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Five- to six-year-old `Redblush' grapefruit (Citrus paradisi Macf.) trees on `Volkamer' lemon [VL = C. volkameriana (Ten. & Pasq.)] or sour orange (SO = C. aurantium L.) rootstock, were grown individually in 7.9-m3 lysimeters for 2.5 years using low to high rates of fertilizer N. Net CO2 assimilation (ACO2) of leaves and leaf dry mass per area (DM/a) increased with leaf N concentration, whereas leaf tissue C isotope discrimination (Δ) decreased. Leaf tissue Δ was negatively related to ACO2 and DM/a. Transient effects of rootstock on leaf N were reflected by similar effects on Δ. There was no effect of leaf N on water-use efficiency (WUE) of leaves (WUEL = ACO2/transpiration); WUEL was not correlated with Δ. Although photosynthetic N use efficiency (ACO2/N) consistently decreased with increased leaf N, Δ was not consistently related to ACO2/N. Annual canopy growth, tree evapotranspiration (ET), and fruit yield increased with whole tree N uptake. Leaf tissue Δ was negatively related to all of these tree measurements at the end of the second year. By that time, whole-tree WUE (WUET, annual canopy growth per ET) also was negatively related to Δ. Larger trees on VL had higher ET than trees on SO, but there were no rootstock effects on WUET or on Δ. Leaf tissue Δ was consistently higher than Δ values of trunk and woody root tissues. Citrus leaf tissue Δ can be a useful indicator of leaf N, characteristics of leaf gas exchange, tree growth, yield, and WUET in response to N availability.
Carbonated water has recently been under study as a potential means of increasing photosynthesis in the field situation. Cahn (1989) and Novero (1991) have demonstrated that carbonated water lowers soil pH in strawberries and tomatoes, respectively. Novero showed greater uptake of zinc and increased marketable fruit yields. Currently, we are evaluating the influence of carbonated water on strawberry (Fragaria × ananassa cv Muir) growth using a high pH, high calcium soil and a low pH, low calcium soil in the greenhouse. Carbonated water applied to a high pH, high calcium soil significantly increased leaf, bud and open flower number, as well as greater crown and leaf dry weights.
Many growers fertigating their orchards with zinc–ethylenediaminetetraacetic acid (Zn-EDTA) are still using supplemental zinc foliar sprays because of a lack of confidence that soil-applied Zn-EDTA is supplying enough Zn to the trees. A field study was conducted in a pecan orchard located near San Simon, AZ, on 8-year-old ‘Wichita’ trees growing in an alkaline, calcareous Vekol loam soil to evaluate the effectiveness of supplemental foliar Zn sprays. All trees were fertigated with 6.0 kg⋅ha–1 Zn in the form of Zn-EDTA in 2018 and 11.0 kg⋅ha–1 Zn in 2019 and did not exhibit visible signs of Zn deficiency. Foliar treatments of 3.75 mL⋅L–1 urea–ammonium nitrate (UAN), 3.6 g⋅L–1 zinc sulfate monohydrate (ZnSO4·H2O), 3.6 g⋅L–1 ZnSO4·H2O with 3.75 mL⋅L–1 UAN, 11 mL⋅L–1 Zn-EDTA, and water alone were applied to individual fruiting shoot terminals of trees on two dates each in 2018 and 2019. Treatments were sprayed directly onto the leaves of the selected terminals. Zn-EDTA was included as a foliar treatment in 2019 only. Leaf photosynthesis was measured to determine the impact of leaf Zn concentrations on plant function. Midday stem water potential (MDSWP) was measured to verify that water stress was not limiting photosynthesis. Both measurements were taken about 2 to 4 weeks after the application of foliar treatments. MDSWP measurements indicated a lack of water stress and therefore no effect on photosynthesis. Leaf samples collected from untreated branches indicated that the average foliar Zn concentration of untreated leaves was 21.3 mg⋅kg–1 in 2018 and 15.7 mg⋅kg–1 in 2019. No differences were observed in photosynthesis rates of treated branches. No additional benefit to leaf photosynthetic function or appearance was observed from spraying Zn on foliage of trees fertigated with Zn-EDTA.
