Christopher Kanema, Mathias Becker:
Production Potential of Wetland Soils of the Kafue Flats in Zambia

CHRISTOPHER KANEMA¹, MATHIAS BECKER^2
1Environmental Council of Zambia, Inspectorate, Zambia
²University of Bonn, Institute of Crop Science and Resource Conservation (INRES) - Plant Nutrition, Germany

Despite the general belief that wetlands are more robust to anthropogenic interventions than uplands, degradation phenomena and productivity declines have been observed in some intensively used wetlands where sites have been abandoned. We hypothesise that the effects of cultivation on resource base quality and production potential in the wetlands of Kafue are likely to depend on the type and hydrologic conditions of the soil as well as on the type, intensity and duration of land use.

Soil samples (0-20cm) were collected under different use types and durations, These were analysed for diverse physio-chemical soil parameters, including carbon fractions and the N supplying capacity. Additionally, rice biomass accumulation and nutrient uptake were determined in a greenhouse pot experiment under both flooded and aerobic soil conditions. Both type and duration of land use affected rice performance and soil quality parameters. Total N and C were highest in undisturbed soil (2.5% C and 0.2% N) and declined to 1.1% C with cultivation under vegetables and 0.04% N under rice. This decline was more pronounced under paddy rice than maize or vegetables. The labile C content and the soil N supplying capacity reacted most sensitively to cultivation history. Labile C declined from 2 to <0.8 mg kg^-1 and the net N supply never exceeded 10 mg NH₄ -N kg^-1 in soils used for >5 years, irrespective of the type of crop. Similarly exchangeable K and available P declines were most pronounced in rice soils. The aboveground biomass accumulation and mean nutrient uptake by pot"=grown rice differed among land use types and was 1.5 to 2 times higher under flooded than aerated soils. Irrespective of soil aeration status, the highest biomass and NPK uptake of rice were observed in uncultivated soil. The negative effects of cultivation duration on plant growth and nutrient uptake was more in soil previously cultivated to rice and higher in aerobic than anaerobic conditions.

In summary, current land use in Kafue Flats results in decline of soil quality. The associated effects on crop production were more pronounced under aerobic than flooded soils.

Keywords: Kafue flats, plant nutrition, wetlands

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Contact Address: Christopher Kanema, Environmental Council of Zambia, InspectorateP.O. Box FW, 439, 10101 Lusaka, Zambia, e-mail: cmkanemagmail.com