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by Prof. Andrei SMAGIN, Dr. Sc. (Biol.), Soil Science Department, M. V. Lomonosov State University
The sustainable development concept upheld by many people the world over presupposes a harmonious interaction between man and nature. It calls for a thrifty and scientifically validated approach in the exploration and use of natural resources. Of soil, too - this treasurehouse of fertility. It is only by taking account of all the characteristics proper to this open, dynamic and biologically conserved (inert) system that we can cultivate land in a rational way. The successful record of our unorthodox and comprehensive technologies of landscape gardening on arid land tracts is a graphic example.
Sloil formation takes centuries and millennia. I Generations of plants and animals enrich soil strata with substances and energies vital for the growth and reproduction of subsequent generations Ancient landtillers, though not versed overmuch in soil management, realized that the fertile value of soil depends primarily on its organic components - humus in particular, and they made a wide use of organic fertilizer. Actual methods and practices differed depending on land and region, though: in Russia and elsewhere in Europe one plowed in manure, compost and stubble remains, while in ancient Egypt and Mesopotamia they practiced runoff (flood-fed) farming, and in ancient China and in the Low Countries-built multilayer soil structures. That was laborious and time-consuming work, but it improved soil fertility, and the coming generations of people could thus inherit flourishing fields and gardens. Technical progress has reoriented agricultural practices to a full-scale use of mineral fertilizer and chemicals to combat weeds and pests - pesticides, herbicides and other weed- and pest-killers. In arid regions artificial irrigation has been developing apace, with no restrictions for irrigation and watering norms, and water quality; all that regardless of the possible impact on the ambient environment. But these are opportunistic, hit - and - run approaches - get bumper crops at min-
Monitoring of the state of natural media: A - salinization trend for irrigation water; B - salinization trend for soil.
These data are by courtesy of the Ministry of Municipalities Affairs and Agriculture of the Kingdom of Bahrain.
Desalinization dynamics for soil structures (according to electroconductivity) in a green lawn growing experiment (Dubai, 1995).
imum labor expenses. As a result, soil fertility has been deteriorating. According to the statistics supplied by the UN Food and Agricultural Organization (FAO), from 1972 to 1999 the area of irrigated dry land farming doubled worldwide, with 30 to 80 percent of irrigated lands turning salinized and abandoned, fully or in part. Desert encroachment (desertification) and degradation of soil have affected large tracts of Iran, Iraq, Jordan, Syria and many other Arab countries, including the advanced and rich states of the Persian Gulf, where billions of dollars have to be spent on planting trees, gardens and cultured vegetation. Surveying the condition of irrigation waters and soil on a selective basis in 1994 to 2002, the Ministry of Municipalities Affairs and Agriculture of the Kingdom of Bahrain promulgated alarming figures on the disastrous rates of secondary salinization.
All this points at the bad ecological problem of arid zones instead of the hoped-for success. Why so? Can present - day science come up with better, innovative technologies instead of intensive irrigated farming? What ways and means are needed for that? Will alternative soil management techniques pay off? We shall try to answer these and related questions insomuch as the space of a magazine article will permit. Our findings are based on the theory of the physical state and performance of soils as dynamic and biologically conserved (inert) systems - a theory advanced and developed at the Soil Science Department and at the Institute of the Ecological Soil Science of M. V. Lomonosov Moscow State University.
The main cause of soil mismanagement in arid areas, where intensive irrigated farming is practiced, resides in the selective approach to landscape gardening, which has an adverse effect on soil conservation. The stake is on open-ended watering and soluble nutrients. Meanwhile soil has not become an object of investments and technologies, it is regarded only as a medium for plant roots and elements of an irrigation system. In fact, such agriculture amounts to hydroponics* applied on a far wider scale.
Yet sustainable (balanced) agriculture should be concerned above all with soil and its functions - often rather complicated and nonlinear-making for the stability, productivity and adequate ecology of landscapes. This kind of knowledge allows proper soil management, it allows to design and use dry land farming without adverse aftereffects. This very approach is a basis of the new technologies of sustainable agriculture in arid climates-technologies developed by Russian soil scientists with financial support from the Russian-Arab NOP-NASS Company, the Russian Fund of Basic Research and the Fund for the Advancement of Russian Science.
