John G. Mexal

A growth-irrigation scheduling model for wastewater use in forest production

Applying wastewater and sludge to land for remediation has been recommended by the Environmental Protection Agency (EPA) as a method to recycle nutrient and organic matter and conserve water resources. The level of sewage treatment can range from simple primary treatment using a lagoon to tertiary treatment using a standard wastewater treatment plant. Small communities are selecting primary treatment and land application as the most cost-effective way of treating municipal wastewater. Wastewater was used to irrigate an Eucalyptus camaldulensis plantation in Ojinaga, Chihuahua, Mexico. The overall objective of the research was to develop a daily growth-irrigation scheduling model (GISM) for Eucalyptus tree plantations based on the trees’ water needs with the source of irrigation water being wastewater from a lagoon sewage treatment system. A second objective was to check this model against measured growth data to determine the limitations of using a simple irrigation-scheduling model to manage the irrigation system to maximize tree growth and wood production. The GISM calculated the evapotranspiration (Et) from the volume balance soil water model and a tree biomass sub-model, based on a water use efficiency (WUE) (biomass/Et) that partitions biomass determined from Et into the component parts of leaves and stems plus branches. The water balance portion of the model computes the Et for grass growing between the trees until a closed canopy system is reached. Weather data and a soil water stress function were used to calculate Et based on calculated reference Et and crop coefficients (Kcs) for both the trees and grass scaled to nonstressed Et. The GISM model accurately modeled height and diameter growth, although, it slightly overestimated the height growth of Eucalyptus for the high irrigation treatment in the second and the third years. The GISM model was successful in predicting height and diameter growth within a 95% confidence level of the measured height and diameter of the trees under all irrigation treatments. Based on the modeled and measured data analysis, the GISM model can be a useful tool to predict tree growth and schedule irrigations for Eucalyptus tree plantations, understand the trees response to environmental and water stress, and to provide better analyses for future research efforts. The climate-driving variables (temperature and rainfall) needed by the model are readily available for any location in the world from the National Climatic Data Center (NCDC).

Root system modification of container stock for arid land plantings

Abstract Root morphology is important for successful seedling establishment in semiarid lands. Production systems that improve root morphology, such as container volume, container configuration, and mycorrhizal inoculation influence root system development and ensure establishment success. Mycorrhizal inoculation has been enhanced by chemical root pruners that inhibit lateral root growth and promote short root development. These factors, when used in concert, ensure successful seedling establishment and rapid growth. This paper attempts to integrate these concepts into a production system.

Coupled Liquid Water, Water Vapor, and Heat Transport Simulations in an Unsaturated Zone of a Sandy Loam Field

Information on the coupled liquid water, water vapor, and heat transport under arable field conditions is still limited, particularly for unsaturated soils of semi-arid and arid regions such as New Mexico. HYDRUS-1D model was applied to evaluate various transport mechanisms associated with temporal variations in water content and soil temperature in the unsaturated zone of a sandy loam furrow-irrigated field located at Leyendecker Plant Science Research Center, Las Cruces, New Mexico. The model was calibrated using measured soil water content and soil temperature at 5-, 10-, 20-, and 50-cm depths during a 19-day period (day of the year [DOY] 85 to DOY 103, 2009) and validated for a 31-day period (DOY 104 to DOY 134, 2009). Measured and optimized soil hydraulic and thermal properties and hourly meteorological data were used in model simulations. HYDRUS-1D simulated water contents and soil temperatures correlated well with the measured data at each depth. The total liquid water flux, composed of isothermal and thermal liquid water flux, dominated the soil water movement during early periods after irrigation, whereas the contribution of total water vapor flux, composed of primarily thermal and much smaller isothermal water vapor flux, increased with increasing soil drying. During the soil drying process, the total liquid flux within 15-cm depth eventually changed to water vapor flux near the surface. The upward total liquid and vapor fluxes decreased from 5 cm, indicating that vapor flux was much higher in the layer near the soil surface. The total vapor flux in this unsaturated soil layer was approximately 10.4% of the total liquid and vapor fluxes during the simulation period.

