Submitted to: American Society of Agricultural and Biological Engineers
Publication Type: Abstract Only
Publication Acceptance Date: 10/24/2008
Publication Date: 10/24/2008
Citation: Jabro, J.D., Evans, R.G., Kim, Y., Iversen, W.M. 2008. Estimating In-situ Soil-Water Retention and Field Water Capacity in Two Contrasting Soil Textures. American Society of Agricultural and Biological Engineers. Paper No. 083753.
Interpretive Summary: Optimal irrigation management practices for crops require measurement of soil water retention data in the field to assess both the amount and timing of irrigation. The in-situ soil water retention curves from simultaneous soil water potential (WP) and volumetric water content (WC) measurements obtained from the WM and TDR sensors were developed for both sandy loam and clay loam soils. The Campbell (Campbell, 1974) and Gardner (Gardner, 1958) equations provided the best fit for the soil water retention curves with R2 = 0.97 and 0.96 for sandy loam and clay loam soils, respectively. The changes of soil WP with time following cessation of infiltration were well described by 3-parameter sigmoid models with R2 = 0.997 and 0.936 for sandy loam and clay loam soils respectively. Based on these relationships, the tFWC were reached at approximately 50 and 450 hrs following cessation of infiltration and soil WPFWC values at these two elapsed times were approximately 18 and 27 kPa for sandy loam and clay loam soils, respectively. Using soil water retention curves, the corresponding WCFWC values at 50 and 450 hours were approximately 0.228 and 0.344 m3 m-3 for sandy loam (Nesson) and clay loam (EARC) soils, respectively. The estimated WCFWC values were within the range of the measured WCFWC values obtained from the NP probe and gravimetric methods. These results indicated that WM and TDR sensors provided accurate in-situ soil water retention data that can be used in agricultural and environmental applications including irrigation management and scheduling.
Technical Abstract: A priori knowledge of the in-situ soil field water capacity (FWC) and the soil-water retention curve for soils is important for the effective irrigation management and scheduling of many crops. The primary objective of this study was to estimate the in-situ FWC using the soil-water retention curve developed from volumetric water content, WC and water potential, WP data collected in the field by means of soil moisture sensors in two contrasting-textured soils. The two study soils were Lihen sandy loam and Savage clay loam. Six metal frames 117 cm * 117 cm ' 30 cm high were inserted into the soil to a depth of 5 to 10 cm at approximately 40 m intervals on a 200 m transect. Two Time Domain Reflectrometry (TDR) sensors were installed in the center of the frame and two Watermark (WM) sensors were installed in the SW corner at 15 and 30 cm depths to continuously monitor soil WC and WP, respectively. A neutron probe (NP) access tube was installed in the NE corner of each frame to measure soil WC used for TDR calibration. The upper 50 to 60 cm of soil inside each frame was saturated with intermittent application of approximately 18 to 20 cm of water. Frames were then covered with plastic tarps. The Campbell and Gardner equations best fit the soil water retention curves for sandy loam and clay loam soils, respectively. Based on the relationship between soil WP and elapsed time following cessation of infiltration, we calculated that the field capacity time (tFWC) were reached at approximately 50 and 450 hrs respectively for sandy loam and clay loam soils. Soil-water retention curves showed that WC values at FWC (WCFWC) were approximately 0.228 and 0.344 m3 m'3 respectively for sandy loam and clay loam soils. The estimated WCFWC values were within the range of the measured WCFWC values from the NP and gravimetric methods. The TDR and WM sensors provided accurate in-situ soil water retention data from simultaneous soil WC and WP measurements that can be used in soil-water processes, irrigation scheduling, modeling and chemical transport.