H. Hadri
Forestry Engineer, B.P. 1055, Tunis RP, Tunisia
3. Plant breeding in the nursery
The soils in the pastoral development areas vary from one region to another. Primarily they consist of:
a) sand dunes and sandy plains;b) undulating slopes dissected by wadis with sandy loam or loamy sand, and the occasional sand deposited in the wadi by wind erosion;
c) stony plateaux dissected by sandy loam or loamy sand wadis. The plateau contains karstic depressions, water distribution areas and sebkhas.
The climate is characterized by:a) low and irregular rainfall;
b) effects resulting from the proximity of the desert: high evaporation, hot winds from the south, strong wind erosion.
The dry period is very long in the summer and frequently lasts over six months. The rain is primarily concentrated in winter, between November and March. It varies in pastoral areas between 100 and 200 mm in the sandy coastal plains, between 100 and 150 mm on the coastal plateaux and between 75 and 150 mm in the project zone of the interior. The karstic depressions and wadis receive extra runoff water.
The pastoral development aspect of the project involves the improvement and increase of forage production and especially the planting of species which are productive under this climate and correspond to the soil situation in each of the pastoral units managed. The following species have been introduced.
Acacia cyanophylla: on deep sandy soils, preferably on dunes; Acacia victoriae: on deep sandy soils, in a drier environment than Acacia cynophylla; Atriplex canescens: on shallower sandy soil; this plant adapts itself to very different ecological environments and is very resistant to drought, since the roots may reach a depth of 5 to 15 m; Atriplex halimus: this species is well adapted to local conditions and resists drought and saline conditions; it is planted in the sandy loam wadis with a fine texture; Atriplex nummularia: generally cultivated on widely differing soils, this plant adapts well to sandy loam soils in the wadis; Calligonum comosum: on shallow sandy soils in dry environments; Opuntia ficus indica inermis: on sandy to sandy loam soils, under relatively favourable rainfall conditions.
This pastoral zone has been divided into two units, each of which is subdivided into farms. This subdivision allows rational utilization of the areas. The farm area is calculated with reference to herd numbers, the productivity of rangeland, etc.
Each farm contains a belt of browse shrubs in the more favourable sites, so to ensure the survival of herds during the critical summer and autumn months. The distribution of species is as follows: Acacia cyanophylla, 29%; Atriplexcanescens, 25%; Calligonum comosum, 9%; Acacia victoriae, 7%; Opuntia ficus indica inermis, 30%.
The planting of browse species in this area is limited to favourable sites receiving extra runoff water, These are the wadis, the water distribution areas and the karstic depressions.
The browse shrubs selected for planting in this area were limited in number, consisting of those varieties which have for many years been successfully grown under similar soil and climate conditions in Libya or in other North African countries. They were as follows: Atriplex halimus, 50%; Atriplex nummularia, 50%.
These two species are characterized by their:
a) resistance to drought;
b) good browse production;
c) tolerance of saline conditions.
The sites used for planting in this area are large and small wadis, and karstic depression often used to cultivate barley. The small wadis are equipped with banks arranged perpendicularly to the water flow direction. The species planted and the distribution were as follows: Acacia cyanophylla, 15%; Acacia tortilis, 2%, Atriplex halimus, 21%; Atriplex canescens, 21%; Atriplex nummularia, 41%.
The favourable sites selected for planting were similar to those chosen for the previous zone. They were large and small wadis, areas of water distribution and karstic depressions. The species planted and the distribution are as follows: Acacia cyanophylla, 9%; Acacia tortilis, 1%; Atriplex halimus, 66%; Atriplex nummularia, 25%.
The method advocated for planting browse species is to introduce plants already grown in the nursery and obtained from seed from an appropriate source. For this purpose we started four nurseries covering a total area of approximately 40 ha. The nurseries are equipped for producing the necessary young plants to a satisfactory quality standard. The nurseries in the pastoral development zones produced 20 million young plants during the 1978/79 growing season.
We also installed artificial windbreaks designed according to aerodynamic standards to protect the young plants against hot winds and sand storms. These windbreaks gave very satisfactory results. At the same time natural windbreaks were also installed. Watering was carried out by using sprinklers, providing very fine drops of water which were evenly distributed on the nursery beds.
In order for planting to be a success we exercised particular care over the young plants while they were being raised in the nursery.
The following factors were of primordial importance:
the balance between the leaf and root systems;
the abundant supply of rootlets in the form of root hair near the neck of the plant;
the fresh condition of the plant before being planted out.
