Phytoextraction du cadmium, du cuivre, du plomb et du zinc par Vetiveria nigritana en sols ferrugineux tropicaux et en sols vertiques au Burkina Faso (Afrique de l’ouest)

La phytorémediation est une technique alternative d’extraction des métaux lourds dans les sols contaminés. La capacité de Vetiveria nigritana à accumuler le cadmium (Cd), cuivre (Cu), plomb (Pb) et zinc (Zn) a été étudiée dans les sols ferrugineux tropicaux et les sols vertiques du Burkina Faso. L’étude a été conduite sous une ombrière et le taux de survie, l’accumulation des métaux lourds et la croissance de Vetiverianigritana aux différentes concentrations de Cd, Cu, Pb et Zn ont été déterminés. Les sols ont été contaminés aux métaux lourds par application de déchets urbains solides aux doses de 0, 10, 15 et 20 tonnes/ha. Les résultats ont montré un potentiel de Vetiveria nigritana à accumuler les métaux lourds. Les feuilles ont exporté 4, 5, 9 et 14 fois plus de Cd, Zn, Cu et Pb que les racines. Les plantes cultivées dans les sols ferrugineux ont exporté des quantités de métaux lourds supérieures (0,91 mg de Cd, 1,75 mg de Cu, 2,30 mg de Pb et 17,69 mg de Zn) comparativement aux plantes cultivées dans les vertiques (0,57 mg de Cd, 0,56 mg de Cu, 0,25 mg de Pb et 6,61 mg de Zn). Les biomasses sèches des feuilles et des racines ont augmenté avec les quantités dedéchets apportées. Elles sont de 13,84 et 26,99 g de feuilles  respectivement avec les applications de déchets aux doses de 0 et 20 tonnes/ha, et 8,88 et 32,99 g de racines avec les doses de 0 et 20 tonnes/ha. L’apport de déchets urbains solides a augmenté la performance des plantes tant du point de vue de la croissance en hauteur(87,5%) que du nombre de talles (84,7%)

Separating autotrophic respiration due to roots from soil heterotrophic respiration in an agroforestry parkland system in Saponé, Burkina Faso

Soil respiration is the largest component of ecosystem respiration but little is known about it and its components in parkland systems. We therefore conducted an experiment to estimate the amount of CO2 respired and to partition it into soil, tree root and crop root contributions in parkland systems in Burkina Faso. Three factors effects were estimated: pruning, species and presence of tree canopy. Pruning showed no significant effect on soil respiration. The soil respiration was significantly higher under Parkia biglobosa (1.54 g CO2 m-2 h-1 against 0.93 in the open area) than under Vitellaria paradoxa (0.98 g CO2 m-2 h-1 against 0.52 in the open area). The autotrophic respiration associated with the P. biglobosa system due to sorghum roots was 0.37 g CO2 m-2 h-1 and due to tree roots was 0.61. For the V. paradoxa system, the figures were 0.13 g CO2 m-2 h-1 for sorghum roots and 0.46 for tree roots. We observed higher CO2 emissions from under trees crowns than in open areas owing to higher tree-root respiratory activities, and higher water and organic matter contents. However, further studies are needed to discover if these low values of soil CO2 fluxes from parklands translate into higher amounts of carbon fixed than emitted taking into consideration the seasonal variations.Keywords: Carbon balance, CO2 flux, carbon-sink, carbon-source

Influence des phosphates naturels sur la qualité et la biodégradation d'un compost de pailles de maïs

Influence of Indigenous Phosphate on Maize Straw Compost Quality and Biodegradation. Soil organic matter and phosphorus scarcities are the main constraints for intensification of crop production in Burkina Faso. To propose an adequate method to produce good quality organic matter, a study, in controlled conditions, was conducted using a Lixisol to evaluate the biodegradation of composts made of maize straw, rock phosphate, animal manure and a synthesis inoculum (SI). Composts obtained from composting maize crop residues + manure ± SI had C/N of 19 and 18, respectively. Influence of composts produced on soil CO2 production was related to the type of compost and to nitrogen application. An increase of 53% of CO2 production due to nitrogen application was observed when compost produced with manure and SI was incorporated in the soil. This increase was 118% with incorporation of the compost obtained with manure, SI and rock phosphate. These results suggest that there is potential to produce high quality organic inputs by composting maize straw in presence of rock phosphate

