Non-irrigated Treatment Research Articles

Temperature and soil water status effects on radiation use and growth of pearl millet in a semi-arid environment

In semi-arid environments, crops are frequently subjected to a combination of high air temperatures, large atmospheric saturation vapor pressure deficits, high soil temperatures and reduced soil water status. To explore the performance of pearl millet ( Pennisetum typhoides S. and H., cv. CIVT) from panicle initiation to flowering (GS 2) when grown in the field under combinations of these conditions, experiments were conducted in northern Nigeria in three seasons in which daily mean air temperatures during 18 days of this stage averaged 22, 27 and 33°C, and saturation vapor pressure deficits averaged 3.7, 4.0 and 5.2 kPa, respectively. In each experiment, half of the crop was irrigated, while the other half received no water after panicle initiation. For irrigated millet, radiation use efficiency (RUE) did not vary significantly ( P = 0.05) for the three experiments (1.7 g MJ −1). RUE of non-irrigated millet was significantly reduced (0.8 g MJ −1) only during the season with the highest temperature. Radiation interception as a function of thermal time was similar in the irrigated and non-irrigated treatments except in the season with the highest temperatures, when radiation interception was reduced about 25% in the non-irrigated relative to the irrigated treatment. Stem extension of non-irrigated millet did not decline relative to irrigated millet, despite the almost complete extraction of plant available water in the upper 30 cm of the soil, except during the season with the highest temperatures, when stem extension rates began to decline as soon as water was withheld. Under high air temperatures and saturation vapor pressure deficits, dry matter accumulation in both irrigated and non-irrigated millet during GS 2 could be reasonably predicted from RUE and radiation interception. However, when high soil temperatures (daily mean at 5 cm of 34°C) occurred in the non-irrigated treatment, both RUE and radiation interception decreased relative to all other treatments.

Over-tree Irrigation in Pear Orchards Influences Persistence of Foliar Residues of Four Pesticides

Residues of two fungicides (dodine and fenarimol) and two insecticide/acaricides (amitraz and formetanate) on pear (Pyrus communis L.) leaves were reduced by over-tree sprinkler irrigation applied 24 or 72 hours after pesticide treatment. The difference in residue persistence following over-tree irrigation applied at 24 vs. 72 hours after pesticide treatment was significant only for fenarimol. Residues on leaves from nonirrigated trees at 96 hours post-treatment had declined 24% to 57% from initial levels. Over-tree irrigation further reduced residues by 14% to 47%. For all compounds except dodine, foliar residues measured at 96 hours post-treatment were reduced from initial levels to a greater extent by factors other than over-tree irrigation. Chemical names used: dodecylguanidine monoacetate (dodine); α-(2-chlorophenyl)-α-(4-chlorophenyl)-5-pyrimidinemethanol (fenarimol); N'-(2,4-dimethylphenyl) -N-[[(2,4-dimethylphenyl) imino]methyl] -N-methylmethanimidamide (amitraz); N,N-dimethyl -N'-[3[[(methylamino) carbonyl]oxy]phenyl]methanimidamide (formetanate).

Irrigation response of Pistachio (Pistacia vera L.)

Pistachio yields normally alternate between high and low values for consecutive years due to management and genetic effects. In this study, irrigated and non-irrigated treatments of old pistachio trees (Pistacia vera L.) were compared for 5 years from 1979 to 1983. Two irrigation treatments consisting of irrigation scheduling at 20- and 30-day interval were compared with the control treatment of no irrigation. Results showed that irrigation practice in pistachio orchards not only increased fruit yield, but also suppressed periodicity, the low fruit yield in alternating years. The frequent irrigation of 20-day interval nearly doubled the dry fruit yield irrespective of whether it was the off-yielding year, compared to non-irrigated control treatment. Three-years average for the irrigation at 20 days interval was 5710 kg per ha during the on-yielding years (1979,1981 and 1983); whereas, the control treatment of no irrigation yielded only 3450 kg per ha during the same period. Two-year average of the non-irrigated treatment, during the off-yielding years (1980 and 1982) was 1730 kg per ha; whereas, the irrigated treatment of 20-day interval, for the same period, showed significantly (P ≤ 0.05) higher fruit yield (4030 kg per ha). Irrigation treatments, during both on and off-yielding years, had no effect on fruit quality characteristics such as nut weight, blank and split shell percent, etc. The root activity under frequent irrigation treatment was confined to shallower soil depth than the longer interval irrigation treatment.

