Desodification from calcareous saline sodic soil through phytoremediation with Phragmites australis (Cav.) Trin. ex Steud. and gypsum

The reclamation of saline sodic soils requires sodium removal and the phytoremediation is one of the proven low-cost, low-risk technologies for reclaiming such soils. However, the role of Phragmites australis in reclaiming saline sodic soils has not been evaluated extensively. The comparative reclaiming role of P. australis and gypsum was evaluated in a column experiment on a sandy clay saline sodic soil with EC_e 74.7 dS m^?1, sodium adsorption ratio (SAR) 63.2, Na⁺ 361 g kg^?1, and pH 8.46. The gypsum at 100% soil requirement, planting common reed (P. australis) alone, P. australis + gypsum at 50% soil gypsum requirements, and leaching (control without plant and gypsum) were four treatments applied. After 11 weeks of incubation, the results showed that all treatments including the control significantly reduced pH, EC, exchangeable Na⁺, and SAR from the initial values, the control being with least results. The gypsum and P. australis + gypsum were highly effective in salinity (EC_e) reduction, while sodicity (SAR) and Na⁺ reductions were significantly higher in P. australis + gypsum treatment. The reclamation efficiency in terms of Na⁺ (83.4%) and SAR (86.8%) reduction was the highest in P. australis + gypsum. It is concluded that phytoremediation is an effective tool to reclaim saline sodic soil.     

Effect of Byproducts of Flue Gas Desulfurization on the Soluble Salts Composition and Chemical Properties of Sodic Soils

The byproducts of flue gas desulfurization (BFGD) are a useful external source of Ca²⁺ for the reclamation of sodic soils because they are comparatively cheap, generally available and have high gypsum content. The ion solution composition of sodic soils also plays an important role in the reclamation process. The effect of BFGD on the soluble salts composition and chemical properties of sodic soils were studied in a soil column experiment. The experiment consisted of four treatments using two different sodic soils (sodic soil I and sodic soil II) and two BFGD rates. After the application of BFGD and leaching, the soil soluble salts were transformed from sodic salts containing Na₂CO₃ and NaHCO₃ to neutral salts containing NaCl and Na₂SO₄. The sodium adsorption ratio (SAR), pH and electrical conductivity (EC) decreased at all soil depths, and more significantly in the top soil depth. At a depth of 0–40 cm in both sodic soil I and sodic soil II, the SAR, EC and pH were less than 13, 4 dS m⁻¹ and 8.5, respectively. The changes in the chemical properties of the sodic soils reflected the changes in the ion composition of soluble salts. Leaching played a key role in the reclamation process and the reclamation effect was positively associated with the amount of leaching. The soil salts did not accumulate in the top soil layer, but there was a slight increase in the middle and bottom soil depths. The results demonstrate that the reclamation of sodic soils using BFGD is promising.     

Response of honelocust (Gleditsia triacanthos L.) to soil solution aluminium

Honeylocust (Gleditsia triacanthos L.) seedlings were grown for 72 days in soil from a BC horizon of a Spodosol altered by adding four levels of AlCl₃. Saturated paste extracts from controls to the highest AlCl₃ treatment contained, respectively, 85 to 831 M Al, 834 to 163 M Ca and 316 to 35 M Mg and had a pH of 4.4 to 4.0 Leaf, stem, and root concentrations of Al and P increased while those of Mg, Ca, and Zn decreased with increasing levels of Al. Growth decreased as Al, Al/Ca, and Al/Mg ratios in the extract increased. Growth was negatively related to tissue concentrations of Al, P, and Zn and positively related to tissue Mg and Ca. Growth was more closely correlated to elemental concentrations in the saturated paste extracts than in the SrCl₂ extracts (1 part 0.01M SrCl₂: 1 part moist soil).The research was supported by EPRI grant RD 2365-01 and by the University of Minesota College of Forestry and Minnesota Agricultural Experiment Station Project 074; listed as Minnesota Agricultural Experiment Station Scientific Series Paper.     

