Knowledge of soil moisture dynamics and its spa al variability is essen al to improve our understanding of root water uptake and soil moisture redistribu on at the local scale and the fi eld scale. We inves gated the poten al and limita ons of electrical resis vity tomography (ERT) to measure three-dimensional soil moisture changes and variability in a large, undisturbed, cropped soil column and examined the interac ons between soil and root system. Our analysis sustained the value of ERT as a tool to monitor and quan fy water contents and water content changes in the soil, as long as the root biomass does not infl uence the observed resis vity. This is shown using a global water mass balance and a local valida on using me domain refl ectometry (TDR) probes. The observed soil moisture variability was rather high compared to values reported in the literature for bare soil. The measured water deple on rate, being the result of combined eff ects of root water uptake and soil water redistribu on, was compared with the evapora ve demand and root length densi es. We observed a gradual downward movement of the maximum water deple on rate combined with periods of redistribu on when there was less transpira on. Finally, the maximum root length density was observed at −70 cm depth, poin ng out that root architecture can strongly depend on soil characteris cs and states.Abbrevia ons: DOY, day of year; DR, deple on rate; EC b , bulk soil electrical conduc vity; ERT, electrical resis vity tomography; ET, evapotranspira on; GPR, ground penetra ng radar; nDR, normalized mean weekly water deple on rates; RLD, root length density; RWU, root water uptake; TDR, me domain refl ectometry; WC, water content; W-S, Waxman and Smits (1968) [model].

a b s t r a c tA stumbling block to the adoption of silvoarable agroforestry systems is the lack of quantitative knowledge on the performance of different crops when competing for resources with trees. In North-Western Europe, light is likely to be the principal limiting resource for understorey crops, and most agronomic studies show a systematic reduction of final yield as shade increases. However the intensity of the crop response depends on both the environmental conditions and the shade characteristics. This study addressed the issue by monitoring winter wheat (Triticum aestivum L.) growth, productivity and quality under artificial shade provided by military camouflage shade-netting, and using the Hi-sAFe model to relate the artificial shade conditions to those applying in agroforestry systems.The field experiment was carried out over two consecutive years (2013-14 and 2014-15) on the experimental farm of Gembloux Agro-Bio Tech, Belgium. The shade structures recreated two shade conditions: periodic shade (PS) and continuous shade (CS), with the former using overlapping military camouflage netting to provide discontinuous light through the day, and the latter using conventional shade cloth. The experiment simulated shading from a canopy of late-flushing hybrid walnut leaves above winter wheat. Shading was imposed 16 (2013-14) and 10 (2014-15) days before flowering and retained until harvest. The crop experienced full light conditions until the maximum leaf area index stage (LAI max ) had been reached. In both years, LAI followed the same dynamics between the different treatments, but in 2013-2014 an attack of the take-all disease (Gaeumannomyces graminis var. tritici) reduced yields overall and prevented significant treatment effects. In season 2014-15 the decrease in global radiation reaching the crop during a period of 66 days (CS: -61% and PS: -43%) significantly affected final yield (CS: -45% and PS: -25%), mainly through a reduction of the average grain weight and the number of grain per m 2 . Grain protein content increased by up to 45% under the CS treatment in 2015. Nevertheless, at the plot scale, protein yield (t/ha) did not compensate for the final grain yield decrease.The Hi-sAFe model was used to simulate an agroforestry plot with two lines of walnut trees running either north-south or east-west. The levels of artificial shade levels applied in this experiment were compared to those predicted beneath trees growing with similar climatic conditions in Belgium. The levels used in the CS treatment are only likely to occur real agroforestry conditions on 10% of the cropped area until the trees are 30 years old and only with east-west tree row orientation.

Preferen al fl ow in soils can manifest itself in several ways. To illustrate this, we analyzed solute transport during a step tracer experiment in two soils expected to diff er in their governing transport processes: a loamy sand and a silty soil. By combining electrical resis vity tomography (ERT), me domain refl ectometry, and effl uent measurements, we observed diff erent preferen al fl ow phenomena. The transport process was characterized using voxel-and column-scale eff ec ve convec ve-dispersive equa on (CDE) parameters, local veloci es, and leaching surfaces. At the column scale, transport in the loamy sand was dominated by a homogenous convec ve-dispersive transport behavior, but at the scale of the voxel, preferen al transport was observed. Transport in the silty soil was considerably more heterogeneous. Preferen al fl ow was iden fi ed using ERT, voxel-and column-scale eff ec ve CDE parameters, local veloci es, and leaching surfaces. In these soils, a clear infl uence of soil layering on solute transport was observed. Abbrevia ons: BTC, breakthrough curve; CDE, convec ve-dispersive equa on; EC, electrical conducvity; ERT, electrical resis vity tomography; LS, loamy sand; S, silt; TDR, me domain refl ectometry. Clothier et al. (2008) defi ned preferential fl ow as "all phenomena where water and solute move along certain pathways, while bypassing a fraction of the porous matrix." Based on the literature, four diff erent preferential fl ow phenomena can be identifi ed:It must be noted that these preferential fl ow manifestations do not necessarily occur simultaneously. Which phenomena or characteristics are present depends on the type of preferential fl ow.

Accepted Article This article is protected by copyright. All rights reserved Ecosystems integrity and services are threatened by anthropogenic global changes. Mitigating and adapting to these changes requires knowledge of ecosystem functioning in the expected novel environments, informed in large part through experimentation and modelling. This paper describes 13 advanced controlled environment facilities for experimental ecosystem studies, herein termed ecotrons, open to the international community. Ecotrons enable simulation of a wide range of natural environmental conditions in replicated and independent experimental units whilst simultaneously measuring various ecosystem processes. This capacity to realistically control ecosystem environments is used to emulate a variety of climatic scenarios and soil conditions, in natural sunlight or through broad spectrum lighting. The use of large ecosystem samples, intact or reconstructed, minimises border effects and increases biological and physical complexity. Measurements of concentrations of greenhouse trace gases as well as their net exchange between the ecosystem and the atmosphere are performed in most ecotrons, often quasi continuously. The flow of matter is often tracked with the use of stable isotope tracers of carbon and other elements. Equipment is available for measurements of soil water status as well as root and canopy growth. The experiments run so far emphasize the diversity of the hosted research. Half of them concern global changes, often with a manipulation of more than one driver. About a quarter deal with the impact of biodiversity loss on ecosystem functioning and one quarter with ecosystem or plant physiology. We discuss how the methodology for environmental simulation and process measurements, especially in soil, can be improved and stress the need to establish stronger links with modelling in future projects. These developments will enable further improvements in mechanistic understanding and predictive capacity of ecotron research which will play, in complementarity with field experimentation and monitoring, a crucial role in exploring the ecosystem consequences of environmental changes.