|
|
| Bildiri Özetleri | |
| Ana Sayfaya Dönüş |
| ISD Ana Sayfası |
|
Michael Shapiro, Vladimir Kurepin Ministry Of Agriculture And Rural Development, Soil Conservation And Drainage Division, Israel ABSTRACT Present intensive development of the Negev desert region (southern Israel) makes it necessary to utilise agricultural plants previos planted in another climatic conditions. One of such plant is the olive tree, traditionally grown in north and central semi-humid portions of the country. For proper assessment of land suitability to the growth of olive trees, both physical and chemical soil properties as well as properties of soil cover heterogeneity should be taken into consideration. On the basis of such properties a number of soil morphological, analytical, and spatial land criteria are proposed. This work is based upon a detailed soil survey, at a scale of 1:2,500, carried out in the central Negev. INTRODUCTION Olives (Olea Europaea) are traditional fruit trees for the majority of subtropical Mediterranean countries, especially Greece, the Mahgreb, and Spain. They also grow in other regions having a Mediterranean climate, such as California, Chile, South Australia and South Africa. In Israel olives have been grown since ancient times and are commercially produced in north and central parts of the country. The main Israeli regions of olive cultivation are the mountains and hills of the Galil, Samaria and Judea. In these mountains and hills olive tree plantations are situated on terra-rossa, rendzina and brown Mediterranean soils. The mountain soils consist of an upper stoneless layer grading into a layer of consolidated parent rock. The layer of parent rock involves a lot of deep vertical and subvertical cracks and wedges (pockets) filled by fine-textured material. Because of this, even shallow mountain soils have a sufficient volume of loose material necessary for tree development. On piedmont plains and river terraces olive trees are grown on different kinds of accumulated soils derived from loose material with significant amount of fine-textured particles. As a rule, all these soils are leached of soluble salts or are saline to an insignificant degree. Olive trees plantations situated in regions of traditional cultivation are characterized by stable surface or surface artificially fixed by means of soil conservation measures carried out over long periods of time. Completely different properties characterize the soils of the central Negev. First of all, the climate of the central Negev is far drier (Table 1) and far hotter than in the northern and central portions of Israel. The central Negev aridity is inordinate even for such highly drought resistant species as Olea Europaea. Secondly, the only suitable soils for growing of olive trees are loessial serozems formed on alluvial fans of small piedmont plains between mountain ridges. The thickness of fine-textured upper layers of these serozems differs from point to point. Within the first 30-80 cm of the soil surface it usually grades into stony alluvial deposits with a high content of carbonates and sometimes gypsum and almost without any fine-textured material. Thirdly, the upper fine-textured serozem's layer is saline, sometimes contains a lot of exchangeable sodium and a large amount of boron. Finally, present-day aeolian-deflation and fluvial processes significantly influence soil cover of alluvial fans. This leads to a considerable spatial soil heterogeneity of agriculture plots and to a high degree of their surface instability. These peculiar landscape conditions determine necessitate detailed soil cover analysis of the plots intended for the growing of olive trees.  MATERIALS and METHODS In order to study the suitability of the central Negev for olive cultivation a sample area was selected in the Revivim region. This is located 120 km south of Tel Aviv and 60 km to the east of the Mediterranean coast, near Kibutz Revivim, in the basin of Wadi Beer-Hajl (Fig.1, 2). The sample area is representative of the Negev Highlands, and is composed of two geomorphologic segments. The first is rocky. It is represented by low mountain ridges, whose highest points are about 600-650 m a.s.l. They consist of consolidated limestones and dolomites of Cenomanian and Turonian age, chalks of Santonian and Campanian age, and flints and chalks of Eocene age. The mountain soils are shallow lithosols: stony brown or rendzinic. All are unsuitable for planting.  The second geomorphologic segment, having some potential for olive trees planting, is represented by intermontane well-drained piedmont alluvial plains. The groundwater level is deep and does not influence soil-forming processes. This segment is formed by coalescing gravel cones, the average altitude of which is about 300-350 m a.s.l. The cones consist of Neogene age conglomerates and are dissected by a network of intermittent streams (wadies). The wadi valleys are about 3-5 m or more in depth. The watersheds (drainage divides) separate these wadies over a distance of about several hundreds of m. On topographical maps at a scale of 1:10,000 these watersheds areas appear as rather homogeneous glacises. Quite another picture is revealed after field inspection of watershed areas and analysis of detailed topographical maps and aerial photographs (scale 1:2,500-1:5,000). The watershed areas are composed of systematically repeating microrelief patterns. These patterns are composed of forms of microrelief which change over small distances (Fig. 3,4). These forms are: 1. Narrow parallel or sub-parallel microcrests between wadies, rising 30-40 cm above the basic surface. Microcrests occupy about 25% of watershed areas. Their surface is bare, sometimes covered by a thin (3-4 mm) vesicular crust composed of carbonate and silicate material often found in other hot desert regions (Souirji&Marcoen 1998). 