Panel 1: The chilean case (Contd.)

THE GENUS PROSOPIS AND ITS MANAGEMENT AT THE TAMARUGAL PAMPA (Contd.)

5. MANAGEMENT TECHNIQUES IN TAMARUGO AND ALGARROBO PLANTATIONS

The following features of the plantations at the Pintados and Bellavista Salt Flats prompted a study on management techniques, in order to improve plantation yields:

1. High variation in fruit yield among trees of a same age;
2. High variation in resistance to pests among individual trees, particularly algarrobo;
3. Different development of plantations established at different sites;
4. Limited knowledge on the normal nutritional level and potential productivity of the plantations.

Fertilization, pruning and regeneration trials have been established.

5.1 Fertilization trials

Two closely related factors were considered for these trials:

• Site, which must be representative of a given growth rate and age, or of a relevant nutritional condition within the plantation, and
• Fertilizers to be used and their application.

5.1.1 Trial sites

The sites selected for the trials were based on stand growth characteristics and nutritional conditions, the latter reflected by foliar nutrient concentration, according to preliminary studies by CORFO-INFOR (1981).

Three sites were selected at the tamarugo plantations and one at the algarrobo plantations. In the former, trials were established at sites where fodder yield measurements had been previously carried out (Stand No. 43); in sites representative of mean growth (Stand No. 113; stand number according to classification made during the inventory carried out by CORFO-INFOR in 1981); at sites with low foliar P content (Stand No. 167). At the algarrobo plantations a site reflecting general growth and sanitary conditions was selected (Stand No. 118).

5.1.2 Fertilizers tested

Neither tamarugo nor algarrobo plantations show symptoms atributable to nutrient deficiency, so the criteria to select a fertilizer for testing were of a different nature. It was deemed interesting to include phosphorus (P) at the trial application, on account of its importance in the reproductive process, which can indicate whether a better fruit yield can be obtained by increasing foliar P content (Valdés 1982). Furthermore, there are some data regarding the correlation between growth gain and foliar P concentration in other species, apart from the trend observed in tamarugo (Layton 1948, cit. in Thimann 1958; Smith 1966; CORFO 1982). P availability is important in leguminous species for the rhizobium activity that fixes nitrogen at the roots (Jarrel 1982; Elke 1980). This would explain the correlation of a greater N concentration in the leaves with increased P content, found by comparing samples from different tamarugo stands at the Pampa (CORFO 1982).

The plantations have been established on saline-sodium soils. A sulphur-water amender is recommended to offset the salinity of the root establishment area, as the acidification of the soil would increase P availability for the tree.

The findings of the leaf and soil analysis conducted in September 1981 (CORFO-INFOR 1981) show a curious amount of zinc in both soil and leaves. The very low zinc content of the soil does not account for its presence in the leaves. Trials including application of this element are therefore considered of interest.

Table 17 presents the fertilizers and doses applied in each case. It must be stressed that the environmental conditions found in the area are very particular, i.e., high soil salinity (saline-sodic), with sodium chloride and sodium sulphate (Valdés 1982); great stratigraphic and chemical variation in the soil (CORFO-INFOR 1981). Additionally, there was no previous study on fertilization with these species.

P doses applied in each case are similar to those applied to citrus trees at the Esmeralda Agricultural Station in the area, and may be rated as high. It is worth mentioning that these doses largely cover the ranges proposed by Jarrel (1982) and Felker (1981). Jarrel (1982) based his recommendation on the foliar content observed and its relationship with foliage density (CORFO-INFOR 1981). Urea and zinc doses correspond to those used in fruit trees.

Figure 7. Irrigation during the tamarugo fertilizing trial with superphosphate.

TABLE 17
FERTILIZATION TRIALS

The description of the treatments included in Table 17 is as follows:

1. Zinc sulphate, urea and sodium hydroxide.

   Consists of a 0.3% zinc sulphate solution (38%); 1% urea; and 10 g sodium hydroxide/10 lt solution as neutralizer, to avoid damaging the leaves.