Leguminous Trees for the Rehabilitation of Sodic Wasteland in Northern India

The study objective was to determine the fuelwood harvesting rotation and magnitude of nutrient accumulation by the sodic tolerant species Dalbergia sissoo and Prosopis juliflora for the rehabilitation of sodic wastelands. Mean annual increment and current annual increment growth of these trees reached a peak in six-year-old stands. Leaves dominated the litter of these species and contained high concentrations of most nutrients. N, Ca, Mg, and Fe were present in larger concentrations than other nutrients. Organic carbon additions at harvest after six years averaged 16 Mg ha ^{? 1}, while soil pH was reduced from 9.8 to 8.6. Exchangeable sodium percentage (ESP) values decreased 65 and 29% under P. juliflora and D. sissoo, respectively, after harvest. These tree species produced significant root spread and deep penetration and were able to rehabilitate sodic soil effectively.     

Effect of Sodium and Magnesium on Kinetics of Phosphorus Release in Some Calcareous Soils of Western Iran

Knowledge of the rate of release of phosphorus (P) from soils resulting from poor water quality application is essential for long-term planning of crop production while minimizing the impact on groundwater quality. In this study, we examined the effect of sodium adsorption ratio (SAR) and Ca:Mg ratio of water on P release of some calcareous soils from western Iran. Nine different solutions at a total electrolyte concentration of 100 mmol_c l^?1 and three levels of SAR (5, 15, 45) each with Ca:Mg ratios of 1:3, 1:1, or 3:1, prepared using solutions of NaCl, CaCl₂, and MgCl₂, were used to extract P from the soils. The geochemical Visual MINTEQ was used to calculate saturation indices and P species at the initial and end of P release. Significantly different quantities of P were extracted by the solutions. The maximum (average of five soils) (233.6 mg kg^?1) and the minimum (162.9 mg kg^?1) P were extracted by an SAR 45 solution with a Ca:Mg ratio of 1:3 and SAR 15 solution with Ca:Mg ratio of 3:1, respectively. Elovich model adequately described P release. The release rate for SAR 15 with Ca:Mg of 3:1 and SAR 45 with Ca:Mg 1:3 ranges from 16.3 to 31.3 mg kg^?1 h^?1 and from 20.0 to 32.8 mg kg^?1 h^?1, respectively. In the initial stage of P release the solution samples in most soils were saturated with respect to hydroxyapatite, octacalcium phosphate, ß-tricalcium phosphate, and undersaturated with respect to dicalcium phosphate dihydrate, dicalcium phosphate, and mangnesium phosphates. At the end of P release, all solutions were saturated with respect to hydroxyapatite and under saturated with respect to other phosphate minerals. The results imply that P release from soils could be increased during use of saline and sodic irrigation water containing high Mg concentration and that P fertilization management may need modification.     

Effects of short-term flooding on growth,yield and mineral composition of wheat on sodic soil under field conditions

In sodic soils of the Indo-Gangetic alluvial plains of Northern India, flooding for short periods often occurs during the growing season of wheat, leading to low yields. A field study was therefore conducted to evaluate the effects of short-term flooding on growth, yield and mineral composition of wheat (Triticum aestivum Linn. emend. Fiori and Paol) in a sodic soil (pH 8.9, exchangeable sodium percentage 25). Flooding wheat for 2,4 and 6 days at the time of first irrigation (25-day old plants), significantly reduced tillering, plant height, delayed head emergence and resulted in 17.6, 29.0 and 46.7% reduction in grain yield, respectively, Flooding decreased oxygen diffusion rate (ODR) values, restricted root grwoth and reduced ion uptake, especially of N, P, K, Ca, Mg and Zn and led to higher absorption of Na, Fe and Mn. Under the conditions of this experiment, the reduced growth and yield of wheat resulting from short-term flooding was not due to Mn, Fe and Na toxicity but may be due to reduced uptake of nutrients resulting from O₂ deficiency in the soil.     

