Showing papers on "Soil salinity published in 1996"

The nature and properties of soils

Abstract: 1. The Soils Around Us. 2. Formation of Soils from Parent Materials. 3. Soil Classification. 4. Soil Architecture and Physical Properties. 5. Soil Water: Characteristics and Behavior. 6. Soil and the Hydrologic Cycle. 7. Soil Aeration and Temperature. 8. Soil Colloids: Seat of Soil Chemical and Physical Activity. 9. Soil Acidity. 10. Soils of Dry Regions: Alkalinity, Salinity, and Sodicity. 11. Organisms and Ecology of the Soil. 12. Soil Organic Matter. 13. Nitrogen and Sulfur Economy of Soils. 14. Soil Phosphorus and Potassium. 15. Micronutrient and Other Trace Elements. 16. Practical Nutrient Management. 17. Soil Erosion and Its Control. 18. Soils and Chemical Pollution. 19. Geographic Soils Information. 20. Global Soil Quality as Affected by Human Activities. Appendix A: Canadian and FAO Soil Classification Systems. Appendix B: SI Unit Conversion Factors and Periodic Table of the Elements. Glossary. Index.

Review: the behaviour and environmental impact of contaminants in fertilizers

Abstract: The risks of contaminants accumulating in soils and crops due to inadvertent addition of impurities in agricultural fertilizers and soil amendments were assessed for Australian conditions. Elements considered of concern were arsenic (As), cadmium (Cd), fluorine (F), lead (Pb) and mercury (Hg). Consideration of background concentrations of these elements in Australian soils, inputs to soil in fertilizers and offtake in harvested crops indicates that Cd and F will accumulate in fertilized soils at a faster rate than As, Pb or Hg. The major factors affecting the accumulation of fertilizer-derived Cd, F, Hg and Pb in soils and their transfer to agricultural crops are reviewed in an Australian context where data are available. Cadmium is the element of most concern as its transfer from soils to the edible portions of agricultural food crops is significantly greater than for other elements. After consideration of the behaviour of F, Hg and Pb in the soil-plant system, we conclude that these elements pose negligible risk of accumulating to toxic concentrations in agricultural food crops. Proposed regulations governing maximum permitted concentrations (MPCs) of F in soils may need review and critical concentrations of F in agricultural soils need definition, given current F loadings to soil from fertilizers. Some agricultural produce currently exceeds Australian MPCs for Cd. However, the levels observed in crops and soils are in a range similar to those found internationally. While Cd concentrations in Australian phosphatic fertilizers have been historically high in comparison with fertilizers used in other countries, lower inputs of fertilizer per unit area and less atmospheric contamination of soils have resulted in similar or lower Cd loadings to agricultural land compared with Europe. In recent years the use of phosphatic fertilizers with lower Cd concentrations and the development of plant cultivars which restrict Cd uptake should assist in control of Cd accumulation by crops. However, acidification and salinization of soils in Australia poses a threat in terms of increasing Cd concentrations in agricultural produce. In comparison with other trace metals, Cd availability to plants appears to decline only slowly with time, if at all. More Cd is currently added to Australian soils than is removed in agricultural produce or by leaching. It is therefore important that the long-term behaviour of Cd in Australian soils be assessed, to determine if Cd concentrations in agricultural produce will slowly increase over time.

A positive feedback : herbivory, plant growth, salinity, and the desertification of an arctic salt-marsh

Abstract: 1 A 2-year study is described which suggests that a positive feedback process results in the destruction of salt-marsh swards and the exposure of bare sediments at La Perouse Bay, Manitoba, Canada. Lesser snow geese initiate the process by grubbing for roots and rhizomes of salt-marsh graminoids (Puccinellia phryganodes and Carex subspathacea) in spring. The increased rates of evaporation from sediments beneath disturbed or destroyed swards in summer result in high soil salinities that adversely affect the growth of the remaining grazed plants. 2 Above-ground biomass and soil salinity differed between sites in the salt marsh. Soil salinity was inversely related to above-ground biomass and shoot density of Puccinellia phryganodes. Increased biomass led to reduced soil salinity at sites where exclosures were erected. 3 Plant growth, measured as the rate of leaf births on Puccinellia shoots, was reduced by high soil salinities at sites where exclosures were erected. 4 Leaf demography of transplanted experimental plants of Puccinellia differed in 1992, but not 1991, between plants transplanted into sites with different amounts of above-ground biomass. Leaf births and deaths were highest for plants grown in sites where above-ground biomass was high and lowest for plants transplanted into bare sites. Grazing had no effect on leaf demography in 1991 and only marginally increased the rate of leaf deaths in 1992. 5 Growth of transplanted individuals of Carex subspathacea was similarly highest at sites where the standing crop of Puccinellia and Carex was high and was lowest in bare sites. 6 Algal crusts, which formed on bare or poorly vegetated sites, also reduced the growth of Puccinellia plants. 7 The effects of this deleterious positive feedback on plant growth are discussed in relation to changes occurring in the lesser snow goose colonies at La Perouse Bay and elsewhere.

