Factors influencing the occurrence of water stress at field scale

Abstract

AbstractAcross a wide range of spatial and temporal scales, the soil water content (SWC) can be perceived as an integral component of the hydrological cycle. The concept of field capacity is insufficient to characterize the limits of ideal moisture conditions for plants and the concept of SWC of limited plant availability (θla) has been introduced to characterize the available SWC threshold value, below which the relative transpiration drops under 1. θla is not a stable property of soil but also depends on the actual evapotranspiration demand of the atmosphere (potential evapotranspiration, Ep). To avoid water stress and ensure high biomass production, water should be supplied to vegetation in order to maintain the optimal range of SWC above θla during important ontogenetic phases. The influence of two factors, one of which is pedological (soil texture) and another is biological (8‐m high hedgerow) on field‐scale fluctuations of θla, was studied in western Slovakia near Moravský Svätý Ján (MSJ) village and in north‐eastern Austria near the village Rutzendorf, respectively. In the MSJ‐field θla values reflected the textural heterogeneity of soil. The intrapopulation range Δθla was 0·15 m3 m−3 in a clay loam Mollic Gleysol, but only 0·08 m3 m−3 in a loamy sand Arenic Regosol. The interpopulation differences in mean θla between two textural classes were 0·06–0·09 m3 m−3. The maximum Δθla caused by changes in textural composition over the 4·5 ha field was 0·18 m3 m−3. It was found during two SWC measurement campaigns with different boundary conditions [Ep and ground water (GW) table] that the loamy sand soil is much more susceptible to the occurrence of water stress than the clay loam. The actual SWC falls below the θla threshold more frequently in loamy sand because of its small water retention capacity, rapid drainage and poorer hydraulic connection with GW. The seasonal variability of θla in 2002 reached 0·06–0·09 m3 m−3, depending on textural class. The hedgerow at Field‐Rutzendorf had a small effect on the spatial variation in θla during days with low Ep rates. Δθla was less then 0·01 m3 m−3 when potential evapotranspiration was less then 1 mm day−1. However, during days with great atmospheric demand for evapotranspiration (6 mm day−1) Δθla reached 0·19 m3 m−3 during the 2004 growing season. The results illustrate that both evapotranspiration intensity and soil texture influence the occurrence of soil water stress. Copyright © 2010 John Wiley & Sons, Ltd.