Effects of some salts and sodicity on the growth of a Rhizobium leguminosarum bv. viceae strain isolated from a salt-affected soil.

The effects of sodium (Na+), calcium (Ca2+), magnesium (Mg2+), and boron (B) concentrations and sodicity, as measured by the sodium adsorption ratio (SAR), on the growth of a Rhizobium leguminosarum bv. viceae strain isolated from a salt-affected soil were studied. The rate of growth was measured in a yeast extract-mannitol broth, amended with salts having electrical conductivity (EC) of 4, 8, and 16 dS x m(-1). Each salinity level was prepared to achieve SAR values of 10, 20, and 30 with or without graded B concentrations of 0.5, 1, 3, and 5 mg x L(-1). We found that salinity levels equal to or more than 8 dS x m(-1) had negative effects on Rhizobium growth during the first days of incubation, but the effects became less pronounced after 1 week. Na+ concentrations of more than 1.1 g x L(-1) retarded growth, especially at high SAR values (i.e., at low Ca2+ concentrations). The retardation of growth increased with increases in EC up to 16 dS x m(-1), at all sodicity levels. Mg2+ added together with Na+ or with Ca2+ + Na+ affected growth more negatively than Ca2+ + Na+ alone. The effect of Mg2+ became more pronounced with increased salinities and sodicities. It was concluded that EC of more than 4 dS x m(-1) retarded growth of Rhizobium, but only at high sodicity levels. The relative specific ion effect on growth was in the order Na+ < Ca2+ < Mg2+. The harmful effect of Mg2+ on this strain was accentuated by adding Ca2+ to the cultural medium. When SAR increased from 10 to 30, Na+ had no clear effect on growth, irrespective of the accompanied cations, i.e, Ca2+, Mg2+, or Ca2+ + Mg2+. Growth was reduced by B concentrations as low as 0.5 mg x L(-1), and the B effect was enhanced by increased salinity.     

The K/Na and Ca/Na ratios and rapeseed yield,under soil salinity or sodicity

Rapeseed (Brassica napus) is a crop relatively tolerant to salt and sodium. Our objective was to study the interactions between Na, K and Ca and their relationship with its yield under the isolated effects of soil salinity or sodicity.Two experiments were carried out using pots filled with the Ah horizon of a Typic Natraquoll. There were three salinity levels (2.3 dS m^-1; 6.0 dS m^-1 and 10.0 dS m^-1) and three sodicity levels, expressed as sodium adsorption ratios (SAR: 12; 27 and 44). The soil was kept near field capacity.As soil salinity increased, the K/Na and Ca/Na ratios in the tissues decreased markedly but yields and aerial biomass production were not affected. As soil SAR value increased, the K/Na and Ca/Na ratios in plants and K-Na and Ca-Na selectivities decreased. Plants could not maintain their Ca concentration in soil with a high SAR. The grain yield and biomass production diminished significantly in the highest SAR treatment. Our results are consistent with those showing detrimental osmotic effects of salts in Brassica napus. Conversely, under sodicity, the K/Na and Ca/Na ratios in plant tissues decreased considerably, in accordance with grain and biomass production. These results show that the effects of sodicity are different from those of salinity.     

Effects of sodium chloride and melibiose on the in vitro growth and sporulation of Frankia strain HFPCcI3 isolated from Casuarina cunninghamiana

The in vitro growth and sporulation of Frankia isolate HFPCcI3, a nitrogen-fixing symbiont of Casuarina, was inhibited by both the toxic and osmotic effects of sodium chloride. This was demonstrated by comparing HFPCcI3 halotolerance with its tolerance to metabolically neutral melibiose osmoticum at sodium chloride and melibiose concentrations from 0 to 500 mmol L^-1. The osmotolerance of this strain is similar to that of other Frankia strains, whereas the halotolerance of this strain is greater than that reported for Frankia strains isolated from actinorhizal plants from moist, temperate regions lacking sodic soils. This finding suggests that differential strain-specific mechanisms are involved in Frankia's ability to tolerate dry versus sodic soil conditions and has important implications for the microbial ecology of soils supporting Casuarina spp.     