* Hydroponics (tank, or tray agriculture) - plant growing without soil by means of injecting a nutrient solution into an artificial substrate. The quality of the end produce is advisedly downgraded thereby - Auth.
Our type plan is in several parts. First and foremost, it provides for soil-and-landscape designing. Next come optimal regimes and modes of irrigation, and pre-emptive measures against secondary salinization. Besides, optimal plant cultures should be selected; their setting time and schedules as well as further cultivation should be determined exactly. Steady ecological support and monitoring by modern instrumental methods is also an important line of our design plan. If need be, it may be supplemented with other procedures, too.
What we call konstruktozems, or structural soils, are the last word in geoecology and landscape architecture. Such skeletal soils are designed with optimal fertility characteristics on the basis of natural resources supplemented with natural or synthetic materials (synthetic soil conditioners). The layered embedding of substrates imitating the natural soil horizons (different in their functional characteristics) has been found to be the most productive method. The basic element of this structure is the uppermost layer ("working layer" in our terminology), where plant roots consuming nutrients and moisture are concentrated. Added to this surface layer are natural or synthetic biopolymers increasing the reserve of nutrient substances in the substrate and optimizing its structure, thermal and hydrophysical characteristics and, in the long run, boosting fertility. Common for this purpose are organic fertilizer, compost, peat and humous preparations; the arsenal of synthetic substances includes ion-exchange resins and strong swelling hydrogels (SHG).
Russian companies have been developing and supplying to international markets two products: solid soil conditioners (Complicated Organic Fertilizer, COF) and liquid ameliorants (humates) produced from domestic stock like high-ash fen peats, sapropels and brown coal (lignites) with mineral additives in the form of macro- and microelements. Owing to the high dispersibility and sorption capacity of the materials (specific surface - 300 - 600 m2/g, absorbing capacity-up to 1500 - 5000 mmol/kg), nutrients and water are fixed in forms readily assimilated by plants. Even rather small supplements - 10 percent COF and 0.1 percent SHG - to the initial sand substrate impart to it a moisture-holding capacity proper to fine loam soil.
The fertile layer density, depth of conditioners' embedding and the number of structural layers are calculated depending on the specifics of an object (its granulometric composition, fertility indicators, degree of salinization and pollution, soil hydrophysical and thermal characteristics, parent and basement rocks, relief features, level of subsoil waters, and so on); also, types and needs of cultivated plants as well the quality and durability of organic additives are considered. It is often the case that several fertile layers have to be formed so as to keep plant roots fully supplied with nutrients and moisture. Structural soil parameters are determined using equations of the theory of the physical state of soil and kinetic models of its dynamics. Such is the know-how of our project.
By placing the above materials in parallel horizons we can much improve the initial hydrophysical properties of fine soil-for one, cut dramatically (dozens of times over) the water expenditure for unproductive filtration (gravitational runoff). Yet another feature of layered structures is essential, namely the presence of breaks in what we call the "continuity (continuum) of soil capillaries". Such thin pores (capillaries) feed dissolved salts from the zone of their natural accumulation (subsoil horizons and mineralized subsoil waters) to surface soil; upon evaporation of moisture such salts are concentrated there. An interlayer of foreign substrate slows down this movement, down to complete blockage, if coarse-grained materials devoid of capillaries are used. Therefore we recommend multilayer structures mounted on a groundwork ("screen") of gravel, crushed stone
Water-holding capacity of sand substrates, natural and synthetic materials, and their mixes.
(ballast), expanded clay aggregate, coarse sand and similar materials.
Salt protective screens are of particular advantage in arid countries of the Persian Gulf, where the natural ground may contain 50 to 80 percent of limestone impurities usually sifted away from fine soil. However, it is advisable to put such inclusions in a 10 to 20 cm layer (4 to 8 inches thick) at the base of a multilayer soil structure. This bed will provide reliable protection to the superstructure against secondary salinization and help get stable crops. In rainfall it will act as a drainage collector. No extra expenses! A layered soil structure will help get rid - in a few months and once for all! - of detrimental salts in the root "working layer" at ordinary irrigation quotas. In analytical terms this fact was confirmed by a model study into the dynamics of soil electrical conduction made on experimental patches in the Emirate of Dubai in 1995.
