For large fields, remote sensing might permit plant low moisture status to be detected early, and this may improve drought detection and monitoring. The objective of this study was to determine whether canopy and soil surface reflectance data derived from a handheld spectroradiometer can detect moisture status assessed using midday stem water potential (ψsmd) in pecan (Carya illinoinensis) during cyclic flood irrigations. We conducted the study simultaneously on two mature pecan orchards, one in a sandy loam (La Mancha) and the other in a clay loam (Leyendecker) soil. We were particularly interested in detecting moisture status in the −0.90 to −1.5 MPa ψsmd range because our previous studies indicated this was the critical range for irrigating pecan. Midday stem water potential, photosynthesis (A) and canopy and soil surface reflectance measurements were taken over the course of irrigation dry-down cycles at ψsmd levels of −0.40 to −0.85 MPa (well watered) and −0.9 to −1.5 MPa (water deficit). The decline in A averaged 34% in La Mancha and 25% in Leyendecker orchard when ψsmd ranged from −0.9 to −1.5 MPa. Average canopy surface reflectance of well-watered trees (ψsmd −0.4 to −0.85 MPa) was significantly higher than the same trees experiencing water deficits (ψsmd −0.9 to −1.5 MPa) within the 350- to 2500-nm bands range. Conversely, soil surface reflectance of well-watered trees was lower than water deficit trees over all bands. At both orchards, coefficient of determinations between ψsmd and all soil and canopy bands and surface reflectance indices were less than 0.62. But discriminant analysis models derived from combining soil and canopy reflectance data of well-watered and water-deficit trees had high classification accuracy (overall and cross-validation classification accuracy >80%). A discriminant model that included triangular vegetation index (TVI), photochemical reflectance index (PRI), and normalized soil moisture index (NSMI) had 85% overall accuracy and 82% cross-validation accuracy at La Mancha orchard. At Leyendecker, either a discriminant model weighted with two soil bands (690 and 2430 nm) or a discriminant model that used PRI and soil band 2430 nm had an overall classification and cross-validation accuracy of 99%. In summary, the results presented here suggest that canopy and soil hyperspectral data derived from a handheld spectroradiometer hold promise for discerning the ψsmd of pecan orchards subjected to flood irrigation.
Yahia Othman, Caiti Steele, Dawn VanLeeuwen, and Rolston St. Hilaire
Yahia Othman, Dawn VanLeeuwen, Richard Heerema, and Rolston St. Hilaire
Demand for New Mexico’s limited water resources coupled with periodic drought has increased the necessity for tree water status monitoring to guide irrigation scheduling of pecan (Carya illinoinensis) orchards. The objectives of this study were to assess the impact of water status developed during the flood irrigation dry-down cycles on photosynthesis (P n), and gas exchange [stomatal conductance (g S) to H2O (g H2O), transpiration (E), and intercellular CO2 (c i)] and to establish values of midday stem water potential (Ψsmd) that are needed to maintain P n and gas exchange of pecan. We conducted the study simultaneously on two southern New Mexico mature pecan orchards from 2011 through 2013. Flood irrigation as determined by grower practice was used on both orchards and P n, g H2O, E, and c i were assessed at Ψsmd of –0.4 to –2.0 MPa. Photosynthesis and gas exchange were higher in pecan trees shortly after irrigation than trees exhibiting water deficit near the end of a flood irrigation dry-down cycle. The decline in P n was markedly noticeable when Ψsmd dropped below –0.9 MPa. We attributed the reduction in P n mostly to stomatal limitation. The decline in P n and g H2O exceeded 50% when Ψsmd ranged from –1.5 to –2.0 MPa. For those reasons, we recommended that pecan orchards be maintained at Ψsmd higher than –0.90 MPa to prevent significant reductions in carbon assimilation and gas exchange.
