Soil water in relation to irrigation, water uptake and potato yield in a humid climate

Efficiently controlling soil water content with irrigation is essential for water conservation and often improves potato yield. Volumetric soil water content ([theta]v) in relation to irrigation, plant uptake, and yield in potato hills and replicated plots was studied to evaluate four water management options. Measurements of [theta]v using a hammer driven probe were used to derive a [theta]v index representing the relative [theta]v status of replicated plots positioned along a hill slope. Time series for [theta]v were determined using time domain reflectometry (TDR) probes at 5 and 15 cm depths at the center, shoulder, and furrow locations in potato hills. Sap flow was determined using flow collars in replicated field plots for four treatments: un-irrigated, sprinkler, surface drip, and sub-surface drip irrigation (40 cm depth). Irrigated yields were high/low as the [theta]v index was low/high suggesting [theta]v excess was a production problem in the wetter portions of the study area. The diurnal pattern of sap flow was reflected in the [theta]v fluctuation it induces at hill locations with appreciable uptake. Hill locations with higher plant uptake were drier as was the case for the 5 cm (dry) depth relative to the 15 cm (wet) depth and for locations in the hill (dry) relative to the furrow (wet). The surface drip system had the lowest water use requirement because it delivers water directly to the hill locations where uptake is greatest. The sub-surface drip system wetted the hill gradually (1-2 days). Measurement of the [theta]v index prior to experimental establishment could improve future experimental design for treatment comparisons.