There cannot be any universal types and parameters of soil structures. Arbitrary, rule-of-thumb arrangement of layers is impermissible: a screen of coarse-grained material built too deep in disregard of particular agronomy will make the root layer dry up and thus suppress the plants.
TO EACH PLANT ACCORDING TO ITS NEEDS
A complex of works on ecological and landscape architecture provides for an irrigation and, if necessary, a drainage system as well. Diverse hydrotechnical facilities (waterways, cascades, canals, ponds) can be created along with terraces, pathways, and so forth so as to prevent underflooding of houses, water and wind erosion of soils and their contamination, landslides and landslips, windfalls of trees in heavy showers, dust storms and other calamities. If need be, design plans and specifications should be filed by skilled landscape architects.
Irrigation-related problems call for particular attention. There are many different irrigation techniques, and each is detailed in our comprehensive project in terms of soil engineering technologies, water-and-salt control and management. The conventional manual technique of water feed is now ever more frequently complemented by automated, computer-assisted systems that make it possible to apportion the needed amounts of water, and pinpoint the rates and times of watering. Simple facilities employ programmed electronic switch timers in the form of checkers mounted on irrigation hoses or distributors. More sophisticated setups make use of feedback when irrigation is realized in keeping with instrumental readings on soil humidity (pressure or electric conductivity of soil moisture) and on the condition of plants.
It is common practice to expend more water than necessary because of the low moisture-holding capacity of arid soils and high losses caused by filtration and evaporation. For instance, the lawn grass Paspalum much cultivated in Persian Gulf countries needs a maximum of 8 l/m2 water daily, but twice as much is actually used here and there. In the municipal objects of Dubai the daily expenditure of water for lawn growing runs into 12 - 15 l/m2 in summertime, and in royal estates of Bahrain (Rowdah palace) it is as high as 15 to 18 l/m2.
The fundamental principle of our watering technology takes account of the evaporation and transpiration characteristics of plants depending on their physiological specifics, growth phases and likewise depending on soil properties (water-holding capacity and salt status), the atmosphere and quality of water. Each plant should get as much water as it is able to consume within a definite span of time not at the expense of its productivity. Precise engineering computations of irrigation parameters give significant economy of water and allow to half its expenditure without detriment to crops (and boost productivity at that). Secondary salinization is prevented, too. Our team has carried out a field experiment in lawn growing with the use of comprehensive technolo-
Data obtained in an experiment on green lawn growing in Dubai with the use of unorthodox comprehensive technologies (July-September, 1995).
gies and multilayer structures on the basis of Russian soil conditioners-peat and polymer hydrogels. We did this work at the experimental station of the Department of Horticulture and Landscape Gardening of the Dubai Municipality during the hottest time of the year (June-September 1995). Besides halfing the water consumption we got stable green produce 50 to 100 percent higher in biomass and chlorophyll content than on control patches cultivated by orthodox technologies.
Our agronomic techniques allow to minimize the impact of negative natural factors and make the best of the plants' potential. One essential condition is that plants should be selected with due account of their characteristics, productivity and tolerance (resistance). Say, if a land plot is much salinized and has no natural shade; if irrigation water is of poor quality and the owner of this plot has no time and money for drastic land improvement - in that case resistant, hardy cultures should be selected.
Once we have selected plants like that, we should determine optimal setting schedules and methods, calculate planted areas on an individual basis by making use of trigger growth models*, and also decide on adequate agronomic and cultivation techniques (soil management, fertilizer, pesticides, insecticides). Ecology and status monitoring is carried out with the use of the latest instrumental equipment including off-power electronic microsensors of the hygrochron type (USA) registering nonstop and memorizing data on temperature and humidity for a long time (1 to 2 years) of observations.
Soil design and sustainable agronomy models developed by us for arid climates on the basis of Russian soil conditioners have undergone all-round tests at different objects of the Persian Gulf area. These were experimental stations of the Ministries of Municipalities Affairs and Agriculture of the Kingdom of Bahrain, and of the Emirates of Dubai and Qatar, palatial and municipal complexes (Sakhir, Rowdah Palace, Supreme Lady Council) as well private villas in Bahrain. Most of the tested plants showed high stable results in root taking, and in growth and reproduction rates. Economy of irrigation water, fertilizer and money proved 50 to 100 percent.
Illustrations supplied by the author
* Nonlinear models of plants' death once growth parameters have reached critical values. - Aulh.
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