Abstract. Long term fallow is no longer possible in densely populated tropical areas, but legume cover crops can help maintain soil fertility. Our work aimed to study changes in soil carbon in a sandy loam Ultisol in Benin, which involved a 12‐year experiment on three maize cropping systems under manual tillage: traditional no‐input cultivation (T), mineral fertilized cultivation (NPK), and association with Mucuna pruriens (M). The origin of soil carbon was also determined through the natural abundance of soil and biomass 13C. In T, NPK and M changes in soil carbon at 0–40 cm were −0.2, +0.2 and +1.3 t C ha−1 yr−1, with residue carbon amounting to 3.5, 6.4 and 10.0 t C ha−1 yr−1, respectively. After 12 years of experimentation, carbon originating from maize in litter‐plus‐soil (0–40 cm) represented less than 4% of both total carbon and overall maize residue carbon. In contrast, carbon originating from mucuna in litter‐plus‐soil represented more than 50% of both total carbon and overall mucuna residue carbon in M, possibly due to accelerated mineralization of native soil carbon (priming effect) and slow mulch decomposition. Carbon originating from weeds in litter‐plus‐soil represented c. 10% of both total carbon and overall weed residue carbon in T and NPK. Thus mucuna mulch was very effective in promoting carbon sequestration in the soil studied.
Summary
The influence of aggregate stability on run‐off and erosion has often been reported from experiments on microplots (about 1 m2) under simulated rain. Our objective was to compare the aggregate stability of topsoil (0–10 cm) with run‐off and erosion from experiments on run‐off plots (about 100–1000 m2) under natural rain. Run‐off and soil losses were measured over three years on 14 plots in Benin, Cameroon and Mexico. All plots were under herbaceous vegetation and had moderate slope length and slope declivity, but differed in climate (400–1600 mm annual rainfall), soil type (sandy clay loam Nitosol, loamy sand Ferralsol, loamy Regosol), and management (from savanna to long‐duration mouldboard ploughing). The stability of aggregates was determined by immersing and wet‐sieving 2‐mm sieved air‐dried samples into water.
Mean annual run‐off rate and soil losses generally increased, and the proportion of stable macroaggregates (> 0.2 mm) decreased, with increasing duration and intensity of tillage, and with decreasing cover on the soil surface. For all 14 plots, run‐off and soil losses were closely correlated with aggregate stability; correlations were improved when slope gradient and climate aggressivity were considered in addition to aggregation. Slaking, the main mechanism of aggregate breakdown which occurs when dry soil is immersed, accounted well for run‐off and erosion. The stability of topsoil aggregates seems therefore to be a valuable indicator of field‐assessed run‐off and erosion for plots on moderate slopes with herbaceous vegetation.
RESUMEEn vue d'évaluer les arrières effets d'une fumure d'engrais minéral sur la croissance du maïs et la capacité des champignons endomycorhiziens à mobiliser le phosphore, quatre cultures successives de maïs ont été conduites en pots sous serre sur des échantillons de sol collectés au niveau de trois types de 'jachère' manioc ayant comporté les variétés de manioc Ben 86052, Bouaké (variété traditionnelle introduite), et odongbo (variété locale utilisée comme référence). Deux doses d'engrais complexe N 14 P 23 K 14 (0 et 100 kg/ha correspondant à 14 kg de N; 10,12 kg de P et 11,62 kg de K) ont été appliquées à la première culture de maïs en champ en 2004. On note une baisse significative (P<0,001) des biomasses racinaires et aériennes du maïs en pot et de la quantité de P mobilisée par les plants au cours des cultures successives avec un effet plus prononcé au niveau de la 'jachère' Ben 86052. Les types de 'jachère', l'effet de la précédente fumure et la succession des cultures influent significativement (P<0,001) sur le taux de colonisation des racines par les spores des champignons endomycorhiziens. On note des corrélations hautement significatives (P<0,001) entre le taux de colonisation des racines par les spores des champignons endomycorhiziens, et la quantité de P mobilisée.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.