There are still few studies on the role that rock fragments (RFs) have in the change in soil structure based on direct observation of the soil‐pore system. Physically degraded soil is of particular interest because small RFs might be considered a factor in its remediation. In our laboratory experiment we mixed five different proportions of 4–8‐mm sized RFs with a Luvisol and a Regosol that have poor ability to self‐structure and were characterized by a massive structure in the field. Nine wetting and drying cycles were applied to repacked samples (15 cm in diameter and height) of soil–RF mixtures to facilitate the formation of soil structure. Image analysis was used to quantify development of the pore system at varying RF contents. The physically degraded soils studied in this research initially showed a decrease and then an increase in porosity with increasing amounts of RFs in the soil–RF mixtures. The results indicated that the Regosol responded more than the Luvisol to RF content. Threshold values of RF content at which the mechanism of pore formation prevails over that of pore reduction depended upon the soil type and can be attributed reasonably to small differences in the coefficient of linear extensibility (COLE). We also identified a mechanism for the propagation of porosity downwards from the soil surface with increasing RF content, together with a vertical homogenization effect on porosity. Our results contribute to understanding the mechanisms by which small rock fragments embedded in physically degraded topsoil induce changes in the pore system and confirm the potential of rock fragments to protect soil structure in soil susceptible to compaction. Highlights Physical interaction between rock fragments and fine earth in degraded soil. Soil porosity examined by combined experimental laboratory approach with image analysis. Soil porosity first decreases then increases with increasing content of rock fragments. Coexistence of two opposing mechanisms: one of porosity reduction and one of formation of new pores.

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A large number of factors that influence soil surface cracking behaviour in swell-shrink soils have been studied, but there are few studies on the influence of rock fragments on crack development. Effects of rock fragments have been investigated with reference to the soil pore system but they have mainly been studied indirectly through measurements of water flow and/or bulk density changes. A laboratory experiment was carried out with repacked soil samples that were prepared by adding rock fragments of three different sizes (2-4, 4-8 and 12-16 mm) to a Vertisol at two different rates (10 and 25% by volume). Soil image analysis procedures were applied in order to describe quantitatively the network of surface cracks and the pore system to a depth of 8 cm below the surface, which developed after wetting-drying cycles. Mean values and standard deviations of surface crack or pore widths decreased with the increase in rock fragment content and the decrease in rock fragment size, while the density of the 'skeleton' of the crack and pore networks increased. Rock fragments also induced vertical homogenization of the soil structure. The number of rock fragments was a key factor in determining some crack network characteristics, inducing inverse variations in mean width and skeleton density of the crack or pore network. Overall results suggested that rock fragments acted as triggering points for crack and pore development in Vertisols. The findings of this work provide a contribution to the understanding of the mechanisms of crack network and soil structure development that are induced by stones in swell-shrink soils.

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Background After uptake from soil into the root tissue, distribution and allocation of nitrate throughout the whole plant body, is a critical step of nitrogen use efficiency (NUE) and for modulation of plant growth in response to various environmental conditions. In legume plants nitrate distribution is also important for the regulation of the nodulation process that allows to fix atmospheric N (N 2 ) through the symbiotic interaction with rhizobia (symbiotic nitrogen fixation, SNF). Results Here we report the functional characterization of the Lotus japonicus gene LjNPF2.9, which is expressed mainly in the root vascular structures, a key localization for the control of nitrate allocation throughout the plant body. LjNPF2.9 expression in Xenopus laevis oocytes induces 15 NO 3 accumulation indicating that it functions as a nitrate importer. The phenotypic characterization of three independent knock out mutants indicates an increased shoot biomass in the mutant backgrounds. This phenotype is associated to an increased/decreased nitrate content detected in the shoots/roots. Furthermore, our analysis indicates that the accumulation of nitrate in the shoot does not affect the nodulation and N-Fixation capacities of the knock out mutants. Conclusions This study shows that LjNPF2.9 plays a crucial role in the downward transport of nitrate to roots, occurring likely through a xylem-to-phloem loading-mediated activity. The increase of the shoot biomass and nitrate accumulation might represent a relevant phenotype in the perspective of an improved NUE and this is further reinforced in legume plants by the reported lack of effects on the SNF efficiency. Electronic supplementary material The online version of this article (10.1186/s12870-019-1978-5) contains supplementary material, which is available to authorized users.

In‐vivo dosimetry techniques are currently being applied only by a few Centers because they require time‐consuming implementation measurements, and workload for detector positioning and data analysis. The transit in‐vivo dosimetry performed by the electronic portal imaging device (EPID) avoids the problem of solid‐state detector positioning on the patient. Moreover, the dosimetric characterization of the recent Elekta aSi EPIDs in terms of signal stability and linearity make these detectors useful for the transit in‐vivo dosimetry with 6, 10 and 15 MV photon beams. However, the implementation of the EPID transit dosimetry requires several measurements. Recently, the present authors have developed an in‐vivo dosimetry method for 3D CRT based on correlation functions defined by the ratios between the transit signal, normalsnormalt(w,L), by the EPID and the phantom midplane dose, normalDnormalm(w,L), at the source to axis distance (SAD) as a function of the phantom thickness, w, and the square field dimensions, L. When the phantom midplane was positioned at distance, d, from the SAD, the ratios normalsnormalt(w,L)/snormalt'(d,w,L) were used to take into account the variation of the scattered photon contributions on the EPID as a function of d and L.The aim of this paper is the implementation of a procedure that uses generalized correlation functions obtained by nine Elekta Precise linac beams. The procedure can be used by other Elekta Precise linacs equipped with the same aSi EPIDs, assuming the stabilities of the beam output factors and the EPID signals. The procedure here reported avoids measurements in solid water equivalent phantoms needed to implement the in‐vivo dosimetry method in the radiotherapy department. A tolerance level ranging between ±5% and ±6% (depending on the type of tumor) was estimated for the comparison between the reconstructed isocenter dose, Diso, and the computed dose, Diso,TPS, by the treatment planning system (TPS).PACS number: 87.55.Qr; 87.56.Fc