Soil salinisation: a local life cycle assessment impact category

Salinity is an increasing environmental problem in agricultural ecosystems and is not adequately represented in conventional life cycle assessment (LCA) impact categories. It is often not the total quantity of salts emitted or the proportion of salt accumulated in the soil profile that is the primary mechanism for deteriorating soil conditions for irrigated salinity, rather the ratio of major cations in the soil matrix and the potential for colloid dispersion and reduced permeability. A soil salinisation potential (SP) is proposed as an indicator for irrigated salinity and potential soil degradation from poor irrigation practices. The indicator uses the threshold electrolyte concentration concept that predicts the adjusted sodium adsorption ratio (SAR)/ Electrical conductivity (EC) ratio that soil will no longer flocculate, but potentially disperse. The SAR is converted to a threshold EC and compared to the measured EC in order to develop a site-specific irrigation equivalence factor (EF). This site/region/process specific EF is then used to weight the sodium load to soil and repeated for each stage throughout the entire life cycle to determine the overall Salinisation Potential (SP). The data required for calculating the SP is generally readily available either on site or from the water chemistry of the local watercourses. Preliminary calculations simply require the volume, pH, electrical conductivity (EC), alkalinity and the concentrations of Na, Ca, and Mg of the irrigation water. The site/process/region specific nature of the indicator ensures a quantitative measure to enable comparisons between different systems and is useful for identifying stages in the life cycle of a product (particularly food products), where the potential for soil salinisation and soil degradation is most severe.     

The effect of sodicity on cotton: plant response to solutions containing high sodium concentrations

Solution culture was used to investigate whether the high solution Na concentrations and Na:Ca ratios found in sodic soils could directly affect the early growth and nutrient uptake of cotton (Gossypium hirsutum L.). Cotton was grown in nutrient solutions with three Na:Ca ratios (46:1, 4:1 and 0.2:1 mM) and three electrical conductivities (EC) (2.5, 4.25 and 6 dS m^?1) combined in a factorial design with four replicates. Most cotton growth parameters (including shoot and root dry weight, fruit number and weight) were unaffected by increasing solution EC or Na:Ca ratio, but at the highest Na concentration (56.6 mM), plant height was reduced. It was concluded that young cotton has the ability to tolerate solution Na concentrations up to those found in moderately sodic soils. Increasing solution Na:Ca increased plant root and shoot concentrations and plant accumulation for Na, and decreased them for Ca. Increasing EC also increased plant Na concentration and accumulation. Shoot K and P concentrations decreased with EC, but actually increased as the sodicity (Na:Ca ratio) of the nutrient solution increased. The results suggest that the low K and P concentrations commonly found in cotton grown in sodic soils are not a direct result of Na:Ca ratio in the soil solution.     

Urease activity in soils

Summary The availability of Ca from different levels of gypsum and calcium carbonate in a non-saline sodic soil has been investigated. Different levels of tagged gypsum (Ca⁴⁵SO₄.2H₂O) and calcium carbonate (Ca⁴⁵CO₃) (i.e. 0, 25, 50, 75, and 100 per cent of gypsum requirement) were mixed thoroughly in 3.5 Kg of a non-saline alkali soil (ESP, 48.4; ECe, 2.68 millimhos/cm). Dhaincha (Sesbania aculeata) — a legume and barley (Hordeum vulgare L.) — a cereal were taken as test crops. Increasing levels of gypsum caused a gradual increase in the yield of dry matter, content of Ca and K in the plant tops and Ca:Na and (Ca+Mg):(Na+K) ratios in both the crops. Application of calcium carbonate caused a slight increase in the dry matter yield, content of Ca and Mg and Ca:Na and (Ca+Mg):(Na+K) ratios in barley, however, in case of dhaincha there was no such effect. Gypsum application caused a gradual decrease in the content of Na and P in both the crops. Total uptake of Ca, Mg, K, N and P per pot increased in response to gypsum application. The effect of calcium carbonate application on the total uptake of these elements was much smaller on dhaincha, but in barley there was some increasing trend.Increasing application of tagged gypsum and calcium carbonate caused a gradual increase in the concentration and per cent contribution of source Ca in both the crops, although, the rate of increase was considerably more in dhaincha. The availability of Ca from applied gypsum was considerably more than that from applied calcium carbonate. Efficiency of dhaincha to utilize Ca from applied sources was considerably more (i.e. about five times) than that of barley     