2. Flat patches between microcrests and microchannels. In most cases their surface is free of vegetation. Sometimes these patches are sporadically covered by shrubs. Barren patches are topped by thin vesicular crust. Patches surface nearby shrubs is covered by a very thin sand veil. 3. Gently undulating patches of diffuse vegetation. Near shrubs there are very small sand hummocks. Patches of flat and gently undulating plains interpenetrate each other and occupy about 50% of watershed areas. 4. Shallow microchannels of weak seasonal (ephemeral) streams, 20-30 cm in depth, part of which are blind creeks. These dry streambeds occupy about 15% of watershed areas. Microchannels have rather dense shrub cover (Hammada scoparia plant associations), favouring accumulation of sandy aeolian deposits. 5. Levees spreading along wadi slopes at watershed edges (10% of watershed areas). Levee height above the watershed surface is about 60-70 cm. As a rule, levee surfaces abound in loose gravelly and cobbly pavement.  The width of the above-mentioned forms of microrelief (except for microchannels) ranges between 25-30 and 50-70 m, the length ranging between 200 and 300 m. All forms are orientated parallel or sub-parallel to lines of the major wadies from S-E to N-W.  The sample area's parent material is composed of three main layers. The surface layer consists of Holocene-Upper Pleistocene aeolian loamy sand. The sandy layer is underlain by Upper-Middle Pleistocene aeolian- and fluvial calcareous loesses. These two fine-textured layers compose an upper fine-textured epipedon, which abruptly grades into Neogene calcareous conglomerates. The main kinds of conglomerate fragments are rounded and subrounded gravels and cobbles. In most cases conglomerates are non- or slightly cemented by carbonates concentrations. Sometimes the degree of cementation rises to moderate. Thickness of the upper fine-textured stratum is one of the most critical soil properties in the course of assessing land suitability for olive tree cultivation. Depending upon microrelief, epipedon thickness ranges from 20-30 cm within microcrests to 70-100 cm or more within microchannels. A detailed (at a scale of 1:2,500) soil survey of 200 ha revealed a high spatial variability of soil cover. A large difference in soil features between adjacent soil areas is connected with the influence of a number of soil- and relief forming processes, and peculiarities of spatial distribution of runoff within watersheds. The main processes governing spatial variability of soil cover are: high level of wind erosion of areas unprotected by vegetation or vesicular crust and accumulation of aeolian dust material within locations covered by desert shrubs; redistribution of eroded particles by local runoff from microcrests to adjoining flat and undulating patches. Local fluvial activity favours transportation and accumulation of fine-textured material within streambeds during winter rainfalls. Intensive winter rainfalls lead to growth of a wadi network and accumulation of gravels and cobbles along watershed edges on levee surfaces. It is worth emphasising the significant degree of input of local runoff water upon the spatial differentiation of soil salt, carbonate and moisture content (Yair 1990). Among landscape features influencing the present status of soil cover, relief of pre-existing conglomerate surface and intensity of Pleistocene denudation should be mentioned. Soils of the Revivim sample area are typical of hot deserts (Singer 1995, Souirji&Marcoen 1998). According to the Israeli classification most of them are related to serozems (Dan 1981). Similar soils in the American soil taxonomy are Calciorthids, Camborthids, Haplargids (Keys… 1998). Table 2 illustrates major soils and geomorphologic locations of their areas. From the applied point of view, main field-inspected soil properties are the thickness of the fine-textured epipedon, the degree of profile differentiation, the degree of internal drainage, and the degree of conglomerate cementation. According to these criteria, the soils are divided to two groups. The first consists of stony soils in which the fine-textured epipedon thickness is less than 30 cm. Ordinary stony soils are formed on microcrests of watersheds, whilst alluvial stony soils are formed on levees along watershed edges. These soils are unsuitable for olive trees planting owing to the extremely high water infiltration rate, very low water-holding capacity, and lack of fine-textured material necessary for tree roots development. All other soils are divided into weakly developed ones and serozems. Weakly developed soils are formed from present-day aeolian or alluvial material. They involve a little pedogenic alteration of parent material: an upper ochrick horizon diffusely grades into a lower salic horizon. The soils have loamy sandy and sandy loamy texture. Shallow