and decreases in soil Nmin, following the fluctuating soil moisture content. Soil mineral N declined throughout the cropping season as rainfall intensity increased. Plant N uptake can partially explain this decrease, but it is likely that large losses from the soil-plant system resulted from the action of surface runoff (nitrate leaching) and lowland moisture saturation (denitrification). The largest decline in mineral soil N (highest N losses) was observed in the period between land clearing and rice crop establishment. Technical options aiming at increasing the use efficiency of native soil N should target this transition period.
Key words
Denitrification, leaching, mineralization, nitrogen, rice-based, systems.
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