   This solution was applied to the foliage with a fine sprayer, estimating 25 l/tree.

2. Sulphur (S); granulated as enmender.

3. Superphosphate: triple superphosphate, 46% P₂O₅ i.e., 20.1% P (1 kg P per 5 kg triple superphosphate).

   Triple superphosphate and sulphur were applied with 50 liters of water per tree. The salt crust was previously removed, digging two l-m-long 0.5-m-wide trenches, at either side of the stem, deep enough to reach the underlying saline layer (beneath the salt crust). Fertilizer and/or enmender application was performed by mixing with soil extracted from the trenches, and placing this mix back in the pit, after working its bottom thoroughly. Water was applied (50 l, shared equally by both trenches). Once the water had seeped, the trenches were covered with 4–5 cm thick leaf litter to check evaporation. In the case of Stand No. 167, the application was made into the planting hole, which, at that time, was visible. Waterings were repeated twice, with a 30-day interval.

4. Irrigation alone

   Same trenches were dug, but the application consisted only of water (3 waterings).

Figure 8 shows the way superphosphate and/or enmender were applied.

Each treatment and control consisted of an 10-tree experimental unit per trial in tamarugo, and 7 trees in algarrobo, trying to employ specimens as homogeneous as possible.

Figura 8. Fertilizer Application at “La Cantera”

a) Superficial salt crust

b) Underlying saline crust

c) Softened soil with fertilizer and/ or enmender, covered with leaf litter

5.1.3 Results

Only preliminary results have been obtained. Six months after fertilizer application, greater zinc and nitrogen foliar concentration was observed in tamarugo and, in one case, an increase in phosphorus, when such nutrient (triple superphosphate) was applied together with the enmender (ground sulphur). The best results, in terms of increase over the controls, were: zinc 300%; nitrogen 10%; and phosphorus 12%. This has demonstrated nutrient uptake in spite of the harsh environmental conditions found in the area.

5.2 Pruning tests

Two types of pruning, commonly used in agriculture, were tried at representative plantations (Fig.9).

One was designed to primarily increase fruit yield and, secondarily, increase foliage thickness (long pruning). The other system was intended for the formation of a great foliar mass, later to increase fruit production by adding vigour to the tree (short pruning).

Pruning in algarrobo was only of a sanitary nature.

The design was 10 trees per type of pruning and ten controls for tamarugo, at two different sites. In the case of algarrobo, a total of 10 trees were pruned.

The result was profuse sprouting 6 months after pruning.

FIGURE 9. Two types of pruning performed during the trials.

5.3 Propagation

Three types of grafting were tested in two different seasons (fall and spring).

Rooting trials were also made with sprouted shoots, using two growth hormones (indolbutiric acid and naphtalenacetic acid), at two different strengths; additionally, a commercial product was used (Rootone).

Bark grafting showed promising results in tamarugo (80% establishment), but the results were less encouraging with algarrobo (27% establishment).

REFERENCES

BILLINGHURST G. 1893. Memorias. Editorial Ercilla 1893. Santiago (From a transcription by the Agrarian Reform Corporation)

CARVALLO N. 1970. Determinación de Tasa de Riego en la Plantación de Prosopis tamarugo Phil. Tesis Ing. For., Universidad de Chile, Facultad de Agronomía, Santiago, Chile.

CASTILLO O. 1966. Profundidad, Sentido de Escurrimiento y Calidad Química de la Superficie Freática del Agua Subterránea del Salar de Pintados. CORFO, Depto. de Recursos Hidráulicos. Santiago, Chile.

CORPORACION DE FOMENTO DE LA PRODUCCION - INSTITUTO FORESTAL. 1981. “Programa Pampa del Tamarugal”. Estudio de las Especies del Género Prosopis en la Pampa del Tamarugal.

