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- Author or Editor: John G. Mexal x
Diurnal and temporal patterns of stem water potential (ψstem) and leaf water potential (ψleaf) were determined during June to Sept. 2010 and 2011 at lower (2.5 m tree height), mid- (4.6 m), and upper (7.6 m) canopy positions for two flood-irrigated, mature pecan [Carya illinoinensis (Wangenh.) K. Koch] orchards near Las Cruces, NM. Diurnal measurements of ψstem and ψleaf at three canopy heights were correlated under both dry and wet soil conditions. However, although soil water contents at Site 2 (silty clay loam texture) remained higher compared with Site 1 (sandy loam), ψstem and ψleaf values, particularly under dry soil conditions at Site 2, were consistently lower, showing the effect of clayey soil texture on pecan water stress. Diurnal patterns of ψstem and ψleaf indicated that measurements of ψstem and ψleaf should be made close to early afternoon (between 1400 and 1500 hr Mountain Standard Time) to evaluate mature pecan water stress, which also corresponded to maximum climatic stress conditions. Midday ψstem and ψleaf measured at three canopy heights over several irrigation cycles during the 2010 season were correlated with one another, midday soil water content at different depths, and atmospheric vapor pressure deficit (VPD). Multiple regression analysis [between midday ψstem or ψleaf and midday θavg (soil water content at 0 to 40 cm), air temperature (Tmd), and relative humidity (RHmd)] during the 2010 season revealed that two-parameter regression models [ψstem or ψleaf = f (midday θavg and Tmd)] were the most significant for the interpretation of midday ψstem or ψleaf at both sites. Using the two-parameter model, predictions of ψstem and ψleaf measured on the both shaded and sunlit sides of trees at three canopy heights for 2011 showed good agreement between measured and predicted ψstem and ψleaf (R 2 ranged from 0.70 to 0.98). Two-parameter models derived in an earlier study generally underpredicted ψstem both in 2010 and 2011, which further supported the importance of the time of midday ψstem and ψleaf measurements suggested in this study.
We integrated the construction and operation of hoop houses into a general education course to provide students with basic agriculture skills such as basic agricultural construction, greenhouse crop production, and greenhouse environmental data collection, while immersing them in an experiential learning environment. Students in the class constructed three 12 × 15-ft hoop houses, installed an irrigation system and climate data acquisition system, and grew radish (Raphanus sativus ‘Cherry Belle’) and lettuce (Lactuca sativa ‘Black-Seeded Simpson’) within each hoop house. At the end of the exercise, 86% of students agreed that they knew the basic techniques of hoop house construction, and 89% agreed that they understood the practical application of building a hoop house. More instruction on calculating crop fertilizer requirements would benefit students because only 43% of students agreed or strongly agreed that they understood how to compute crop fertilizer requirements. Climate data demonstrated that air temperature within the unvented hoop houses exceeded the optimal growing temperature for lettuce and radish. We conclude that construction and operation of hoop houses provided practical agricultural skills in an experiential learning environment while revealing subject areas that warrant further instruction.
A field study was conducted in 1997 and 1998 in Ojinaga, Chihuahua, Mexico, to compare biomass production potential and ion uptake capacity of seven tree species and clones, Eucalyptus camaldulensis (4016, 4019, and 505), hybrid Populus (029, 197, and 367), and seedlings of Robinia pseudoacacia irrigated with saline municipal wastewater. Total dry biomass production was greatest with poplar clone 367 (657 g) and eucalypt clone 4019 (643 g). Both clones also provided the most aboveground biomass (463 and 528 g, respectively), essentially because of their greater stem biomass (274 and 234 g, respectively). Poplar clone 367 had the highest lateral branch biomass (84 g), followed by eucalypt clone 4019 (75 g). The clones with the greatest leaf biomass were eucalypt clone 4019 (179 g), followed by eucalypt clone 505 (148 g) and poplar clone 367 (145 g). In all tree selections, Cl concentration was highest in the leaves with poplar clone 197 having the highest concentration (>2%), but the lowest subsequent winter survival at just 55%. The tree with the second lowest survival rate, poplar clone 029 (76%), also had the second highest Cl concentration in its leaves, almost 1.5% Cl. Eucalypt clones 4019 and 4016 accumulated the most total Cl in its tissues (327 and 236 g per tree, respectively) followed by poplar clone 029 (216 g per tree). Eucalypt clone 4019 accumulated the most Na in its tissues (109 g per tree) followed by poplar clone 367 (74 g per tree). In conclusion, poplar clone 367 and eucalypt clone 4019 seem to be sufficiently salt-tolerant for these saline conditions, having high survival, growth, and biomass capacity and perform well under high biomass-generating, short rotation conditions. Eucalypt clone 4019 is also an effective accumulator of Cl and Na ions and may be the most suitable tree for the remediation of salt-affected land in these experimental conditions.
