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Abstract
Water-use characteristics of irrigated pecan trees [Carya illinoensis (Wang) K. Koch] were evaluated in 7 commercial orchards in the El Paso—Las Cruces valleys. Test trees (8- to 35-years-old) were surface-irrigated ‘Western’, having various sizes (13–53 cm in trunk diameter) and planting densities (60–120 trees/ha). A neutron moisture probe was used for evaluating soil water depletion. Soil water depletion below a depth of 100 cm was minimal and independent of the horizontal distance from tree trunks except in young trees. Consumptive water use was highly dependent of tree size and planting density, and close-spaced, full-grown trees used 100 to 130 cm per season. Based on these field data, an empirical equation was developed for computing crop coefficients and consumptive use from trunk diameters, planting densities, and weather data.
Irrigated pecans in the southwestern United States have been planted in every soil imaginable, and tree performance has become highly soil-dependent. Desperate attempts to deal with this poor soil selection has led to advancements in soil management, consisting primarily of physical measures, such as chiseling and trenching. Chemical amendments appear to have played a secondary or supplemental role. Meanwhile, soil structural degradation, mainly compaction and aggregate destruction, began to cause poor water penetration, die-back of deep roots, and resultant loss of tree vigor. These problems have been dealt with primarily by chiseling. In the future, spiking and sodded-floor management are likely to become increasingly important. Scientific examination of soil management practices has lagged, but has provided some rationale and targets for soil management. H should play an increasingly important role in refining these measures and in establishing a comprehensive soil management program in which the soil is viewed as a plant growth medium and an integral component of cost-effective orchard management.
Irrigated production of pecans in the southwestern United States started with notoriously inefficient flood irrigation along river basins. Today, most surface-irrigated orchards are laser-leveled, and many orchards in upland areas are under sprinkler or drip irrigation. Technical and scientific knowledge for improving water management also has evolved from studying drought effects on tree performance to an improved understanding of water relations, salt effects, evapotranspiration processes, and the distribution of water and salts in irrigated fields. Yet, many growers still experience difficulties with water management and may benefit from maintaining the soil water suction above saturation but below 30 to 40 cb until shuck opening. The soil salinity should be kept below 2.5 dS·m−1, and irrigation water should be applied to essentially the entire root zone for optimum tree growth. Due to extreme soil variability existing in most irrigated fields of the southwestern region, these guidelines alone are not adequate. Soil profiles, root distributions, water quality, and irrigation methods may have to be examined to improve water management.
Growth and B uptake of five pecan [Carya illinoensis (Wangenh.) C. Koch] seedling cultivars were evaluated in two greenhouse experiments. Seedlings were exposed for 7 to 8 months to various B-containing irrigation solutions. In one study, the growth of `Apache', `Riverside', and `Burkett' seedlings declined significantly with a 5.0-mg B/liter application that provided 12.3 mg B/liter in the soil saturation extract. In the second study, B application of 2.5 mg·1iter-1 (6.4 mg·liter-1 in the saturation extract) reduced growth of `Western' and Wichita' seedlings. Seedling sources differed in susceptibility to B applications. `Apache' and `Wichita' seedlings were the more sensitive cultivars in the experiments. Leaf B concentrations increased linearly with concentrations in the saturation extract (r = 0.96 to 0.99), but did not depend on the cultivar. Boron toxicity (leaf interveinal chlorosis and tip necrosis) occurred within several weeks following B application of 1.25 to 2.5 mg·liter-1 (2.8 to 6.6 mg·liter-1 in the saturation extract, depending on cultivar). Three months later, chlorotic areas became necrotic in leaves containing >900 mg B/kg dry weight. Severe necrosis and some defoliation occurred when B concentrations were increased further. Leaves with no injury contained ≤325 mg B/kg.
Seedlings of three pistachio rootstock (Pistacia atlantica Desf., P. terebinthus L., and P. integerrima Stewart × atlantica) and of the pistachio scion cultivar Kerman (P. vera. L.) were grown in calcareous sandy loam irrigated with B solutions (0 to 15 mg·liter-1) in a greenhouse. After 10.5 months of B treatment, rootstock seedling growth (root + stem weight and leaf dry weight, area, and number per plant) had decreased linearly with B application, which provided up to 48.9 mg B/liter in the soil saturation extract. Growth of P. terebinthus was greater than P. atlantica throughout the concentration range, but species sensitivity to B did not differ. Nine months of B at concentrations up to 10.7 mg·liter-1 in the saturation extract did not alter the growth of P. vera seedlings. Leaf B concentrations of all species increased linearly with saturation extract B concentration after each of two growing periods and were higher in leaves of P. terebinthus than P. atlantica. From 62% to 75% of B was present in leaf tissue of the rootstock seedlings, with lower quantities in roots and stems. Boron toxicity appeared initially as interveinal chlorosis and apical necrosis of 1-month-old, fully expanded leaflets of the rootstock species. By 4 months, symptoms in some treatments advanced to severe necrosis of leaflets. Boron addition increased the concentrations of total leaf sugars (glucose, fructose, and sucrose) and root starch, decreased root glucose concentrations, and had no effect on other root carbohydrates of P. vera seedlings. Leaf carbohydrate supply limitations and altered root carbohydrate status may be consequences of high B in P. vera seedling leaves.