Salinity Effects on Four Sunflower Hybrids

Abstract: Sunflower (Helianthus annuus L.) is becoming an increasingly important source of edible vegetable oil throughout the world because of its high polyunsaturated fatty acid content and no cholesterol. The increasing demand for this oil may promote increased hectarage of sunflower in the western USA, where some soils are saline or have the potential to become so. Since there is little information concerning the response of sunflower grown under saline conditions, a 2-yr field plot study was conducted. Six salinity treatments were imposed on a Holtville silty clay (clayey over loamy, montmorillonitic [calcareous], hyperthermic Typic Torrifluvent) by irrigating with Colorado River water artificially salinized with NaCl and CaCl2 (1:l by weight). Electrical conductivities of the irrigation waters both years were 1.4 (control), 2.0, 3.0, 4.0, 6.0, and 80 dS m-‘. Seed yield and oil content of the seed were measured. Relative seed yield of four hybrids was unaffected by soil salinity up to 4.8 dS m-’ (electrical conductivity of the saturation extract, EC,). Each unit increase in salinity above 48 dS m-t reduced yield by 5.0%. These results indicate that sunflower is appropriately classified as moderately tolerant to salinity. Yield reduction was attributed primarily to a reduction in seeds per head. Oil concentration in the seed was relatively unaffected by increased soil salinity up to 10.2 dS m-‘. Sunflower appears to be well adapted for growth under moderately saline soil conditions. S UNFLOWER (Helianthus annuus L.), a New World plant, has been developed into a valuable source of edible oil and meal. In 1992, world production of sunflower oil was about 7.8 million tonnes. As an edible vegetable oil, only soybean [Glycine max (L.) Merr.] and rapeseedcanola (Brassica napus L. and B. campestris L.) oil production exceeded that of sunflower (USDA, 1993). In the USA, about 839000 ha of sunflower were harvested in 1992, with oilseed hybrids constituting about 88% of the harvest and nonoilseed hybrids making up the remaining 12%. Most production in the USA is in Minnesota, North Dakota, South Dakota, and Kansas (USDA, 1993). However, with the increasing popularity of edible vegetable oils that, like sunflower, contain high percentages of polyunsaturated fatty acids and low cholesterol, the potential

Reduction of excessive bioavailable phosphorus in soils by using municipal and industrial wastes

Abstract: Poultry and swine production has created both economic growth in Oklahoma and concern over the effect of excessive land application of animal manure on water quality. The objectives of this study were to evaluate the ability of two drinking water treatment alum hydrosolids (HS1, HS2), cement kiln dust (CKD), and treated bauxite red mud (RM) to reduce excessive amounts of bioavailable P in soil and to determine potential environmental impacts from these treatments. Two soils that contained 553 and 296 mg kg -1 Mehlich III-extractable P, as a result of prior treatment with poultry litter or dairy manure, were mixed with amendments at the rate of 30 and 100 g kg -1 soil and incubated at 25°C for 9 wk. Reductions in Mehlich III-extractable P from 553 mg kg -1 to 250 mg kg -1 followed the trend HS2, CKD ≥ HS1 ≥ RM in the slightly acidic Dickson soil (fine-silty, siliceous, Thermic Glossic Fragiudult). Reductions in Mehlich III-extractable P from 296 mg kg -1 to 110 mg kg -1 followed the trend HS2 > HS1 > RM > CKD in the calcareous Keokuk soil (coarse-silty, mixed, Thermic Fluventic Haplustoll). Reduction of soluble P followed similar trends. Most treatments did not result in excessive soil pH or increases in soil salinity, in extractable Al, or in heavy metals in soils. Application of alum hydrosolids to soils with excessive amounts of bioavailable P in sensitive watersheds may improve drinking water quality and provide financial savings for municipalities.