Optimal pecan (Carya illinoiensis) production in the southwestern United States requires 1.9 to 2.5 m of irrigation per year depending on soil type. For many growers, scheduling flood irrigation is an inexact science. However, with more growers using computers in their businesses, and with soil moisture sensors and computerized data-collection devices becoming more inexpensive and accessible, there is potential to improve irrigation and water use efficiencies. In this project two low-cost soil monitoring instruments were introduced to a group of pecan producers. They were also given instruction on the use of Internet-based irrigation scheduling resources, and assistance in utilizing all of these tools to improve their irrigation scheduling and possibly yield. The objectives were to determine whether the technology would be adopted by the growers and to assess the performance of the sensors at the end of the season. Three out of the five growers in the project indicated they used either the granular matrix (GM) sensors or tensiometer to schedule irrigations, but compared to the climate-based irrigation scheduling model, all growers tended to irrigate later than the model's recommendation. Graphical analysis of time-series soil moisture content measured with the GM sensors showed a decrease in the rate of soil moisture extraction coincident with the model's recommended irrigation dates. These inflection points indicated the depletion of readily available soil moisture in the root zone. The findings support the accuracy of the climate-based model, and suggest that the model may be used to calibrate the sensors. Four of the five growers expressed interest in continued use of the tensiometer, but only one expressed a desire to use the GM sensor in the future. None of the participants expressed interest in using the climate-based irrigation scheduling model.
Commercial production of pecan [Carya illinoinensis (Wangenh.) K. Koch.] generates significant woody biomass from hedge prunings with little economic value. Value-added uses could aid pecan growers, and one possible use is wood chips for potting substrates to lessen dependence on peatmoss, thereby aiding greenhouse growers. We evaluated vegetative growth and leaf nutrient responses of ‘Carpino’ garden chrysanthemum (Dendranthema ×grandiflorum) over a 60-day period. Plants were grown in five pecan wood chip substrate levels that substituted 0%, 25%, 50%, 75%, and 100% of peatmoss by volume. Three water soluble fertilizer (WSF) rates—N at 0, 200, or 400 mg·L−1 (0–N, 200–N, and 400–N, respectively)—were applied with each irrigation and to each of the wood substitution treatments. The WSF and wood substitution treatments interacted strongly. In the presence of wood, (25−100% substitution levels), increasing WSF to 400–N increased cumulative evapotranspiration (ET), crop height, total leaf number and area, total leaf and stem dry weight, and leaf N and P concentrations. However, with 0% wood substitution, 400−N provided little or no such enhancements. With 25% to 50% wood substitution, root dry weight increased by 61% to 91% from 0–N to 200–N, which may be an adaptive response to nutrient-limiting conditions at 200–N. Appearance of a white rot fungal species in and atop pecan wood-supplemented substrate supports the likelihood that microbial activity was, at least in part, responsible for the nutrient limitations. High WSF at 400–N in combination with 25% pecan wood substitution maintained adequate fertility and shoot growth that was comparable to the conventional peat-only substrate at 200–N. With low to moderate amounts of pecan wood, further adjustments to WSF rate and irrigation volume would support sustainable fertigation practices, reduce dependence on peatmoss by greenhouse industry, and provide a value-added recycling option for pecan growers.
For farmers to accurately schedule future water delivery for irrigations, a prediction method based on time-series measurements of soil moisture depletion and climate-based indicators of evaporative demand is needed. Yet, numerous reports indicate that field instruments requiring high in-season labor input are not likely to be used by farmers. In New Mexico, pecan (Carya illinoensis) farmers in the Mesilla Valley have been reluctant to adopt new soil-based or climate-based irrigation scheduling technologies. In response to low adoption rates, we have developed a simple, practical irrigation scheduling tool specifically for flood-irrigated pecan production. The information presented in the tool was derived using 14 years of archived climate data and model-simulated consumptive water use. Using this device, farmers can estimate the time interval between their previous and the next irrigation for any date in the growing season, in a range of representative soil types. An accompanying metric for extending irrigation intervals based on field-scale rainfall accumulation was also developed. In modeled simulations, irrigations scheduled with the tool while using the rainfall rule were within 3 days of the model-predicted irrigation dates in silty clay loam and loam soil, and less than 2 days in sandy loam and sand soil. The simulations also indicated that irrigations scheduled with the tool resulted in less than 1% reduction in maximum annual consumptive water use, and the overall averaged soil moisture depletion was 45.14% with an 18.1% cv, relative to a target management allowable depletion of 45%. Our long-term objective is that farmers using this tool will better understand the relationships between seasonal climate variation and irrigation scheduling, and will seek real-time evapotranspiration information currently available from local internet resources.
The authors used a simple procedure to teach how to generate evapotranspiration (ET) data for both 1- and 5-gal pots of the xeric shrub apache plume (Fallugia paradoxa) and the mesic vine japanese honeysuckle (Lonicera japonica ‘Halliana’). In-class instruction and assigned reading prepared students for collecting data over a 22-day period (12 Apr. to 3 May), processing data on an electronic spreadsheet, accessing the Internet to acquire reference plant ET data, calculating a crop coefficient (Kc), preparing graphs, organizing a digital presentation, and presenting the findings to commercial nursery participants and instructors. When averaged across days and pot sizes, ET of japanese honeysuckle was 1.22 cm·d−1, whereas ET of apache plume was only 0.80 cm·d−1. This finding supported the students' hypothesis that a nursery block of potted mesic vines would use more water than a nursery block of potted xeric shrubs per unit of ground area. Commercial nursery participants adopted the ET monitoring technique after viewing the student presentation, indicating effective transfer of information by the students. The simple, inexpensive, 3-week exercise furthered the students' horticulture knowledge and comprehension while allowing for a collaborative effort with the local nursery industry.