|
|
| Bildiri Özetleri | |
| Ana Sayfaya Dönüş |
| ISD Ana Sayfası |
|
A.A. Jafarzadeh 1 , J.A. Zinck 2 1 University of Tabriz, Faculty of Agriculture, Soil Science Department, Tabriz, I.R. Iran 2 ITC, PO Box 6, 7500 AA Enschede, the Netherlands ABSTRACT The prosperity and even the very existence of humankind depend on the food produced from the agricultural resources, with a global demand for food, fiber and bio-energy products growing at an annual rate of 3.2% in developing countries (FAO, 1989). To maintain and enhance the sustainability of agriculture and meet the basic food needs of rising population, it is necessary to use appropriate land management practices, especially in problem-soils. Soils with gypsum are a kind of problem-soils when gypsum is present in considerable amount. According to available information (Driessen and Dudal, 1989; FAO, 1990; Mashali, 1993, 1996; Boyadgiev and Verheye, 1996; among others), the worldwide extent of gypseous soils exceeds 100 milion ha, but an inventory carried out at country level shows that it might be as large as 186 million ha (1.5% of the worldwide soil cover), including countries of the Middle East, Eurasia, the Mediterranean belt, Africa, North America and Australia. This paper also summarizes the management practices applied to gypseous soils for sustainable management, as reported by several authors during the last decades. Chemical, physical, biological, hydrological and human features, which affect the productivity and management of gypseous soils, are highlighted. INTRODUCTION Problem-soils are frequent in arid and semi-arid environments, including soils with high amounts of gypsum. It is thus important to assess the distribution and suitability of gypseous soils for sustainable management, since the possibility of incorporating new land into the agricultural production is limited whereas food requirements are steadily increasing. World population is projected to rise from 5.3 billion people in 1990 to 8.5 billion in 2025 and 10 billion by 2050 (Bongaarts, 1994). In contrast, the land resources are finite, fragile and nonrenewable, because land suitable for agricultural use is only a small fraction of the total land area (22% of all land). There are vast areas with gypsum in the world, but precise information about their distribution and extent is still lacking. The present paper draws attention on the worldwide distribution of gypseous soils, the production constraints caused by high gypsum content and the management experience gained during the last decades. EXTENT AND DISTRIBUTION OF GYPSEOUS SOILS Gypseous soils are found in arid and semi-arid areas on gypsiferous rocks and sediments of different origin, where rainfall is insufficient to leach the gypsum out of the soil mantle. They usually occur in the same regions as calcareous soils but are much less widespread. For being of marginal interest to agricultural use, they were given little attention in the past until it was realized that they have potential for both rainfed and irrigated agriculture. Figures provided in the literature about the worldwide extent of gypseous soils are far from accurate. According to earlier estimates (Van Alphen and De Los Rios Romero, 1971), these soils would cover roughly 85 million ha, mainly in North and East Africa, South Europe and Southwest Asia. More recent figures (Driessen and Dudal, 1989; FAO, 1990) increase the extent of gypseous soils to 100-150 million ha, with major areas in the Middle East and the southern parts of the former USSR. Also at regional level, data provided by Boyadgiev and Verheye (1996) show that gypseous soils are widespread in North, Central and East Africa (51,1 million ha), in North-Central Asia (16.5 million ha ) and South-Central Asia (2.1 million ha).This might still be an underestimation of the real extent, when data from individual countries are taken into account. Iran, for instance, has about 10 million ha of gypseous soils according to the above-mentioned global information sources, while a recent estimate based on the land capability map of the country at 1:250,000 scale, reaches a figure of 27-28 million ha, representing 16-17% of the country area (Mahmoodi, 1998). In an attempt to update the knowledge about the worldwide extent and distribution of gypseous soils, existing countrywide data were compiled as presented in table 1, using earlier inventories from Van Alphen and De Los Rios Romero (1971), Driessen and Dudal (1989), FAO (1990, 1993, 1998), Jafarzadeh (1991, 1996), Mashali (1993, 1996), Eswaran, Van den Berg and Almarz (1993), Boyadgiev and Verheye (1996), Mahmoodi (1998), among others. In total, gypseous soils amount to approximately 186 million ha, representing1.5% of the worldwide soil cover. Spatial aggregation shows a large concentration of gypseous soils in three main geographic regions, the Middle East (72 million ha), Eurasia (51 million ha) and the