Tomato Growth in Response to Salinity and Mycorrhizal Fungi from Saline or Nonsaline Soils

Abstract: Tomato (Lycopersicon esculentum Mill. 'Heinz 1350 VF 402') seedlings were inoculated with populations of vesicular-arbuscular mycorrhizal (VAM) fungi collected from saline or nonsaline soil or remained nonmycorrhizal as a control. Plants then were salinated for 8 weeks at 1.0, 2.0, 5.0, or 10.0 dS.m -1 produced by dilutions of 1 M NaCl : 1 M CaCl 2 in deionized water. Inoculation with VAM fungi from nonsaline soil enhanced shoot growth, while VAM fungi from saline soil suppressed shoot and root growth. Plants inoculated with VAM fungi from nonsaline soil and non-VAM control plants showed a quadratic increase in leaf Cl- concentration in response to an increased salinity level, whereas plants inoculated with VAM fungi from saline soil showed a linear increase in leaf Cl - concentration. Mycorrhizal-induced growth responses and changes in leaf Cl - concentration were not associated with any apparent alterations in tomato plant P status. Although VAM fungi originating from saline soil did not promote plant growth, reduction in leaf Cl - concentration mediated by these VAM fungi at moderate salinity levels may have beneficial implications for plant survival in saline soil.

Soil nutrients and salinity after long-term grazing exclusion in a Flooding Pampa grassland.

Abstract: Soil organic C, total N, extractable P, and salinity were evaluated after 12-16 years of protection from grazing in 2 native grassland sites which differed in frequency of soil waterlogging in the Flooding Pampa of Argentina. We tested the hypothesis that flooding regime would affect the impact of grazing on soil chemical properties. We sampled soil to 10-cm depth in adjacent grazed and ungrazed plots in each site, and assessed the percentage dissimilarity (PD) in vegetation composition among pastures. Grazing condition significantly interacted with site (p<0.001) in affecting topsoil C, N, and salinity. Soil C and N were higher in grazed grassland (C = 4.8%; N = 0.42%) than in long-term exclosure (C = 3.7%; N = 0.35%) for the more frequently flooded, lowland site, but did not vary between grassland plots in the upland site (C = 3.1%; N = 0.29%). Soil electrical conductivity (E.C.) was low in both ungrazed plots (< 2 dS/m), yet in grazed condition salinization was higher in the upland (E.C.= 6.85 dS/m) than in the lowland site (3.88 dS/m). Soil extractable P did not change in any consistent way with grazing treatment. Grazing apparently amplified differences in soil chemistry between lowland and upland sites, while differences in botanical composition between topographical positions were smaller for grazed (PD = 44%) than for ungrazed (64%) grassland. Moreover, contrasting responses between sites occurred for various soil parameters, whereas compositional differences between grazed and ungrazed plots were similar in each site (PD approximately 65%). Thus, soil-vegetation changes in response to grazing appeared to be loosely coupled in this rangeland ecosystem.

Salt‐tolerant forage cultivation on a saline‐sodic field for biomass production and soil reclamation

Abstract: Chemical reclamation of sodic and saline-sodic soils has become cost-intensive. Cultivation of plants tolerant of salinity and sodicity may mobilize the CaCO3 present in saline-sodic soils instead of using a chemical approach. Four forage plant species, sesbania (Sesbania aculeata), kallar grass (Leptochloa fusca), millet rice (Echinochloa colona) and finger millet (Eleusine coracana), were planted in a calcareous saline-sodic field (ECe = 9·6–11·0 dS m−1, SAR = 59·4–72·4). Other treatments included gypsum (equivalent to 100 per cent of the gypsum requirement of the 15 cm soil layer) and a control (no gypsum or crop). The crops were grown for 5 months. The performance of the treatments in terms of soil amelioration was in the order: Sesbania aculeata ≅ gypsum > Leptochloa fusca > Echinochloa colona > Elusine coracana > control. Biomass production by the plant species was found to be directly proportional to their reclamation efficiency. Sesbania aculeata produced 32·3 Mg forage ha−1, followed by Leptochloa fusca (24·6 Mg ha−1), Echinochloa colona (22·6 Mg ha−1) and Eleusine coracana (5·4 Mg ha−1). Sesbania aculeata emerged as the most suitable biotic material for cultivation on salt-affected soils to produce good-quality forage, and to reduce soil salination and sodication processes.

