Spatiotemporal variation of moisture in rooted-soil

Abstract

Soil moisture is of high variability both in space and time, and root growth may greatly alter the soil texture and lead to distinctive moisture patterns. In order to explore the spatiotemporal variability of rooted soil moisture, this study conducted a series of greenhouse tomato growth experiments using loess and under certain irrigation regimes. The experiment lasted for three months, and throughout the growth period, root lengths and hourly moisture values of different positions in the root zone soil were measured. It is found that the root length satisfies the Weibull distribution and the parameters are well related to the weight and area of the root system. As root grows, soil structure changes dramatically and becomes highly heterogeneous, then the moisture presents distinctive patterns, falling into subareas of high, middle, and low moisture levels. The patterns vary remarkably in the three growth stages (growing, developing, and maturation), and the subareas approach to a balance state at the end of growth. Furthermore, from the spatial moisture patterns one may derive the root-affected water routines, which approaches to a uniform moisture in the zone far away from the root. Finally, the spectrum analysis of the moisture series at hour scale indicated that the moisture in near root area bears a weak persistence character, responding to the rainfall (or irrigation) fluctuation, while the moisture in area distant to root system bears high persistence character, having power exponent similar to slope soils in general and hence representing the ordinary state of soil moisture. In summary, the findings of spatial moisture patterns and temporal spectrum exponents are expected to be heuristic for understanding the spatiotemporal variability of soil moistures in general.