Preharvest Watersprout Removal Influences Canopy Light Relations, Fruit Quality, and Flower Bud Formation of `Redskin' Peach Trees

Three separate blocks of mature, nonirrigated trees of `Redskin' peach [Prunus persica (L.) Batsch] on `Lovell' rootstock, all uniformly dormant-pruned to an open center, were summer pruned 43, 31, and 21 days before harvest (DBH) in 1988, 1989, and 1990, respectively, and compared to unpruned controls in respect to light penetration and fruit characteristics. Summer pruning consisted of watersprout removal (WSR), selectively including all shoots more upright than 45° on scaffolds from the crotch to the top of the tree. WSR increased photosynthetic photon flux density (PPFD) in the center of the fruiting zone of the canopy to four times the level measured in unpruned trees, but only to an average of 16% of above-canopy PPFD. The greatest effect of WSR on PPFD occurred in the center of the tree, increasing light levels from <10% full sun before WSR to 90% full sun following WSR. WSR resulted in higher PPFD in the center of the tree for the remainder of the season. Fruit ground color and red pigmentation were not affected by WSR. WSR increased the percentage of fruit that exceeded 62 mm in diameter and decreased the percentage of fruit < 55 mm in diameter in 1988 and 1990. In 2 of the 3 years, WSR increased flower count per cm shoot length in the fruiting zone of the canopy.

Water relations and productivity of alfalfa populations divergently selected for leaflet size

Several investigators have identified genetic variability for water-use efficiency (WUE=forage production/unit transpired water) in alfalfa ( Medicago sativa L.). However, WUE as a component of drought resistance (drought avoidance by conserving water) has received limited emphasis in cultivar development. The objective of these studies was to evaluate the water relations and productivity of two alfalfa populations selected for large- or small-leaflet size. Forage yield, WUE, leaf transpiration, stem pressure potential and leaf temperature were determined under moisture regimes ranging from field capacity to midday plant wilting in a controlled environment. Plant WUE decreased as moisture stress increased for both populations in the controlled environment. The large-leaflet population produced an average of 11% more forage per unit of water used. Greater root mass was also observed for the large-leaflet population. Instantaneous transpiration per unit leaf area average 0.06 and 0.05 g m −2 s −1 ( P<0.05) for the small- and large-leaflet population, respectively when avaraged across the six moisture regimes. A field study was also conducted which included irrigated and nonirrigated treatments. The small-leaflet population also had a significantly higher transpiration rate in the field under irrigated conditions. Photosynthesis was higher for the small- than the large-leaflet population in three of the four field observations. A more negative water potential was observed for the large-leaflet population in the three drier regimes in the controlled environment and for three of the four field observations. The small-leaflet population had 40% greater stand loss compared to the large across the three years of the irrigated field study and this contributed to higher plot yield for the large-leaflet population. Under nonirrigated conditions stand loss did not occur for the small-leaflet plants however, their forage yield was 40% lower than for the large-leaflet plants. The results indicate that under cool climates, more forage production per unit of transpired water would be expected if alfalfa were selected for larger leaves. This response is attributed to the higher growth rate and reduced transpiration rate of large leaves compared to small leaves.