CORPORACION DE FOMENTO DE LA PRODUCCION. 1982. Manejo de plantaciones de Prosopis en la Pampa del Tamarugal. Santiago, Chile.

ELKE J.B.N. 1980. Efectos de factores biológicos y no biológicos sobre la nodulación y fijación de nitrógeno. Apuntes de Curso, Microbiología, Mircen, Centro de Recursos Microbiológicos.

FELKER, P. 1980. Opportunities for improving tamarugo (Prosopis tamarugo Phil.) and algarrobo (Prosopis spp) plantations in Northern Chile. College of Agriculture, Texas University.

FAO/BID. 1970. Informe sobre el proyecto de plantaciones de tamarugo y explotación ganadera en el Norte Grande. Programa Cooperativo FAO/BID, Washington D.C., USA. Informe N^o 1/70.

FROEHLICH, E. 1957. Informe a CORFO, Canchones (citado en INFOR, 1964).

GONZALEZ C., MUÑOZ C. et al. 1978. Evolución de nutrientes en hojas de tamarugo. Agricultura Técnica, Vol. 38 N^o 2.

INFOR. 1964. Posibilidades de Reforestación en la Pampa del Tamarugal. Report to the Corporación de Fomento de la Producción, 13 p. Santiago, Chile.

INFOR 1971. Estudio del Tamarugo como Productor de Alimento del Ganado Lanar en la Pampa del Tamarugal. Informe Técnico N^o 38. Santiago, Chile.

JARREL W. 1982. Soil Factors Affecting Productivity of Prosopis spp (Algarrobo) in the Pampa del Tamarugal. Report to CORFO. University of California. Riverside.

LAMAGDELAINE, L. 1972. Programa Forestal Ganadero Pampa del Tamarugal y Programa Altiplano de Tarapacá. Universidad de Chile. CORFO - Iquique. Centro de Documentación, Depto. de Ciencias Sociales, Publicación N^o2.

LANINO R.I. 1966. Comparación de 3 razas ovinas alimentadas con tamarugo (Prosopis tamarugo Phil.) en la Pampa del Tamarugal. Tesis Fac. de Agronomía, Universidad de Chile. Santiago, Chile.

LEYTON L. 1948. The Relationship Between the Growth and Mineral Nutrition of Conifers (in: The Physiology of Forest trees. Thimann, 1957).

SOCIEDAD AGRICOLA DE CORFO. 1982. Usos Alternativos de Tamarugo y Algarrobo. CORFO, Gerencia de Desarrollo.

SMITH P.F. 1966. Nutrition in Temperate to Tropical Fruit Production. Norman Childers, Ed. Horticultural Publications p. 174–228.

VALDES A. 1982. Proyecto de Investigación: Mejoramiento del Desarrollo y Productividad del Tamarugo (Prosopis tamarugo Phil.). Informe presentado al Instituto Forestal, Santiago, Chile.

ENVIRONMENTAL MOISTURE UTILIZATION BY PROSOPIS TAMARUGO PHIL.

Fusa Sudzuki
Agronomist

GENERAL

This physiologic research study on tamarugo (Prosopis tamarugo Phil.) was begun in 1966 under a request from the Production Development Corporation of Chile (CORFO).

CORFO needed to determine tamarugo water consumption, so as to program the area possible to afforest with this species at the Tamarugal Pampa without jeopardizing the groundwater reserves, already partially used as source of drinking water for the city of Iquique.

It was thought that tamarugo tapped its water from the groundwater table, thanks to its deep root system. It was further believed that, due to the temperatures, the considerable luminosity and the total lack of rainfall prevailing at the area, the amount of water required by the tree to produce —and sustain— its considerable dry matter output (80–100 kg/year of leaves and fruit per tree) would necessarily have to be considerable.

The primary goals of this research were to gather environmental data (climate and soil) and to study the morphology of the plant, particularly as regards the root system, stomatal behaviour and foliar anatomy.