Vesicular - arbuscular mycorrhizae in prairie pothole wetland vegetation in Iowa and North Dakota

Abstract: Vesicular–arbuscular mycorrhizae (VAM) fungal colonization was measured in June and August 1993 for 19 plant species in several vegetation zones in three wetlands in central Iowa and in three wetlands in North Dakota, U.S.A. Percent VAM fungal colonization in all the plants sampled varied greatly with species, ranging from 0.2 to 52.1% (mean = 13, SE = 2.4) in Iowan wetlands and 7.3 to 71.8% (mean = 32, SE = 4.7) in North Dakotan wetlands. The Iowan wetlands had more fertile soils (higher organic matter, higher phosphorus, and lower pH) than the North Dakotan wetlands. Soil salinity was higher in the North Dakotan wetlands. A principal components analysis of environmental factors (soil water matric potential, soil pH, available soil phosphorus, soil specific conductance, and season) indicated that when data for all plant species were pooled, there were only three significant components: location (which reflected differences between Iowa and North Dakota in soil pH, phosphorus, specific conductance, and se...

Foliar and root absorption of Na+ and Cl− in maize and barley: Implications for salt tolerance screening and the use of saline sprinkler irrigation

Abstract: Above-canopy sprinkler irrigation with saline water favours the absorption of salts by wetted leaves and this can cause a yield reduction additional to that which occurs in salt-affected soils. Outdoor pot experiments with both sprinkler and drip irrigation systems were conducted to determine foliar ion accumulation and performance of maize and barley plants exposed to four treatments: nonsaline control (C), salt applied only to the soil (S), salt applied only to the foliage (F) and salt applied to both the soil and to the foliage (F+S). The EC of the saline solution employed for maize in 1993 was 4.2 dS m−1 (30 mM NaCl and 2.8 mM CaCl2) and for barley in 1994, 9.6 dS m−1 (47 mM NaCl and 23.5 mM CaCl2). The soil surface of all pots was covered so that in the F treatment the soil was not salinized by the saline sprinkling and drip irrigation supplied nutrients in either fresh (treatments C and F) or saline water (treatments S and F+S). Saline sprinkling increased leaf sap Na+ concentrations much more than did soil salinity, especially in maize, even though the saline sprinkling was given only two or three times per week for 30 min, whereas the roots of plants grown in saline soil were continuously exposed to salinity. By contrast, leaf sap Cl− concentrations were increased similarly by saline sprinkling and soil salinity in maize, and more by saline sprinkling than saline soil in barley. It is concluded that barley leaves, and to a greater extent maize leaves, lack the ability to selectively exclude Na+ when sprinkler irrigated with saline water. Moreover, maize leaves selectively absorbed Na+ over Cl− whereas barley leaves showed no selectivity. When foliar and root absorption processes were operating together (F+S treatment) maize and barley leaves accumulated 11–14% less Na+ and Cl− than the sum of individual absorption processes (treatment F plus treatment S) indicating a slight interaction between the absorption processes. Vegetative biomass at maturity and cumulative plant water use were significantly reduced by saline sprinkling. In maize, reductions in biomass and plant water use relative to the control were of similar magnitude for plants exposed only to saline sprinkling, or only to soil salinity; whereas in barley, saline sprinkling was more detrimental than was soil salinity. We suggest that crops that are salt tolerant because they possess root systems which efficiently restrict Na+ and Cl− transport to the shoot, may not exhibit the same tolerance in sprinkler systems which wet the foliage with saline water. ei]T J Flowers

Soil, Water and Plant Characteristics Important to Irrigation

Abstract: Irrigation, applying water to assure sufficient soil moisture is available for good plant growth, as practiced in North Dakota is called "supplemental irrigation" because it is used to augment the rainfall that occurs during the growing season. Irrigation is used on full season agronomic crops to provide a dependable yield every year. It is also used on crops where water stress affects the quality of the yield, such as flowers, vegetables and fruits.