Mediterranean belt (37 million ha), together with minor areas unevenly distributed over the rest of the world. In some countries, gypseous soils cover as much as one-third of the total land area. SOIL CONSTRAINTS AND CROP TOLERANCE FAO (1993) has estimated the potential rainfed production area worldwide at 2580 million ha, which is considerably in excess of the land presently cultivated (756 million ha) in 91 developing countries, excluding China. In arid and semi-arid regions, low-productivity gypseous soils might be increasingly put under agriculture, but they require appropriate management practices to make their use sustainable in the future. Many factors affect plant growth in gypseous soils, including gypsum content within the root zone, depth to a gypsic layer, depth to impermeable layers, crop tolerance level and gypsum solubility. Also physical properties are often unfavorable, causing low water availability, slaking of loamy topsoils, piping and collapse of irrigation canals. Most research on nutrition and performance of crops grown in gypseous soils has been done under greenhouse and laboratory conditions, with little field experimentation. The tolerance, yield and product quality of many agricultural crops grown on soils with gypsum are not yet well known. FAO (1990) and Mashali (1996) have classified the main agricultural crops into five groups according to their sensitivity to gypsum: (1) tobacco is sensitive; (2) cotton, groundnut, potato and sunflower are semi-sensitive; (3) broad beans, sugar beet, sorghum, corn, soybean and sesame are semi-tolerant; (4) alfalfa, trifolium, wheat, barley, lentil, oat, tomato and onions are tolerant. When the gypsum content in the root zone is more than 40%, land is considered unsuitable for cropping. The management of gypseous soils requires a set of agronomic practices depending on a careful definition of crop requirements. This should be based on investigation of topography, soil characteristics (structure, texture, water holding capacity, salinity, drainability and forms of gypsum), climate, community conditions (economic, social, political and cultural environment), local knowledge and existing farming systems (Mashali, 1996). CHEMICAL PROPERTIES AND FERTILIZER REQUIREMENTS The effect of gypsum on crops depends on several factors including nature, solubility, form, amount, horizontal and vertical distribution, and depth of gypsum accumulation in the soils (Mashali, 1996). Nitrogen, phosphorus and trace elements are virtually always needed to optimize crop production, together with potassium and magnesium in some cases. In soils with gypsum, almost all crops show deficiency of most plant nutrients, in particular phosphorus and micronutrients. Barzanji et al. (1981) reported that soil fertility can be a limiting factor for crop production, especially in places where excessive gypsum (>50 %) is present at shallow depth. Considering the influence of gypsum content on structure, aeration, moisture retention, solubility of gypsum as a function of seasonal soil moisture conditions, and the crop tolerance level, Boyadgiev and Verheye (1996) distinguished five classes of gypsum content in the solum and root zone: 0-3% low, 3-10% medium, 10-25% medium to high, 25-40% high and >40% very high, the latter being unsuitable for cropping. Therefore, fertilizer requirements should be assessed for various crops with regard to depth and amount of gypsum. Similarly, the rates of fertilizer application should be based on farming practices, local conditions, crop species and varieties, and soil characteristics (Mashali, 1996). In the irrigation scheme of the Ebro Valley, Spain, 70 kg N per ha as ammonium nitrate are applied before wheat and sugar beets are sown (Mashali, 1996). Sugar beets receive an additional 100 kg N per ha. For wheat, a top dressing of 50-60 kg N per ha as ammonium nitrate or ammonium sulphate is applied. In places where wheat is sown in the cold season when nitrification is inhibited, it is more profitable to apply complex fertilizers with about half of the nitrogen content in the form of nitrate rather than ammonium or urea, since the nitrate-N is preferred for uptake by wheat before the soil warms up. In Mexico, the rate of nitrogen application to wheat and sugar beet ranges between 70 and 140 kg per ha (FAO, 1990). On Typic Haplogypsids in the Balikh Basin of Syria, wheat and sugar beet need 150 kg N per ha (Mardoud, 1996a), while Barzanji et al. (1981) recommended a dose of 80-160 kg N per ha for wheat in Irak, depending upon the initial soil fertility status, for a soil having a gypsic layer at shallow depth (25-50 cm). The grain/straw ratio of wheat decreased with increasing levels of N but increased by adding phosphate (Mashali, 1996). In gypseous soils there are more calcium ions in the soil solution and, for this reason, crops need higher phosphorus application than in non-gypseous