CLIMATE

The Tamarugal Pampa climate is rated as desert climate, characterized by almost total lack of rainfall and by a wide day-to-night temperature range.

The most relevant data recorded by the meteorological stations in the study area —Refresco and Canchones—showed an average of 250 clear days per year and 550 cal/cm² per day. Relative air humidity recorded by the hydrographs showed great daily variations, particularly from September through March, when it reaches 3–10% during the day and 80–100% during the night, remaining constant for about 4–5 hours, to fall sharply around midday.

SOIL

There are two types at different sectors. The first one, corresponding to the higher ground of the eastern sections, is a great piedmont with coarse stratification, unstructured, with high salt content and lacking organic matter. The second sector corresponds to the western portion, formed by stratified soils of finer material, and covered with a salt crust ranging in thickness from a few centimeters to one meter or more.

The groundwater table is located at depths ranging from 1 to 10 m, and even at 60 m or deeper.

Tamarugo grows on soils with a thin or thick salt layer and in places where the groundwater table is located from 2 to 40 m below the surface. Naturally growing tamarugo occurs reportedly more often at areas where the groundwater table is located 20 to 40 m below the surface.

The water content of open soils (no trees), measured up to a depth of 120 cm, fluctuates from 1.5 to 2.5%, as can be seen in Table 1 and Figure 1.

The study of the tamarugo root system revealed a fact which Gindel (1966) had reported for trees growing at the Negev desert: only the soils containing the root mass have high moisture content, as shown in Table 1 and Figure 1.

PLANT

- Root System:

The findings of the study of the root system of 16 uneven-aged trees (ranging from seed lings to 50-year-old trees) growing at various sites (Canchones, Junoy, Gatica, Yamará, Sulfatera, Baquedano), with different types of soil and water table depth (2 to 60 m), may be summarized as shown below:

Figure 1. 2–3-year-old tree at Refresco. Soil moisture content at different depths.

:	% stomatal opening. Junoy forest (~ 35-year-old trees).
:	% stomatal opening. Canchones forest (~ 10-year-old trees).
- - - -:	% relative humidity. Junoy forest.
——:	% relative humidity. Canchones forest.

Figure 2. Stomatal opening during daylight hours and relative humidity at two different forests. The Junoy forest is growing on a salt crust, and the Canchones forest on sandy soil, without salt crust. Readings were taken in November.

A.			B.
C.			D.

Stomatal behaviour of tamarugo leaves over a period of 24 hours. Junoy Forest, calm cloudless day.

A. At 12 h the leaves had 17% of slightly opened stomata and the rest completely closed. Air R.H. 33% and 30° C.

B. At 20 h, 63% of the stomata were relatively open.
R.H. 63%, 24° C.

C. At 24 h, 72% of the stomata were open.
R.H. 72% and 14°C.

D. At 04 h 80% of the stomata were open.
R.H. 84% and 8° C.

TABLE 1
Moisture content of soils containing the root mass of tamarugo trees, and open soil. Sandy soil and groundwater table at 8 m depth. Canchones II.

* Absorbing root mass zone.

1. In the early developmental stages (seedling) tamarugo grows a scantly ramified tap root which quickly reaches a length of 80 to 120 cm, while the shoot is only 6–8 cm tall. The lengthening of the tap root subsequently stops and begins to develop abundant lateral roots, about 3 to 5 cm from the collar.

2. When the shoot has reached 30 to 40 cm and a dense lateral superficial root mass has taken shape, the tap root continues to grow, but this time horizontally and branching out into 3–5 tap roots.

3. Adult trees have a root system made up by a dense superficial root mass with scant lignification, 40 to 80 cm thick, and one or several tap roots, growing horizontally at 100–120 cm depth. These tap roots subsequently continue reaching deeper, without developing secondary ramifications, reaching usually 4 m; if the plant is growing on very sandy soils, as is the case in Canchones, tap roots may reach greater depths without growing secondary roots, up to 7 or 8 m. The absorbing root mass covers an area approximately equal to the crown projection area.