soils are underlain by conglomerate at a depth of 40-50 cm, whilst moderately deep soils are underlain by conglomerate at a depth of 60-100 cm. Physical properties of these soils don't restrict the growing of olive trees. Ultimate suitability for olive planting depends upon the degree of salt content and alkalinity. In comparison with weakly developed soils serozems have a rather distinct profile. Typical ordinary serozems are composed of ochric, calcic and salic horizons underlain by conglomerates. In the profile of typical argilly serozems, the calcic horizon is replaced by an argillic horizon or by a calcic-argillic intergrade. Some serozems are covered by a thin vesicular crust. Thickness of shallow serozems is about 50-60 cm; thickness of moderately deep ones is about 80-110 cm. There is a sufficient difference in suitability of such soils for the growing of olive trees. Ordinary serozems are much more suitable than argilly ones due to their higher permeability, and lower salinity and alkalinity. The main negative feature of argilly serozems is connected with an argillic horizon enriched in clay content and secondary carbonates. As a rule, the upper ochric horizon of argilly serozems abruptly grades into the argillic horizon without a transitional horizon or with only a very thin transitional horizon. So called in this studu denuded (wind eroded) serozems have been found most unsuatable for growing olive trees. The profile of denudeded serozems lacks an upper ochric horizon. Instead, there is a thin ochric-calcic intergrade, grading with depth into a calcic, or calcic-argillic, or argillic horizon. As a rule, denuded serozems have a thin vesicular crust at their surface. There is no any distinct trend in the differentiation of conglomerate cementation. Generally, conglomerates are not cemented at all. Occasionally, the degree cementation rises to slight or moderate. Salt, SAR, and boron levels of the soils vary within a wide range. Less salty soils are weakly developed ones and shallow typical ordinary serozems. With additional fine-textured epipedon thickness and additional soil profile differentiation, salt content also increases. For instance, typical ordinary serozems are characterised by an EC of 5-15 dS/m, SAR of 10-15, and 2-3 ppm of B content. The most saline soils are argilly serozems, especially denuded argilly serozems (the EC of argillic horizons being about 20-25 dS/m, SAR of 25-35, and B content of around 5-10 ppm). DISCUSSION In order to define land suitability for the growth of olive trees a number of criteria concerning soil properties must be delineated. These are: physical and chemical properties, and properties of spatial soil distribution. Physical properties deal with the thickness of the upper fine-textured layer, soil horizon texture, penetration and resistance classes, distinctness of horizons (the distance over which one horizon grades into another), and the degree of cementation of conglomerates. These properties are all evaluated with respect to the fact that the major portion of olive tree roots is concentrated in upper layer of 40-50 cm thickness and that olives trees don't tolerate waterlogged soils or soils with a low degree of percolation. Open, perfectly aerated, welldrained loamy soils without slow-permeability horizons within their upper 80-100 cm are ideal. The high sensitivity of olive trees to the degree of soil drainage is a critical restriction in arid regions where trees plantations are irrigated with significant amounts of water. (The amount of irrigation water nessessary for commercial olives production is about 450-500 mm. Taking into account the fact that at least a portion of irrigated water is obtained from local wells and has high levels of electroconductivity -EC- approx. 4-5 dS/m, exchangeable sodium -SAR- approx. 8, and approx. 1-2 ppm of boron content, the amount of irrigation water might be increased up to 700-800 mm). A moderate and moderately rapid infiltration rate of arid soils is also an obligatory initial condition for successfully reducing soluble salts and boron from upper horizons by leaching. On the other hand, soils with either very rapid and slow infiltration rates are unsuitable for growing olive trees. The best combination of physical properties for olive trees cultivation in the Revivim sample area are found in loamy sandy to sandy loamy, rather loose, slightly carbonated soils. They consist of two or three horizons very gradually grading one into another, with a stoneless epipedon thickness of 60-80 cm, underlain by loose non-cemented conglomerates. Such properties characterize some weakly developed soils and ordinary typical serozems. The worst combination of the above-mentioned properties for growing olive trees involves both stony soils whose fine-textured epipedon's thickness is less then 30 cm, and fine-textured soils with carbonated upper horizons abruptly grading into highly carbonated, rather hard horizons enriched in clay (denuded argilly serozems), as well as ordinary serozems with thin clay loamy laminaes (2-3 cm of thickness).  