Rolston St. Hilaire, Dawn M. VanLeeuwen, and Patrick Torres
We surveyed homeowners with residential landscapes in Santa Fe, NM, to determine their attitudes toward high desert plants and to assess their preferences for urban landscapes and water conservation strategies in a high desert urban environment. While there was low acceptance for the traditional turf lawn, 64% of residents agreed that high desert plants provided the variety they needed in their residential landscapes and 92% of residents would use high desert plants to landscape their front yard. Homeowners had a strong preference for retaining their current desert landscapes and converting traditional landscapes to high desert-adapted landscapes. Logistic regression revealed a negative relationship between length of residency in the southwestern United States and the willingness to use high desert plants. When homeowners who irrigated their landscape were asked whether water shortages, environmental concerns, information on water, city regulations, high water bills, or water rate increases would cause them to use less water on their landscapes, the highest level of agreement (94%) was for water shortages. Eighty-eight percent of respondents agreed that they liked any type of landscape that contains interesting features and is well planned. We conclude that homeowners have a preference for desert-adapted landscapes and agree that high desert plants provide an adequate palette of plants for urban landscapes. Additionally, the length of residency in the southwestern U.S. and the possibility of water shortages have the potential to impact water conservation strategies in high desert urban landscapes.
Malik G. Al-Ajlouni, Dawn M. VanLeeuwen, Michael N. DeMers, and Rolston St. Hilaire
The apparent heterogeneity of human-generated materials in residential urban landscapes sustains concerns that the quantitative classification of urban residential landscapes is impossible. The objective of this research was to develop a method to quantitatively classify urban residential landscapes in a desert environment. Using a purposive sampling procedure, we studied the landscapable area around each of 54 residential homes in Las Cruces, NM. All materials in the landscape were identified, measured, and categorized. Using 30% as the cutoff to indicate that a material was dominant in the landscape, we classified 93% of all landscapes into nine common landscape types. Mulch-dominant landscapes were the most common, and landscape types differed between front- and backyards. Shrubs did not feature prominently in any of the common landscape types. Our classification method clearly identifies multiple landscape types, and for the first time, provides quantitative evidence that landscape types are distributed differently in front- and backyard landscapes in the desert environment of Las Cruces. Information on common landscape types will be valuable to landscape horticulturists wanting to craft water conservation plans that are landscape specific if the common landscape type can be linked to a landscape water budget.
Yuqing Wang, Richard J. Heerema, James L. Walworth, Barry Dungan, Dawn VanLeeuwen, and F. Omar Holguin
Pecan (Carya illinoinensis) has high kernel antioxidant activity and unsaturated fatty acid content, which contribute to its nutraceutical properties. In the western United States, where soils are typically alkaline, pecan trees require frequent zinc (Zn) fertilizer applications to maintain normal canopy growth and nut production. Our objective was to investigate the effects of tree Zn fertilization on nutraceutical properties of ‘Wichita’ and ‘Western’ pecan kernels. Trees were fertilized with ethylenediaminetetraacetic acid (EDTA) chelated Zn, which was applied to the soil at one of three seasonal rates for a total of three treatments: 0 (control), 2.2, or 4.4 kg·ha−1 Zn. Nut samples were collected and homogenized for analyses of kernel oil yield, hydrophilic antioxidant capacity, fatty acid profile, and γ-tocopherol content. Although soil Zn treatments did not significantly affect antioxidant capacity of defatted pecan kernels, Zn application had significant positive effects on both total kernel oil yield and γ-tocopherol content compared with the control. In conclusion, soil application of Zn fertilizer may increase the human health-promoting aspects of pecan kernels, a valuable attribute among health-conscious consumers.
Clare A. Bowen-O'Connor*, Rolston St. Hilaire, John Hubsten-berger, and Dawn VanLeeuwen
Bigtooth maple (Acer grandidentatum Nutt.) is indigenous to the southwestern United States. This species is not widely used in managed landscapes but the plant holds promise as a useful ornamental tree. Micropropagation might provide additional sources of selected genotypes for the nursery industry, but tissue culture has not been used successfully to propagate this species. We cultured double-node explants from greenhouse-grown, 2-year old seedlings of bigtooth maples that originated from Utah, Texas and New Mexico. Seedling height ranged from 15-90 cm. The shoot region was divided into three equal zones designated as terminal, intermediate and basal. Explants were selected from each of those zones. Explants were established on Murashige-Skoog (MS), Linsmaier-Skoog (LS), Woody Plant Medium (WPM) and Driver-Kuniyuki (DKW) tissue culture media. Shoot proliferation, area of the plate covered by callus and foliar pigment development (hue as determined by Royal Horticultural Society Color charts) were monitored for 17 weeks. Media affected shoot proliferation (P = 0.0042) but the zone of origin (P = 0.6664) of the explant did not. Callus area showed no significant difference among the four media and three zones (P = 0.2091) and averaged 3.60 centimeters2. After four subcultures, each lasting 30 days, explants on DKW media produced 10 shoots per explant. This media might hold promise for the micropropagation of bigtooth maple. Twenty-nine percent of all explants expressed foliar pigmentation, which ranged from red-purple to orange-red. Whether foliar pigment development in tissue culture correlates with expressed pigmentation in nature warrants further investigation.
