Jorge López Hermosilla
Director, Forest Seed Center, Chilean Forest Service
Bernardo Avilés Rosales
Professor, Department of Forest Sciences
Universidad de Concepción, Chillán, Chile
Introduction
Nambiar (1946), Martin and Alexander (1974), Chatterji and Molinot (1969) have reported that water-impervious teguments are the major cause behind seed dormancy in the genus Prosopis. Ffolliott and Thames (1983), working with Prosopis seeds collected throughout Latin America, suggested two methods to insure seed germination: soaking in water and gas exchange. However, they add that several types of inhibition caused by seed tegument, e.g. water and oxygen impermeability or mechanical barriers against radicle protrusion, produce seed dormancy. Various trials to make untreated seeds germinate have reportedly produced germination rates no higher than 5%.
To break physical dormancy, the seeds must be scarified, either by filing the tegument away or using different kinds of treatments to enable water permeability, improve germination or shorten the period required to obtain optimum germination. Ffolliott and Thames (1983) state that one possible exception to the degree of physical dormancy occurring in the genus Prosopis is the just-harvested fresh seed. This seed has been observed to germinate quickly without any pretreatment.
The same authors point out that Prosopis seed pretreatments are generally classified into “wet” and “dry”. Of these, the most common are soaking in hot water and soaking in sulphuric acid.
Goord (1956) recommends hot water treatment for Prosopis spp., without specifying how long this treatment should be.
Martin and Alexander (1974) suggest the following treatments for Prosopis juliflora: a) cut seed end with a knife; b) immerse for 72 hours in absolute ethyl alcohol; and c) immerse in concentrated sulphuric acid for 20 to 30 minutes. Donoso and Cabello (1978) recommend twenty minutes in sulphuric acid for Prosopis chilensis, and forty minutes for Prosopis tamarugo; with these treatments, they reported 99.5% germination rate. They observed that with 4 minutes in acid, a germination rate of 81% was achieved. Sudzuki (1980) reports that Prosopis tamarugo seeds germinate well with 48-hour soaking in water, but that some researchers scarify the seeds with sulphuric acid. Ffolliott and Thames (1983) mention mechanical scarification; soaking in boiling water for 24 hours, warning that this treatment is not suitable for all tree species of the genus Prosopis; 60° C–80° C dry-heat for 24 hours; 8 to 12 hour immersion in absolute ethyl alcohol; concentrated (98%) sulphuric acid for 15 to 30 minutes; and electrical treatment, whereby the seeds are subjected to dielectric heating by radiofrequency over various lengths of time.
This research was carried out within the framework of the fao/cirf Project on Arid and Semi-Arid Forest Genetic Resources for rural life improvement. The Chilean Forest Service takes active part in this project since 1981, mainly providing seeds of species of native Acacia, Atriplex and Prosopis. These three genera were selected on account of the different uses they offer and which make them highly attractive for the objectives of the fao/cirf Project.
Some research work has been carried out on Prosopis tamarugo and Prosopis chilensis, but none on Prosopis alba and Prosopis flexuosa, species as valuable as the first two.
Prosopis tamarugo seeds for these experiments were harvested in September 1984 at the Pampa del Tamarugal, 1,200 m above sea level, average annual rainfall below 10 mm. Prosopis alba seeds were collected in July 1985 at San Pedro de Atacama, 2,800 m above sea level, 50 mm annual rainfall. Prosopis flexuosa seeds were collected in July 1985 at Hacienda Margarita, 1,500 m above sea level. Prosopis chilensis seeds were collected in July 1985 at Diaguitas, 1,300 m above sea level.
The trials were conducted at the Seed Analysis Laboratory of the Forest Seed Center, Chilean Forest Service. Healthy seed subsamples were collected for each of the four treatments, and all germination trials were carried out in a Karl Kolb “Jacobsen”-type germinator with automatic temperature control. Temperature was 22° C during 16 daytime hours, and 30° C during eight nighttime hours. Artificial light was used. The substratum was double filter paper, disinfected with thiuram and sodium hypochlorite, and each treatment was placed under well adjusted bell-shaped covers.
The first three trials were aimed at ascertaining the effects of boiling water, sulphuric acid and dry heat treatments, with different durations. The fourth trial was aimed at comparing the effects of the optimum chemical and physical treatments. For the statistical analysis, the percentages of germinated seeds were used.
Experiment I
Materials and Method
The experimental layout used was factorial blocks, distributed among divided plots. The four species of Prosopis were placed at the level of major plots. Subplots were four and included the following treatments: control (no imbibition in hot water), and imbibition in hot water (initial temperature 100° C) for 6, 12 and 24 hours.
The seeds were counted and placed in flasks; then, boiling water was added, and the seeds were left in imbibition over the periods of time indicated above. Four replications were made, with 50 seeds in each unit. After pretreatment, they were placed under duly identified bell-shaped covers. The response was measured by counting germination daily at the moment the radicle reached 0.5 cm, expressing the results in percentage.
TABLE 1
Response of Prosopis Seeds to Imbibition in Hot Water over Different Lengths of Time
(mean values in %)
| Treatments | P. alba | P. flexuosa | P. chilensis | P. tamarugo | Mean value of treatments |
|---|---|---|---|---|---|
| 0 | 18.5 | 46.0 | 35.0 | 75.0 | 43.6 |
| 6 | 96.4 | 91.5 | 90.0 | 73.0 | 87.7 |
| 12 | 99.5 | 93.5 | 88.0 | 79.0 | 90.0 |
| 24 | 98.0 | 96.5 | 87.0 | 86.0 | 91.9 |
| Mean value for species | 78.1 | 81.9 | 75.0 | 78.3 |
| MSD | = | 3.8 | P ≤ 0.05 Mean value for species. |
| MSD | = | 5.3 | P ≤ 0.01 Mean value for treatments. |
| MSD | = | 10.5 | P ≤ 0.01 Mean value species × treatments. |
Results and Discussion
Significant differences were observed (P≤0.05) among the species (Table 1). The highest germination rate was obtained for P. flexuosa, with 81.9%, and the lowest for P. chilensis, with 75%. P. alba and P. tamarugo showed similar levels, without statistically significant differences. The low variability of the mean values for the species does not entail conclusive segregation concerning relative dormancy. However, compared with the controls, the differences are considerable.
