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1.
Accurate estimation of the available potassium (K+) supplied by calcareous soils in arid and semi‐arid regions is becoming more important. Exchangeable K+, determined by ammonium acetate (NH4OAc), might not be the best predictor of the soil K+ available to crops in soils containing micaceous minerals. The effectiveness of different extraction methods for the prediction of K‐supplying capacities and quantity–intensity relationships was studied in 10 calcareous soils in western Iran. Total K+ uptake by wheat grown in the greenhouse was used to measure plant‐available soil K+. The following methods extracted increasingly higher average amounts of soil K+: 0.025 M H2SO4 (45 mg K+ kg?1), 1 M NaCl (92 mg K+ kg?1), 0.01 M CaCl2 (104 mg K+ kg?1), 0.1 M BaCl2 (126 mg K+ kg?1), and 1 M NH4OAc (312 mg K+ kg?1). Potassium extracted by 0.01 M CaCl2, 1 M NaCl, 0.1 M BaCl2, and 0.025 M H2SO4 showed higher correlation with K+ uptake by the crop (P < 0.01) than did NH4OAc (P < 0.05), which is used to extract K+ in the soils of the studied area. There were significant correlations among exchangeable K+ adsorbed on the planar surfaces of soils (labile K+) and K+ plant uptake and K+ extracted by all extractants. It would appear that both 0.01 M CaCl2 and 1 M NaCl extractants and labile K+ may provide the most useful prediction of K+ uptake by plants in these calcareous soils containing micaceous minerals.  相似文献   

2.
Aerobic incubations to estimate net nitrogen (N) mineralization typically involve periodic leaching of soil with 0.01 M calcium chloride (CaCl2), so as to remove mineral N that would otherwise be subject to immobilization. A study was conducted to evaluate the accuracy of leaching for analysis of exchangeable ammonium (NH4+)-N and nitrate + nitrite (NO3?+ NO2–)-N, relative to conventional extractions using 2 M potassium chloride (KCl). Ten air-dried soils were used, five each from Illinois and Brazil, that had been amended with NH4+-N (1 g kg?1) and NO3–-N (0.6 g kg?1). Both methods were in good agreement for inorganic N analysis of the Brazilian Oxisols, whereas leaching was significantly lower by 12–48% in recovering exchangeable NH4+-N from Illinois Alfisols, Mollisols, and Histosols. The potential for underestimating net N mineralization was confirmed by a 12-wk incubation experiment showing 9–86% of mineral N recoveries from three temperate soils as exchangeable NH4+.  相似文献   

3.
The effectiveness of lime-ammonium-nitrate (LAN) as a nitrogen (N) fertilizer in weathered soils depends on the respective selectivity for ammonium (NH4) and calcium (Ca) by the soils. The study assessed Ca2+/NH4+ exchange selectivity of two benchmark soils from Botswana and examined the soil fertility management implications. Surface horizons (0–20 cm) of Pellustert and Haplustalf were equilibrated with 50 ml stock solution containing variable concentrations of Ca2+ and NH4+. The Ca2+/NH4+ exchange data were fitted into the Vanselow (KV), Gaines and Thomas (KGT), Davies (KD), and the regular solution (KRS) equations. The selectivity coefficients for the Ca2+/NH4+ exchange reactions varied widely with the soil exchanger composition except for the relatively stable KRS. The selectivity coefficients indicated strong preference for NH4+ to Ca2+. The thermodynamic exchange constant, Kex, was 5.75 ± 1.24 in the Pellustert, indicating preferential adsorption of NH4+, but not in the Haplustalf with Kex = 0.92 ± 0.27. The free energy for Ca2+/NH4+ exchange (ΔG°ex) was negative (?4.26 ± 0.59 kJ mol?1) in the Pellustert but slightly positive in the Haplustalf (0.34 ± 0.87 kJ mol?1). In conclusion, the soil-NH4 complex was more stable than soil-Ca complex in the Pellustert, indicating LAN as a N fertilizer would have greater potential effectiveness in the Pellustert than in the Haplustalf.  相似文献   