Richard J. Heerema, Dawn VanLeeuwen, Rolston St. Hilaire, Vince P. Gutschick, and Bethany Cook
Photosynthetic function in nut trees is closely related to nitrogen (N) nutrition because much of tree N is held within the leaf photosynthetic apparatus, but growing fruit and seeds also represent strong N sinks. When soil N availability is low, nut trees remobilize and translocate N from leaves to help satisfy N demand of developing fruit. Our objective was to describe shoot-level impacts of pecan [Carya illinoinensis (Wangenh.) K. Koch.] fruiting on leaf N and photosynthesis (Pn) during kernel fill under a range of tree N statuses. Our study was conducted in a mature ‘Western’ pecan orchard near Las Cruces, NM. In 2009, 15 trees showing a range of N deficiency symptom severity were grouped according to leaf SPAD into low, medium, and high N status categories. Differential N fertilizer rates were applied to the soil around high and medium N trees to accentuate differences in N status among the three categories. Light-saturated leaf Pn was measured on fruiting and non-fruiting shoots during kernel fill in 2009 and 2010. After measurement of Pn, the leaflet and its leaflet pair partner were collected, dried, and analyzed for tissue N. Leaf N concentration was significantly lower on fruiting shoots than non-fruiting shoots on all three sampling dates. The tree N status main effect was also significant, whereas the two-way interaction of shoot fruiting status and tree N status was not. Photosynthesis of leaves on fruiting shoots was significantly lower than that of non-fruiting shoots on all sampling dates. These data suggest that N demand by the growing kernel reduced N in leaves on the same shoot. Consequently, Pn of those leaves was reduced. The effect of tree N status and shoot fruiting status was best summarized with an additive model where there is a larger relative reduction in leaf N and Pn for fruiting shoots on trees with low N status.
Walter F. Ray, Geno A. Picchioni, Dawn M. VanLeeuwen, and Ryan M. Goss
Tall fescue (Festuca arundinacea) has desirable attributes as a cool-season turfgrass for the semiarid southwestern United States and the transition zone, but effects of cultural practices on newer cultivars within a desert climate are not adequately known. A field study was conducted between Sept. 1996 and Nov. 1997 to evaluate establishment of 15 turf-type tall fescue cultivars under two mowing heights (2 or 3 inches) and two different annual nitrogen (N), phosphorus (P), and potassium (K) application rates (N at 13.2 or 26.4 g·m−2, P at 0.9 or 1.8 g·m−2, and K at 11.0 or 22.0 g·m−2). The cultivars included ‘Amigo’, ‘Apache’, ‘Aztec’, ‘Bonanza’, ‘Chieftain’, ‘Cochise’, ‘Confederate’, ‘Coronado’, ‘Crossfire II’, ‘Falcon’, ‘Guardian’, ‘Kentucky 31’, ‘Leprechaun’, ‘Shortstop’, and ‘Virtue’. The fertilizer rate had no effect on turfgrass quality ratings throughout the establishment period, although overall quality was higher in Fall 1997 than during Spring and Summer 1997. The mowing height of 2 inches increased summer quality ratings of 11 of the 15 cultivars as compared with ratings under the 3-inch mowing height. The 2-inch mowing height improved fall quality ratings of seven of the 15 cultivars. No cultivars responded positively to the 3-inch mowing height. Consistently high summer through fall quality ratings were observed when ‘Apache’, ‘Aztec’, and ‘Crossfire II’ were mowed at the 2-inch height as compared with the other cultivar × mowing height treatment combinations. For turf-type tall fescue establishment in semiarid climates, findings support use of a 2-inch mowing height combined with the selective planting of ‘Apache’, ‘Aztec’, and ‘Crossfire II’ over other cultivar × mowing height combinations tested in the study.
