Disentangling the Effects of Land Management and Soil Heterogeneity on Soil Moisture Dynamics

Abstract

Soil moisture is the essential control of water and energy dynamics atarable sites. Time series of soil moisture reflect the interplay ofvarious processes, each of which influences the overall soil moisturedynamics. In this study we tested an approach to break down observedsoil moisture behavior into the respective contributions of individualprocesses. We applied a principal component analysis to soil moisturetime series from a field experiment comprising two crop rotation systemsand two different soil tillage practices. We concentrated on 57 soilmoisture time series measured over nearly 4 yr at 12 plots and five soildepths, down to 1.5 m. About 77.9% of the variance was reflected by thefirst component being almost identical to a time series of averaged soilmoisture. It described the effect of the meteorological boundaryconditions. The second component described the effect of the inputsignal damping increasing with soil depth and accounted for 7.8% oftotal variance. The signal transformation over depth proved to be moreor less uniform throughout the test site, despite considerable soilheterogeneity. Another 3.6% of the total variance ( third component)was unambiguously explained by the different cropping systems. On thecontrary, different soil tillage practices had no significant effect.The suggested approach opens up many possibilities to analyze and betterunderstand complex soil system behavior. The data-based approach of timeseries analysis provides model-independent, quantitative informationabout the key factors and processes controlling soil water dynamics.Hence, it is especially valuable for model building, calibration, andevaluation.