Stability of soil moisture and temperature in a rainfed organic vineyard with two cultivars and permanent ground cover of resident vegetation under temperate oceanic climate

Abstract

<p>Soil water content (SWC) and temperature (ST) are key parameters in farmland, but are difficult to predict. Under no-tillage (three mowing passes per year) and homogeneous ground (permanent cover of resident vegetation), soil (no significant difference within each soil layer) and topographic (steep and straight slope near the divide) conditions, this study quantified the index of temporal stability (ITS) of the soil hydro-thermic response in a rainfed organic vineyard with humid climate –in Galicia, NW Spain– and two cultivars (Agudelo –Ag– and Blanco Legítimo –BL–). By using 12 capacitance-based technology probes (six per cultivar: 3 per row (R) and 3 per inter-row area (IR)), SWC and ST were measured every 15 min at 5, 15 and 25 cm depth over the crop cycle (242 days). On average, wetter and cooler values appeared in Ag than in BL that may be associated with differences in vine water demand. IR had wetter and cooler conditions than R due to higher water consumption by vines. Time-series analysis was split into three periods: Drying and warming (spring), dry and warm (summer), and wetting and cooling (autumn). The vertical analysis of the relative differences (soil layers) showed that the lowest values of ITS<sub>V</sub> appeared at 15 cm in all cases for ST, regardless the hydro-thermic periods, vine varieties and field zones, and also at 15 cm for SWC, especially in R over the three periods, and during spring and autumn in IR. The prevailing conditions observed at this layer were the representative conditions of the field during the crop cycle. Conversely, the less representative conditions of the hydro-thermic status of the soil were those obtained in the upper-most layer in all cases of ST and almost all cases of SWC. At 25 cm, the representativeness of SWC and ST was intermediate, but the most representative conditions of SWC appeared at 25 cm during the summer. The horizontal analysis of the relative differences (zones and cultivars) revealed that the values of ITS<sub>H</sub> showed a homogeneous pattern of soil moisture: R always had more representative values of SWC than IR in the three layers and during the three periods. Regarding ST, the pattern was more variable and R only had more representative values than IR at 15 cm in summer and at 25 cm in spring and summer. The behaviour of SWC and ST differed in terms of temporal stability and spatial representativeness. When the varieties were analysed, BL had more representative values of SWC than Ag, but Ag always had more representative values of ST than BL. These findings explained the low correlation between ITS<sub>H</sub>-SWC and ITS<sub>H</sub>-ST. For the first time, ITS was calculated for SWC and ST in a woody crop. These findings prove the complex and distinct spatial and temporal dynamic of SWC and ST in a commercial vineyard, even under homogeneous physiographic conditions, and support the necessity of implementing precision farming practices based on soil water and temperature management.</p>