Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/4/2014
Publication Date: 6/4/2014
Citation: Evett, S.R., Schwartz, R.C., Bell, J.M. 2014. Precipitation, irrigation and crop growth signals in COSMOS data. Presented at the 2014 Workshop at MOISST: Advancing Soil Moisture Science and Applications, Stillwater, Oklahoma, 4-5 June 2014. Available at http://soilphysics.okstate.edu/research/moisst-2014-presentations-1.
Technical Abstract: Soil water sensors are used to characterize water content in the root zone and below for water management and environmental monitoring, but only a few are capable of sensing soil volumes larger than a few hundred liters. Scientists with the USDA-ARS Conservation & Production Research Laboratory, Bushland, Texas, and Texas A&M AgriLife evaluated three soil water sensing systems against each other and against precipitation and irrigation amounts measured using a large weighing lysimeter. The three sensor systems were: 1) the Cosmic Ray Soil Moisture Observing System (COSMOS), which responds to surface soil water content changes in a circular area of radius up to several hundred meters; 2) electromagnetic (EM) soil water sensors (model CS655, Campbell Scientific, Inc., Logan, Utah) that each sense only a few hundred cubic centimeters, and that were used in a wireless sensor network to interrogate larger volumes of soil; and 3) the neutron probe (NP), used in a network of eight access tubes to take readings from 0.10 to 2.30 m in depth increments of 0.20 m. The large precision weighing lysimeter measured soil water storage changes to within 0.04 mm (<0.01 inch) accuracy. COSMOS was well correlated R-square=0.87 with 0-0.30 m (1 ft) water content and storage as measured by the field-calibrated CS655 sensors. COSMOS was more sensitive to increases in soil water from rainfall compared with those from subsurface drip irrigation at 0.30m depth. COSMOS water content data were biased upward by green, living vegetation. The COSMOS “effective depth” algorithm did not work well in this study. However, assuming that the effective depth was constant at 0.30 m depth resulted in good correlation with CS655 measured soil water storage. The wireless CS655 sensor system worked very well, providing timely information that correlated well with weighing lysimeter soil water storage data. This wireless sensor system would be very useful for irrigation scheduling since the tall corn crop did not result in signal and data loss, and the data accurately represented soil water content as it changed over time due to irrigation and precipitation. Data from the COSMOS system were not accurate enough for irrigation scheduling. Data from the neutron probe were accurate but labor intensive, and the neutron probe lacked both automation and wireless data transfer.