Fruiting and lint yield of cotton cultivars under irrigated and nonirrigated conditions

Cotton ( Gossypium hirsutum L.) production in the United States often is located in semi-arid, nonirrigated regions where poorly distributed or insufficient rainfall limits yields. A 2-year field study was conducted to evaluate six cotton cultivars for flower and boll production, lint yield, and earliness under nonirrigated (dryland) and irrigated treatments, and to determine the effect of water stress on the measured traits. In addition, two commercially available cultivars, which represented the near-extreme range for lint production in the nonirrigated treatment were evaluated for water use efficiency (WUE) in a greenhouse experiment. Cultivars included in the studies were: ‘Tamcot CD3H’ (CD3H), ‘Tamcot SP37H’ (SP37H), TX-CABUCS-2-1-83 (CABUCS), TX-MACAOS-3-84 (MACAOS), ‘Deltapine 41’ (DPL41), and ‘Paymaster 303’ (PAY303). Cultivars differed significantly for flower and boll production, lint yield, and earliness in crop maturity. CD3H and CABUCS produced significantly greater nonirrigated lint yields (290 and 276 kg ha −1, respectively) compared to SP37H, MACAOS, and PAY303 (211, 206, and 196 kg ha −1, respectively). Nonirrigated yield results indicated differences between CABUCS and CD3H compared to PAY303 could be related to the lack of flower production by PAY303 under soil water deficits, as well as possible escape mechanisms associated with earliness in crop maturity. Average lint yield under irrigation was 310% greater than nonirrigated yield. A greenhouse experiment indicated that CD3H, a relatively drought-tolerant cultivar, had a greater WUE in the nonstress treatment than PAY303, a drought susceptible cultivar. Results demonstrated that genetic variability exists among currently available cotton germplasm sources for flower and boll production, lint yield, earliness and water use efficiency. Among cultivars evaluated in this study, flowering potential appeared to have a major role in drought tolerance. Identification of germplasm with increased drought tolerance could provide breeders with valuable genetic traits and mechanisms for increasing lint yield in areas subject to soil water deficits.

WATER USE OF GREEN ASH AND NORWAY MAPLE IN TREE SHELTERS DURING ESTABLISHMENT

We investigated how tree shelters affected seedling water use as a fractional coefficient of potential evapotranspiration (ETo) and ability to delay water stress in a nursery setting. A field study investigated water relations of newly planted whips with-and-without shelters irrigated at 100% of ETo or unirrigated. Trees in shelters were shade acclimated based on higher specific leaf area, but in diurnal studies had consistently higher stomatal conductances (gs) than non-sheltered trees. Non-irrigated trees with shelters had higher gs than treatments without shelters. There were no consistent overall differences in water potential (ψ) between irrigation treatments. Predawn ψ of trees in shelters was more negative, but midday ψ was similar to non-sheltered trees regardless of irrigation treatment. A separate study placed shelters over foliage of container-grown whips of green ash and Norway maple and enclosed the roots in plastic to eliminate evaporation. Daily gravimetric water use and ETo was followed for six weeks in 1992. Trees in shelters used substantially less water than control trees. Gravimetric water use normalized to depth units varied from 5-10% as a fraction of ETo. This was less than half that of control trees without shelters. Tree shelters reduced water loss while maintaining high gas exchange, but whether shelters helped tree seedlings to delay water stress during establishment was inconclusive from these data.

MECHANICAL PEACH HARVESTING LIMITED POTENTIAL

The purpose of this six year study was to re-evaluate the potential of mechanical peach harvesting in a mechanized irrigated peach production system. `Redhaven', `Harvester' and `Autumnglo' peach cultivars were trained to a free-standing “Y” form and received: a) full season irrigation; b) irrigation during the ripening period; or c) no irrigation. Trees were 2.5 m within the row and individual plots contained 10 trees with 4 replications in a split plot design. All three cultivars were mechanically harvested using the USDA inertial shaker. In addition, the cultivar `Autumnglo' was hand harvested as a control. The percentage of mechanically harvested firm ripe fruit ranged from 64 to 95%. Fruit damage ranged from 5 to 36%. In all years, non-irrigated trees tended to have the highest harvest percentage suggesting that irrigation may widen the maturity range of peach. Fruit damage occurred due to roughly cut shoot stubs and when debris in the canopy became lodged in the harvester's conveyor system. Accelerated tree death from mechanical harvesting was noted in `Autumnglo'. We concluded that the limitations to mechanical peach harvesting outlined in the 1970's have not been overcome.