Consumption of sweetpotato (Ipomoea batatas) has increased in the past decade in part because of its nutritional and health attributes, and because of the availability and convenience of processed products. The sweetpotato processing industry is expanding and supplying more sweetpotato products than ever before. Unlike the medium-sized roots (U.S. no.1) preferred for fresh market, large (jumbo) roots is accepted and in certain cases desired by the processing industry, and overall yield is preferred over strict sizing requirements and aesthetic appeal. Therefore, this study investigated the yield increase and grade proportions in response to plant spacing and extension of the growing period to improve profitability of the production system. Experiments with ‘Beauregard’ and ‘Evangeline’ sweetpotato were conducted in Mississippi and Louisiana during 2010 and 2011. Treatments consisted of a combination of early and late planting date and delay in harvest, in-row plant spacing, and row width. Yield increase was inconsistent with delaying harvest and appears to depend on environmental conditions at harvest late in the season. Marketable yield was consistently greater in early plantings than late plantings. Yield of U.S. no.1 grade was unaffected by delaying harvest regardless of planting date. Delaying harvest in early plantings contributed to increase jumbo-sized roots and marketable yield. The economic assessment of delaying harvest in early plantings indicated a gain in net benefit either when hand harvested for fresh market or field run bulk harvested for processing. Row width and in-row plant spacing had only a marginal effect on yield of canner grade (small-sized roots). The economic assessment of changing plant density indicated no gain in net benefit, which indicates that choice of plant density can depend on other factors.
Common bacterial blight (CBB), rust (RU), and white mold (WM) are serious diseases of great northern (GN) and pinto (P) beans in Nebraska and Colorado. The bacterial diseases halo blight (HB) and brown spot (BS) are sporadic. Severe Fe-induced leaf chlorosis (Fe ILC) occurs on calcareous sites. Separate inoculated disease nurseries are used to screen for resistance to the pathogens causing the above diseases. Yields and seed quality of lines are also determined in non-disease trials. Sources of exotic resistance to the above pathogens and to Fe ILD have been identified and their inheritance determined. A non-structured recurrent selection scheme has mainly been used, occasionally with a backcross program, to combine high levels of the desired traits. Selection for highly heritable traits such as seed size, shape and color, maturity, plant architecture, and RU resistance occurs in early generations while traits of low heritability, such as CBB resistance, WM avoidance, yield, seed coat cracking resistance, and canning quality, are evaluated in separate replicated tests over several years and finally for yield in on-farm-trials. A number of multiple disease resistant, high-yielding, well-adapted GN and P lines are or will be released; P `Chase' (on about 30,000 acres in 1996) and GN WM 3-94-9 (for possible release).
Legume ground covers were evaluated in pecan orchards to reduce nitrogen inputs and increase beneficial insects. Treatments were established at two sites in Oklahoma, each with 5 ha of a `Dixie' crimson clover/hairy vetch mixture and 5 ha of grass sod. Nitrogen was applied at 0-200 kg·ha-1 to the sod plots, but legume plots were not fertilized. Aphids and selected arthropods were monitored on ground covers and in the pecan canopies. Data indicated that a mixture of crimson clover/hairy vetch supplied up to 186 kg·ha-1 N to the trees. Beneficial arthropods monitored were Coccinellidae, Chrysopidae, Nabid, Syrphid, and spiders. Lady beetles, primarily Hippodamia and Coleomegilla, were the most important aphid predator in the spring, and green lacewing was the most important fall predator. There were fewer aphids infesting pecans using a crimson clover/hairy vetch ground cover than a grass sod.