Influence of alpine plants on soil nutrient concentrations in a monoculture experiment

The ability of different alpine species to influence soil nutrient concentrations was quantified by growing monocultures of 17 species on a homogenized acid alpine soil mixture. The experiment was carried out at 2750 m a.s.l. in the Teberda Reserve, Northwest Caucasus. Soil nuturient contents (NH₄, NO₃, P, Ca, Mg, and K) and pH were analyzed after 6 years. The same soil mixture but without plants was used as a control. The plant species had significant effects on all soil properties. Different species groups tended to decrease different nutrients to different extents, e.g.Matricaria caucasica had the lowest level for NO₃ andFestuca ovina for P. Many species increased the cation content (Ca, Mg, K) in the soil in comparison with the control. Prevention of cation leaching seems to be the main mechanism of these increases, because initial cation contents were higher than the final. All species, exceptSibbaldia procumbens, increased soil pH in comparison with the final control. Significant differences among taxonomic groups (families) were found for exchangeable Ca, Mg, and pH.Fabaceae decreased cation contents (Ca, Mg), but tended to increase nitrogen (NH₄, NO₃).Cyperaceae (Carex spp.) tended to decrease ammonium content, and bothAsteraceae andCyperaceae tended to decrease nitrate concentrations. The phosphorus content tended to be reduced by grasses. There was no strong correspondence between properties of native soils of 4 alpine communities and nutrient concentrations for species preferring those communities.     

Electromechanical uncoupling in a molluscan muscle examined by the sucrose gap technique

Summary Membrane potential and tension ofBusycon radular protractor muscles were studied by sucrose gap methods.Excitation-contraction (EC) coupling was examined in response to acetylcholine (ACh) and high K which depolarized the fibres and induced tension, but without action potential firing. Potassium depolarization did not follow predictions expected from the Nernst equation at low and very high K levels, and maximum tension was found at about 100 mM K. EC coupling was very sensitive to [Ca]_o. Ca-free media eliminated K- and ACh-induced tension but with normal depolarization, showing full electromechanical uncoupling.Ionophore A23187 enhanced K- and ACh-induced responses and X-537A enhanced ACh responses, demonstrating acute dependence of activation on [Ca]_o in this muscle. The calcium antagonists nifedipine and nisoldipine reduced tension in the muscle only at very high concentrations, and both agents slightly reduced K- and ACh-induced depolarization.Verapamil reduced K- and ACh-induced tension but paradoxically it enhanced the depolarizing actions of these agents leading to electromechanical uncoupling. Abscisic acid (ABA) enhanced ACh- and K-induced tension and simultaneously enhanced their depolarizing actions. Ionophores and ABA appear to enhance calcium influx which may secondarily influence sodium influx.Calcium antagonists have no consistent actions on this muscle, suggesting that calcium channel activity of the radular protractor may be different from that seen in mammalian visceral muscles.Abbreviations ABRM Anterior byssus retractor muscle - ACh acetylcholine - ABA abscisic acid - EC excitation-contraction - SR sarcoplasmic reticulum - EGTA ethylene-diamine-tetraacetic acid     

Biological indicators provide short term soil health assessment during sodic soil reclamation