Summer Irrigation of Established Oak Trees

Two trials in California have shown that Valley oaks {Quercus lobata) are benefited by summer irrigation. In the first plot, 30 trees (± 125 years old) were near summer turf irrigation and 135 trees were not. In 1992, six years into a continuing drought, 28% of the non-irrigated trees were dead, while no trees near irrigation died. In a second plot, 11 of 12 irrigated trees had current year shoot growth of 5 to 31 cm, while only 2 of 12 non-irrigated trees showed similar results.

Growth and Adaptation of Soybean Cultivars under Water Stress Conditions. I. Leaf movement and leaf temperature.

乾燥条件下でのダイズの葉の調位運動の実態と葉温との関係を調査するため, 乾燥地域である中国新疆ウイグル自治区石河子のコンクリート枠圃場で実験を行なった. 適宜かん水処理した区 (かん水区) と一定期間かん水を行なわなかった区 (無かん水区) を設け, 調位運動の活発な珍珠塔2号と不活発な黒農33号の2品種を栽培し, 登熟中期に, 葉群構造, 頂小葉の葉温を調査した. 黒農33号の無かん水区は茎長が小さくなり, 葉面積指数もかん水区の約半分になった. 珍珠塔2号の無かん水区は茎長は余り変わらないものの, 各層の葉面積指数が小さくなり, 全体の葉面積指数がかん水区の半分になった. 珍珠塔2号の無かん水区は早朝から葉身が立ち上がり, 日中は太陽光線と平行に近い状態となった. かん水区も調位運動を行なったが無かん水区ほど顕著ではなかった. 最上層の葉温はかん水区で午前中気温より少し高くなったが, 正午前から低く推移した. 無かん水区ではほとんどの時間気温より低く推移した. 黒農33号の無かん水区では葉身に萎れがみられた. かん水区では珍珠塔2号ほど活発ではなかったが, 昼間太陽光線と平行になろうとする調位運動を行なっていた. かん水区の最上層の葉温は正午前から気温より低く推移したが, 無かん水区では朝から気温よりかなり高く推移し日射量の変化に影響されていた. 珍珠塔2号の無かん水区に一時的にかん水を行なったところ, かん水5日後においても水分ストレス条件下と同様な太陽光線を避ける調位運動が認められた.

Water Relations of Fruit End Cracking in French Prune (Prunus domestica L. cv. French)

Irrigation of previously water-stressed French prune trees is known to induce fruit end cracking. The relationships between end cracking, water relations, and mechanical properties of the skin of French prune were studied as a function of irrigation regimes under field conditions. Water stress resulted in the accumulation of solutes in the fruit of nonirrigated trees. A gradient in osmotic potential (ΨS) existed along the vertical axis of fruit from all treatments; ΨS was always lower at the stylar than stem end. Irrigation of previously water-stressed trees (irrigated-dry treatment) resulted in ΨS gradients exceeding those of all other treatments. Moreover, estimated turgor (ΨP) at the stylar end of the fruit increased 2-fold within 24 hours after irrigation. These changes were accompanied by the onset of fruit end cracking, and neither the well-watered controls nor the continuously droughted fruit exhibited such changes. During the 24 hours following irrigation, the overall ΨS of irrigated-dry treatment fruit was diluted by the same amount as the calculated increase in fruit volume. However, during the same period, ΨS at the stem end of the fruit showed more dilution than expected, and ΨS at the stylar end of the fruit concentrated, indicating a redistribution of solutes. There were no differences in skin mechanical properties along the fruit vertical axis and, hence, this could not have accounted for the observed changes in ΨS and ΨP. Thus, when previously stressed French prune trees were irrigated, the overall recovery in water potential (Ψ) and the subsequent movement of solutes to the stylar end of the fruit resulted in apparently excessive turgors in this region and hence the observed pattern of end cracking.

