Abstract
In situ measurements of crop transpiration can enhance field studies of crop water use and productivity. Five sap flow heat gauges, controlled by an automated data acquisition system, were deployed in each of four replicated field plots of corn irrigated to minimize water deficits at Garden City, KS in 2004 and 2006. Water flux through each stem was estimated as a residual of a heat balance equation. Gauges were transferred to adjacent plants after 13 to 21days to evaluate and mitigate functional stem damage. Loss of gauge operation, primarily due to stem damage, commonly occurred approximately one to two weeks following installation. Gauges installed at tassel formation reduced kernels per ear and kernel mass by 20%, attributed to stem damage, relative to that of plants with gauges installed during mid-grain fill. Data screened using operational metrics (derived from sensitivity analysis) were used to evaluate a scaling relationship between calculated flow to transpiration calculated following the Penman-Monteith (P-M) form. Transpiration calculated from gauge data was linearly related to that calculated from the P-M, with R2 exceeding 0.80. Assumptions regarding canopy resistance (rc) altered potential evaporation calculated by P-M. Greater precision was obtained by assuming constant rc, but bias was reduced by assuming rc was proportional to solar radiation. Sap flow gauges provided information useful for calibrating an rc model for P-M to calculate the transpiration component of ET.
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