Evaluation of SLAKES, a new smartphone technology for measuring aggregate stability: a case study in silty loam soils with contrasted managements

International audienceThe measurement of aggregate stability is widely used to evaluate soil condition being an important indicator of soil quality. The SLAKES mobile app, implemented in Australia, is an alternative tool to measure soil aggregate stability avoiding high-cost experiments and using simple equipment. It provides aggregate stability measurements through Slaking Index (SI) in only 10 minutes. SI close to 0 suggests a high stability and values above 7 indicate minimum stability. As SLAKES has proven its efficiency in previous studies, the app could be very attractive for scientists and no-scientists.This study was conducted to determine whether the SLAKES mobile app could be adapted to French soils and spread out. Indeed, it then could be an alternative to the Mean Weight Diameter (MWD) method, method normalized in France (ISO 10390). More specifically, this study explored three main objectives: (i) determining whether the aggregate stability measurements depend on the phone used for the experiment, (ii) estimating the number of measurements necessary to get reliable results, (iii) determining whether the app has the ability to detect the effect of contrasting soil managements (effects previously shown with the MWD method).We measured SI for 24 silty loam samples from EFELE (Effluents d’Elevage et Environnement) experimental site at le Rheu (Brittany, France) which is part of the French “Organic waste products” research observatory (SOERE PRO). The experimental scheme combines two different tillage practices (conventional tillage and shallow tillage) with two fertilization treatments (mineral and farm effluent: cattle manure) randomly replicated three times. Soil samples, at both 0-15 cm and 15-25 cm depth, were collected in March 2017 from the 12 plots.Four different mobile devices (phones) of the same brand and generation were used. The SI was measured on three aggregates simultaneously. This process was repeated 15 times for each sample providing 45 SI per sample. Before statistical studies, outliers above SI=11 were removed.First, the device used did not affect the SI measurements. This was demonstrated by analyses of variance applied on 3 results from three contrasted samples in terms of SI.The SLAKES results were comparable with the results obtained by the MWD method regarding significant separation of means (p < 0.0001) between each soil management. According to the results of an analysis of variance, SI was significantly lower in reduced tillage than in conventional tillage condition (p-value = 2.10-16). These results indicate a higher soil stability in reduced tillage. Yet, no effect of fertilization was observed on the SI (p-value = 0.28), confirming the previous findings obtained with the MWD method.This study proved that some effect of soil management practices can be detected with a mobile app and a relatively simple experimental system, with similar performance than the MWD method. This conclusion was reinforced by the existing correlation between the SI and the MWD index (p-value = 0.00059, R2 = 0.39). Since, we studied samples with identical texture, we recommend to perform similar tests in other pedological and soil management contexts, taking at least 15 measures per soil sample