FERTIGATION EFFECTS ON APPLE TREE GROWTH, CROPPING, AND DRY WEIGHT PARTITIONING

In two field studies with `Redchief Delicious'/MM.106, 'Empire'/M.9/MM.106 and 'Mutsu'/M.9/MM. 106 trees on fertile silt loam soils, trickle irrigation increased vegetative growth during the first three years and resulted in a 16%-20% increase in cumulative yield over the first five years. When fertilizer was injected into the irrigation water weekly from mid-April until the end of June, tree growth was further increased and cumulative yield was improved an additional 11%-15% for a total of 27%-35% greater yield than the non-irrigated trees. In these studies, ground fertilization did not improve growth or yield unless trickle irrigation was also applied. However, ground fertilization was not as effective as fertigation. Irrigation and fertigation increased the dry weight of roots by 23% and that of shoots by 36% in the first year resulting in a 10% reduction in the root/shoot ratio. Total tree dry weight was increased by 30% if trees were planted early (April 14) but only 14% if trees were planted late (June 10). Early planting resulted in 17% greater cumulative yield than trees planted late. Initial tree caliper also had a significant effect on early growth and yield with large caliper trees yielding 12% more than the small caliper trees. The interaction of planting date, tree caliper and fertigation resulted in a 50%-70% increase in yield during the first five years.

IRRIGATION, WATER RELATIONS, AND CRABAPPLE GROWTH IN ROOT-CONTROL BAGS IN A FIELD NURSERY

Limited root development of nursery stock in root-control bags facilitates harvest but without irrigation may predispose stock to water stress. The effect of bags and irrigation on growth and water relations of field-grown Malus sieboldii var. zumi were investigated following transplanting as large liners into a silty-clay soil. Predawn leaf water potential (ψ), and midday stomatal conductance (gs) and ψ, were measured periodically through the season. Late-season osmotic potential (ψπ), caliper, leaf area, and root growth were also measured. Non-irrigated treatments exhibited water stress during an extended mid-summer drought, as predawn ψ and particularly gs were less than irrigated treatments, resulting in lower vegetative growth and ψπ. For combined bagged treatments water relations did not differ, but leaf area, root growth, and ψπ, but not caliper, were less than non-bagged trees. Growth measurements and ψπ of non-irrigated bagged trees, however, were consistently lower but nonsignificant than the other treatments. Bag-induced root reduction can limit some top growth even with optimum soil water. Moreover, in terms of potential Type-II errors extrapolated over a conventional production cycle, trees grown in root-control bags in normally non-irrigated soils may be more susceptible to water stress and subjected to further cumulative growth limitation.

Water requirement of Aloe vera in a dry caribbean climate

As hardly any data can be found on the water requirement and yield response to water of Aloe vera, an irrigation experiment on transplanted aloe poles was conducted on the Caribbean island of Aruba. Compared to non-irrigated treatments irrigation shows a positive influence on growth, number of developed leaves, raw gel figure and gel production per plant. The amount of irrigation water to apply can be best calculated based on crop coefficients (Kc) between 0.20 and 0.30. Treatment based on a Kc value higher than 0.30 did not further increase production. A lysimeter study conducted over a relatively short period revealed that the crop coefficient for Aloe vera varied between 0.25 and 0.40 which is characteristic of the so-called agave/pineapple group.

