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J.A. Franco, M.J. GarcÌa, and V. Cros

A study was conducted with Limonium cossonianum O. Kuntze to analyze the influence of irrigation regime in nursery on the dynamics of root development after being transplanted with minimum management conditions. Plants were potgrown in a greenhouse. Each plant was potted into 625-mL plastic pot filled with a 1 silica sand medium: 1 peat mixture (v/v) amended with osmocote plus (3.7 g•kg-1 substrate). Drip irrigation was used with a 2-L•h-1 emitter per plant. Two irrigation treatments were used: T3, plants watered 6 days a week at the water-holding capacity (leaching 20% of the applied water) and T1, plants watered twice a week, receiving an amount of water at 30% of T3 plants troughout the nursery period (45 days). After nursery period, plants were transplanted in the open air at the southeast Mediterranean coast of Spain (37°47′N, 0°′54′W), and just one establishment irrigation was applied (50 mm). There were three replications. Plant root and top growth were measured weekly for 13 months. For the root dynamics study, minirhizotrons were used. Acrylic tubes, 2 m long and 80 mm in outside diameter, were placed at a inclination of 24°, reaching a total depth of 160 cm. The evolution of the root length density (RLD) was measured by seven 23-cm-deep soil layers. Results indicate that those plants that were less watered in nursery showed a greater RLD for the whole soil profile. Plants root growth for the top 46 cm of soil were not significantly affected by irrigation treatments; between 46 and 115 cm deep, T1 plants showed greater RLD than T3 (average values of 0.6 vs. 0.3 cm•cm-3); and under 115-cm deep (where root growth was more limited), there were not significant differences. For the first 6 months, a important plant top growth was observed, there being no significant differences among irrigation treatments. Research suported by CICYT grant AGF-96-1136-C02-02.

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P. Lecomte, M. Laganière, and Y. Desjardins

Increasing costs associated with the disposal of industrial and urban wastes necessitate the development of alternatives which are economical and environmentally safe. With >3000 ha in Quebec, sod production represents an interesting alternative for the use of new amendments, such as composted de-inked paper sludges and municipal waste compost. The objective of this trial was to evaluate the potential benefits of these amendments (nutrient retention in the root zone and chemical and physical soil benefits) and question potential environmental hazards. Chemical dynamics of N, P, K, micronutrients and heavy metals were examined over four soil layers (0 to 15, 15 to 30, 30 to 60, an >60 cm) on sandy and clay soil. Preliminary results for 1993 and 1994 indicate that nutrient concentrations in water extract are high following the establishment of sites. When sod is absent, high concentrations of lead (500 mg·kg–1 in urban compost) show only a slight trend to accumulate. Nevertheless, this new approach toward using industrial and urban composts seems to be adequate and economically attractive.

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Pinghai Ding* and Leslie H. Fuchigami

Differential exothermal characteristics in relations to bud water content and dormant periods were dynamically investigated within the buds of apple, pear, peach, plum, Grape, persimmon, and black walnut from late autumn to early spring. Differential thermal analysis (DTA) indicated that bud cold hardiness and two exotherms, the high temperature exotherm (HTE) and low temperature exotherm (LTE), were different among species and dormant periods. According to whether buds have deep supercooling during the dormant winter period the species tested can be divided into two groups. The first group, without supercooling, includes the buds of apple and pear, in which LTE was undetectable. The second group, with supercooling, includes the buds of peach, plum, grape, persimmon, and black walnut, in which LTE was detectable. The second group can be further divided into peach and plum subgroup, and grape, persimmon, and black walnut subgroup. Both HTE and LTE can be detected in the buds of peach and plum subgroup, in which bud cold hardiness can be further divided into three different stages; whereas in the buds of grape, persimmon and black walnut subgroup only LTE can be detected, in which bud cold hardiness can be further divided into five stages according to the detection dynamics of HTE and LTE. Bud differential exothermal characteristics and deep supercooling dynamics are closely related to bud water content and cold hardiness stages. No detection of LTE in the buds of apple and pear and no detection of HTE in the buds of grape, persimmon and black walnut were both closely associated with bud water content.