Highly significant differences (P≤0.01) were observed among treatments. The highest germination rate was obtained with 24-hour imbibition (91.9%); the lowest corresponds to the control, with 43.6%. In general terms, imbibition treatments showed similar germination rates.
The species × treatment interaction level shows highly significant differences (P≤0.01) with different treatments for the same level of species; unlike the control, the species × treatment combination induces a clear improvement in germination rates with regard to species and treatment.
Experiment II
Materials and Methods
The seeds of all four Prosopis species were treated with concentrated sulphuric acid (98%). A factorial layout with divided plots, distributed in blocks, was used. The species were placed in the major plots; treatments were placed in four subplots, with four replications, including control (no imbibition), and 6, 12, and 24 minutes under acid treatment.
The seeds were counted and placed in flasks with concentrated sulphuric acid for the periods of time indicated above.
Fifty seeds were used for each unit, placed under duly identified bell-shaped covers. The response was measured by counting germination daily, expressing the results in percentage.
TABLE 2
Germination Response of Prosopis Seeds to Treatment with Concentrated Sulphuric Acid
over Different Lengths of Time
(mean values in %)
| Treatments (minutes) | P. alba | P. flexuosa | P. chilensis | P. tamarugo | Mean for treatments |
|---|---|---|---|---|---|
| 0 | 12.5 | 45.5 | 44.0 | 75.0 | 44.3 |
| 6 | 99.5 | 99.5 | 96.0 | 93.5 | 97.1 |
| 12 | 99.5 | 99.5 | 94.5 | 93.5 | 96.8 |
| 24 | 99.5 | 100.0 | 94.5 | 95.5 | 97.4 |
| Mean value for species | 77.8 | 86.1 | 82.3 | 89.4 |
| MSD | = | 3.2 | P ≤ 0.01 | Mean value for species. |
| MSD | = | 32.0 | P ≤ 0.01 | Mean value for treatments. |
| NS | 0.01 Mean species × treatments. |
Results and Discussion
Highly significant differences (P≤0.01) were observed at species level (Table 2) among P. alba, P. flexuosa, P. chilensis, and P. tamarugo. This last species showed the highest germination rate (89.4%), while P. alba showed the lowest (77.8%).
No significant differences were observed between treatments, but each treatment differed from the control. The highest germination response was obtained with 24-minute soaking in sulphuric acid, while the lowest corresponded to the control. Germination difference between treatments and control ranged from 53.1% to 52.5%.
No statistically significant difference was observed for the species × treatment interaction in the F test.
Experiment III
Materials and Method
The seeds of the four Prosopis species were treated with dry heat at average temperature of 60 ± 2° C. A factorial layout with divided plot and block distribution was used, with the species in the major plots. The four treatments were placed in the subplots, with four replications; they included control (no exposure to dry heat), and 6, 12, and 24 hour exposure.
The seeds were counted and placed in metal containers in a Pasteur-type oven, for the periods of time indicated above. Treatments and controls were placed under duly identified bell-shaped covers. The response was measured by counting germination daily when the radicle attained 0.5 cm. The results were expressed in percentage.
TABLE 3
Prosopis Seed Response to Exposure to Dry Heat (60° C) over Three Different Lengths of Time
(mean values in %)
| Treatments (hours) | P. alba | P. flexuosa | P. chilensis | P. tamarugo | Mean value for treatments |
|---|---|---|---|---|---|
| 0 | 15.5 | 43.5 | 34.5 | 81.5 | 43.8 |
| 6 | 17.0 | 26.5 | 13.5 | 74.0 | 32.8 |
| 12 | 19.5 | 43.0 | 19.0 | 68.5 | 37.5 |
| 24 | 16.5 | 27.5 | 17.0 | 73.0 | 33.5 |
| Mean value for species | 17.1 | 35.1 | 21.0 | 74.3 |
| MSD | = | 27.7 | P ≤ 0.01 | Mean value for species. |
| N.S. | Mean value for treatments. | |||
| N.S. | Mean value species × treatments. |
Results and Discussion
Highly significant differences were observed (P≤0.01) between Prosopis chilensis and P. tamarugo (Table 3). The highest germination rate was obtained for P. tamarugo, with 74.3%, and the lowest for P. alba, with 17.1%. The response difference was 57.2%.
No statistically significant difference was observed with the F test for treatment mean value and for species × treatment mean value.
The column corresponding to P. tamarugo shows that 60° C dry heat, with different exposure times, produces a negative effect on germination with respect to the control. This effect is easy to verify, and the treatment mean value shows a general trend towards this effect.
Experiment IV
Materials and Method
The experimental layout used was similar to that of the previous trials, and was aimed at comparing the effects of the chemical and physical treatments. The species were placed in the major plots. Subplots were four, with four replications, and included the following treatments: control (no treatment); seeds treated with concentrated sulphuric acid for 24 minutes; seed soaked for 24 hours in 100° C water, and seeds exposed for 12 hours to 60° C dry heat.
The method used was identical to that of experiments i, ii, and iii, with 50 seeds per replication and all in the same germinator. Response was measured by counting germination daily at the moment the radicle reached 0.5 cm, expressing the results in percentage.