The ecological origin of the seeds was similar to the ecology of the project zones. The seed came primarily from arid areas in the United States, Morocco and Tunisia.
For raising the young plants we used polyethylene bags with holes in them. These were filled with equal amounts (33%) of vegetable mould, sand and loam. The results using these containers are satisfactory and this technique is a well tried and tested one in Tunisia.
Plants should not remain longer than six months in the nursery. At this stage their height is about 30 cm, the diameter of the neck should be equivalent to the thickness of a pencil. The plants are cut down to the optimum height whenever necessary.
Substantial difficulties arose during the raising of the plants. The hot, sand-laden winds blowing from the south, known as the Guebli, caused some damage. The windbreaks were fairly effective against these sand winds and limited the damage.
Nurseries covering large areas are often well suited to the development of insects and fungi. Several insect attacks and outbreaks of sporophytic diseases were experienced, but these were quickly got under control. During the sowing period the swift rise in temperature posed problems for seed germination, especially in the case of Atriplex canescens.
The results obtained in the nursery are generally satisfactory, if certain number of precautions are observed:
the quality of seeds;
the treatment of the seeds before sowing;
the depth of the seeds when sown in the containers;
the sowing period;
maintenance (watering, weeding singling and protection).
The success achieved varied according to the species and The nursery: Atriplex canescens, 40–60%; Atriplex halimus, 50 70%; Atriplex nummularia, 60%; Acacia cyanophylla, 70–80%; Acacia tortilis, 40%; Acacia victoriae, 40%; Calligonum comosum, 60%.
According to observations in the field successful planting is largely due to good soil preparation. Most of the soils on the pastoral unit were degraded on account of overgrazing. As a result they have become resistant to permeation by rainwater. Furrows were dug for planting, so as to enable the infiltration and storage of rain water, as well as the elimination of competitive plants. The holes for the plants were dug by hand in the furrows.
The favourable time for planting generally begins after the first autumn rains, when the soil has become sufficiently damp. Planting is carried out by hand and reaches on average 150,000 plants per day, throughout the pastoral development zones.
The following procedure was used for planting:
a) the polyethylene sacks were removed;
b) the plant was placed in the holes;
c) the hole was filled with surrounding earth;
d) the soil was pressed around the plant;
e) a small basin was formed around the plant;
f) superphosphate and nitrogen were spread in the basin;
g) the plant was watered just after planting.
The cactus joints introduced came from the Kasserine-Thala region in Tunisia. This is an area which ecologically resembles the project area in which the cactus was planted. The joints were collected at the end of February and were left exposed to sun and air for several days before being transported to the plantation sites.
Some organic fertilizer was introduced into the cactus plantation furrows. Subsequently the furrows were covered over with a layer of earth. The planting holes were prepared by hand. The joints were buried up to half their length in the holes and the earth was pressed firmly round them.
The criteria of successful planting are primarily the following:
survival after the dry period of the first summer;
growth in height;
plant vitality;
the number of new shoots (for cactus).
a) survival after the dry period of the first summer;
b) growth in height;
c) plant vitality;
d) the number of new shoots (for cactus).
The most serious difficulties in recovery were recorded mostly after planting rather than after the dry summer period. Most of the plants which survive the shock of transplantation also survive the dry summer period. Very few failures were recorded for all species after the dry summer period. Raising good plants in the nursery, providing adequate transport, careful handling of the plants and the use of good planting out techniques considerably increase the chances of success.
The following table shows the result for planting out after ten months for each species:
Species |
Success rate (%) |
Height |
No. of new shoots (average) |
Acacia cyanophylla |
70–95 |
40–170 cm |
|
Atriplex canescens |
95 |
30–150 cm |
|
Atriplex halimus |
80–95 |
40–120 cm |
|
Opuntia ficus indica |
95 |
4 joints |
The planting of Atriplex canescens, Opuntia ficus indica inermis, Atriplex halimus and Atriplex nummularia may be considered successful on account of:
a) resistance to drought and survival after summer;
b) resistance to cold;
c) growth in height and good development of the plants.
Acacia cyanophylla poses problems during plant out. The recovery rate of Acacia cynophylla is les good than that of Atriplex, but the growth of successful plants in areas where the species was introduced is remarkable. It is too early yet to pronounce judgement on Acacia victoriae, Acacia tortilis and Calligonum comosum, at only four months of age. However, the latter species is already providing encouraging indications.