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R. Fernández-Escobar, R. Moreno, and M.A. Sánchez-Zamora

Olive shoots were collected at monthly intervals during an off and an on year from nonirrigated, mature `Picual' olive trees fertilized or nonfertilized with nitrogen. Young and mature leaves and stems and flowers and fruit developed during the on year were removed separately from the shoots to determine N concentration and N content per organ. N concentration decreased in young leaves and stems in spring and summer, and increased during the autumn in both off and on years. N concentration in old leaves and stems remained almost constant during the off year, and drops from April to October during the on year. The new tissues accumulated N during the off year and mobilized it during the on year to support growth. Leaves stored larger amounts of N than stems, and fruit developed during the on year became the main sink for N of the bearing shoot. Although the adjacent, mature leaves may have supported part of the N demand from the fruit, nitrogen must also have been mobilized from other storage organs to support fruit growth. No differences between fertilizer treatments were observed in the allocation pattern of N, although N reserves increased in shoots of fertilized trees.

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Patricia I. Garriz, Hugo L. Alvarez, and Graciela M. Colavita

The objective of this work was to predict `Packham's Triumph' (Pyrus communis L.) fruit growth as a function of time using an empirical mathematical model. A mature crop was studied at the Experimental Farm of the Comahue National Univ., Rio Negro, Argentina, during the 1992–93, 1993–94, and 1994–95 growing seasons. Trees were selected at random and fruits were collected at weekly intervals. The range of sampling dates was 27 and 178 days after full bloom (DFB). Fresh fruit mass (FM) was measured using an electronic scale (n = 1169). Fruit number/trunk cross-sectional area was also determined; cultural practices were performed according to the local standard program. Equations were developed with SYSTAT procedure. Results showed that the following logistic model provided the most satifactory fit to the pooled data, as compared to the power and linear models: FM (g)= 316.081/(1+ e^5.030–0.039 DFB) R 2=0.84 P < 0.001. The accuracy of predictions was tested on an independent crop in the 1995–96 growing season. According to the values of the statistical F test, no significant differences (Pr0.05) were detected between the mean squared deviations of the observed and the estimated values, suggesting that, overall, the model works well. It can provide growers with a means of determining adequate fruit mass at harvest, considering that unless a certain minimum size is obtained, the fruit will be given a lower grade and price.

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T.K. Hartz, J.P. Mitchell, and C. Giannini

Nitrogen and carbon mineralization rates of 19 manure and compost samples were determined in 1996, with an additional 12 samples evaluated in 1997. These organic amendments were mixed with a soil: sand blend at 2% by dry weight and the amended blends were incubated at constant moisture for 12 (1996) or 24 weeks (1997) at 25 °C. Net N mineralization was measured at 4- (1996) or 8-week (1997) intervals, C mineralization at 4-week intervals in 1997. Pots of the amended blends were also seeded with fescue (Festuca arundinacea Shreb.) and watered, but not fertilized, for 17 (1996) or 18 weeks (1997); N phytoavailability was estimated from fescue biomass N and mineral N in pot leachate. An average of 16%, 7%, and 1% of organic N was mineralized in 12 weeks of incubation in 1996, and an average of 15%, 6%, and 2% in 24 weeks of incubation in 1997, in manure, manure compost, and plant residue compost, respectively. Overall, N recovery in the fescue assay averaged 11%, 6%, and 2% of total amendment N for manure, manure compost, and plant residue compost, respectively. Mineralization of manure C averaged 35% of initial C content in 24 weeks, while compost C mineralization averaged only 14%. Within 4 (compost) or 16 weeks (manure), the rate of mineralization of amendment C had declined to a level similar to that of the soil organic C.