4.
We analyzed in soils with contrasting cultivation histories the depletion of P following sequential extractions with soil testing solutions. Soil samples were collected in three experiments in eastern Canada (L’Acadie, Lévis, and Normandin) and P was sequentially extracted 16 times, once daily, using Mehlich-3 (M3) or Olsen (Ol) solution. The cumulative amount of P extracted was 252 mg PM3 kg?1 and 77 mg kg?1 POl for L’Acadie, 212 mg PM3 kg?1 and 66 mg POl kg?1 for Lévis, and 424 mg PM3 kg?1 and 83 mg POl kg?1 for Normandin. The depletion of P was described by a logarithmic function (Y = a ln (N) + b) for PM3, and a power function (Y = αNβ) for POl. The inorganic P pool decreased in the three soils. The organic P pool did not decrease possibly because soil testing solutions did not directly extract P from this pool. This study demonstrated that laboratory soil testing analysis using M3 or Ol solution principally target P from the inorganic pool, suggesting that P fertilizer recommendations to mineral soils relying on these methods do not account for the potential of the organic P pool to contribute to soil P availability.  相似文献   

5.
Nutritional status of vegetable crops is often monitored by analysis of dried plant tissues, which is costly and often time consuming. Two greenhouse trials were conducted, at the University of Hawaii at Manoa, Magoon facilities, to evaluate the portable cardy ion meter (CIM) in determining potassium (K+) status in fresh petiole sap of pak choi as compared with standard laboratory methods. In the first greenhouse trial, three algae species (Gracilaria salicornia, Kappaphycus alvarezii, and Eucheuma denticulatum) were used to apply five rates of K+ (0, 84, 168,252, and 336 kg.ha?1). The pak choi was directly seeded into 4 L pots and was grown in peat moss. In the second greenhouse trial, K+ was provided through Eucheuma denticulatum and potassium nitrate (KNO3) at five rates (0,112, 168, 224, 280, and 336 kg.ha?1) in peat moss and soil media. At harvest, K+ concentrations in fresh petiole sap were analyzed immediately with CIM and the dried samples were analyzed by inductively coupled plasma spectroscopy (ICP) measurement. The results showed increase in leaf K+ content at higher rates and the maximum concentration of leaf K+ at 4500–5300 mg/L for sap and 8–9% for tissue was obtained when K+ was provided between 224 and 284 kg.ha?1. There was a close correlation between the CIM readings and the ICP method (r = 0.8048 and 0.8314) from the first and second GH results, respectively. The results suggest that the CIM could be used for the rapid monitoring of the relative K+ status of plants. The data further suggested 4500–5000 mg K/L for fresh petiole sap and 7.5% K+ in tissue as critical levels for K+ concentration in pak choi.  相似文献   

6.
The effect of two hydroxides (NaOH and KOH) and two chlorides (NaCl and KCl) on aggregate stability and saturated hydraulic conductivity (Ks) was studied in three New Zealand soils using concentrations (0.003, 0.03, and 0.3 m ) typical of the range of pH found in strongly alkaline industrial liquid wastes. The different solutions were used as pretreatments prior to aggregate stability measurements and as influent solutions for Ks measurements. The concentration of hydroxide appeared to be the most important factor affecting aggregate stability and KS in all soils. Aggregate stability and Ks decreased with increasing hydroxide concentration, but were generally unaffected by chloride solutions. Relative Ks decreased to <2.5% of initial kS with all hydroxide concentrations, but the time until a decrease ocurred depended on concentration. In contrast, relative kS remained > 100% with chloride solutions, but decreased substantially when distilled water replaced the chloride solutions. Differences in aggregate stability and Ks due to the cation present (either Na+ or K+) appeared to be very small. A surface crust formed in the upper 1 cm of the soils leached with hydroxide solutions. This surface crust had substantially less organic carbon than the upper 1 cm of soil from the cores leached with chloride. A two-stage process explains the decrease in ks when strongly alkaline solutions are applied to soil. First, organic matter dissolution decreases aggregate stability, with the rate of organic matter dissolution depending on hydroxide concentration; and second, increased repulsion of soil particles (due to increased pH) causes movement of dislodged particles into pore spaces, resulting in decreased Ks.  相似文献   

