Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/2007
Publication Date: 1/30/2008
Citation: Starr, G.C., Rowland, D., Griffin, T.S., Olanya, O.M. 2008. Soil Water in Relation to Irrigation, Uptake, and Potato Yield in a Humid Climate. Agricultural Water Management. 95:292-300. Interpretive Summary: Efficient irrigation water use is achieved when the amount of water stored in soil is balanced with the plants’ root uptake needs for water. However, this balance is not easy to achieve with either irrigation or natural rainfall in a humid climate such as Maine’s. We measured the amount of water stored in the soil across potato hills and the amount of water taken up by the plant. In addition, A soil water index was derived and measured that quantifies the relative soil water storage of replicated plots for each treatment. The entire plant uptake was found to be within the potato hill, with little or no uptake from beneath the furrow. The sub-surface drip system delivered water to the hill very slowly by upward movement from the deeply buried water emitters. By contrast, the surface drip system emitted water at the surface of the hill which had a rapid and efficient wetting pattern for the hill. Irrigated yields were relatively high in the drier portions of the field but were reduced with increasing wetness over the wetter half of the study area. Persistent field-scale pattern of soil water as quantified by the soil water index strongly influences the yield response for irrigated potato production.
Technical Abstract: Efficiently controlling soil water content with irrigation is essential for water conservation and often improves potato yield. Volumetric soil water content ('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 'v using a hammer driven probe were used to derive a 'v index representing the relative 'v status of replicated plots positioned along a hill slope. Time series for '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 'v index was low/high suggesting 'v excess was a production problem in the wetter portions of the study area. The diurnal pattern of sap flow was reflected in the '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 subsurface drip system wetted the hill very gradually (1-2 days). Measurement of the 'v index prior to experimental establishment could improve future experimental design for treatment comparisons.