Sodic soil remediation is an expensive, lengthy process during which producers need tools to demonstrate that sodium (Na⁺) remediation practices are improving soil health. The objective of this study was to determine if soil biological indicators can provide a short term assessment of the effectiveness of chemical management strategies used to remediate northern Great Plains sodium affected soils. This randomized complete block split-plot research experiment was conducted in a grassland which was converted to annual row crops. The soil at the site was an Exline (fine, smectitic, frigid Leptic Natrudolls). The experiment contained two drainage treatments (tile drained and no-drainage) and four chemical amendments (4.5 Mg ha⁻¹ of gypsum, 9.1 Mg ha⁻¹ of gypsum, 9.1 Mg ha⁻¹ spent sugar beet lime, and a no amendment control). Base-line soil samples for biological assessment were collected in the fall of 2012 after tile drainage was installed. The sodium adsorption ratio (SAR) ranged from 0.4 to 16.7 with a range of electrical conductivity (EC) of 0.4–0.8 dS m⁻¹. Gypsum and lime amendments were applied in 2013. Soil samples were collected for assessing soil health before and after application of amendments and throughout the growing season. This study utilizes a novel application of successional vector trajectories to compare shifts in measured soil health parameters associated with land use change and remediation of sodicity. Soil samples were analyzed for percent total soil carbon (C), nitrifier and denitrifier gene copies, soil enzyme assays (nitrate reductase, ammonia monooxegenase, urease, β glucosidase, alkaline phosphatase, arylsulfatase and fluorescein diacetate hydrolysis), EC, pH, SAR, and soil texture. Gene copies and enzyme activities were successfully used to differentiate between land uses and amendment applications. Ammonia oxidizing bacterial gene copies were higher where cropland was amended with gypsum. Successional vectors verified a significant shift in soil health due to land use change and amendment application. Gypsum applications reduced SAR, but increased soil EC. This work demonstrates that soil enzyme activities and gene copy numbers can be used to detect improvements in soil health.     

Effect of sulphur inoculated with Thiobacillus on soil salinity and growth of tropical tree legumes.

A greenhouse experiment was carried out with the objective of evaluating the effects of the elementary sulphur inoculated with Thiobacillus, compared with gypsum, in the amendment of a alluvial sodic saline soil from the Brazilian semiarid region, irrigated with saline water and grown with the tropical legumes leucena and mimosa. The treatments consisted of levels of sulphur (0; 300 and 600 kg/ha) and gypsum (1,200 and 2,400 kg/ha), irrigation using different waters containing the salts NaHCO3, MgCl2, CaCl2, NaCl and KCl, with different electrical conductivities (ECs: 0.2. 6.1 and 8.2 dS/m at 25 degrees C). Based on the results it appears that saline water increased exchangeable Na+, K+, Ca2+, Mg2+, and soil pH. Sulphur inoculated with Thiobacillus was more efficient than gypsum in the reduction of the exchangeable sodium of the soil and promoting leaching of salts, especially sodium. Sulphur inoculated with Thiobacillus reduced the EC of the soil saturation extract to levels below that adopted in soil classification of sodic or saline sodic. Leucena was more tolerant to salinity and mimosa more resistant to acidity promoted by sulphur inoculated with Thiobacillus.     

Influence of organic matter and flooding on the chemical and electrochemical properties of sodic soil and rice growth

The influence of organic matter, added in the form ofCasuarina equisetifolia andAcacia nilotica leaves, on the chemical and electrochemical kinetics of a flooded sodic soil and rice growth, was studied in a pot experiment. With the addition of organic matter, not only the peaks of CO₂ production and maximum concentrations of extractable Fe and Mn and other cations occurred earlier, but their concentrations were also significantly higher as compared to the control (no organic matter). The high concentrations of CO₂ and reduced redox potential (Eh) appeared to influence the soil pH, exchangeable sodium percentage (ESP) and the accumulation of cations and to be chiefly responsible for better rice growth. Acacia proved more effective than Casuarina in improving rice yield and the sodic soil.     