Storage and Remobilization of Water‐Soluble Carbohydrates in Stems of Spring Wheat

Grain yield of wheat (Triticum aestivum L.) depends, in part, on carbohydrate reserves available in the stem. This study was conducted to determine the effects of water deficit during the post‐jointing period on quantitative changes in water soluble carbohydrates (WSC; including simple sugars, starch, and fructans) in the stems of spring wheat. Cultivars Edwall and Waverly were planted in 1983 and 1984 at Spillman Agronomy Farm near Pullman, WA, at rates of 84 and 168 kg ha−1 in rows 30 and 15 cm apart, respectively, in both irrigated and nonirrigated treatments. Beginning at jointing, plants were harvested weekly. Stem material was dried, milled, digested with amyloglucosidase, and analyzed for WSC by iodometric titration. Results were similar for both varieties and both years. Anthesis and peak stem carbohydrate concentration occurred 4 to 7 d earlier in nonirrigated than irrigated plants; and physiological maturity of the grain occurred 6 to 14 days earlier. The concentration of WSC in stems increased to between 250 and 380 mg g−1 dry wt. at ≈10 to 14 d after anthesis and then declined to less than 50 mg g−1 dry wt. by physiological maturity of the grain. From the time of peak WSC content until physiological maturity in 1984, 859 to 1235 mg WSC were lost from the stems of irrigated plants but only 619 to 662 mg WSC were lost from stems of nonirrigated plants. The data indicate that stems are an important temporary storage site for reserve carbohydrates in both irrigated and nonirrigated plants.8

Water Relations and Productivity of Alfalfa Leaf Chlorophyll Variants

Plant improvement to increase the water‐use efficiency of affalfa (Medicago sativa L.) has been limited. This study compared leaf color variants (pale and dark) to evaluate the effect of alfalfa leaf chlorophyll on water relations and yield of alfalfa. Leaf color populations were selected from ‘Ladak 65’ and visually selected sub‐populations evaluated under controlled‐environment and field conditions. Seven moisture regimes were established in controlled environment studies in which a commercial root medium with high water‐holding capacity was used. The field study was at Laramie, WY, on a Wyocolo soil (fine, loamy, mixed Borollic Haplargid) and consisted of irrigated and nonirrigated treatments. Traits measured for the two populations included leaf chlorophyll (Chl), leaf photo‐synthesis (as CO2 exchange rate: CER), transpiration (T), stem pressure potential (ψw), water‐use efficiency (WUE), leaf area, forage yield. Controlled. environment conditions produced pale plants that contained 15% less total Chl than dark‐leaved variants. The Chl concentration of pale variants was equal between the moisture extremes, while the dark variants decreased 20% for the low‐moisture (compared with high moisture) regime in the controlled environment. The WUE in the controlled environment of pale and dark leaf types averaged 1.47 and 1.22 g dry forage kg−1 water, respectively. This difference in WUE was attributed mostly to the greater growth of pale leaf types. The CER and CER/T ratio of the dark leaf types were more sensitive to moisture stress than the pale types. In the 2‐yr field study, the pale leaf types had a 22% lower CER than the dark leaf types across moisture regimes and 19% lower T under the irrigated regime. Even though leaf photosynthesis was lower for the pale leaf types, the forage yield was 25% higher under the irrigated regime.

Soil water content and stomatal conductance in a mature peach orchard as influenced by various irrigation regimes

Available soil water (ASW) in the rooting zone of mature peach (Prunus persica (L.) Batsch 'Harken/Siberian C.') trees was determined with a neutron probe at incremental depths down to 240 cm between 1979 and 1982. The trees were either not irrigated (I0) or irrigated at a frequency necessary to prevent ASW from falling below 25% (I25) or 50% (I50) in the top 30 cm of soil. Water content in the top 120 cm from May to September for I0 plots was about 37 mm less than I25 plots and 73 mm less than I50 plots. Nonirrigated plots (I0) had the lowest ASW (&lt; 30%) in the soil profile to a depth of 240 cm from mid-growing season onwards. By contrast, irrigated plots (I50) had high ASW (100%) at and below the 100-cm depth during the whole growing season. Leaf stomatal conductance was significantly lower for non-irrigated trees indicating that they were the most severely stressed. The severity of plant water stress increased with decreasing frequency of irrigation as indicated by reduced stomatal conductance. Key words: Prunus persica, available soil water, stomatal conductance

