Impact de l&8217;agriculture climato-intelligente sur les stocks de carbone organique du sol à Madagascar

Climate smart agriculture is presented as a solution to alleviate food insecurity, mitigate climate change and contribute to climate change adaptation. In Madagascar, different sustainable agricultural practices were implemented in the last 20 years by many non-governmental organizations in order to increase crop yields, maintain soil fertility and increase household income. These practices are conservation agriculture, agroforestry systems and the use of organic fertilizers as compost and manure. This study aimed to compare the soil organic carbon storage of some climate smart practices in the Malagasy context. The soil organic carbon stock of each practice, distributed in several sites among the island, was measured and compared with the traditional practices of each study site. For conservation agriculture, the differences in the soil organic carbon content varied from 0 to 1.82 MgC ha(-1) year(-1) when compared with traditional practices (tillage and crop residues exported). For agroforestry, a difference in the soil organic carbon content of 0.68 Mg Cha(-1) year(-1) was found when comparing with the slash and burn practices in the East Coast of Madagascar but no significant soil organic carbon content was found in the Malagasy Highlands. The use of organic fertilizers such as manure, compost and urban organic waste led to an increase of soil organic carbon of 0.16, 0.81 et 0.42 Mg Cha(-1) year(-1) respectively, but these increases were not significant due to the great variability of soil organic carbon values. Results confirm the capacity of some climate smart practices to store more carbon in the soil and hence to compensate for greenhouse gases emissions. However, the storage potentiality is quite different according to the practice and its spatial extent

Impact de l&8217;agriculture climato-intelligente sur les stocks de carbone organique du sol à Madagascar

Climate smart agriculture is presented as a solution to alleviate food insecurity, mitigate climate change and contribute to climate change adaptation. In Madagascar, different sustainable agricultural practices were implemented in the last 20 years by many non-governmental organizations in order to increase crop yields, maintain soil fertility and increase household income. These practices are conservation agriculture, agroforestry systems and the use of organic fertilizers as compost and manure. This study aimed to compare the soil organic carbon storage of some climate smart practices in the Malagasy context. The soil organic carbon stock of each practice, distributed in several sites among the island, was measured and compared with the traditional practices of each study site. For conservation agriculture, the differences in the soil organic carbon content varied from 0 to 1.82 MgC ha(-1) year(-1) when compared with traditional practices (tillage and crop residues exported). For agroforestry, a difference in the soil organic carbon content of 0.68 Mg Cha(-1) year(-1) was found when comparing with the slash and burn practices in the East Coast of Madagascar but no significant soil organic carbon content was found in the Malagasy Highlands. The use of organic fertilizers such as manure, compost and urban organic waste led to an increase of soil organic carbon of 0.16, 0.81 et 0.42 Mg Cha(-1) year(-1) respectively, but these increases were not significant due to the great variability of soil organic carbon values. Results confirm the capacity of some climate smart practices to store more carbon in the soil and hence to compensate for greenhouse gases emissions. However, the storage potentiality is quite different according to the practice and its spatial extent

Fonctionnement du sol sous SCV au Brésil et à Madagascar : Abondance et rôle des ingénieurs du sol sur la dynamique du carbone du sol = Fonctionnement du sol sous SCV au Brésil et à Madagascar : Abondance et rôle des ingénieurs du sol sur la dynamique du carbone du sol.

Direct seeding mulch-based cropping (DMC) systems in the tropics are often described as decreasing erosion, increasing soil carbon storage, decreasing greenhouse gas emissions and increasing biomass production. Soil biota, either microorganisms or fauna, are also said to be strongly modified in DMC systems when compared to traditional tilled systems. Here we present results concerning the abundance (in terms of density and biomass) of soil macrofauna in DMC, traditional and natural systems from Brazil (Rio Verde) and Madagascar (Antsirabe). In a second part we analyse and discuss the role of the main ecosystem engineers (earthworms and Coleopteran larvae) on soil carbon dynamics. The role of ecosystem engineers was approached by laboratory and field experiment in Madagascar. In laboratory, we observed that Coleopteran larvae concentrate organic carbon in their faeces at the difference of endogeic earthworms. In a mesocosm field experiment we studied the effect of endogeic earthworms on soil organic matter and soil functioning according to the localization and quality of residues. In this short-term experiment (5 months) we observed that earthworms increased the amount of soil carbon in their casts and that this carbon was not protected against mineralization.Les systèmes en semis direct sous couverture végétale (SCV) dans les tropiques sont souvent décrits comme diminuant l’érosion, augmentant le stockage du carbone, diminuant les émissions de gaz à effet de serre et augmentant la production de biomasse. Les organismes du sol, microorganismes et faune, semblent également être fortement modifiés dans les systèmes SCV si on les compare à des systèmes traditionnels labourés. Nous présentons ici des résultats concernant l’abondance (en termes de densité et de biomasse) de la macrofaune du sol dans des systèmes SCV, traditionnels et dans des systèmes naturels au Brésil (Rio Verde) et à Madagascar (Antsirabe). Dans une deuxième partie, nous analysons et discutons le rôle des principaux ingénieurs du sol (vers de terre et larves de Coléoptères) sur la dynamique du carbone du sol. Le rôle des ingénieurs du sol a été étudié par des expériences en laboratoire et au champ à Madagascar. Au laboratoire, nous avons observé que les larves de Coléoptères concentraient le carbone organique dans leurs déjections, à la différence des vers de terre endogés. Dans une expérience au champ en mésocosmes, nous avons étudié l’effet des vers de terre endogés sur la matière organique du sol et le biofonctionnement du sol, en fonction de la localisation et de la qualité de résidus apportés. Dans cette expérience à court terme (5 mois), nous avons observé que les vers de terre augmentaient le taux de carbone dans les turricules mais que ce carbone n’était pas protégé contre la minéralisation