7.
Sorption characteristics of phenanthrene were studied in batch equilibrium experiments with 32 Australian soils that varied widely in physicochemical properties. Sorption of phenanthrene varied widely among the soils and was generally nonlinear, with the nonlinearity index (n) of the Freundlich isotherm varying from 0.62 to 1.01. Simple regression analyses revealed that total organic carbon (TOC) accounts for about 68 % of the variation in the partition coefficient (K′ f ) for sorption among the soils at an equilibrium concentration (C e ) of 0.05 mg/L. The organic carbon normalized distribution coefficient (K OC ), varied considerably between soils with >70 % of the variance of logK OC being accounted for by logTOC, clay and log dissolved organic carbon (DOC). These results show that the phenanthrene C e is influenced by both TOC as well as the DOC in soil suspensions. The effects of ionic strength (IS) and index cation were investigated using four contrasting soils. Results show that with an increase in IS from 0.03 to 0.15 M sorption of phenanthrene generally increased in CaCl2 background solutions, whereas the effect was less significant and variable in NaCl background solutions. Sorption of phenanthrene was slightly higher at low IS (0.03 M) with Na+ as index cation compared with that of Ca2+, whereas an opposite trend was observed at higher IS (0.15 M). For two soils high in TOC, the flocculation of endogenous DOC in the presence of Ca2+ reduced the influence of background electrolyte and resulted in a more linear sorption isotherm as well as higher sorption capacity. This trend was more significant with Ca2+ relative to Na+.  相似文献   

8.
The effectiveness of eight chemical extraction methods was evaluated on 15 Indian soils for the prediction of plant-available potassium (K+) to Sudan grass (Sorghum vulgare var. sudanensis) grown in modified Neubauer technique. Average amounts of soil K+ extracted were in descending order: Morgan’s reagent > 0.5 M sodium bicarbonate (NaHCO3) > neutral 1N ammonium acetate (NH4OAc) > 1N nitric acid (HNO3) > 0.02 M calcium chloride (CaCl2) > 0.1N HNO3 > Bray and Kurtz No.1> distilled water. The highest simple correlation with plant K+ uptake was obtained with NH4OAc-K+ (r = 0.866**) and the lowest with CaCl2-K+ (r = 0.45*). To develop the predictive models using stepwise regression, plant K+ uptake was used as the dependent variable and the extractable soil K+, pH, sand, silt and organic carbon (C) contents as the independent variables. Based on the final R2, the NH4OAc model was found to be the best predictor of plant-available K+ in the soils when used along with sand and organic C.  相似文献   

9.
Potassium (K) and nitrogen (N) are essential nutrients for plants. Adsorption and desorption in soils affect K+ and NH + 4 availabilities to plants and can be affected by the interaction between the electrical double layers on oppositely charged particles because the interaction can decrease the surface charge density of the particles by neutralization of positive and negative charges. We studied the effect of iron (Fe)/aluminum (Al) hydroxides on desorption of K+ and NH + 4 from soils and kaolinite and proposed desorption mechanisms based on the overlapping of diffuse layers between negatively charged soils and mineral particles and the positively charged Fe/Al hydroxide particles. Our results indicated that the overlapping of diffuse layers of electrical double layers between positively charged Fe/Al hydroxides, as amorphous Al(OH) 3 or Fe(OH) 3 , and negatively charged surfaces from an Ultisol, an Alfisol, and a kaolinite standard caused the effective negative surface charge density on the soils and kaolinite to become less negative. Thus the adsorption affinity of these negatively charged surfaces for K+ and NH + 4 declined as a result of the incorporation of the Fe/Al hydroxides. Consequently, the release of exchangeable K+ and NH +4 from the surfaces of the soils and kaolinite increased with the amount of the Fe/Al hydroxides added. The greater the positive charge on the surfaces of Fe/Al hydroxides, the stronger was the interactive effect between the hydroxides and soils or kaolinite, and thus the more release of K+ and NH + 4 . A decrease in pH led to increased positive surface charge on the Fe/Al hydroxides and enhanced interactive effects between the hydroxides and soils/kaolinite. As a result, more K+ and NH + 4 were desorbed from the soils and kaolinite. This study suggests that the interaction between oppositely charged particles of variable charge soils can enhance the mobility of K+ and NH + 4 in the soils and thus increase their leaching loss.  相似文献   