A field study was conducted to evaluate tolerance of pecan rootstocks to soil salinity and sodicity. Seven cultivars—Elliott, Giles, Ideal, Peruque, Riverside, ‘Shoshoni, and VC1-68—were selected from a range of geographic regions of origin. The soil of the experimental plot was a poorly drained, saline–sodic Pima silty clay variant. The irrigation water was a moderately saline mix of Gila River and local groundwater with an electrical conductivity of 2.8 dS⋅m–1, containing primarily ions of Na and Cl. Eighty seeds of each cultivar were planted in a greenhouse in late Feb. 2016; 48 seedlings of each cultivar were transplanted into field plots in Feb. 2017. Half the trees received a soil-based application of Zn–ethylenediaminetetraacetic acid (EDTA) at planting. The trees were observed and rated for both vigor and resistance to salt injury on seven separate occasions. Trunk diameter was measured each dormant season. Leaf samples were collected on 9 Oct. 2019 and 6 Oct. 2020, and were analyzed for nutrient content. Zn-EDTA was not found to have a significant effect on growth, vigor, or resistance to salt injury. ‘Elliott’ seedlings exhibited greater tolerance for the alkaline, saline–sodic soil conditions than other cultivars. ‘Giles’ and ‘Peruque’ were most severely affected. Resistance to salt injury (ranging from marginal leaf burn to necrosis of entire leaf), vigor, and growth correlated more strongly with foliar concentrations of Na than Cl or K during 2019. Vigor and growth were not significantly correlated with foliar Na, Cl, or K concentrations in 2020. The foliar K:Na ratio had a nearly equal correlation with resistance to salt injury and a greater correlation with growth than that of Na alone in 2019. However, although the correlation of the K:Na ratio with vigor was stronger than that of Cl or K, Na had the strongest correlation with vigor in 2019. In 2020, the only significant correlation of growth and vigor was with the K:Na ratio. The strongest correlation with resistance to salt injury in 2020 was with foliar Na concentration.
Analysis of composite pecan leaf samples typically used to determine need for nutrient applications does not account for variability among trees in the sampled area. To account for this unmeasured variability, pecan orchard block nutrient standards are greater than actual single tree nutrient requirements. In 2018 and 2019, we measured variability in a pecan orchard block by evaluating nutrient status of all trees in a study area consisting of two cultivars (Wichita and Western) grafted on open-pollinated ‘Ideal’ seedlings. Foliar zinc (Zn) coefficient of variation (cv) ranged from 0.186 to 0.255 within individual cultivars and years but was as high as 0.30 when combining cultivars within a year. The ‘Western’ cultivar had higher foliar Zn concentrations than ‘Wichita’, but Zn concentrations were not consistently associated with other leaf nutrient levels, soil Zn status, or other soil properties. Using observed foliar Zn variability, we determined that it is necessary to sample 35 trees for a composite sample to achieve a relative margin of error of 10% and 95% confidence level in a pecan orchard block with more than 1000 trees. We developed field scale foliar Zn recommendations based on individual tree research that indicates a minimum acceptable leaf Zn concentration of ≈15 mg·kg–1 is needed to maintain optimal photosynthetic function in Zn chelate fertigated pecan trees. Assuming a Zn cv of 0.30 and a composite sample comprised of leaves from 35 trees, the minimum acceptable orchard block Zn level to ensure that less than 5% of trees had suboptimal levels of Zn was 27.6 mg·kg–1. An orchard block Zn level below 23.4 mg·kg–1 indicates that more than 5% of trees in the block had suboptimal foliar Zn concentrations.
Annual legume ground covers were evaluated in pecan (Carya illinoinensis) orchards to supply nitrogen and increase beneficial arthropods. Treatments were established at two sites, each with 5 ha of a `Dixie' crimson clover (Trifolium incarnatum) /hairy, vetch (Vicia villosa) mixture and 5 ha of grass sod. Data indicated that the legume mixture supplied over 100 kg·ha-1 N to the pecan trees. Beneficial arthropods were greater in orchards with legume ground covers than in orchards with a grass groundcover. Lady beetles and green lacewings were the most important spring predators, and green lacewings were the most important fall predator. The Species distribution on the ground covers differed from that in the canopy. Coleomegilla maculata lengi, Hippodamia convergens and Coccinella septempunctata were the most abundant lady beetle species in the legume ground covers, and Olla v-nigrum, Cycloneda munda, and Hippodamia convergens were the most abundant species in the pecan canopies. Beneficial arthropods appeared to suppress injurious pecan aphids.