Evaluation of Spatial and Temporal Root Water Uptake Patterns of a Flood-Irrigated Pecan Tree Using the HYDRUS (2D/3D) Model

AbstractQuantitative 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 we...

Size hierarchy in conifer seedbeds. I. Time of emergence

Studies conducted at two pine nurseries in the South and one in the West empirically related the genesis of seedling size hierarchies to time of emergence (TOE). Pinus taeda seeds were operationally sown at the southern nurseries in late April and P. ponderosa in late July at the western nursery. Germinated seedlings were tagged with color-coded plastic rings (20 turn dia.) every other day until germination was complete. Emergence was complete in 16–20 days. Growth response to TOE effects was determined 8 and 15 months, respectively, after sowing.Results were strikingly similar across nurseries; TOE strongly influenced germinant mortality and shoot biomass decreased 3.5% per day elapsed from initial emergence. That is, seedlings emerging 10 days after emergence began were 35% smaller at harvest than those emerging first. Late germinants accounted for significantly more culls among harvested seedlings than early germinants. Also, TOE accountend for more than 80% of variation in harvest biomass. Findings suggest that the germination period should not exceed 5 days. Response models are proposed to elucidate TOE effects in nursery operations.

Performance of Pinus halepensis/brutia Group Pines in Southern New Mexico

Abstract An international provenance trial of Pinus eldarica, P. brutia and P. halepensis was established the southern Rio Grande Valley of New Mexico in 1978. The test was planted in a randomized complete block with 10-tree row plots. Pinus eldarica, P. brutia and P. halepensis were represented by seven, seven and nine seed sources, respectively. After five growing seasons, P. eldarica height, diameter at breast height (DBH) and stem volume were, respectively, 1.6, 2.0 and 5.0 times greater than the other two species, and eldarica pine was least variable across all parameters. Pinus brutia showed good survival, but growth variation among provenances was high. Survival among P. halepensis provenances varied greatly because of winter injury. The potential value of P. eldarica for multipurpose plantings in arid and semiarid zones is discussed.

Spatial Variability of Electrical Conductivity of Desert Soil Irrigated with Treated Wastewater: Implications for Irrigation Management

Knowledge of spatial variability is important for management of land affected by various anthropogenic activities. This study was conducted at West Mesa land application site to determine the spatial variability of electrical conductivity (EC1:1) and suggest suitable management strategy. Study area was divided into five classes with EC increasing from class I to V. According to the coefficient of variation (CV), during 2009 and 2010, EC1:1 values for different classes were low to moderately variable at each depth. Semivariogram analysis showed that EC1:1 displayed both short and long range variability. Area coverage of classes I and II were much higher than classes III, IV, and V during 2009. However, during 2010 area coverage decreased from 26% to 14.91% for class II, increased from 12.11% to 22.97%, and 10.95% to 20.55 for classes IV and V, respectively. Overall area under EC1:1≥ 4 dS/m increased during 2009. Soil EC map showed EC classes IV (4.1–5 dS/m) and V (>5.1 dS/m) were concentrated at northwest and southeast and classes I and II were at the middle of the study plot. Thus, higher wastewater should be applied in the center and lower in the northwest and southwest part of the field.

Spatial Variability of Soil Properties in an Arid Ecosystem Irrigated With Treated Municipal and Industrial Wastewater