TABLE 4
Germination Rates of Four Species of Prosopis under Different Treatments
over Various Lengths of Time
(mean values in %)
| TREATMENTS | |||||
|---|---|---|---|---|---|
| Sulphuric acid | Hot water | Dry heat | Control | Mean for Species | |
| P. alba | 99.8 | 99.5 | 18.5 | 17.1 | 58.7 |
| P. chilensis | 95.5 | 87.1 | 16.5 | 35.1 | 58.6 |
| P. flexuosa | 100.0 | 98.7 | 42.8 | 45.0 | 71.6 |
| P. tamarugo | 96.0 | 88.1 | 70.1 | 75.9 | 82.5 |
| Mean value for treatments | 97.8 | 93.4 | 36.9 | 43.3 | |
| MSD | = | 13.9 | P ≤ 0.01 Mean value for species. |
| MSD | = | 7.9 | P ≤ 0.01 Mean value for treatments. |
| MSD | = | 26.3 | P ≤ 0.01 Mean for species × treatments. |
Results and Discussion
Highly significant differences (P≤0.01) were observed between the species (Table 4). The highest average response was obtained for P. tamarugo, with 82.5%, and the lowest for P. chilensis, with 58.6%, practically identical to the 58.7% of P. alba.
Significant differences (P≤0.01) were observed between treatments and their control. Sulphuric acid and hot water treatments produced similar responses. The highest response was obtained with sulphuric acid, with 97.8%, and the lowest with dry heat (36.9%), seven percent below the control.
The species × treatments interaction level showed significant differences (P≤0.01) for species under dry heat treatment and control.
The findings show the sulphuric acid treatment to have been more effective in P. alba, with 100%. With the dry heat treatment, the least effective, the best response was obtained in P. tamarugo.
Ascertainment of dormancy
The control germination data was grouped in accordance with the data produced by experiments i, ii, iii, and iv, respectively, thus arbitrarily classifying the species into three dormancy categories: low, medium and high dormancy.
TABLE 5
Controls (No Treatment) Germination Rates for the Four Prosopis Species
(mean values in %)
| P. alba | P. flexuosa | P. chilensis | P. tamarugo | |
|---|---|---|---|---|
| Germination % | 12.5 | 45.5 | 44.0 | 75.0 |
| 15.5 | 43.5 | 34.5 | 81.5 | |
| 22.0 | 45.5 | 28.5 | 69.5 | |
| 18.5 | 46.0 | 35.0 | 75.0 | |
| Mean for species | 17.1 ± 2.0 | 45.1 ± 0.6 | 35.1 ± 3.2 | 75.3 ± 2.5 |
The difference in treated seed response of each Prosopis species with respect to germination of their untreated seeds suggests that the above classification is fairly accurate.
The highest dormancy is shown by P. alba, with 17.1% germination without treatment. P. flexuosa and P. chilensis can be considered as having medium dormancy, with 45.1% and 35.1% germination, respectively, while P. tamarugo is the species with the lowest dormancy, exhibiting 75% germination of its untreated seeds.
General Discussion
The findings of experiments i, ii, and iii, confirmed by experiment iv, show that, on average, over 13.5% of healthy Prosopis seeds are in a condition to germinate without any difficulty in a period of time shorter than that described by ista (1976).
Basing on the data from the above experiments, it was possible to derive a relative dormancy table for untreated seeds made to germinate under the trial conditions. The following ranges are suggested: 0–33.3%, high dormancy; 33.4–66.3%, medium dormancy; and 66.4–100%, low dormancy. Thus, it is possible to observe that the highest relative dormancy was exhibited by P. alba (17.1%). P. flexuosa and P. chilensis have medium dormancy, with 45.1% and 35.5%, respectively. P. tamarugo, in turn, shows the lowest dormancy, with 75.3%.
Experiment IV confirms the findings of experiment II, and indicates that the best germination response is obtained with the concentrated sulphuric acid treatment, which had no negative effects in terms of germination response derived from treatment duration. The high response percentages, germination ranging from 93.5% to 100%, regardless of treatment duration, suggest that the higher efficiency is due to the strength of the acid used (98%). P. flexuosa exhibited the highest response to this treatment, with 100% germination.
Experiment I, with water at 100° C, whose data was confirmed by experiment IV, is recommended as a promising treatment, as it produced high responses, germination ranging from 73.0% to 99.5%. The highest response was shown by P. alba (99.5%) and P. flexuosa (98.7%). Next came P. chilensis (87.1%) and P. tamarugo (88.1%). In general terms, germination response depended more on temperature rather than on imbibition duration. Nevertheless, as imbibition time increases, P. tamarugo showed up to 13% better response, for periods of time between 6 and 24 hours.
López and Avilés (1985) found, for the same species and treatments but using sterilized sand as substratum, that at species level a drop in response occurs, varying from 1% to 18% in P. alba and P. tamarugo, respectively. They also found that P. tamarugo is strongly affected by treatment duration, with a 13% drop in germination response.
Experiment iii, 60° C dry heat, showed a marked drop in germination response, ranging from 17.1% to 74.3%. P. alba, P. flexuosa, and P. chilensis do not respond to the treatment, and show a germination response which in all three species falls below that of their corresponding controls. The response drop varies from 2% to 12.5% (Table 3). The treatment is not advisable in the case of P. tamarugo, with 74.3% germination. Comparing this treatment with the other treatments (Table 4), the germination drop is seen to range between 13% and 21%, with hot water and sulphuric acid, respectively, and compared to its control the drop is 5.8%. As regards treatment duration, it may be observed that as treatment duration increases, a different drop in germination occurs for each species, with erratic behavior and no time correlation pattern.
López and Avilés (1985) tested higher temperatures (80° C) for the dry heat treatment, with the same species and treatment durations. They concluded that germination drop at species level reached 18%, and at duration level 30% maximum, between 6 and 24 hours.
From the above it may be concluded that for these species and treatment, the upper temperature level has been delimited, with a certain likelihood that with temperatures below 60° C and less than 6 hour duration the results will be more promising. In this regard, Nambiar (1946) showed that exposure of P. juliflora seeds to a constant 35° C temperature during 24 hours increased germination rates.
In all treatments, the significance for species × treatment shows, in general, that not all species are equally affected by the same durations. Each of the experiments suggests an optimum combination of treatment duration and species; in most cases, this does not differ extremely from the general trend.
A marked tendency was observed towards more efficient response to the treatments when the dormancy exhibited by the species is smaller.
For large amounts of seeds, the treatment recommended as optimum is concentrated sulphuric acid during 24 minutes, and hot water (100° C) imbibition for 24 hours, as alternative treatments.
