Soil interrill erodibility is a key component of soil erosion models. However, when using aggregate stability to assess soil erodibility, samples are usually collected from the plough layer, while soil erosion occurs at the soil surface. Hence, the potential changes in erodibility caused by crusting are ignored. Moreover, soil interrill erodibility is difficult to predict accurately. This lack of predictability means that current erosion models use a constant erodibility value for a given soil, and thus do not consider potential heterogeneity of erodibility. This study was conducted to (i) assess the heterogeneity of aggregate stability for a crusted soil and (ii) relate this heterogeneity to the aggregate stability of the underlying material (sub-crust) and to standard soil properties. A field study was conducted in a small area of the Loess Plateau in China in which the crust and the sub-crust soils were sampled. Standard soil properties (organic matter content, sand content, silt content, clay content, cation exchange capacity (CEC), pH in water, and water content at the time of sampling) were measured as potential explanatory factors of aggregate stability. The results showed a large heterogeneity in aggregate stability among the sites, even though the sites had the same soil type. The mean weight diameter (MWD) of the crust varied between 0.33 and 2.04 mm while the MWD of the sub-crust varied between 0.23 and 1.42 mm. Soil texture and pH were uniform among the sampling sites, whereas water content, organic matter content and CEC varied more. Even though some correlations existed (for example r = 0.57 between MWD for the slow wetting test and organic matter content), none of the standard soil properties was able to predict aggregate stability accurately. The aggregate stability of the crust was significantly greater than that of the sub-crust. The large differences in aggregate stability imply large differences in soil interrill erodibility. Because a single soil type was investigated, this finding proves that erodibility can vary greatly in space even for a given soil type. Soil interrill erodibility should be estimated from the exact material exposed to erosive forces, the soil surface material. Using the sub-crust would have led to greatly over-estimated erodibility and thus to a marked bias in erosion model predictions. Resume La stabilite structurale d'un sol encroute : differences entre la croute et le materiau sous-jacent, et consequences pour l'estimation de l'erodabilite inter-rigole. Un exemple dans le Plateau de Loess (Chine) L'erodabilite inter-rigole est un parametre clef des modeles d'erosion du sol. Cependant, lorsque des tests de stabilite structurale sont utilises pour evaluer l'erodabilite, les mesures sont habituellement realisees sur des echantillons preleves dans l'horizon laboure alors que l'erosion a lieu a la surface du sol. Ainsi, les changements potentiels d'erodabilite causes par la formation de croute sont ignores. De plus, l'erodabilite inter-rigole reste encore difficile a predire avec precision. Ces difficultes conduisent les modeles d'erosion a utiliser une erodabilite constante pour un type de sol donne, et donc a ne pas considerer l'heterogeneite potentielle de l'erodabilite. Cette etude a ete conduite pour (i) evaluer l'heterogeneite de la stabilite structurale pour un sol encroute et (ii) relier cette heterogeneite a la stabilite structurale du materiau sous-jacent (sous-croute) et aux proprietes standards du sol. Une etude de terrain a ete realisee sur un secteur de surface limitee du Plateau de L oe ss (Chine). Des echantillons provenant de la croute et de la sous-croute ont ete collectes. Les proprietes standards (teneur en carbone organique, teneurs en sable, limon et argile, CEC, pH, et teneur en eau au prelevement), ont ete mesurees en tant que facteurs explicatifs potentiels de la stabilite structurale. Les resultats ont montre une grande heterogeneite de la stabilite structurale entre les differents sites alors que ces derniers presentaient le meme type de sol. Le MWD de la croute variait entre 0.33 et 2.04 mm tandis que le MWD de la sous-croute variait entre 0.23 et 1.42 mm. La texture du sol et le pH etaient tres homogenes entre les sites etudies, tandis que la teneur en eau, la teneur en matiere organique et la CEC variaient plus fortement. Bien que certaines correlations aient ete identifiees (par exemple r = 0.57 entre le MWD du test a l'humectation lente et la teneur en carbone organique), aucune de ces proprietes n'a permis de predire precisement la stabilite structurale. La stabilite structurale de la croute etait significativement superieure a celle de la sous-croute. Les grandes differences de stabilite structurale mesurees impliquent des erodabilites tres contrastees. Comme un seul type de sol a ete etudie, ce resultat prouve que l'erodabilite peut etre tres variable spatialement pour un type de sol donne. L'erodabilite inter-rigole du sol devrait etre mesuree sur le materiau exact qui subit l'erosion, c'est-a-dire le materiau de surface. L'utilisation du materiau sous-jacent aurait engendre une forte surestimation de l'erodabilite et donc un biais important dans les predictions d'un modele d'erosion.