10.
Determining potassium (K) fertilizer requirement using sorption isotherms is considered more accurate than conventional soil K tests. A total of 59 surface soil samples were used to establish K exchange isotherm. To evaluate K requirement sorption test, a glasshouse experiment using perennial ryegrass (Lolium perenne, cv. Roper) was carried out on 10 soil samples. The experiment was laid out as a completely randomized design with four replications and four K levels (K0, K20, K40, K80). Concentrations of K in solution established by adding K in the pots estimated from the sorption curve ranged from 20 to 80 mg K l?1 including check treatment (no K). Dry matter yield of ryegrass in most soils approached maximum as adjusted K levels were increased to 20 mg K l?1. The amounts of K required to bring the soils to 20 mg l?1 in soil solution varied among soils and ranged from 99 to 399 mg kg?1, on average 205 mg kg?1 soil. It was found that a useful regression model for the prediction of standard K requirement (K20) included the combination of plant available K extracted by NH4OAc (Av-K) and clay content: K20 = ?41 ? 0.63 Av-K + 9.0 Clay (R2 = 0.61, p < 0.001, n = 59).  相似文献   

11.
Adequate regulation of mineral nutrients plays a fundamental role in sustaining crop productivity and quality under salt stress. We investigated the ameliorative role of potassium (K as K2SO4) in overcoming the detrimental effects of sodium chloride (NaCl) on sugarcane genotypes differing in salt tolerance. Four levels of NaCl (0, 100, 130 and 160 mM) were imposed in triplicate on plants grown in gravel by supplying 0 and 3 mM K. The results revealed that application of NaCl significantly (p ≤ 0.05) increased sodium (Na+) but decreased K+ concentrations in shoots and roots of both genotypes with a resultant decrease in K+/Na+ ratios. Physical growth parameters and juice quality were also markedly reduced with increasing NaCl concentrations compared with controls. However, addition of K alleviated the deleterious effects of NaCl and improved plant growth under salt stress. Cane yield and yield attributes of both genotypes were significantly (p ≤ 0.05) higher where K was added. Juice quality was also significantly (p ≤ 0.05) improved with the application of K at various NaCl levels. The results suggested that added K interfered with Na+, reduced its uptake and accumulation in plant tissues and consequently improved plant growth and juice quality in sugarcane.  相似文献   

12.
Abstract

Urea applications to soil are subject to loss by ammonia (NH3) volatilization, unless incorporated. It has been proposed that this loss can be reduced by stimulating populations of soil nitrifiers by an ammonium sulfate [(NH4)2SO4] pretreatment two to four weeks before urea application. The objective of this laboratory trial was to evaluate this concept with five diverse soils, two North American Mollisols and three South American Oxisols. The soils were incubated untreated for two weeks, followed by pretreatment with 0 or 5 kg nitrogen (N) ha‐1 as (NH4)2SO4, on a soil surface area basis. After another two weeks of incubation, the soils were treated with the equivalent of 0 or 50 kg N ha‐1 as urea. Ammonia loss was estimated after trapping into phosphoric acid (H3PO4). Ammonium sulfate pretreatment reduced NH3 loss with the two Mollisols and a sandy Oxisol and increased the recovery of the urea application as mineral [ammonium (NH4 +) + nitrate (NO3 ‐)] N in these soils. Little NH3 loss was detected from the two clay Oxisols, and (NH4)2SO4pretreatment did not influence NH3 loss or recovery of urea as mineral N. An example of a cropping system where this concept may have utility is discussed.  相似文献   