References
chatterji, v.a. and mohonot, k., 1969: “Ecophysiological investigations on the imbibition and germination of seeds of Prosopis juliflora Linn.,” Recent Advancements in Tropical Ecology, Symposium, pp. 261–68.
donoso, c. and cabello, a., 1978: “Antecedentes fenológicos y de germinación de especies leñosas chilenas,” Ciencias Forestales, Vol. 1, No. 2, Facultad de Ciencias Forestales de la Universidad de Chile, pp. 31–41.
ffolliott, p. and thames, j., 1983: “Recolección, manipuleo, almacenaje y pretratamiento de las semillas de Prosopis de América Latina,” fao/cirf, Proyecto sobre Recursos Genéticos Forestales de Zonas Aridas y Semi-Aridas, fao, Rome, pp. 29–31.
goord, y., 1956: “Métodos de plantación en zonas áridas,” Colección fao, Cuaderno de Fomento Forestal No. 6, United Nations Food and Agriculture Organization, Rome, Italy.
international seed testing association, 1976: “International rules for seed testing,” Annexes 1976, Seed Science and Technology, 4: 51–177.
martin, c. and alexander, r., 1974: “Agricultural Handbook,” 450, u.s. Forest Service, Washington d.c., 656–657.
nambiar, k., 1946: “A novel method of improving the germination of Prosopis juliflora seeds,” Indian Forester, 72: 193–95.
lopez, j. and aviles, b., 1985: “Ensayos de germinación de cuatro especies de Prosopis,” internal document, Chilean Forest Service, Chillán, Chile.
national academy of sciences, 1979: “Tropical legumes: resources of the future,” Washington, d.c., pp. 153–161.
sudzuki, f., 1980: “Firewood crops. Shrub and tree species for energy production,” National Academy of Sciences, Washington, d.c., pp. 148–156.
A. Montesions
H. Lam
W. Calderón
O. Villarreal
Agronomists specialized in arid zone improvement
and development
Piura, Peru
Introduction
In spite of being a forest resource of great economic importance for the Peruvian arid zones, Prosopis pallida is one of the least studied species. At the Piura district, located in northern Peru, there are approximately 150,000 ha of natural P. pallida forests, with an average yield of 2 ton/ha (Ocampo, 1971). Three important varieties are predominant: decumbeis, pallida and affinis (Ferreyra, 1984). Although the extension covered by the existing Prosopis pallida forests is vast, it could be further extended applying basic research aimed at enabling the establishment of this species in the 1,300,000 hectarxes of desert at the Piura zone, thus allowing its incorporation into the regional economy.
Considering the constraints imposed by the limited water resources available within the zone, the present research project was proposed with the following objectives:
Determination of plant growth rate during the first six months of its vegetative cycle.
Influence of the volumes applied on the plant's morphologic characteristics.
Determination of leaf, root, stem ratio during the first six months of the vegetative cycle.
Material and Methods
Work took place at the afforestation pilot area of the Universidad de Piura, from July to December 1984.
The plot covered 19,500 m2, and the experimental system used was a randomized block layout with four replications. The irrigation system used was the trickle method with an equipment consisting of 2" head; main and secondary pipes and dropper holders; the dropper flow was two liters per hour. The seed used was from Prosopis pallida in its commercial form. Treatments and trial volumes are shown in Table 1.
TABLE 1
Treatments and Trial Volumes
| Treatment | Level | Cue |
|---|---|---|
| T1 | 192 m3/ha | V1 |
| T2 | 336 m3/ha | V2 |
| T3 | 480 m3/ha | V3 |
TABLE 2
Watering Distribution and Duration per Treatment
| Cue | Month | Volume applied | Total | Volume applied | liters per plant | Watering duration | ||
|---|---|---|---|---|---|---|---|---|
| No. of waterings | m3/ha watering | m3/ plot watering | Total | |||||
| V1 | 1 | 10 | 1.2 | 12 | 0.195 | 1.95 | 3 | 45' |
| 2 | 10 | 2.0 | 20 | 0.325 | 3.25 | 5 | 1h 15' | |
| 3 | 10 | 2.8 | 28 | 0.455 | 4.55 | 7 | 1h 45' | |
| 4 | 10 | 3.6 | 36 | 0.585 | 5.85 | 9 | 2h 15' | |
| 5 | 10 | 4.4 | 44 | 0.715 | 7.15 | 11 | 2h 45' | |
| 6 | 10 | 5.2 | 52 | 0.845 | 8.45 | 13 | 3h 15' | |
| V2 | 1 | 10 | 3.6 | 36 | 0.585 | 5.85 | 9 | 2h 15' |
| 2 | 10 | 4.4 | 44 | 0.715 | 7.15 | 11 | 2h 45' | |
| 3 | 10 | 5.2 | 52 | 0.845 | 8.45 | 13 | 3h 15' | |
| 4 | 10 | 6.0 | 60 | 0.975 | 9.65 | 15 | 3h 15' | |
| 5 | 10 | 6.8 | 68 | 1.105 | 11.05 | 17 | 4h 15' | |
| 6 | 10 | 7.6 | 76 | 1.235 | 12.35 | 19 | 4h 15' | |
| V3 | 1 | 10 | 6.0 | 60 | 0.975 | 9.75 | 15 | 3h 45' |
| 2 | 10 | 6.8 | 68 | 1.105 | 11.05 | 17 | 4h 15' | |
| 3 | 10 | 7.6 | 76 | 1.235 | 12.35 | 19 | 4h 45' | |
| 4 | 10 | 8.4 | 84 | 1.365 | 13.65 | 21 | 5h 15' | |
| 5 | 10 | 9.2 | 92 | 1.495 | 14.95 | 23 | 5h 45' | |
| 6 | 10 | 10 | 100 | 1.625 | 16.25 | 25 | 6h 15' | |
The parameters measured were: weight, vertical and horizontal root size; stem weight; plant height; length between knots; growth rate; weight, length and number of leaves.