soils. Like N application, phosphorus application should be according to crop requirements, local conditions, amount of gypsum and gypsic layer depth. Sugar beets and cotton receive 45 and 50 kg P2O5 per ha as superphosphate, respectively, but irrigated alfalfa is given up to 450 kg per ha (Van Alphen and De Los Rios Romero, 1971). In Tunisia, Amami et al. (1967) reported a dressing of only 150 kg P2O5 per ha as superphosphate for irrigated alfalfa. On Typic Haplogypsids, wheat, cotton and sugar beet need 80-100 kg P2O5 per ha and corn needs 50 kg P2O5 per ha (Mardoud, 1996b). Discussion about the need for potassium fertilizer on irrigated and non-irrigated gypseous soils has been under way for some time. In general, at equal content of exchangeable K, the concentration of potassium in the soil solution varies considerably depending on pH, amount and type of CaCO3, amount and type of clay, and amount and form of gypsum present (FAO, 1990). The K:Ca and Mg:Ca ratios in the soil solution are very low when the gypsum content is high, resulting in a very low uptake of K and Mg from the soil solution, which accounts for low crop yields (Van Alphen and De Los Rios Romero, 1971). In general, it is recommended to apply 30-50 kg K2O per ha to a range of crops including wheat, maize, alfafa and cotton in irrigated land, but Barzanji et al. (1981) found no response of wheat to potassium application. Under rainfed conditions, plants grown in gypseous soils may not suffer from K or Mg deficiencies, because potassium and magnesium cations leached during the wet season can return to the surface during the drier part of the year and become available to plants. Potassium fertilizer application is essential on soils with gypsum in places where fruit trees, vegetables and grasses are intensively cropped, because potassium increases the resistance to certain diseases, helps to overcome water stress and improves the quality of crops. The availability of micronutrients is affected by the presence and level of gypsum, but also by the negative effect of phosphorus and possibly potassium fertilizers added in large doses (FAO, 1990). The application of zinc in gypseous soils reduces the rate of uptake of Cu, Mn and, to some extent, Fe because of ion competition (Safaya, 1976). In Iraq, Barzanji et al. (1981) found negative correlation between gypsum content and Mn and Fe availability, but only weak negative correlation with Zn and Cu. They concluded that the availability of Mn, Fe and maybe Cu and Zn, is likely to be adversely affected by excessive gypsum content near the soil surface. In general, yield is not limited by one kind of micronutrients alone. Major factors influencing the micronutrient status and requirement include pH, gypsum content, calcium content, irrigation water quality, amount and application system (Devaux, 1980), soil texture, increasing use of NPK (Finck, 1984; Fritz et al., 1984), use of high yielding varieties (El-Fouly, 1983; Fritz et al., 1984;) and climatic conditions (Sillanpaa and Vlek, 1985). Therefore, more information is needed on the interactions between micronutrients and conditioning factors. PHYSICAL CONDITIONS AND TILLAGE In general, the physiographic setting where gypseous soils tend to occur favors runoff. High erosion rates were registered on Gypsic Calcisols with lithic phase. Microtopography is mostly irregular to undulating, with elevation differences of less than one meter (Mashali, 1996). Often land leveling is needed to increase irrigation water use efficiency and application uniformity, especially in furrow, flood and basin irrigation systems. Irrigation must be carefully conducted to avoid excessive water percolation beneath the root zone to gypsum-rich layers. Special consideration must be given to tillage in soils with hard gypsum layer or surface crusting. Tillage is carried out to prepare the seedbed, break the surface crust and improve water infiltration, but tillage might also contribute to the formation of an impermeable layer if improperly executed. The selection of the right plough type, tillage sequence, ploughing depth and moisture content at the time of ploughing should provide good tilth, improve soil structure and break surface crusts (Mashali, 1996). In soils with surface crust and in shallow soils, germination rate is low and it is difficult to obtain a statisfactory stand of crops. According to Jafarzadeh et al. (unpublished), penetration resistance of gypsum crust is controlled by texture (38%), NaCl (21%), water table height (15%), gypsum (9%) and CaCO3 (5%). EFFECT OF ORGANIC MANURE According to Hazzah et al. (1986), organic manure in amounts of 12-24 t per ha improved the chemical and physical properties of gypseous soils with a significant increase in crop production (e.g. millet). They have reported that poultry manure had more effect on vegetative growth, while cattle manure had more effect on soil physical