Root dynamics of Melaleuca halmaturorum in response to fluctuating saline groundwater

Abstract: Melaleuca halmaturorum is a salt and waterlogging tolerant tree and thus often occurs in saline areas fringing permanent wetlands and in ephemeral swamps. The dominance of this tree in natural groundwater discharge areas may result in M. halmaturorum transpiration making a major contribution to groundwater discharge. To quantify this the seasonal changes in tree water sources in response to fluctuating soil salinity and waterlogging were examined. This study was conducted in a natural system where seasonally fluctuating saline groundwater (64 dS m−1; 0.3–1.2 m deep) allowed the patterns of M. halmaturorum root water uptake to be followed over a 15 month period. Tree water sources were examined using the naturally occurring stable isotopes of water, while new root growth was examined using a field root observation window and from soil cores. The presence of isotopic fractionation of 2H under conditions of soil salinity and waterlogging was tested in a glasshouse experiment. Measurements of soil and leaf water potential were also made to examine the possible water sources and limits to water uptake. No isotopic fractionation was found by tree roots under conditions of salinity and waterlogging. M. halmaturorum trees were active in taking up groundwater at most times and combined this with a shallower soil water source replenished by rainfall in winter. Water uptake was concentrated in the deeper parts of the soil profile when the groundwater was at its deepest and salt had accumulated in the surface soils, at the end of summer. When groundwater rose, at the end of winter, roots responded by extracting water from near the soil surface (0–0.1 m), at the new watertable. This pattern of water uptake in response to groundwater fluctuations and salt accumulation in the surface soil was also reflected in new root tip appearance at the root observation window. Fluctuations in leaf water potential fallowed fluctuations in surface soil (0.1 m depth) water potential at all times. In winter leaf water potential reflected the absolute values of the surface soil water potential but in summer it was between surface soil and groundwater water potentials. We conclude that M. halmaturorum used groundwater in summer and a combination of rainfall and groundwater from the surface soils in winter. The ability to take up water from saline substrates through the maintenance of low leaf water potential, combined with this ability to rapidly alter root water uptake in response to changes in soil water availability contributed to the survival of M. halmaturorum in this saline swamp.

Contribution of Individual Culms to Yield of Salt-Stressed Wheat

Abstract: Grain yield in wheat (Triticum aestivum L. emend. Thell.) is highly dependent upon the number of spike-hearing tillers produced by each plant. Soil salinity can greatly decrease their number and productivity. Knowing the contribution of specific tillers is essential for breeding salt-tolerant genotypes and for developing wheat growth simulation models. Our objective was to determine the effects of soil salinity on the contribution of individual cuhns to total grain and dry matter yields of two spring wheat cultivars, Anza and Yecora Rojo. Plants were grown in Pacbappa fine sandy loam soil (mixed, thermic, Mollic Haploxeralf) in outdoor lysimeters for 2 yr. Three salinity treatments were imposed by irrigating with waters containing equal weights of NaCl and CaClr (electrical conductivities z 1, 12, or 18 dS m-r). Despite substantial losses in the number of tillers at moderate levels of salt stress, grain yields of the main stem (MS) and tillers Tl and T2 were as great or greater than those on nonstressed plants of both cultivars. The contribution of the MS to yield on a land area basis increased from about 25 to 35% in nonsaline treatments to over 80% with increasing salinity. The contribution of primary tillers (E 5865% in nonsaline conditions) decreased substantially only at the highest salinity levels. Salinity stress significantly decreased the number of spikelets per spike but the number of kernels per spike either increased or was unaffected except at the highest level of stress. Increasing salinity decreased total straw yields primarily because of fewer tillers, but dry weights of the MSs and remaining tillers were also smaller. Results show that loss of spike-bearing tillers accounts for most of the yield reduction in salt-stressed wheat.

