Soil Moisture Drydown Curves After Flooding Events Accross An Irrigated Farmland

Presenter: Francisco Javier Gaxiola Ortiz1
Co-Author(s): Álvarez-Yepiz J. C., Franz T., Garatuza-Payan J., Guevara M., Peñuelas-Rubio O., Rosolem R., Torres-Velázquez J. R., Yepez E. A.
Advisor(s): Dr. Zulia Mayari Sánchez Mejía
1Water and Environmental Sciences, Instituto Tecnológico de Sonora

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Soil moisture (θ) is a key variable for agriculture, a gap remains in observations at intermediate scales, the cosmic-ray neutron sensor (CRNS) is a novel tool for such applications. We designed an experiment using a CRNS and time domain reflectometry (TDR at vegetated and bare soil sites) to measure θ in the Yaqui Valley, at a wheat (Triticum spp) farmland with flooding irrigation. We used a drydown analysis of the daily rate at which θ is lost (θdecay) after every irrigation, and the θ that represents 1/3 of the remaining θ as soil dries (θthreshold); multivariate correlations (Spearman) and a principal components analysis (PCA) using θ , meteorological variables, and vegetation greenness. With TDR’s we observed differences in θdecay, it was higher at the vegetation site θdecay= 0.53 cm3/cm3 /day, while θthreshold was higher at bare soil site 0.33 cm3/cm3. After each irrigation, the meteorological variables correlated with θ varied, highlighting air temperature (Tair, r=-0.7) for irrigation 1, evapotranspiration (ET, r>0.5) and vapor pressure deficit (VPD, r=0.6, r=-0.8) for irrigations 2 and 3, and normalized difference vegetation index (NDVI, r=0.8) for the 3rd irrigation. The variation explained by PC1 and PC2 increases with each irrigation event, relevant variables in PCA where θ, Tair, VPD, NDVI, and precipitation. The results of this study suggest that CRNS is a suitable technique at field scale and that drydown curves are useful to quantify soil dryness and the influence of meteorological variables and crop development, thus providing an opportunity for water management in agriculture.

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