properties and root growth. Studies on the gypseous soils of the Aldoor experimental farm in Iraq showed that addition of 12-24 t cattle manure per ha improved soil water retention, infiltration rate, structure and aggregate stability, with yield increase of wheat and broad beans (Mashali, 1996). Nafie (1989) also mentioned that the application of organic manure in gypseous soils of Iraq significantly increased the fresh and dry weight of shoots and roots, plant height, tiller height and number, while decreasing the compressive strength of wheat. WATER MANAGEMENT, IRRIGATION AND DRAINAGE Yields of 3-4 t of wheat grain per ha were obtained in Spain, Syria and Iraq using irrigation on soils with gypsum. The suitability of gypseous soils for irrigation in arid and semi-arid regions depends on several factors such as texture, structure, water holding capacity, relief and micro- relief, depth to a layer limiting root penetration, form and content of gypsum in different layers, salinity and drainage, with their relative importance related to factors such as climate, type of crops and soil management (Van Alphen and De Los Rios Romero, 1971). Soils with a gypsic layer at 30-60 cm depth are moderately suitable for irrigated agriculture and give relatively good yields for many crops, provided the surface layer is fine-textured. If the texture of the surface layer is medium to coarse, the suitability is poor. Mousli (1981) stated that a soil with a gypsic layer at 60 cm depth and a maximum of 20% gypsum content in the top 60 cm can be placed under irrigation, preferably sprinkler irrigation. In general, shallow soils containing less than 15% gypsum in the surface 20 cm and a maximum of 40% in the 30-60 cm layer may be used with some reservation for irrigated shallow-rooted crops, using localized irrigation or sprinkler systems with precisely metered water application rates (Mashali, 1996). But the quality of the water that can be stored in the root zone becomes marginal when a gypsic or calci-gypsic layer is at less than 60-75 cm depth (Driessen and Dudal, 1989; FAO, 1990). Using slightly saline water, having common ions with gypsum (i.e. Ca2+ or SO2-), will decrease gypsum solubility. Using well water with high concentrations of calcium and sulphate ions, even if it contains similar amounts of chloride or sodium, inhibits terrain subsidence and sinkhole formation (Mashali, 1996). The method and frequency of irrigation and the amount of irrigation water applied are of prime importance when gypseous soils are put under irrigation. Al-Kubaisi (1988) observed gypsum mobilization after dissolution under flood irrigation because of the high amounts of irrigation water applied in short periods. This did not occur with sprinkler irrigation. He also noted that the germination rate was higher (90%) with sprinkler irrigation than with flood irrigaton (80%), probably due to the hardness of the surface crust formed under flood irrigation. Leaching requirements depend on the salt content of the soil and irrigation water and on the maximum salt concentration permissible in the soil solution, which in turn depends on the salt tolerance of the growing crop. An effective drainage system is required to maintain the water table low and control salinity. The optimum depth and spacing of field drains are governed by several factors, of which the most important are the construction costs, soil texture and structure, depth to and gypsum content of the gypsic layer, hydraulic properties of the soil mantle, optimum depth to the water table and its salinity (Mashali, 1996). THE HUMAN CONTEXT Gypseous soils often occur in densely populated areas within arid and semi-arid environments with irrigated agriculture. With increasing population, land management needs to be improved to increase and sustain crop yields. According to Mashali (1996), attention must be given to the following aspects: (1) development of appropriate technology; (2) adequate infrastructure and appropriate socio-economic conditions for the application and adoption of proper technology (3) strong and effective extension service able to support technical improvements. In general, gypseous soil management decisions should be based on cost-benefit analysis, including feasibility studies and environmental impact assessment (Mashali, 1996). A special development authority is necessary for the organization, operation and maintenance, and a sufficient budget of local funds must be reserved. CONCLUSION Worldwide, soils with gypsum cover 186 million ha, representing 1.5% of world land surface reported by FAO (1993). Although the properties and productivity of gypseous soils have been studied by many researchers at country level, measures have not always been directed to the heart of the problem. A basic precaution to be taken before development of gypseous soils for agriculture is studying their chemical, physical, biological and hydrological properties and calling for appropriate management practices in an integrated system. This could be achieved through technology transfer between countries and adaptive research on a regional and global basis.  