Flood irrigation agriculture: the challenges of in-situ soil moisture
monitoring in lands with high clay contentΑ
Abstract
Soil moisture is an essential measurement to manage water and improve
crop production. However, agricultural research in the Yaqui Valley (in
northwestern Mexico) with extensive wheat fields (Triticum sp.) have
focused on other monitoring schemes (e.g. remote sensing) with less
attention to soil moisture. Most of this cultivated soil contains up to
~ 50% clay, which results in changes to soil properties
from wet to dry conditions and challenges in the implementation of
in-situ measurements of soil moisture. For this research, we selected a
1-ha wheat field in the Yaqui Valley representative of a typical flood
irrigation system. We measured meteorological variables (ClimaVUE™50),
and soil moisture for the winter crop-cycle from December 2019 to Abril
2020. Volumetric water content (VWC) was recorded from 5 to 50 cm using
two TDR (SoilVUE™10), one located in the bottom of the furrow under bare
conditions, and the other on the top under the vegetated condition for
further integration and comparison. A Cosmic Ray Neutron Sensor (CRNS)
was located alongside the meteorological sensor. The universal
calibration equation was used to estimate VWC based on neutron counts.
The comparison from the CRNS and the integrated TDR (5 to 50 cm)
resulted in an RMSE of 0.02 m3m-3 and an r2 = 0.73. While both
technologies respond to water inputs, the CRNS is a more reliable
measurement during the dry-down periods when the high-clay soil cracks
to the extent of 40 cm where soil is exposed to air. During this driest
period, recorded VWC at 50 cm was, on average, 0.25 m3 m-3, while
measurements with the CRNS was on average, 0.16 m3 m-3. Interestingly,
both sensors peaked at 0.56 m3 m-3 during the flood irrigation event.