Abstract Information on spatial variability of soil properties is important for designing site-specific management practices for soils affected by human activities. Spatial variability study was conducted at West Mesa near Las Cruces, New Mexico, to identify the areas where remediation is needed and suggest sustainable management strategies to reduce the effect of treated saline and sodic wastewater application on soil environment and existing native vegetations based on the spatial variability of soil physical and chemical properties. Bulk and core soil samples were collected from the center of 54 (50 × 50 m) grid points, and additional 30 samples were collected from smaller grids at 0- to 20- and 20- to 40-cm depth during summer 2010. Geostatistical software (GS+) was used to obtain semivariograms and cross-variograms. Coefficient of variation (CV) indicated that sodium adsorption ratio (SAR), chloride (Cl−), wilting point, saturated hydraulic conductivity (Ks), and nitrate (NO3−) were most variable with CV of greater than 0.35, whereas sand, clay, bulk density, and pH were least variable (CV <0.15). Cross-variogram showed that SAR was spatially correlated with Ks and sand content; Ks, with bulk density; therefore, kriging or cokriging can be used to estimate SAR from Ks. Blocked kriged spatial distribution maps showed positional similarity, and most of the higher chemical properties were concentrated in the northwest and southeast portion and lower near the center of the experimental field. Average SAR concentration in the northwest portion was 22.77, and a southeast portion of the field was 18.12, which were above the threshold limits (>15) for most plants. So, it is necessary to monitor SAR on a regular basis and change the wastewater application pattern, with more wastewater application in the middle and less in the northwest and southeast part of the experimental site.

Spatial Variability of Soil Properties in Agricultural Fields of Southern New Mexico

Estimating the spatial variability of soil physical and chemical properties is a prerequisite for soil and crop-specific management. The objectives of this study were to determine the degree of spatial variability and variance structure of soil physical and chemical properties on a 40-ha agricultural field in Las Cruces, New Mexico, to observe any change in the variance structure caused by the cropping system and to suggest future sampling designs to make efficient management decisions. Soil samples were collected at the center of a regular grid of 50 m × 50 m and on the grid line during November 2008 and 2009 from 0 to 15 cm of depth. The software package GS+ was used to model the variance structure of sand, silt, clay, soil bulk density, saturated hydraulic conductivity (Ks), pH, electrical conductivity (EC), nitrate-nitrogen (NO3-N), chloride, and volumetric water content at six different matric potentials (−33, −100, −300, −500, −1,000, and −1,500 kPa). The coefficient of variation ranged from 4% (pH) to 141% (Ks). The semivariograms showed that the range of spatial dependence varied from 86 m (pH, 2008) to 563 m (Ks) for all measured soil properties. Cross-semivariograms showed that NO3-N and EC were spatially correlated; therefore, kriging or cokriging can be used to estimate NO3-N values throughout the growing season from easily available EC data. Correlograms with Moran I indicated that a distance of 140 m was sufficient to yield independent samples for measured soil physical and chemical properties. The kriged contour maps showed positional similarities. These contour maps of soil properties, along with their spatial structures, can be used in making better future sampling designs and management decisions.

Chemical and Physical Properties of Chihuahuan Desert Soils Irrigated with Industrial Effluent

Land application of secondary industrial effluent to Chihuahuan Desert upland near Las Cruces, New Mexico, was designed to meet the water demand of creosote and mesquite shrubs. The major objective of this study was to assess changes in chemical and physical properties of desert soils after 4 years (2002–2005) of irrigation with secondary industrial effluent. Soil texture and bulk density (pb) did not differ between irrigated and control plots, but did so between bare ground and mesquite sites in the control and irrigated plots. Reductions in saturated hydraulic conductivity (K s ), drainable porosity (θd), and effective porosity (θe) in the upper 0–15 cm of irrigated plot soils were attributed to decline of soil structure and dispersion of clays resulting from the addition of highly sodic and alkaline effluent to irrigated plots. Although rarely significant, consistently higher electrical conductivity, sodium adsorption ratio, chloride, exchangeable sodium percentage, and Na+ in the soil profile (between 30 cm and 210 cm) at creosote and mesquite sites compared to the bare ground site suggested deeper leaching of wastewater constituents at shrub sites. Deeper leaching of wastewater constituents beneath shrubs compared to bare ground areas may be attributed to higher water inputs caused by sprinkler spray interception, and higher Ks, θd, and θe of soils beneath creosote and mesquite canopies. Continued application of industrial effluent to a Chihuahuan Desert ecosystem over the long term should consider the relative importance of canopy and intercanopy areas.