REFERENCES Al-Kubaisi A.A.J. (1988) Effect of sprinkler and basin irrigation methods on some properties of Al Dour gypsiferous soils and growth of corn plant. MSc. Thesis, University of Baghdad, Iraq. Amami S., El-Baldy Ch., Pouget M.J. (1967) Rénovation d'une palmeraie littorale ancienne, étude de la remise en culture intensive. Annales Inst. Nat. Rech. Agron. de Tunisie, Vol.40, Fasc.8. Barzanji A.F., Paliwal K.V., Mittu K.T., Abbas H.A. (1981) Fertility status of the gypsiferous soils of Iraq. Technical Bulletin 94. Research Centre for Gypsiferous Soils, Aldour, Iraq. Bongaart J. (1994) Can the growing human population feed itself? Scientific American, March 1994: 36-42. Boyadgiev T.G., Verheye W.H. (1996) Contribution to a utilitarian classification of gypsiferous soils. Geoderma 74: 321-338. Devaux R. (1980) Fertilization of the citrus in Morocco. In: M.M. El-Fouly (ed). Proceedings 2nd Workshop on Micronutrients in Plant Nutrition. Mariut, Egypt: 89-111. Driessen P.M., Dudal R. (eds) (1989) The major soils of the world. Lecture notes on their geography, formation, properties and use. Agricultural University Wageningen, the Netherlands, and Katholieke Universiteit Leuven, Belgium. El-Fouly M.M. (1983) Micronutrients in arid and semi-arid areas: levels in soils and plants and the need for fertilizers with reference to Egypt. Proceedings 17th Colloquium of the International Potash Institute: 163-173. Eswaran H., Van den Berg E., Almarz R. (1993) Global distribution of Aridisols and their characteristics. Proceedings Int. Workshop on Classification and Management of Arid Desert Soils. Uramqi, China: 388-405. FAO (1989) Yearbook. Rome, Italy. FAO (1990) Management of gypsiferous soils. Soils Bulletin 62. Rome, Italy. FAO (1993) Agriculture: Toward 2010. Rome, Italy. FAO (1998) World Reference Base for Soil Resources. World Soil Resources Report 84. Rome, Italy. Finck A. (1984) Micronutrient problems in high yield cropping. In: E. Watte and I. Szabolcs (eds). Proceedings 9th World Fertilizer Congress. Budapest, Hungary, 1: 263-267. Fritz A., Jurgens G., Wichmann W. (1984) Micronutrient fertilization. Means to increase and secure production. International Colloqium Optimization of Plant Nutrition. Montpellier, France. Hazzah A.H., Al-Rawi A.A.H., Abdul Ameir A.R. (1986) Effect of some organic fertilizers on the properties of gypsiferous soils and the growth of millet (Panicum miliacum). Symposium on Gypsiferous Soils - Their Effect on Construction and Agricultural Production. Baghdad. Iraq. Jafarzadeh A.A. (1991) Experimental studies of gypsum migration and deposition in soil profiles. PhD Thesis, Wye College, University of London, U.K. Jafarzadeh A.A. (1996) Gypsum formation and classification of gypsiferous soils. Agricultural Sci. Scientific J.Vol.6 (1,2). College of Agriculture, University of Tabriz, Iran. Jafarzadeh A.A., Zinck J.A., Burnham C.P. (unpublished). Penetration resistance of gypsum crust from laboratory experiments. Mahmoodi S. (1998) Gypsiferous soils: characteristics, management and land suitability evaluation. Soils and Water, Special Issue, Vol.12 (3). Mardoud T. (1996a) Behavior of roots and properties of soils with different content of gypsum under irrigation (Balikh Basin, Syria). In: R.M. Poch (ed). Proceedings Int. Symp. on Soils with Gypsum. Lleida, Spain. Mardoud T. (1996b) Main results of field experiments on irrigated soils with gypsum in Granada Station, Syria (1973-1984). In: R.M. Poch (ed). Proceedings Int. Symp. on Soils with Gypsum. Lleida, Spain. Mashali A.M. (1993) Management practices for gypsiferous soils under irrigated conditions. Proceedings Int. Workshop on Classification and Management of Arid Desert Soils. Uramqi, China. Mashali A.M. (1996) Soil management practices for gypsiferous soils. In: R.M. Poch (ed). Proceedings Int. Symp. on Soils with Gypsum. Lleida, Spain. Mousli O.F. (1981) Methods of evaluation and classification of gypsiferous soils and suitability for irrigated agriculture. Soil Taxonomy Workshop, ACSAD, 1980: 278-320. Nafie F.A.A. (1989) The properties of highly gypsiferous soils and their significance for land management. PhD Thesis, Wye College, University of London, UK. Safaya N.M. (1976) Phosphorus-zinc interation in relation to adsorption rates of phosphorus, zinc, copper, manganese and iron in corn. Soil Science Society of America Journal 40: 719-722. Sillanpaa M., Vlek P.G.L. (1985) Micronutrients and the agroecology of tropical and Mediterranean regions. Fertilizer Research 7: 151-167. Van Alphen, De Los Rios Romero F. (1971) Gypsiferous soils, notes on characteristics and management. Int. Inst. of Land Recl. and Improv. Bulletin 12. Wageningen, the Netherlands. |