13.
Five peat soils and a mineral soil were artificially contaminated with 137Cs. Soil solution activity and radio–lability of 137Cs were monitored over 709 days to quantify progressive 137Cs fixation. The peat soils fixed large amounts of 137Cs, but less than the mineral soil did. Distribution coefficients (Kd, cm3 g?1) ranged from 30 to 5000 at the end of equilibration. A labile 137Cs distribution coefficient, Kdt, was estimated by a method involving solid ? solution equilibration in dilute solution. In a separate study several concentrations of KCl were added to soils in increasing concentration both before and after the addition of 137Cs. Differences in apparent adsorption strength of radiocaesium indicated that K+ induced the collapse of expanded mineral interlayers, thereby trapping ions. It seemed that I37Cs adsorbs at sites in the small micaceous clay fraction of the peat soils. The different rates of 137Cs adsorption and fixation in the peat and mineral soils, in which the rate of access of 137Cs to fixation sites in peat soils is less, seems to have been caused partly by lack of K, and partly by the scarcity of fixation sites.  相似文献   

14.
Abstract

Release of native and added K+ and NH+ 4 from two soils was monitored during a 166 day incubation/leaching experiment. One soil (Brookston) represented a major soil series In Ontario whereas the other (Harriston) was suspected having a relatively large fixation capacity. Treatments were imposed involving addition of 50 μM g‐1 soil of K+(KCl) or NH+ 4 (NH4Cl) only or one added after the other on successive days. The addition of either K+ or NH+ 4 on day 2 tended to inhibit the release of the other added on day I. Also the addition of either K+ or NH+ 4 on day 1 tended to inhibit the sorption or fixation of the other on day 2. The release rate of K+ during the 10 to 166 day period was almost constant and not affected by the addition of NH+ 4. Alternatively, the addition of K+ on day 2 slowed the release rate of NH+ 4 measured by NO? 3 appearance from day 10 to 40 but had no effect thereafter. At the end of the experiment considerably more K+ than NH+ 4 was retained suggesting that K+ was more firmly fixed. However, the continuing nitrification of NH+ 4 must be contrasted with periodic removal of K+ by leaching with 0.01 M CaCl2 solution since the equilibrium between exchangeable and fixed ions was affected. There were no notable differences between the two soils inspite of a considerable difference in clay content.  相似文献   

15.
The different responses of two populations of Suaeda salsa (Linn.) Pall. (saline seepweed) from an intertidal zone and a saline inland zone to salinity [1 or 500 mM sodium chloride (NaCl)] and nitrogen [N; 0.05, 1, or 10 mM nitrate (NO3 ?)‐N] were investigated. Greater NO3 ?‐N supply (10 mM) increased shoot dry weight for the two populations of S. salsa, especially for S. salsa from the saline inland zone. Greater NO3 ?‐N supply (10 mM) increased the concentrations of chlorophyll and carotenoid in leaves and the NO3 ? and potassium (K+) concentrations in shoots for both populations. Greater NO3 ?‐N supply (10 mM) increased shoot Na+ in S. salsa from the intertidal zone. In conclusion, S. salsa from the saline inland zone is more responsive to NO3 ?‐N supply than the intertidal population. Greater NO3 ?‐N supply can help the species, especially the intertidal population, to grow and to mediate ion homeostasis under high salinity.  相似文献   