Soil physical chemical analyses and water quality analyses were performed prior to the trials.
Results
Trickle Watering Influence on the Root
Root Weight
The influence of trickle irrigation on Prosopis pallida root weight was observed to increase linearly in each of the first six months. The greater the water volume, the greater the root weight. Table 3 and Chart 1A show water volume effect on root weight.
Chart 1B shows the effect of each volume. This has significance until the third month of the vegetative cycle, after which behavior varies.
TABLE 3
Effect of Trickle Watering on Prosopis pallida Root Weight,
During the First Six Months of the Vegetative Cycle
Duncan 0.05 (1): Root weight (g)
| Volume (m3/ha) | Month 1 | Month 2 | Month 3 | Month 4 | Month 5 | Month 6 |
|---|---|---|---|---|---|---|
| 192 | 0.380 c | 0.722 c | 7.300 c | 2.600 b | 4.725 b | 6.765 b |
| 336 | 0.534 b | 0.997 b | 1.507 b | 3.200 b | 6.195 a | 8.190 a |
| 480 | 0.747 a | 1.130 a | 1.732 a | 3.640 a | 6.810 a | 9.015 a |
| Linear effect | Yes | Yes | Yes | Yes | Yes | Yes |
| Quadratic effect | No | Yes | No | No | No | No |
| cv | 6% | 3% | 4% | 12% | 6% | 6% |
| (1) Monthly evaluation; averages with the same letter are equal to each other, otherwise the difference is significant. | ||||||
Chart 1A
Chart 1 B
Charts 1A and 1B: Effect of trickle irrigation on Prosopis pallida root weight during the first six months of the vegetative cycle.
Vertical root size
The effect of trickle irrigation volume on root vertical size in each of the first seven months of the vegetative cycle is also linear (Chart 2A). From the first to the fourth months of the vegetative cycle, the 480 and 336 m3/ha watering volumes are significant as compared against the 192 m3/ha volume; during the fifth and sixth months the treatments differ from each other (Chart 2B).
Horizontal root size
Table 5 shows the effects of watering volume on horizontal root size, with both linear and quadratic characteristic responses, thus describing a curve for each of the first six months of the vegetative cycle (Chart 3A).
The greatest root horizontal size response was at 480 m3/ha watering volume (Chart 3B).
TABLE 4
Effect of Trickle Watering Volume on Prosopis pallida Root Vertical Size
During the First Six Months of the Vegetative Cycle
Duncan 0.05 (1): Root vertical size (cm)
| Volume (m3/Ha) | Month 1 | Month 2 | Month 3 | Month 4 | Month 5 | Month 6 |
|---|---|---|---|---|---|---|
| 192 | 12.412 b | 19.390 b | 27.78 b | 41.745 b | 53.817 c | 63.577 c |
| 336 | 16.095 a | 21.482 a | 32.74 a | 49.012 a | 60.122 b | 76.45 b |
| 480 | 16.905 a | 23.062 a | 33.60 a | 50.047 a | 69.582 a | 84.00 a |
| Linear effect | Yes | Yes | Yes | Yes | Yes | Yes |
| Quadratic effect | Yes | No | No | No | No | No |
| cv | 4% | 4% | 6% | 8% | 5% | 5% |
Chart 2A
Relation among root characteristics
The most important practical relationship was that found for horizontal and vertical root size, which at different root weights shows 81% correlation at the least water volume.
The simple and partial correlation values for weight, vertical and horizontal size at every watering volume applied are shown in Table 6.
Chart 2B
Charts 2A and 2B: Effect of trickle irrigation on Prosopis pallida vertical root size during the first six months of the vegetative cycle.
TABLE 5
Effect of the Trickle Watering Volume on Prosopis pallida Root Horizontal Size
During the First Six Months of the Vegetative Cycle
Duncan 0.05 (1): Root horizontal size (cm)
| Volume (m3/ha) | Month 1 | Month 2 | Month 3 | Month 4 | Month 5 | Month 6 |
|---|---|---|---|---|---|---|
| 192 | 3.982 b | 8.862 b | 13.75 b | 19.20 b | 24.66 c | 28.925 c |
| 336 | 5.462 b | 10.367 b | 15.81 b | 21.825 b | 27.13 b | 33.875 b |
| 480 | 8.515 a | 24.212 a | 20.97 a | 30.425 a | 38.60 a | 46.945 a |
| Linear effect | Yes | Yes | Yes | Yes | Yes | Yes |
| Quadratic effect | No | Yes | No | Yes | Yes | Yes |
| cv | 15% | 8% | 8% | 10% | 10% | 6% |
Chart 3A
Chart 3B
Charts 3A and 3B: Effect of trickle irrigation on Prosopis pallida root horizontal size during the first six months of the vegetative cycle.
Trickle Irrigation Influence on the Stem
Stem weight and diameter
The greater the water volume applied to Prosopis pallida, the heavier the stem. This relationship increases at both linear and quadratic rates (Chart 4A).
Furthermore, it may be seen that the 480 m3/ha treatment increases faster than the other two watering volumes during the first six months of the vegetative cycle (Chart 4B).
TABLE 6
Simple and Partial Correlation Regarding Weight, Vertical and Horizontal Size of Root
(weight in grams, size in cm)
| Variable grouping | 192 m3/ha | 336 m3/ha | 480 m3/ha | |||
|---|---|---|---|---|---|---|
| Simple C. | Partial C. | Simple C. | Partial C. | Simple C. | Partial C. | |
| Root weight - vertical size | 0.962 ** | 0.629 ** | 0.965 ** | 0.680 ** | 0.981 ** | 0.787 ** |
| Root weight - horizontal size | 0.940 ** | -0.259 No | 0.955 ** | -0.094 No | 0.953 ** | -0.264 No |
| Vertical size - horizontal size | 0.989** | 0.906 ** | 0.974** | 0.775** | 0.982** | 0.804 ** |
* Significance level: 0.05.
** Significance level: 0.01.
Chart 4A
Chart 4B
Charts 4A and 4B: Effect of trickle irrigation on Prosopis pallida stem weight during the first six months of the vegetative cycle.