4. The root system of the 14 adult trees (11 to 50 years of age) invariably showed the pattern described in point 3 above, but with a few modifications: in places where the groundwater table was located at a depth of some two meters (Sulfatera), it was very superficial and spreadout, while at the opposite situation, where the groundwater table was about 60 m below the ground surface, the root mass extended to a mere 60 cm, and the tap roots penetrated only up to 3–3.5 m depth.

5. Superficial mass roots keep their bark and do not form a periderm on the stela. Bark cells are dead and contain an apparently disorderly cytoplasm, strongly dyed with methylene blue; the stela is white, which shows it to be still active. Curiously, this structure is similar to that of rhizome from epiphytic plants.

- Leaf Anatomy:

The study of tamarugo foliole anatomy shows the presence of stomata on both faces, a thin cuticle covering the epidermis, the presence of conic cells without chloroplast among the palisade cells and, slightly modified, forming the bundle sheath. The amount of mucilaginous substances it contains is striking, a fact which suggests that the matric potential plays a major role in water economy.

The study of stomatal behaviour through the day showed that tamarugo opens the stomata during the night, and that the percentage of opened stomata is in direct relation to relative humidity, as shown in Figures 2 and 6. This stomatal opening is greater from 0:00 h to 8:00 AM in summer; in winter only a low proportion of the stomata open, either during day or night.

EXPERIMENTAL TRIALS

The research works by Breazeale et al. 1950; Haine 1952; Stone et al. 1950; Gindel 1966; Jensen et al. 1961; Vartanian 1968, and others, evidence the fact that for many years the possibility of inverted potentials has been studied, as a way to enable the plant to absorb atmospheric water either as liquid or gas.

The fact that water intake by the leaves exists under arid and semi-arid conditions is generally accepted, as well as the discharge of small amounts of water into the soil through the roots, which enables the plant to stay alive (Slatyer 1967).

The first trial made in the present research work included a series of treatments, which gave an indication of the possible utilization of environmental moisture.

• Foliar Spraying

a. Foliar spraying vs. ground irrigation:

The trial included three basic treatments:

1. No irrigation

2. Ground irrigation

3. Foliar spraying.

The material used were 17-cm tall seedlings.

The findings of this 30-day trial were as follows:

• The plants in the foliar spraying trial lost 32 g of water

• Unwatered plants lost 65 g of water

• Plants with ground irrigation (165 g of water in total): 175 g of water

• Soil without plant* evaporated 77 g of water.

* The soil was previously air dried, adding 100 g of water at the beginning of the trial.

In this trial, all pots containing plants were left without irrigation for 60 days prior to the experiment; consequently, the plants which were not sprayed or irrigated totaled 90 days without water. No seedlings died, but those without irrigation stopped growing. Those receiving 165 g of water showed symptoms of ethiolation, while those under foliar spray had a normal appearance, although with minimum growth. It is worth mentioning that ethiolation symptoms appear at the nursery when the seedlings are excessively irrigated.

This first trial incurred in two basic errors:

1. The trial was conducted under laboratory conditions, where the day-to-night temperature range was not very significant (March-May) and air dryness was marked.

2. Shoots were sprayed unprotected at 8:00 and 18:00, so that moisture remained only a short time on the leaves.

Pastenes (1972) repeated this trial (avoiding these errors) under natural Pampa conditions and with seedlings of different size. His findings were coincident with those of Sudzuki (1969a) and indicated, furthermore, that: foliar spraying improved leaf and sprout development; that the seedlings under water stress, when sprayed, accelerated their absorption process and subsequent exudation or translocation of water onto the soil, which, at times, “was so considerable that moisture at the latter exceeded field capacity” (Pastenes 1972).

b. Leaf spraying with tritiated water (THO):

With the purpose of gathering more data on the possible foliar absorption of atmospheric water, a trial consisting of the application of tritiated water to seedlings, 2– 3-year-old and 7–8-year-old plants was devised. Tritiated water was given to a group of plants with the shoots duly isolated with polyethylene tents, until 100% R.H. was achieved at midday, and to another group at 24:00 hours, for 5 consecutive days. Soil samples to determine tritium content were taken 24 h after each application. The water was extracted from the soil by means of a pseudo-lyophilization, i.e., evaporating the water from the soil (40° C) and subsequently condensing the vapor in a double-walled tube using dry ice (Sudzuki 1969b).