Sara Andrea Moran-Duran, Robert Paul Flynn, Richard Heerema, and Dawn VanLeeuwen
In recent years, nickel (Ni) deficiency symptoms has been observed in commercial pecan [Carya illinoinensis (Wangenh.) K. Koch.] orchards in New Mexico. Nickel deficiency can cause a reduction in lignin formation, which could affect the risk for breakage on pecan tree shoots. Ni deficiency might furthermore disrupt ureide catabolism in pecan and, therefore, could negatively affect nitrogen (N) nutrition in the plant. The objective of this study was to identify the effects of Ni and N fertilizer applications, at two rates, on net photosynthesis (Pn), leaf greenness (SPAD), and branch lignin concentration in New Mexico’s nonbearing pecan trees. Sixty trees for year 2012 (Pawnee and Western cultivars) and 40 trees for year 2013 (Pawnee cultivar) were used at two New Mexico locations (Artesia and Las Cruces) to evaluate the effects of Ni and N on tree measures. Treatments were as follows: (1) High N plus Ni (+Ni); (2) Low N no Ni (−Ni); (3) High N −Ni; and (4) Low N +Ni. In 2012 and 2013, there was an increase in leaf greenness for each location and cultivar (tree group) through time (June to September). Photosynthesis measures in 2012 differed between tree group, time in the season, and N and Ni treatments. In 2013, Pn was influenced by tree group and time (P < 0.0001), but N and Ni interaction did not present a significant effect related to Ni benefits. Photosynthesis varied over time in 2012 and 2013, with an inconsistent pattern. In this study, Ni application at the high N rate had a negative effect on ‘Pawnee’ Pn early in the season at the Artesia site, but this application had a positive effect for ‘Western’ from Artesia at the low N level, also early in the season. Lignin content varied between tree groups only. The application of N and Ni did not affect lignin in pecan shoots. The results show an inconsistent pattern regarding the benefits of Ni on nonbearing pecan orchards for leaf greenness, Pn, and lignin content during the 2-year study. Future studies on Ni should focus on pecan trees exhibiting leaf Ni deficiency symptoms or on soils with less than 0.14 mg·kg−1 of DTPA extractable Ni, as well as the long-term effect of Ni on pecan growth and development to optimize the addition of Ni into an efficient fertilization program.
Robert F. Heyduck, Dawn VanLeeuwen, and Steven J. Guldan
We examined the effect of harvest schedule on the yield of ‘Red Russian’ kale (Brassica napus ssp. napus var. pabularia) grown during the winter in 16 × 32-ft high tunnels in northern New Mexico. We conducted the study for two growing seasons: 2013–14 and 2014–15. All plots were sown on 16 Oct. and harvested four times according to four harvest schedules: A) 8, 16, 20, and 24 weeks after sowing; B) 10, 17, 21, and 25 weeks after sowing; C) 12, 18, 22, and 26 weeks after sowing; and D) 14, 19, 23, and 27 weeks after sowing. The first harvest of each treatment was the greatest, averaging 216 g/ft2, compared with 88, 109, and 104 g/ft2 for harvests 2, 3, and 4, respectively. Season total yield of treatments B, C, and D (harvests beginning at 10, 12, and 14 weeks after sowing) yielded significantly more than treatment A, but only in year 2, when delayed growth resulted in very low yields for treatment A at harvest 1. Considering the entire 240-ft2 cropped area of the high tunnel, staggered harvests of 60 ft2 at a time can yield 2.6 to 17.5 kg per harvest or up to 124 kg over an entire season. Although we examined the yield of mature leaves, harvests could possibly begin earlier than in this study for “baby” kale or salad mixes, and the area harvested could be tailored to plant growth stage and market demand.