Relation between stem characteristics
Table 7 shows simple and partial correlation regarding stem weight, stem diameter and plant height, at the three water volumes applied.
A high positive correlation between weight and stem diameter can be seen, while the partial correlation between these characteristics with constant plant height is highly significant with volumes of 192 y 336 m3/ha, but not when the volume is 480 m3/ha.
This means that stem weight and diameter are correlated at the various plant height levels with the low and medium volumes, but not with the high volume.
There are no significant results regarding stem diameter up to the third month of the vegetative cycle. As from the fourth month, the stem diameter response increases linearly (Chart 5A).
The 480 m3/ha treatment surpassed the 192 m3/ha treatment during the fourth and sixth months, achieving the best response during the fifth month (Chart 5B).
TABLE 7
Simple and Partial Correlation Regarding Stem Weight, Stem Diameter and Plant Height
(weight in g; diameter in mm; height in cm)
| Variable grouping | 192 m3/ha | 336 m3/ha | 480 m3/ha | |||
|---|---|---|---|---|---|---|
| Simple C. | Partial C. | Simple C. | Partial C. | Simple C. | Partial C. | |
| Stem weight - stem diameter | 0.951 ** | 0.498 ** | 0.977 ** | 0.802 ** | 0.984 ** | 0.212 No |
| Stem weight - plant height | 0.9982 ** | 0.845 ** | 0.937 ** | 0.218 No | 0.997 ** | 0.918 No |
| Stem diameter - plant height | 0.934 ** | -0.012 No | 0.943 ** | 0.374 ** | 0.983 ** | 0.187 No |
* Significance level: 0.05.
** Significance level: 0.01.
Chart 5A
Chart 5B
Charts 5A and 5B: Effect of trickle irrigation on Prosopis pallida stem diameter during the first six months of the vegetative cycle.
Plant Height and Growth Rate
The trickle irrigation effect on plant height increases linearly (Chart 6A). After the third month it increases with every water volume applied.
Plant growth rate, as evaluated monthly, increases linearly (Chart 7A). A tendency to slower growth rate can also be observed during the first three months.
Chart 6A
Chart 6B
Charts 6A and 6B: Effect of trickle irrigation on Prosopis pallida seedling height during the first six months of the vegetative cycle.
Chart 7A
Chart 7B
Charts 7A and 7B: Effect of trickle irrigation on Prosopis pallida growth rate during the first six months of the vegetative cycle.
Influence of Trickle Watering on the Leaf
Leaf weight, length and width
The weight of the leaf is not significant during the first month of the vegetative cycle; however, as from the second month there is a linear effect of water volume and all three watering volumes are significant (Charts 8A and 8B).
There is a linearly growing effect on leaf length: the greater the trickle irrigation volume, the longer the leaves are during the first six months of the vegetative cycle.
Regarding leaf width, there is a linear quadratic effect of watering volume during the fourth, fifth and sixth months, showing a decreasing increment curve; while in the second month the significant tendency is only linear. This is related to leaf length: as the length increases, so does the width.
Relation among leaf characteristics
Table 8 shows both simple and partial correlation regarding weight, length, width and number of leaves; there is a highly significant partial correlation between leaf weight and width at 336 m3/ha.
Leaf-stem-root relation
Considering the variables root vertical size; plant height; and number of leaves, taking two of them and keeping the third constant, a highly significant correlation may be observed in all cases and with every watering volume (Table 9).
Chart 8A
Chart 8B
Charts 8A and 8B: Effect of trickle irrigation on Prosopis pallida leaf weight during the first six months of the vegetative cycle.
TABLE 8
Simple and Partial Correlation of Leaf Weight, Length, Width and Number
(weight in g; length and width in cm)
| Variable grouping | 192 m3/ha | 336 m3/ha | 480 m3/ha | |||
|---|---|---|---|---|---|---|
| Simple C. | Partial C. | Simple C. | Partial C. | Simple C. | Partial C. | |
| Leaf weight - leaf length | 0.945 ** | -0.629 No | 0.925 ** | 0.086 No | 0.953 ** | 0.102 No |
| Leaf weight - leaf width | 0.825 ** | -0.561 No | 0.919 ** | -0.521 ** | 0.957 ** | -0.283 No |
| Leaf weight - leaf number | 0.985 ** | 0.870 ** | 0.977 ** | 0.873 ** | 0.977 ** | 0.719 ** |
| Leaf length - leaf width | 0.983 ** | 0.377 ** | 0.963 ** | 0.456 ** | 0.992 ** | 0.742 ** |
| Leaf length - leaf number | 0.975 ** | 0.672 ** | 0.959 ** | 0.111 No | 0.982 ** | -0.042 No |
| Leaf width - leaf number | 0.865 No | 0.112 No | 0.969 ** | 0.704 ** | 0.989 | 0.618 ** |
* Significance level: 0.05.
** Significance level: 0.01.
TABLE 9
Simple and Partial Correlation of Root Vertical Size, Plant Height and number of Leaves
(size and height in cm)
| Variable grouping | 192 m3/ha | 336 m3/ha | 480 m3/ha | |||
|---|---|---|---|---|---|---|
| Simple C. | Partial C. | Simple C. | Partial C. | Simple C. | Partial C. | |
| Root vertical size - plant height | 0.984 ** | 0.318 ** | 0.953 ** | 0.533 No | 0.988 ** | 0.421 ** |
| Root vertical size - leaf number | 0.986 ** | 0.441 ** | 0.978 ** | 0.808 ** | 0.991 ** | 0.617 ** |
| Plant height - leaf number | 0.991 ** | 0.703 ** | 0.934 ** | 0.035 No | 0.989 ** | 0.445 ** |
* Significance level: 0.05.
** Significance level: 0.01.
Discussion
Root-Stem-Leaves
From the data obtained regarding weight, horizontal and vertical root size, it can be said that the greater the water volume applied, the greater the weight. Davies and Stocker found similar results with other plants.
