The continuum approach is a classical framework to describe and understand the soil—water dynamics and the soil effective—stress state in unsaturated soils. This approach is greatly dependent on the soil—water constitutive laws, viz soil—water retention curve, relative hydraulic conductivity, and those derived by these two principal ones. They link the real soil and its model. Advancements along their development and the comprehension of their role stand at the intersection of experimental measurements, mathematical representation and modelling, numerical solutions, theoretical understandings and practical applications. The growing possibility of monitoring soil moisture with rather simple tools has allowed to perform many field experiments devoted to understand the links between environmental variables and soil moisture. Also, climate change research has boosted this field of knowledge. Many terrestrial critical zone observatories have been installed, therefore new information both at the local and at the catchment scale is now available. Many open issues still exist in understanding the role of soil moisture in the environment, in combination with other factors such as soil and air temperature, air humidity, carbon and nitrogen availability, etc. Also, it is necessary the study of the structure of time and spatial variability of soil moisture itself, for example to combine the different scales of measurements. Usually soil moisture is measured at the local scale, but hydrogeophysics allows to have larger scale measurements and micrometeorological tools such as eddy covariance provide even larger scale estimation of gas and energy fluxes. The cosmic ray have increasing applications and the remote sensing images are powerful tools, therefore interesting issues regard the spatial upscaling, and the sampling frequency.

We invite contributions related to the understanding of the soil--water constitutive laws and to soil moisture monitoring, both finalised to understand the effects of its time and spatial variability, and to study soil moisture itself.

Scientists working both in the biogeosciences, and in soil sciences field are encouraged to participate, for example with study related to the implications of soil moisture on carbon and nitrogen dynamics, as well as on root and plant growth. The growing possibility of monitoring soil moisture with rather simple tools has allowed to perform many field experiments devoted to understand the links between environmental variables and soil moisture. Also, climate change research has boosted this field of knowledge. Many terrestrial critical zone observatories have been installed, therefore new information both at the local and at the catchment scale is now available.