The findings of this trial were as follows (Sudzuki 1969c):

• No tritium was found in soils of treatments where the tritiated water was applied during the day.

• A significant amount of THO was found in the soil of seedlings after the first nocturnal spraying.

• Relative humidity during the night had to remain high for a period of 2–3 hours.

• Relative humidity must exceed 80%, at 10–15° C.

• The greater the amount of days sprayed, the greater is the amount of tritium found in the soil (Table 2 & Figure 3).

TABLE 2
Amount of THO (cpm) detected in the soil of 2- to 3-year-old and 7 to 8-year-old plants sprayed some at midday and others at midnight, with 3–5 applications. Canchones, February.

0*     Soil of control plants
cpm Counts per minute
+     Significant 0.5
+ +   Very significant 0.1

Figure 3. Spraying tamarugo plant foliage with THO (4μc/ml). Counts per minute (cpm) of the water extract from the soil.

Figure 4. Soil moisture content (dry weight basis) through a day in February, at different depths beneath the tree and 10 m away from it. The rhizosphere is located between 15 and 45 cm depth.

Figure 5. Soil moisture content in August, under the tree and away from it, at different depths in the profile.

WATER POTENTIAL OF THE ATMOSPHERE-PLANT-SOIL COMPLEX

Water absorption by the leaves is a passive process which follows a gradient directed principally by transpiration.

To determine whether the conditions to enable the occurrence of inverted potentials were present, trials including the simultaneous reading of the following items were planned:

1. Atmospheric, plant and soil water potential

2. Stomatal opening

3. Leaf relative turgor

4. Sap flow direction.

All readings were taken every four hours for 6–7 days; one of the series was from the 12th to the 18th of February (summer) and the other from the 4th to the 14th of August in a 6-m-tall 9–10-year-old tree. The findings from this trial are summarized in Tables 3 and 4.

Soil moisture content, measured with the neutron counter from 20 cm to 125 cm, revealed that, far from the tree, it stays around 1 to 1.5%, both in summer and winter. Moisture at the root zone of the tree reached 18.5% in summer and 10–11% in winter (Figures 4 and 5).

TABLE 3
Readings made in February at different times of the day in a 9– 10-year-old tamarugo plant at the Canchones forest: Temperature (Temp.), Relative humidity (R.H.), Atmospheric potential (ψA), Plant potential (ψP), Stomatal opening (S.O.), Relative turgor (R.T.) and Sap flow direction (Sap f. direct.).

Sap F. = Sap flow direction
(+) from root to leaf
(-) from leaf to root
— no movement detected

TABLE 4
Readings taken in August at different times of the day in a 9– 10-year-old tamarugo plant at the Canchones forest: Temperature (Temp.), Relative humidity (R.H.), Atmospheric potential (ψA), Plant potential (ψP), Stomatal opening (S.O.), Relative turgor (R.T.) and Sap flow direction (Sap f. direct.).

TABLE 5
Soil water potential and of its matric and solute components, under the tree and 10 m away from it, at different depths of the profile.

Total soil water potential read in summer showed the values included in Table 5 above.

Sap flow direction was detected with an instrument with a heat source located between two thermocouples, and a microamperimeter with the zero placed at the middle. The heat source and the thermocouples were introduced into the xylem of the subject tree. Thus, if the amperimeter needle moved to the right, sap flow was from the roots to the leaves, i.e., positive (+). If the needle moved to the left (-), sap flow was from the leaves to the roots, directions which had been previously calibrated at the laboratory.