The degree of salt resistance of Pistacia spp. grown in the western United States is not adequately known. This study evaluated seedling growth and ion uptake characteristics of two Pistacia spp. and one hybrid in outdoor lysimeters for two seasons. After 12 weeks, seedling stem elongation of P. atlantica Desf., P. terebinthus L. (three selections), and P. integerrima Stewart × atlantica (referred to as Gold II) was reduced by an average of 33% at soil solution salinity of 12.6 dS·m-1 (or 8.0 dS·m-1 in the saturation extract). Gold II was the most vigorous genotype and produced the greatest biomass in control and high-salt solutions. Decreases in root and stem growth (average of all seedlings combined) occurred at soil solution salinity of 13.8 dS·m-1 (or 8.7 dS·m-1 in the saturation extract). Increasing salinity resulted in a higher root to stem ratio, which was most pronounced in P. terebinthus. Comparatively small but significant differences in leaf Na and Cl concentrations between species and selections occurred. All species limited Na transport to leaf tissue up to 125 meq Na/liter in soil solution, storing the greatest amount in roots. Chloride concentrations on a dry-weight basis were substantially higher in leaves than in roots. Increasing salinity did not affect leaf K and Mg concentrations, whereas Ca was significantly reduced. Leaf Na and Cl concentrations of P. atlantica and P. terebinthus had significant correlation with Na and Cl concentrations in soil solutions (r = +0.83 to +0.94).
Excised root tips from 3-year-old pistachio rootstock (Pistacia atlantica Desf., P. terebinthus L., and P. integerrima Stewart × atlantica) were exposed to laboratory saline solutions for 24 hr. Treatments simulated the compositions of soil solutions in a previous 2-year study made in outdoor lysimeters. Leakage of UV-absorbing solutes, an indication of cellular damage, occurred with 175 mM Na/12.5 mM Ca, which was comparable to soil salinity which increased leaf Na concentrations and decreased root growth of these species Up to. five times higher leakage occurred from roots of a P. terebinthus genotype having least Na exclusion potential during the lysimeter study. Use of isotonic levels of CaCl2, mannitol, and simulated Na/Ca solutions resulted in similar damage. However, isotonic Na (-Ca) caused highest leakage overall. Correlation between long-term observations in the lysimeters and leakage occurrence-in the laboratory indicates that solute leakage tests may aid in characterizing responses of Pistacia spp. roots cocks to saline conditions.
A laboratory procedure was used to evaluate saline tolerance of pistachio rootstock species. Results were compared to those from a 2-year, outdoor lysimeter study to test reliability of the method. Excised root tips from seedlings of Pistacia atlantica Desf., P. terebinthus L. (two selections), and P. integerrima Stewart × atlantica (Pioneer Gold II, or PG II), were exposed to laboratory solutions that simulated soil solution electrical conductivity (EC) and Na: Ca ratios in the lysimeters. Following 24 hours of incubation, the efflux of ultraviolet (UV)-absorbing solutes was measured, providing an indication of cell membrane permeability. Leakage occurred with saline solutions comparable to lysimeter soil water salinity that increased leaf Na concentrations and decreased average root growth (175 mm NaCl with 12.5 mm Ca, or EC of 18.1 dS·m-l). Cell injury increased linearly with salinity (R2 = 0.81) and was highest in root tips of a P. terebinthus selection having least Na exclusion capability in the lysimeters. On average, these excised roots lost 38% more solutes than roots of a stronger Na-excluding genotype. There were no differences in leakage responses of the other species and selections. Leakage intensity was independent of various stress media, including isosmotic CaC12, mannitol, and the simulated Na/Ca mixtures in molar ratios of 10:1 to 20:1. With no Ca, however, damage caused by isosmotic NaCl was 76% to 87% higher, indicating that for these species, the Na: Ca ratio can alter root cell membrane permeability. Correlation between long-term observations in the lysimeters and leakage occurrence in the laboratory indicates that solute leakage tests with roots may aid in characterizing Pistacia spp. rootstocks for saline condition.