Stomatal Responses and Whole-Tree Hydraulic Conductivity of Orchard Macadamia integrifolia Under Irrigated and Non-Irrigated Conditions

Diurnal patterns of stomatal conductance (gs) and leaf water potential (Ψ1) were determined for leaves on irrigated and non-irrigated 5-year-old Macadamia integrifolia trees over a 4-month period from September to December 1989. An empirical model for stomatal conductance was developed for irrigated trees using relationships to photon irradiance (I), leaf temperature (T1) and vapour mole fraction difference (D). This model accounted for 69% of the variance in gs, and was not improved by the inclusion of Ψ1 as an independent variable. Fitted parameters led to the effective prediction of gs for untried combinations of environmental variables. By using a simple expression to link leaf water potential to transpiration rate (E), the model was extended to prediction of Ψ1 from measurements of I, T1 and D. Stornatal conductances were significantly lower on non-irrigated trees after a 2-month dry period. Lower stornatal conductances were not accompanied by more negative Ψ1 indicating that soil rather than leaf water status may control gs in macadamia trees under non-irrigated conditions.

Water use of a winter wheat cultivar ( Triticum aestivum)

A field trial with a winter wheat cultivar ( Triticum aestivum) was conducted at the experimental field of the Introduction and Plant Resources Institute at Sadovo, Bulgaria, during 1982–1983 and 1983–1984. Three treatments, two irrigated and one non-irrigated, were used to determine the water use of winter wheat at the central-eastern region of Bulgaria. Irrigation was given to maintain two soil moisture regimes of 65-70-65% and 75-85-75% of field capacity during the periods emergence to jointing, jointing to flowering and flowering to dough stage, respectively. To maintain both the regimes irrigations were required in both the experimental years, but in different growth stages. Among the treatments the non-irrigated one showed the lowest peak evapotranspiration of 3.7 mm day −1 and the treatment irrigated at 75-85-75% of field capacity showed the highest peak of 5.8 mm day −1. The total water use under non-irrigated condition and irrigated at 75-85-75% of field capacity was 335 mm and 482 mm, respectively. Three irrigations during the post-winter period were required to maintain the latter moisture level, which used the highest amount of water among all the treatments. Both in irrigated and non-irrigated conditions 50% of the post-winter water use was contributed by the 0−20 cm root zone and no significance difference in soil moisture depletion along the deeper zones by the irrigated or non-irrigated treatments was observed.

Shoot Elongation Patterns of Loblolly Pine Families Selected for Contrasting Growth Potential

Abstract Ten half-sib families of loblolly pine chosen to represent a wide range of size in 8-year-old field trials, exhibited different shoot elongation patterns during their second year in retrospective seedling trials. In all but two families, the different patterns of annual shoot elongation were consistent in irrigated and nonirrigated treatments. Two families that ranked high for growth rate in the 8-year-old field trials also had greater annual shoot growth in the seedling trial without irrigation, but performed poorer than expected when well watered. The different patterns in annual height increment arose as a consequence of changes in the relative contributions of numbers of stem units, the average shoot length per stem unit, and the percentage of trees elongating. However, total annual height increment produced during the second year was a better predictor of the size of half-siblings after 8 years in field trials than any of the components of shoot growth. Families with greater size after 8 years in field trials had longer annual leaders in the seedling trial, but for varying reasons. Some were longer primarily because they had more stem units, while others had average numbers of stem units but greater-than-average stem unit lengths. The percentage of trees elongating near the end of the season was of little or no importance in determining the relative ranks of families within each of two geographic populations studied, but contributed to the differences between the two populations. For. Sci. 36(3):641-656.