Root impact on the stability and types of micro-aggregates in silty soil under maize

Summary We wished to assess the impact of maize roots on the stability, nature and formation of soil organomineral aggregates under field conditions. We sampled coarse‐textured soil, cropped with maize for 3 years, and combined in situ study of the root system with evaluation of soil structural stability. We examined root morphology (i) on thin sections of still recognizable root tissues, and (ii) at the interfaces between roots and soil, using transmission electron microscopy (TEM) to differentiate between fine and coarse roots. Soil structural stability was evaluated in relation to a spatial gradient of increasing distance from the roots. For that we distinguished between soil adhering to roots and that not adhering in the rhizosphere, and soil between the rows of this crop, and used two methods of granulodensimetric soil fractionation involving different disaggregation strengths. We isolated and identified the organomineral associations in the soil fractions determining soil stability. We found that the roots at the soil–root interface generated stable aggregates of 2–20 µm size, which were much involved in the structural stability of the soil adhering to roots. We identified by TEM several types of organomineral associations that depended on the nature of the plant or microbial organic matter. The distribution of the different types of aggregates varied according to their positions in relation to the roots. We showed that humification of roots contributes significantly to the development of stable organomineral associations in the soil. L'influence des racines de maïs sur la stabilité et la nature des microagregats d'un sol limoneux Résumé L'objectif de cette étude est de suivre au champ, l'influence des racines de maïs sur la stabilité des associations organo‐minérales, leur nature et leur formation. Pour cela, nous avons échantillonné au sein d'un sol à texture grossière, cultivé depuis trois ans en maïs, et associé deux approches: une étude in situ du système racinaire du maïs et une évaluation de la stabilité structurale du sol. L'étude du système racinaire comporte en particulier une description morphologique (i) des tissus racinaires observables à l'échelle de la lame mince et (ii) des interfaces racines–sol à l'échelle ultrastructurale en microscopie électronique à transmission (MET), en distinguant les racines fines et les racines adventives. L'évaluation de la stabilité structurale du sol est réalisée selon un gradient spatial d'éloignement pa