Micro-variability of hydrological processes at the maize row scale: implications for soil water content measurements and evapotranspiration estimates

In this paper, we analyse the micro-variability of hydrological processes (i.e. rainfall redistribution, root water uptake and evapotranspiration) at the maize row scale during a long drying period. Then, we study the impact of the variability of these processes on the spatio-temporal dynamics of the soil water content and on the sampling strategies to estimate soil water content and evapotranspiration at the maize row scale. Results of our study firstly show that the rainfall reaching the ground under the maize canopy is very variable with coefficients of variation ranging between 77.87 and 188.7%. Some locations receive up to 4.47 times more water than the incident rainfall. The estimated root water uptake (RWU) is also extremely variable, laterally within the maize rows with CV values ranging between 13.9 and 137%. Well-defined cyclical patterns of RWU due to the row layout are observed at some depths. Throughout the long drying period, maximum RWU progressively moves downwards and towards the middle of the row. Evapotranspiration (ET) is less variable across the rows with CV values ranging between 11.95 and 29.07%. Cyclical patterns are also observed except at the end of the considered period. The spatio-temporal dynamics of soil water content are clearly influenced by the maize row layout, with the progressive appearance of a fingered pattern within the rows due to the spatially variable RWU. The maximum difference of soil water content measured within a maize row is important and ranges between 0.046 and 0.079 cm3 cm(-3). In absolute terms, coefficients of variation for soil water content range between 1.05 and 12.1%. For estimates of soil water content and ET at the maize row scale, we show that the location of soil water content sensors is critical. Estimates of mean row scale soil water content and ET by the use of 'central' sampling locations in the middle of each row leads to maximum error of 0.022 cm3 cm(-3) and 9.09 mm, respectively. More research is needed to generalize the results obtained in this study for other climatic conditions and for other soil water content measurement techniques.