The response recorded in Chart 1 can be explained considering that plant formation is obtained in about six to nine weeks (Daniel and Helms, 1982), and in the particular case of Prosopis pallida, Valdivia (1979) says that this species needs four months to form its root structure; however, attention must be paid to the curve shape found for root vertical size, because it is linear convex, while that for horizontal root size is linear concave.
According to Daniel (1982), this is due to the transient pivoting structure so frequently found in the initial root, and to the lateral development (which begins after the primary root elongation) rapidly overcoming the main root length. This type of observation has been made on conifers in the United States.
Regarding the results obtained for such stem variables as weight, stem diameter, plant height and growth rate, the behavior described by the curves show that within the first three months there is a slow increase, which accelerates in the following months. This is explained by the plant consuming its energy initially to form the root system (Daniel, 1982; Barriera, 1978).
On the other hand, it may be observed that those plants having greater water availability increase their photosynthetic activity, thus yielding the carbohydrates needed for the sencondary “changing” fibers and for stem thickening, which has incidence on its weight (Conquist, 1977; Turner and Henry, 1968).
Regarding the curves describing leaf behaviour, specifically leaf weight, during the first months leaf weight increases slowly, speeding up the following months. Similar results have been described by Bonner and Galston (1970), who indicate that the solid matter diminishes slightly during germination due to decrease in seed energy. Thereafter occurs a rapid weight increase, which at last attains a relatively high constant level, accompanied by photosynthesis from the new leaves.
The high simple correlation found for the leaf-stem-root relation supports what Foggs (1973) says, that the growth of any part of the plant is not independent, but occurs in concordance with the rest of the plant.
Due to the lack of practical partial correlation, it is concluded that trickle irrigation changes the plant's morphologic balance (Goldberg, 1974).
Conclusions
In each of the first six months of the vegetative cycle of P. pallida, the stem and leaf characteristics increase linearly, slowly during the first three months, accelerating from then on.
P. pallida develops better its vertical root system when minor water volumes are applied; with the increase in water volume there is horizontal growth instead.
There is a great interdependence between root horizontal and vertical growth and water volumes, getting close to the xerophytic plant conditions, in this case 192 m3/ha.
Trickle irrigation changes the morphologic balance of P. pallida, as it does with other plants.
References
ahorni, a. and ayalon, y., 1973: “Riego del algodón por aspersión,” Ministerio de Agricultura, Servicio de Extensión, Israel, 24 p.
barriera, e. a., 1978: “Fundamentos de edafología para la agricultura,” Editorial Hemisferio Sur, Argentina, 154 p.
black, c.a., 1975: “Relaciones suelo planta,” Vol. i, Editorial Hemisferio Sur, Argentina pp. 119–443.
bonner, j. and galston, a., 1970: “Principios de fisiología vegetal,” Ediciones Omega s.a. España, 465 p.
conquist, a., 1977: “Introducción a la Botánica,” 2nd Edition, Mexico. p. 622.
dale de remer, e., 1972: “Riego por goteo,” Agricultura de la Américas, No. 11 pp. 12, 14.
daniel, w. t.; helms, j.a. and baker, f.s., 1982: “Principios de Silvicultura,” Libros Mc Graw Hill de México, 492 p.
de la flor badaracco, f. d., 1984: “La Planta,” Biblioteca Agropecuaria del Perú, Nets Editores, 61 p.
donahue, r. l.; miller, r. and schickluna, j., 1981: “Introducción a los suelos y al crecimiento de las plantas,” Editorial Prentice Hall Colombia, pp. 72–370.
fao, 1981: Producción y protección vegetal, “Prosopis tamarugo, arbusto forrajero para zonas áridas,” Plant Production and Protection Division, Food and Agriculture Organization of the United Nations, Rome, p. 180.
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ocampo, almanza, 1971: “El algarrobo, especie forestal,” Ministerio de Agricultura, Proyecto de plantaciones forestales con fines silvopecuarios, p. 73.
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russel, j. and russell, w.f., 1969: “Las condiciones del suelo y el desarrollo de las plantas,” 3rd Edition, p. 736.
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Rafael Bahamondes
Claudio Campos
Foresters, Chilean Forest Service (conaf)
Introduction
The Prosopis tamarugo forest dealt with in this paper is located in Chile's Region I, between 19° 33' and 20° 50' south latitude stretching within a biogeographical zone known as Pampa del Tamarugal.
The Pampa del Tamarugal is a very regular desert plateau stretching uninterruptedly from 19° 33' south lat. to 23° south lat., at an average altitude above sea level of 1,000 m.
Its climate is normal desert, according to Köppen's classification, with very marked, harsh features. Temperatures range between absolute minima of -5° C to -12° C, and absolute maxima of 35° C and 36° C, with an average of 250 cloudless days per year. No precipitation occurs as rainfall. One of the most outstanding characteristics of this climate is the high luminosity, derived from the very clear atmosphere. Relative humidity is low during the day, varying from 10% to 30%, and high during the night, with 80% to 100%, with no precipitation. Due to the low night temperatures, frosts can occur any time of the year, but mostly in wintertime.
Two well defined and identified soil sectors exist. The first occurs at the higher eastern reaches of the Pampa del Tamarugal, with coarse permeable material, and a finer material in the lower western sector, with depressions presently covered with saltpeter deposits. The eastern portion of the Pampa is a great piedmont made up by the confluence of alluvial fans formed at the outlet of gorges descending from the Andes Mountains. Sediments show a gross stratification, generally of coarse, medium and fine sand, separated by thin saline strata; occasionally, some extraordinarily hard sands occur with high salt content. Soils are deep, stratified, sandy, gray-hued, non-structured, with simple, loose, non-plastic and non-adhesive grain; flat or slightly sloped, good to excessive drainage; alkaline with low to very low natural fertility and highly variable plant establishing capacity. The piedmont ends in the western portions of the Pampa and the filling materials are finer, predominating sand and loam.