Chemical properties defining soil suitability for olive trees cultivation are pH, EC, exchangeable sodium, and the amount of boron. Lime content in central Negev soils doesn't play restrictive role in growing olive trees. pH level shouldn't exceed 8-8.5. Taking into consideration the fact that olive trees are considered moderately tolerant to salinity (Maas 1986, Zinger 1985) and that all plots would undergo initial leaching and then be regularly irrigated, rather high levels of EC, SAR, and B content were recognised as permissible for virgin soils. These levels are: EC 8-12 dS/m, SAR 10-15, B 2-4 ppm. These criteria are less strict then those acceptable in Israel for other kinds of fruit trees (Criteria… 1995). Practical Israeli experience indicate that while saline soils are leached, their SAR level is also reduced. As for boron, it should be noted that high levels of boron in soils can also be reduced by leaching but in lower proportions than other soluble salts. As a rule, soils having favourable physical properties for planting generally also have proper chemical properties (weakly developed soils and typical ordinary serozems). The worst soils are argilly denuded serozems. Extremely high spatial variability, or heterogeneity, is one of the most important properties of studied soil cover. This variability is expressed by different kinds of elementary soil areas (in the meaning of V.Fridland 1972) adjoining one to another and altering one another over a distance of tens of metres. This soil cover mosaic forms due to the local influence of soil formation factors mentioned above. The main consequence of high soil cover variability is varying predictability of the soils by means of some landscape indicators, both at the initial stage of map and aerial photograph interpretation and during field investigation without pit digging. In the Revivim sample area, the degree of soil predictability varied from high to low (Table 2). The most predictable soils are ones formed on distinct forms of microrelief: microcrests, levees, and microchannels of seasonal streambeds. Soils of microcrests and levees are unsuitable for olive trees planting. Streambeds soils are suitable for this purpose but don't play substantial role from a spatial point of view. Gently undulating and flat patches have much lower predictability. These involve geomorphological locations within which all kinds of serozems may be found. According to predictability variations, the density of soil pits is planned. It is rather low on microforms with highly predictable soils (about 1 pit to 2-3 ha) and rather high (1-2 pits to 1 ha) on microforms with low predictability soils. It is worth mentioning that soils eliminated due to their negative physical properties don't require a chemical analysis. On the other hand, all soils which seem suitable for planting according to their physical properties are strongly recommended to be investigated in a chemical laboratory. A practical consequence of high spatial variability in soil cover is the nessessity to unite soil areas having different arable values while splitting territories into individual agricultural blocks. This splitting is performed on the base of detailed soil maps (1:2,500-1:3,000). The minimal size of such a block is about 1 ha. All blocks should be planted using drip irrigation, and each block might be irrigated in its own way with regards to soils chemical features. It is desirable that physical and chemical differences between soils of adjacent areas within the same block don't prevent use of the same cultivation measures. In spite of inclusion into recommended planting blocks soils with a wide range of physical and chemical properties, the main portion of the studied sample area is not considered as suitable for growing of olive trees. The relation between blocks recommended for future planting blocks and eliminated soils areas is about 3:7. An obligatory condition of splitting territory into blocks is a requirement for soil cover protection. The main desirable soil cover protection measures include: remoteness from watershed edges at the distance of 50 m and more, preservation of vegetative cover on wadi valley slopes, use of non-inversing plowing in order to minimize disturbance of upper soil horizons, avoidance of heavy agricultural vehicles, regulation of runoff water flow from adjusent mountain slopes, etc. REFERENCES Criteria of land selecting for fruit trees planting. (1995). Min. of Agriculture: 1-4. Bet Dagan, Israel. [In Hebrew]. Dan J. The nortwestern part of the Negev hills and mountains. (1981). In: Aridic soils of Israel. The Volcani Center:223-238. Bet Dagan, Israel. Fridland V.M. (1972). Structure of soil cover. Moscow. [In Russian]. Keys to soil taxonomy. Eigth edition. (1998). USDA. Washington. Maas E.V. (1986). Salt tolerance of plants. Applied Agr. Res. 1:12-26. Singer A. The mineral composition of hot and cold desert soils. (1995). In: Arid ecosystems. Advances in Geoecology, 28:13-28. Souirji A.& Marcoen J.M. Using topsoil characteristics to classify desert soils. (1998). 16th World Congress of Soil Science. Montpellier. Yair A. The role of topography and surface cover upon soil formation along hillslopes in arid climates. (1990). In: Soils and Landscape Evolution. Geomorphology, 3: 287-299. Zinger A. Olive trees plantation. (1985). Bet Dagan, Israel. [In Hebrew]. ACKNOWLEDGEMENT We would like to thank Mr.R.Zaidenberg (Ministry of Agriculture and Rural Development, Israel) for friendly assistance with the work at all its stages. We are also grateful to Dr. M.L.Collin (Ministry of National Infrastructures, Israel), who edited this paper. |