Inula crithmoides: A candidate plant for saline agriculture

Abstract: Inula crithmoides L., a common halophyte from the coast of Lebanon was evaluated for use in saline agriculture. The plant is traditionally consumed in Lebanon and is claimed to have medicinal properties. Inula crithmoides offshoots were collected from the wild and propagated in a controlled environment. Germination and rooting tests under various salinity regimes ranging from 0.5 to 80 dS m‐1 (NaCl) demonstrated a severe restriction of germination above 20 dS m‐1 and indicated that vegetative propagation is probably the main reproduction strategy in saline environments. The growth of potted plants grown under 5 levels of salinity for a period of 87 days was only affected by salinity exceeding 20 dS m‐1. Yield of plants irrigated with 40 dS m‐1 saline water was nearly half that of the no‐salt control. Mean yield value for plants grown at 20 dS m‐1 reached 18.3 g dry weight (DW) per plant. At this salinity, crude protein content averaged 12.7% mg kg‐1, and shoot iodine contents ranged between 0.8 and 1.4 mg...

Growth and Photosynthetic Responses of Scaevola sericea, A Hawaiian Coastal Shrub, to Substrate Salinity and Salt Spray

Abstract: Growth patterns, water relations, and photosynthetic traits in Scaevola sericea plants grown under different levels of substrate salinity and salt spray were studied. Scaevola sericea is a dominant shrub species in coastal strand ecosystems throughout the tropical and subtropical Pacific and Indian Oceans. Seventy-two cuttings from two coastal sites on the island of Oahu (Hawaii) were grown in a greenhouse under six treatments that resulted from the combination of three levels of substrate salinity (0, 100, and 335 mOsm kg-1) and two levels of simulated salt spray (0 and 1200 mg salt m-2 d-1). Several characteristics of S. sericea were strongly affected by substrate salinity but only weakly affected by salt spray. New stem and leaf biomass per plant decreased by ca. 65% as substrate salinity increased from 0 to 335 mOsm kg-1; photosynthetic rates decreased by only 20% over the same salinity range. Leaf sap osmolarity increased 300 mOsm kg-1 as substrate salinity changed from 0 to 335 mOsm kg-1, allowing t...

Potentiality of Landsat, SPOT and IRS satellite imagery, for recognition of salt affected soils in Indian Arid Zone

Abstract: Landsat, SPOT and IRS data, black and white and false colour composite (FCC) imagery of the summer (April, May), rainfed crop season (October) and winter irrigated crop season (January, February) of Indian Arid Zone were interpreted for recognition or three types of salt affected soils, viz. (1) natural salt affected; slight, moderate and severe, (2) saline soils due to saline water irrigation, (3) sodic soils due to high residual sodium carbonate (RSC) water irrigation. These were field checked and supported by analytical data. The Landsat-MSS band 4 could only provide the overall extent of salinity. The moderate and severe natural salt affected soils were identified by Landsat-MSS band 2, Landsat-MSS and TM, IRS LISS-I and LISS-II and SPOT HRV2 data for April and January. But the differentiation between the saline and sodic soils was possible only by the use of multi-date imagery (October and January) and the clue provided by the cropping pattern. The potentiality of remote sensing data product...

Seed germination and salinity tolerance in plant species growing on saline wastelands

Abstract: Seven plant species including three chenopods:Suaeda fruticosa, Kochia indica, Atriplex crassifolia and four grasses:Sporobolus arabicus, Cynodon dactylon, Polypogon monspeliensis, Desmostachya bipinnata, varied greatly in their seed germination and growth responses to soil moisture or salinity. The germination percentage of each species was significantly lower at soil moisture level of 25 % of water holding capacity than at the levels ranging from 50 to 125 %. Increase in salinity resulted in gradual decrease in seed germination of each species. Growth responses of species to salinity varied widely from significant decrease with slight salinity to stimulation up to salinity levels of 20 dS m-2. Higher K+Na+ratios in plant shoots of all species compared to that in the root medium indicated selective K+uptake. Higher tolerance in chenopod species seems to be attendant on their ability for internal ion regulation.

Does intertidal vegetation indicate specific soil and hydrologic conditions

Abstract: Six distinct plant zones were identified within a mesohaline tidal marsh in the Cape Fear Estuary, North Carolina. USA. All six vegetative zones were found within an 18-cm portion of the 1.35-m tidal range. Aerial photographs show that these six zones have existed within the marsh for the past 20 years. A monotypicJuncus roemerianus stand occupied soils with the highest salinity porewater (17 ppt), while stands dominated (>90%) by eitherScirpus robustus orTypha angustifolia were found associated with the least saline soil water (7 ppt) in areas of the marsh least flooded by tidal waters.Spartina cynosuroides dominated areas of the marsh at lowest elevations. In general, Eh was highest in theJuncus zone and lowest in theSpartina alterniflora zone. Four of the six vegetative zones represented distinct physical and chemical environments and could be statistically separated via canonical discriminate analyses. We suggest that established vegetation may be an accurate analog for specific hydrogeomorphic conditions.