柠檬酸和EDTA-Na2对黑麦草吸收Pb及营养元素特性的影响

为探究柠檬酸或EDTA-Na_2对Pb污染下黑麦草(Lolium perenne L.)吸收Pb和营养元素特性的影响,对水培黑麦草进行不同处理,研究黑麦草一些生理生化指标的变化。结果表明,与对照相比,Pb处理降低黑麦草干重,增加质膜透性和根系脱氢酶活性,且在叶和根中积累Pb,而叶和根中6种营养元素含量的变化不尽相同。与Pb处理同时加入低浓度的柠檬酸或EDTA-Na_2对其生长影响较小,且叶片的Pb积累量较低;而同时加入高浓度的柠檬酸或EDTA-Na_2,虽然强化Pb在叶片中的积累,但是加重了生长的抑制作用和营养元素的稳态失衡;1 mmol L~(–1)的柠檬酸强化叶片积累Pb的效应强于同浓度的EDTA-Na_2,而5和10 mmol L~(–1)柠檬酸的强化作用则弱于同浓度的EDTA-Na_2。因此,适当浓度的柠檬酸或EDTA-Na_2在治理Pb污染环境中具有一定作用。     

Effects of inorganic nitrogen application on the dynamics of the soil solution composition in the root zone of maize

The effect of inorganic nitrogen (N) fertilizer on the ionic composition of the soil solution under maize (Zea mays L.) was studied. A pot experiment was carried out with two treatments combined factorially, with or without N application (Ca(NO₃)₂; +N and –N treatments, respectively), and with or without plants. Three looped hollow fiber samplers were installed in each pot to sample soil solutions nondestructively from the root zone, seven times during the 50-day growth period. Plants were harvested on the 50th day, and their nutrient contents determined.Effects of N fertilizer on the soil solutions were observed by the first sampling, 2 days after sowing. The concentrations of Ca and NO₃ ^– and electrical conductivity (EC) increased significantly in the +N treatments as direct effects of fertilizer application. In addition, the concentrations of Mg, K, Na and H⁺ also increased and that of P decreased significantly as indirect effects caused by the re-establishment of chemical equilibria. This suggested the greater supply as well as the greater possibility of leaching loss not only of NO₃ ^– but also of Ca, Mg and K. In the treatments with plants, the concentrations of NO₃ ^–, Ca, Mg and K decreased with time and pH increased significantly compared with the unplanted soil. The depletion of N in the soil solution roughly agreed with the amount of N taken up by the plant. The depletions of K from the soil solution amounted to less than 10% of the amount of the K taken up, suggesting intensive replenishment of K from exchange sites in the soil. Depletions of Ca and Mg were several times higher than the amounts taken up, indicating that the depletions resulted from the adsorption of the divalent cations by the soil rather than uptake by plants. Because NO₃ ^– is hardly absorbed by exchange sites in soil and was the dominant anion in solution, it was concluded that NO₃ ^– had a major role in controlling cation concentrations in the soil solution and, consequently, on their availability for uptake by plants as well as their possible leaching loss. ei]H Marschner     

Analysis of acid-soil stress in sorghum genotypes with emphasis on aluminium and magnesium interactions

Acid-soil stress in 12 sorghum (Sorghum bicolor (L.) Moench) genotypes was attributed mainly to aluminium (Al) toxicity. Root damage and magnesium (Mg) deficiency are two independent aspects of plant sensitivity to Al, either in acid soil or in nutrient solution. At moderate soil acidity, Mg deficiency dominantly limited growth whilst at high acidity root damage overruled the effect of Mg deficiency on the growth response. In nutrient solutions containing Al, increased Mg supply improved both root development and Mg nutrition of plants, whereas increased calcium (Ca) supply, or nutrition with ammonium (NH₄) instead of nitrate (NO₃), alleviated root damage but amplified Mg deficiency. At lowered pH the syndrome of Al toxicity was more profound. The implications of Mg-Al interactions, root damage, Mg supply and genotype selection are elucidated.