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David M. Modise, Michael D. Glenn, and Morris Ingle

The split root technique was used to study water afflux in peach [Prunus persica (L.) Batsch] from wet to dry soil through root systems that bridge wet and dry soil. Peach trees conduct hydraulic lift (HL) to ameliorate water deficits in dry soil layers, under conditions of low transpirational demand. The objectives of this study were to examine the magnitude of HL in peach and to determine its effect on nutrient uptake from dry soil. In addition, the split root system was used to measure peach water uptake from soil supporting `Kentucky 31' tall fescue [Festuca arundinaceae (Schreb)] and determine the diurnal partitioning of water use from covered and bare soil treatments. A Scholander pressure bomb was used to record hourly measurements of water potentials (10 am to 4 p m), daily for a total of 14 days in 3 replicates (1 tree/rep.). Leaf stomata1 resistance was measured using a porometer, simultaneously with the water potential measurements. The CR 7 datalogger was used to record water transfer into the dry root section. 15N was applied in the 15-30 cm root zone, and the concentration in the leaves was determined using a mass spectrometer. Results obtained will be discussed in relation to objectives stated above.

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José A. Franco and Daniel I. Leskovar

Containerized `Lavi' muskmelon [Cucumis melo L. (Reticulatus Group)] transplants were grown in a nursery with two irrigation systems: overhead irrigation (OI) and flotation irrigation (FI). Initially, root development was monitored during a 36-day nursery period. Thereafter, seedling root growth was monitored either in transparent containers inside a growth chamber, or through minirhizotrons placed in the field. During the nursery period, OI promoted increased early basal root growth, whereas FI promoted greater basal root elongation between 25 and 36 days after seeding (DAS). At 36 DAS leaf area, shoot fresh weight (FW) and dry weight (DW), and shoot to root ratio were greater for OI than for FI transplants, while root length and FWs and DWs were nearly the same. Total root elongation in the growth chamber was greater for FI than for OI transplants between 4 and 14 days after transplanting. Similarly, the minirhizotron measurements in the field showed a greater root length density in the uppermost layer of the soil profile for FI than for OI transplants. Overall, muskmelon transplants had greater root development initially when subjected to overhead compared to flotation irrigation in the nursery. However, during late development FI transplants appeared to have a greater capacity to regenerate roots, thus providing an adaptive mechanism to enhance postplanting root development and to withstand transplant shock in field conditions. At harvest, root length density and yield were closely similar for the plants in the two transplant irrigation treatments.

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Edward F. Gilman and Michael E. Kane

Shoot and root growth were measured on Chinese juniper (Juniperus chinensis L. `Torulosa', `Sylvestris', `Pfitzeriana', and `Hetzii') 1, 2, and 3 years after planting from 1l-liter black plastic containers. Mean diameter of the root system expanded quadratically, whereas mean branch spread increased linearly. Three years after planting, root spread was 2.75 times branch spread, and roots covered an area 5.5 times that covered by the branches. Percentage of total root length located within the dripline of the plants remained fairly constant for each cultivar during the 3 years following planting. Root length density increased over time but decreased with distance from the trunk. During the first 2 years after planting, shoot mass increased faster than root mass. In the 3rd year, the root system increased in mass at a faster rate than the shoots. Root length was correlated with root weight. Root spread and root area were correlated with trunk cross-sectional area, branch spread, and crown area.

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Chris A. Martin and Dewayne L. Ingram

Thermal properties of pine bark: sand container media as a function of volumetric water content and effectiveness of irrigation as a tool for modulating high temperatures in container media were studied. Volumetric water and sand content interacted to affect container medium thermal diffusivity. Adding sand to a pine bark container medium decreased thermal diffusivity if volumetric water content was less than 10 percent and increased thermal diffusivity if volumetric water content was between 10 and 70 percent. Thermal diffusivity was greatest for a 3 pine bark : 2 sand container medium if volumetric water content was between 30 and 70 percent. Irrigation was used to decrease temperatures in 10-liter container media. Irrigation water at 26°C was more effective if 1) volumes equaled or exceeded 3000 ml, 2) applications were made during mid-day, and 3) sand was present in the container medium compared to pine bark alone. However, due to the volume of water required to lower container media temperatures, nursery operators should first consider reducing incoming irradiance via overhead shade or container spacing.