Interaction of Phosphate and Salinity on the Growth and Yield of Rice (Oryza sativa L.)

Abstract: The role of phosphorus application on growth and yield of rice under saline conditions was studied in a set of two experiments, one in nutrient and the other in soil culture. In experiment 1, the effect of inorganic phosphate (P-i) on the growth and ionic relations of four rice cultivars, varying in salt tolerance and phosphorus use efficiency, grown in nutrient solution with and without 50 mol m(-3) NaCl was measured in a 2 week trial. The growth of ail rice cultivars was affected to different degrees due to external P; in the presence of sale. External P-i concentration up to 100 mu M in the presence of NaCl caused stimulation of all growth parameters (shoot, root, tillering capacity), above this concentration P-i had an inhibitory effect. Salt-induced P toxicity was exhibited at a much lower P-i concentration (10 mu M) by the salt sensitive cultivar. Increasing the supply of phosphorus (from 1 to 100 mu M P-i) to the saline medium tended to decrease the concentrations of Na+ and Cl- in all cultivars except IR 1561. Shoot concentrations of these saline ions were much lower in the salt tolerant and moderately salt tolerant rice cultivars. Shoot P and Zn concentrations showed an increasing trend in the presence of external P-i and salt in the rooting medium but most strikingly P:Zn ratio was lower in salt tolerant and moderately salt tolerant cultivars. Significantly higher concentrations of Na+, P and Cl-, and lower concentrations of Zn, were determined in the shoots of salt sensitive cultivars when exposed to salt stress in the presence of P-i. Results were confirmed in naturally salt-affected soils of two different types (saline-sodic and saline) where paddy yield of NIAB 6 (salt tolerant) and IR 1561 (salt, sensitive) showed improvement through moderate phosphorus supply (18 kg P ha(-1)).

The influence of free convection on soil salinization in arid regions

Abstract: Evaporation of groundwater in a region with a shallow water table and small natural replenishment causes accumulation of salts near the ground surface. Water in the upper soil layer becomes denser than in the depth. This is a potentially unstable situation which may result in convective currents. When free convection takes place, estimates of the salinity profile, salt precipitation rate, etc., obtained within the framework of a 1-D (vertical) model fail.

Soil salinity in the irrigated area of the Yellow River in Ningxia, China

Abstract: Soil salinity has plagued irrigated lands along the Yellow River in the arid Ningxia Hui Autonomous Region of China since shortly after the first canal was built in BC 214. By 1985, approximately 40% of the 300,000 ha of irrigated land was adversely affected by salt accumulation. Several factors have contributed to the increase in salinity. They include high groundwater tables caused by overirrigation, leaky main and lateral canals, and an inadequate drainage system. Other factors are the flatness of the terrain, the high level of the Yellow River during the flood season, widespread production of paddy rice, introduction offish ponds, and the presence of numerous lakes in the Yinchuan Plain. Effective methods of rehabilitating salt‐affected land have been devised but are not yet in wide use. Sediment from the highly eroded Loess Plateau complicates water control in the irrigation system. Despite the salinity problem, irrigation agriculture has prospered over the past 2,000 years.

Coastal plain halophytes and their relation to soil ionic composition

Abstract: Halophytic coastal communities in Bahia Blanca, Argentina, were examined in relation to soil salinity along a transect from inland to the sea. The relationships between soil electrical conductivity and dominance-abundance values for different species were determined. The ‘Chanaral’ community with its most conspicuous species Geoffroea decorticans was present in soils with the lowest salinity levels in the area. Halophytic underbush develops at soil salinity values of intermediate soil electrical conductivity, the characteristic species being Cyclolepis genistoides, Atriplex undulata and Salicornia ambigua. Halophytic shrub-like steppe vegetation, dominated by Allenrolfea patagonica or Heterostachys ritteriana, is present in soils with high salinity. It is concluded that the ionic composition of plants was a stable characteristic for different species and did not vary with changes in soil salinity.