Effect on stone lines on soil chemical characteristics under continuous sorghum cropping in semiarid Burkina Faso

In the semiarid Sahel, farmers commonly lay stone lines in fields to disperse runoff. This study was conducted in northern Burkina Faso to assess the chemical fertility of soil under a permanent, non-fertilised sorghum crop, which is the main production system in this area, 5 years after laying stone lines. The experimental design consisted of four plots in which stone lines had been laid. The spacing between the lines was 100 m in the first plot, 50 m in the second, 33 m in the third, and 25 m in the fourth. To determine soil chemical characteristics in relation to the stone line spacing patterns studied, soil samples were taken from subplots at regular and fixed distances from the lines at the start of the trial and then 5 years later. Under the continuous non-fertilised sorghum cropping system, the beneficial effect of stone lines on soil fertility was limited. Five years after installing stone lines, soil organic C, total N, available P and Na concentrations and soil pH had decreased. Within the plots, these same variables were higher upslope than downslope of stone lines, probably because of water storage and sediment accumulation in front of the stone lines. In plots where stone lines were relatively close together (<33 m) the decrease in soil fertility was less. It is concluded that in Sahelian zones, stone lines alone are not sufficient to insure the conservation of soil fertility. Combining soil and water conservation techniques with soil fertility management practices are needed to sustain soil productivity

Connaissance endogène de la classification et de la fertilité des sols en zone Sud-Soudanienne du Burkina Faso

Indigenous knowledge has been neglected by policy leaders and research for development. This study was carried out in October 2012 in two localities (Mahon and Diéri) located in the Kénédougou province (Burkina Faso). The aim was to valorize indigenous soil classification and soil fertility perception. We studied soil units along topographic units. The toposequences were selected according to geology and geomorphology. Soils classification was established in the field, based on semi structured interviews by using focus group method with tagba and sɛmɛ farmers. Visual method was used to describe topography, color, vegetation and tactile method was used to determine texture and coarse elements. The description was focused on the upper soil (0-20 cm) only. Soil composite samples were taken in the first 20 cm, to assess indigenous soil fertility perception. We found that soil classification criteria were based on topography and soil morphological characteristics and vegetation. Soils fertility was assessed on the basis of color and vegetation. In spite of a few minor variations in some soil qualities, soil physicochemical properties perception was consistent with laboratory results, proving tagba and sɛmɛ farmers had good knowledge on soil classification criteria

Connaissance endogène de la classification et de la fertilité des sols en zone Sud-Soudanienne du Burkina Faso

Indigenous knowledge has been neglected by policy leaders and research for development. This study was carried out in October 2012 in two localities (Mahon and Diéri) located in the Kénédougou province (Burkina Faso). The aim was to valorize indigenous soil classification and soil fertility perception. We studied soil units along topographic units. The toposequences were selected according to geology and geomorphology. Soils classification was established in the field, based on semi structured interviews by using focus group method with tagba and sɛmɛ farmers. Visual method was used to describe topography, color, vegetation and tactile method was used to determine texture and coarse elements. The description was focused on the upper soil (0-20 cm) only. Soil composite samples were taken in the first 20 cm, to assess indigenous soil fertility perception. We found that soil classification criteria were based on topography and soil morphological characteristics and vegetation. Soils fertility was assessed on the basis of color and vegetation. In spite of a few minor variations in some soil qualities, soil physicochemical properties perception was consistent with laboratory results, proving tagba and sɛmɛ farmers had good knowledge on soil classification criteria