Soil water depletion in irrigated mature pecans under contrasting soil textures for arid Southern New Mexico
Irrigation Science (Impact Factor: 2.06). 01/2013; 31(1):69-85. DOI: 10.1007/s00271-011-0293-1
Relationship between plant water stress and soil water depletion (SWD) is not investigated thoroughly for irrigated pecans of southern New Mexico. In this study, transient soil water contents, rootzone SWD, and midday stem water potential (SWP) were monitored in mature pecan orchards in sandy loam (Site 1) and silty clay loam (Site 2) soils near Las Cruces, New Mexico. Corresponding to transient variations of soil water content at different depths, daily SWD varied with soil depth but not spatially. The SWD within the rootzone (0–80 cm) was higher in the shallow depths (0–40 cm) where root length density (RLD) was also higher than in the deeper depths (40–80 cm). The SWD at Site 1 was higher compared to Site 2 due to the higher clay content of the latter. The SWD patterns at outside the tree driplines were similar to those under-canopy locations because of similar RLD at the shallow depths. At both pecan orchards, differences in SWP at 2.5, 4.5, and 7.6 m tree heights were evident particularly 10–14 days after irrigation. This was due to the stress caused by decreasing soil water contents at different depths, which were generally significantly correlated with SWP. Midday air temperature was as useful as midday atmospheric vapor pressure deficit for interpreting SWP. Combined influence of soil water content (0–40 cm) and air temperature on midday SWP was significant at both orchards, which can be used as an adjunct for the clear interpretation of SWP to help refine irrigation scheduling.
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- "Sensor data were recorded every 10 min using a CR10X datalogger connected to an AM16/32B multiplexer (Campbell Scientific, Inc., Logan, UT). All TDR sensors were calibrated in situ against gravimetric water content and bulk density data (Deb et al. 2013). We expected that soil temperatures at different distances of 100, 350, and 440 cm from the trunk of the selected pecan tree would be similar in this closed-canopy experimental plot. "
ABSTRACT: Quantitative information about the spatial and temporal patterns of compensatory root water uptake (RWU) in flood-irrigated pecan orchard is limited. We evaluated spatio-temporal compensated and uncompensated RWU patterns of mature pecan tree in a silty clay loam orchard using the HYDRUS (2D/3D) model. HYDRUS (2D/3D) simulations, which agreed well with measured water contents and temperatures at different soil depths and horizontal distances from the tree trunk, suggested that while both compensated and uncompensated RWU varied with soil depth they did not do so laterally because of similar spatial vertical distributions of root length density (RLD) for the under-canopy and the tree canopy dripline locations. Considering compensated RWU resulted in an increase in actual transpiration by 8%, and a decrease in evaporation and drainage by 5% and 50%, respectively, during a growing season. Simulated transpiration and relative transpiration (a ratio between actual and potential transpiration) values were correlated with measured transpiration and plant-based water stress indicators (stem and leaf water potentials), respectively. Overall, our results of the spatio-temporal compensatory RWU provide support to use HYDRUS (2D/3D) as a tool for managing efficient water use of pecan. (C) 2013 American Society of Civil Engineers.
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ABSTRACT: The timing and amount of irrigation water are critical to the optimum production of pecans in semi-arid, irrigated agriculture systems. However, few tools are available to managers for measuring or estimating water use compared to deep percolation (DP) below the root zone. The RZWQM2 model was compared to the daily water balance method at two flood-irrigated mature pecan orchards, with different soil textures and depths to water table, in the lower Rio Grande Valley near Las Cruces, New Mexico, to characterize: (1) DP below the upper 100 cm soil profile, and (2) the effects of DP on water table levels. At site 1 (sandy loam) and site 2 (silty clay loam), comparisons between measured and simulated soil water contents at different soil depths during March to December in 2009 and 2010 demonstrated that RZWQM2 generally provided satisfactory predictions of soil water dynamics but consistently undepredicted soil water content after irrigation. Total estimated and simulated DP at site 1 were 489.1 and 445.2 mm in 2009, and 541.5 and 465.8 mm in 2010, respectively. Thus, at site 1, 25% to 29% of the applied water percolated below the root zone, but the model underpredicted these values by 3 to 4 percentage points. In contrast, total estimated DP at site 2 was 37% and 35% of the total water, and again the model underpredicted by 4 to 5 percentage points. Water table levels at site 1 were affected by DP following irrigation events. This was likely related to the relatively shallow water table and the highly permeable sandy loam soil in the upper layers. Nevertheless, the root zone water balance at site 1 did not appear to be influenced by the water table since downward hydraulic fluxes were predominant below 40 cm depth and soil water content remained constant at 160 cm depth. In contrast, the deeper water table at site 2 was not influenced by DP. Calibration and validation of RZWQM2 with field data at pecan orchards with different soil textures and water table depths allow managers to use the model to address water management issues to minimize DP while optimizing pecan production. © 2012 American Society of Agricultural and Biological Engineers.
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ABSTRACT: Salinity responses and salinity-related suppression of budbreak of dripirrigated pecan [Carya illinoinensis (Wangenh.) K. Koch] seedlings under different irrigation water salinity (ECIRR) levels were investigated in the pot-in-pot system. The 1-year-old pecan seedlings of rootstock 'Riverside' grafted with 'Western Schley' scions were transplanted in pots filled with sandy loam soil and grown for 2 years under the same amount of irrigation water but four irrigation ECIRR treatment levels consisting of 1.4 dS·m-1 (control), and three qualities of irrigation water obtained by using a solution of calcium chloride (CaCl2) and sodium chloride (NaCl) in a ratio of 2:1 (by weight) to reach the ECIRR levels of 3.5, 5.5, and 7.5 dS·m-1, respectively. The leachate electrical conductivity (ECd) was highly correlated with soil salinity (EC1:1) and was significantly higher when the irrigation ECIRR treatment levels increased from 1.4 (control) to 7.5 dS·m-1. However, both ECd and EC1:1 remained nearly constant within the same irrigation ECIRR treatment level during both years. Increasing salinity in irrigation water, particularly the ECIRR levels of 5.5 and 7.5 dS·m-1, showed significantly low seedling height and stem diameter growth and delayed or even inhibited budbreak in the seedlings. The EC1:1 that inhibited seedling heights, stem diameters, and budbreak was somewhere between 0.89 and 2.71 dS·m-1 (or ECIRR between 1.4 and 3.5 dS·m-1 and ECd between 2.10 and 4.86 dS·m-1), providing that soil water content was not a limiting factor in the root zone and irrigation water was uniformly distributed in the confined root zone to obtain uniform salt leaching. The visual symptoms of leaf scorch for irrigation ECIRR levels of 3.5, 5.5, and 7.5 dS·m-1 also indicated that somewhere between 0.89 and 2.71 dS·m-1 of the EC1:1, salt injury started to occur. Increasing salinity in irrigation water significantly increased chloride (Cl-) accumulation but reduced nitrogen (N) content in the scorched leaves, particularly under the irrigation ECIRR levels of 5.5 and 7.5 dS·m-1. Leaf scorch symptoms in pecan seedlings were likely associated with Cl-toxicity. No pecan seedlings under the irrigation ECIRR treatment levels of 5.5 and 7.5 dS·m-1 survived to the end of the 2-year growing period. Thus, threshold EC1:1 was somewhere between 0.89 and 2.71 dS·m-1 beyond which plant injury increases with increasing EC1:1 threatening the survival of pecan seedlings.