Carbon, nitrogen and phosphorus allocation in agro-ecosystems of a West African savanna III. Plant and soil components under continuous cultivation

Manlay, R. J.; Chotte, J-L.; Masse, D.; Laurent, J-Y.; Feller, C.

Abstract:

Carbon (C) and associated nutrient budgets related to land use in agro-ecosystems in West African savannas (WAS) are a matter of both local (sustainability of farming systems) and global (C balance) concern. In a mixed-farming system in southern Senegal, patterns of C, nitrogen (N) and phosphorus (P) allocation in the plant-soil system (down to a 40 cm soil depth) were compared at harvest in 14 plots, six being under semi-permanent cultivation with groundnut (Arachis hypogaea L.), others being under continuous cultivation with millet (Pennisetum glaucum L.), maize (Zea mays L.) or rice (Oryza sativa L.). Carbon stored in the plant-soil system amounted to 25.0, 27.4, 34.9 and 71.9 t per ha, respectively, in groundnut, millet, maize and rice fields. Ninety percent of C and P (total in plant P-t, available P in soil (POD)) and 95% of N of the whole ecosystem were stored in the soil. The high C and nutrient amounts found in rice plots were attributed to the clayey texture of the soil and to seasonal flooding. The lower values for C, N and POD found in soils in the bush ring (groundnut crops) compared to those of the compound ring (millet and maize crops) stemmed from land management. Higher values for C, N and POD in soils in the compound ring were maintained under continuous cultivation thanks to higher organic and nutrient inputs originating from crop residue recycling, manuring and, in the maize plots, spreading of household wastes. In the compound ring, the amount of C stored seemed to depend as much on the amount of C input as on the chemical richness of organic inflow. The effect of land management (bush versus compound ring) on soil properties was generally restricted to the 0-20 cm layer (except for P, cations and pH), and the better soil status in the compound ring was linked to nutrient depletion of the bush ring. From the perspective of global change, the estimated potential of the WAS for C sequestration under continuous cultivation was found to be low. From a methodological point of view, soil carbon status may be considered as a relevant indicator for the fertility of agro-ecosystems in the WAS belt, provided that its biotic components are included, and that both the quality and dynamics of soil organic matter (assessment of seasonal variations, and C flows) and soil texture are characterised. (C) 2002 Elsevier Science B.V. All rights reserved.

Year:

2002

Type of Publication:

Article

Keywords:

carbon continuous cultivation manure nitrogen phosphorus plant biomass root savanna senegal soil organic-matter farming system management agriculture balances amazonia tropics manure Sénégal climat tropical sub-humide zone soudanienne

Journal:

Agriculture Ecosystems {&} Environment

Volume:

88

Number:

3

Pages:

249-269

Note:

Times Cited: 0 Article English Cited References Count: 47 531jn