Response time of soil moisture to rain in a vineyard with permanent cover

Abstract

The time elapsed between the moments of maximum rainfall intensity and maximum soil moisture, known as peak to peak (P2P), is part of the hydrological response of the soil, but literature has missed this metric in any woody crop. In a vineyard with permanent vegetation cover (humid climatic conditions), the influence of two cultivars (Agudelo and Blanco Legítimo) and two zones (rows and inter-row areas) on the values of soil moisture response time, absolute change in moisture (ΔS) and P2P was evaluated for 118 rainfall events in three soil layers. 12 capacitance probes and a weather station were used, and data measured every 15 min. A positive response (ΔS > 0) was observed in 79 %, 73 % and 67 % of all events at soil depth of 5, 15 and 25 cm, decreasing ΔS with increasing soil depth. Differences of ΔS were significant among layers, but not among cultivars and zones. The maximum ΔS occurred at 15 cm, while the minimum was observed at 25 cm. No response was evident when specific thresholds were not reached: rainfall depth (0.60 mm event−1), maximum intensity (1.20 mm h−1) or duration (30 min). Topsoil conditions –high rainfall interception by the dense cover and high soil organic matter content– influenced the results at 5 cm. Rain parameters correlated well with ΔS, but weak with the response time and P2P. P2P occurred earlier in the rows than between the rows, especially at 15 cm. Shorter P2P appeared in Agudelo, with significant differences in the rows at 5 cm. P2P differed significantly among layers, increasing P2P with soil depth. Similar ΔS values appeared in Spring and Autumn, and were significantly different than those in Summer, but P2P did not differ significantly among seasons. Therefore, the magnitude and timing of the soil hydrological response were independent processes.