The findings of these readings are presented in Tables 3 and 4, from which the following conclusions may be drawn:

1. The maximum relative humidity occurs at 24:00; 4:00 and 8:00 h.

2. Maximum stomatal opening takes place at the same times. Figure 6.

3. Coincidentally, reverse sap flow (-), i.e., from the leaves to the roots, was detected on the 12th, 14th, 17th and 18th days at 4:00 and 8:00, when relative humidity was 80% or higher, and there was a minimum of 80% of the stomata open (Table 3).

% of stomata open
Relative humidity %
Temperature ° C

Figure 6. Relationship between amount of open stomata and relative humidity during the February trial.

TABLE 6
Sap flow direction and speed at different times of the day, measured with thermocouples

4. Sap flow speed was not recorded, but the movement of the microamperimeter needle coincided with the relative humidity and the proportion of stomata open (Table 3). The positive movement was always slow and not marked, being in certain cases nearly undetectable (Table 6).

5. According to the relative water turgor, the plants were never under water stress (Tables 4 and 5).

6. Soil potential readings (Table 5) at 10–45 cm depth gave values near -52.7 bars while, at the same depth in soils away from vegetation, the potential read 14.9 bars. These potentials, compared with the average value of 32 bars found in the plant, would account for the possibility of water flow from the plant to the soil.

7. Data collected in August (Table 4) support the assumption that the tree, under the environmental conditions recorded, is practically in a state of dormancy, despite the large proportion of foliage it keeps. In cold winters, when the minimum temperatures frequently fall below -5° C, tamarugo sheds all its leaves.

REFERENCES

1. BREAZEALE E.L., McGEORGE W.T. & BREAZEALE. 1950. Moisture absorption by plants from an atmosphere of high humidity. Plant Physiol. 25: 413–419.

2. BOTTI C. 1970. Relaciones hídricas del tamarugo (Prosopis tamarugo Phil.) en la localidad de Canchones. Thesis for Agronomist Deg. Fac. Agr. U. de Chile.

3. GINDEL I. 1966. Attraction of atmospheric water by woody xerophytes. Empire For. Rev. 48: 217–42.

4. HAINE F.M. 1952. Absorption of water by leaves in an atmosphere of high humidity. Jour. Exp. Bot. 3:95–8

5. PASTENES G.J. 1972. Efecto de aplicación foliar de humedad en plántulas de Prosopis tamarugo Phil. Univ. Chile. Fac. Filosofía y Educación. Depto. Biología-Antofagasta. Thesis for Professor's Deg.

6. SLATYER R. O. 1967. Plant Water Relationships. Acad. Press London.

7. STONE E. C., WENT F. W., YOUNG C.L. 1950. Water absorption from atmosphere by plants growing in dry soil. Science III: 546–8.

8. SUDZUKI F. 1969. Absorción foliar de humedad atmosférica en Tamarugo (Prosopis tamarugo Phil.) Bol. Téc. N^o 30. U. de Chile. a.I. Observaciones sobre riego foliar en plántulas de tamarugo. b.II. Aplicación foliar de THO en plántulas de tamarugo. c.III. Absorción foliar de agua atmosférica en tamarugo. Bol. Tec. N^o 30. U. de Chile. Fac. Agronomía. Est. Exp. Agr. 3:23.

9. SUDZUKI F., BOTTI C., ACEVEDO E. 1973. Relaciones hídricas del tamarugo (Prosopis tamarugo Phil.) en la localidad de Canchones. Bol. Téc. N^o 37 U. de Chile. Fac. Agr. Est. Exp. Agr. 1:23.

10. VARTANIAN N. 1968. Mise en evidence d'un gradient inversé de potentiel hydrique dans la plante en atmosphére saturée du humidité. Comptes Rendus, 267, Serie D. p. 1090–1101.