The western section had some lakes in ancient times, which later became salt flats, predominating clay and loam material, stratified and with a salt cover varying in thickness from a few centimeters to one meter or more. These salts are deliquescent and mainly of sodium, calcium, magnesium and potassium, giving the impression that the ground is always moist. The salt flats have a variable phreatic layer, ranging from 2 to 25 meters.
These Prosopis tamarugo forests are the largest and most important in the country. They are located mostly within the Pampa del Tamarugal National Reserve (around parallel 20° 30' south) and are included in the National Protected Wildlands System under the administration of the Chilean Forest Service (conaf). The Reserve covers about 101,000 ha; there are 24,000 ha of man made forests and 3,400 ha of natural forests. The establishment of this Reserve aims at preserving these fragile ecosystems.
Several rural communities are located in the vicinity of the National Reserve, with a total population of around 3,000 people, who own approximately 4,000 ha of mostly natural Prosopis tamarugo forests. Together with the forests within the Reserve, these constitute the largest Prosopis tamarugo resource in Region I.
Within the natural P. tamarugo forests, species such as Prosopis chilensis, P. strombulifera, P. burkartii and P. alba also occur, although in much smaller proportion.
Among the shrubs associated to Prosopis forests in the Pampa del Tamarugal, are Atriplex atacamensis, Caesalpinia aphylla, Tessaria absinthioides, Euphorbia tarapacana and Tagetes glandulosa. In the herbaceous stratum, are Cressa cretica and Distichlis spicata.
The man-made Prosopis tamarugo forests starred to be established in 1964, when the Chilean Production Development Corporation (corfo) started an afforestation program on lands where former natural Prosopis tamarugo forests had been intensely exploited by mining operations last century. The purpose of this afforestation effort was to transform the desert into a silvo-pastoral ecosystem which would contribute to the region's economic development.
Since 1983, the Chilean Forest Service has been encharged with the administration of these forests by including them within a National Reserve; it afforested around 900 ha between 1983 and 1985.
The man-made forests are established by planting seedlings in pots; the seedlings are raised in a nursery, for 4 to 6 months; sowing is carried out at any time of the year. Planting rate is around 100 plant/ha, considering the objective of silvo-pastoral production and the fragility of the water resources available. In this regard, the optimum plantation period, mostly for reasons of the costs involved, is from February to June, when the heat is less intense and, therefore, less watering is required. Otherwise, planting can be carried out any time of the year.
The most important dasometric data of these forests are: rotation age estimated at 30–40 years; mean height, 11 m; 3–4 stems per tree; mean dbh, 14–16 cm; mean crown diameter, 9 m; and mean fruit output, 8–10 kg/tree.
The silvopastoral production and management system is based fundamentally on using the fruit as feed for minor livestock, such as sheep and goats. Among the former, Corriedale, Australian Merino, Suffolk Down and Karakul breeds stand out, while, among the second, Angora, Anglo Nubian and Native breeds are the most relevant.
The herds are alloted, in an attempt to optimize the space-time relation, among 100-ha plots, at a carrying capacity of 1 sheep or 0.5 goat per ha/year. This average carrying capacity was arrived at from studies on fodder production (pods and foliage) vis-a-vis animal consumption, and fodder production vis-a-vis canopy area.
As regards fodder production/canopy area, the following equation models were used:
Y1 = D2 · P1
Y2 = D2 · P2
| where | Y1 | = | fruit and foliage production per tree |
| P1 | = | fruit and foliage production per m2 crown projection | |
| Y2 | = | fruit production per tree | |
| P2 | = | fruit production per m2 of crown projection | |
| D | = | crown diameter in m |
The values obtained for the correlation coefficient (r) show the canopy area to be closely related to fodder production, with the highest correlation between fruit and leaves-foliage per tree (y1).
The square of the correlation coefficient, known as determination coefficient, showed that for fruit and foliage production, 18.1% of the variation is not accounted for by canopy area, i.e. it depends on other independent variables, such as stand age, stocking rate, etc., or other site conditions not taken into account. Around 40% of the variation in fruit production is not accounted for by canopy area.
At present, an annual average of 7,500 animals are being managed under this system, belonging to 40 private owners who manage 3 or 4 one-hundred-ha plots each.
These private owners are an important productive sector within the regional economy, as they market an animal protein resource which constitutes an interesting alternative for the local consumers.
The Silvopastoral Management option here considered includes training these private owners through a Technology Transfer program, which operates every year under an agreement with the Region's Universidad Arturo Prat. It aims at providing theoretical and practical silvopastoral management knowledge.
As regards livestock farming, emphasis is laid on sanitary management (parasitary disease, infectious-contagious disease, prophylaxis and treatments); breeding management (breeding, gestation and lambing), and productive management (lactation, weaning and production). The silvicultural aspects include pruning, thinning, fodder output and nutritional values. All training is carried out under the silvopastoral management concept.
As a complement thereto and within the framework of more intensive silvopastoral management of the Prosopis tamarugo forest, a number of research projects are under way related to the use of the forest resource as an energy and timber producer, thus enhancing the multiple use concept behind these efforts.
Worthy of mention is the research currently under way through the conaf/unpd/fao Project, aimed at developing other uses for Prosopis tamarugo wood, at present limited by form and size to firewood and charcoal. The aspects studied are Prosopis tamarugo wood drying, some physical properties for workability and uses. In this regard, a preliminary evaluation based on the opinion of specialists and a review of literature, has warranted the conclusion that for certain tree species characterized by high-density hardwood growing in arid zones (such as Prosopis tamarugo), interesting use prospects exist for the manufacturing of non traditional implements, such as railroad car brake shoes, parts and pieces for transmission systems, textile elements, parquet flooring, etc.
Some studies on pruning and thinning are also relevant, which assess, in addition to dasometric data (stem size, canopy, fruit yield, etc.), firewood and charcoal yields.
Other important research studies under way at the Pampa del Tamarugal National Reserve focus on insects associated to P. tamarugo, tamarugo genetic improvement, melliferous production, and species introduction trials.
Prosopis sp. firewood. The quality of this wood warrants other uses as well.
References
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