16.
Nonexchangeable K+ constitutes a slowly available reserve that may significantly influence K+ fertility of soils. Laboratory and greenhouse experiments were conducted to characterize the K+ supply and nonexchangeable K+–release kinetics in 10 calcareous soils using 0.01 M CaCl2 and 0.01 M oxalic acid extractions. Total K+ uptake by wheat (Triticum aestivum L.) grown in the greenhouse was used to measure plant‐available K+. The release of K+ was characterized by an initial fast rate followed by a slower rate. The nonlinear relationship in the early stages of the K+ release may be attributed to the edge sites, and release of K+ from interlayer exchange sites may be responsible for the second part of the K+ release. Kinetics of K+ release was described best with power function, which showed the best fit of the four models tested. Parameters of kinetics models in 0.01 M CaCl2 were significantly related to K+ uptake by wheat. Potassium release was also correlated to initial NH4OAc‐extratable K+ and to HNO3‐extractable K+.  相似文献   

17.
When evaluating phosphate rock (PR) dissolution, previous to the extraction with sodium hydroxide (NaOH), dry soil samples with PR were extracted with three solutions to remove exchangeable and solution calcium (Ca) [sodium chloride (NaCl) 1 M, buffered NaCl with ethylenediaminetetraacetic acid (EDTA) (NaCl–EDTA), and NaCl buffered at pH 7 with triethanolamine (TEA) (NaCl–TEA)] for comparison with the extraction of soil samples without any prewash. In acidic soils, up to 51% of applied P was recovered during the NaCl extraction because of the high exchangeable acidity released during the extraction. In soils with exchangeable Ca>2 cmol(+)kg?1, high EDTA quantities also promoted PR dissolution. The NaCl–TEA solution efficiently removed Ca, avoiding PR dissolution and P retention by calcium hydroxide [Ca(OH)2] during the NaOH extraction. Thus, when evaluating PR dissolution we recommend the use of NaCl–TEA to remove Ca. We also recommend the same procedure when applying the Chang and Jackson fractionation to calcareous soils and soils submitted to PR application.  相似文献   

18.
ABSTRACT

Salt-affected soils expand around the world and become a critical handicap for high crop yield. Saline-sodic soil contributed a major portion in salt-affected soils. Such types of soils have a sizable amount of Na+ in nutrient medium and that reduce the K+ uptake in plants. A hydroponic experiment was performed to investigate the ameliorative effect of different doses of potassium fertilizer (K1 = 0.3, K2 = 0.6 and K3 = 1.2 mM L?1) on rice (Oryza sativa L.) under different ECw (6 dS m?1) and SARw [12 and 24 (mmol L?1)1/2] levels. Application of K+ at elevated levels under saline-sodic conditions improved the concentration of anti-oxidant enzymes, plant physiological, and biochemical attributes by improving the K+: Na+ ratio in plant tissues. Total phenolic content, total soluble protein, and soluble sugar content of rice plant were increased with an increase in potassium dose and saline-sodicity. Maximum K+: Na+ ratios, 4.13 and 2.0 were observed in shoot and root, respectively upon application of K+ at 1.2 mM L?1 in a solution having ECw: SARw level of 6: 12. This study suggested that application of potassium at elevated levels (1.2 mM L?1) has enhanced the rice growth by reducing the harmful effect of Na+ salts on plant physiology, biochemical attributes, and anti-oxidant enzymes under specific saline-sodic conditions.  相似文献   

19.
La(NO3)3 对盐胁迫下黑麦草幼苗生长及抗逆生理特性的影响   总被引：2，自引：0，他引：2  
为探讨稀土元素镧(La)对牧草盐胁迫伤害的缓解作用, 采用水培法研究了叶面喷施20 mg·L-1La(NO3)3 对NaCl 胁迫下黑麦草幼苗生长及其抗逆生理特性的影响。结果表明: 盐胁迫显著抑制黑麦草幼苗的生长, 提高叶片电解质渗漏率及丙二醛(MDA)、O2- 和H2O2 含量, 其作用随盐浓度的增大而增强。超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)活性和抗坏血酸(AsA)、谷胱甘肽(GSH)、可溶性蛋白质、脯氨酸含量随盐浓度增大呈先升后降趋势, 可溶性糖和Na+/K+比逐渐增大, 质膜H+-ATP 酶活性逐渐降低, 过氧化物酶(POD)活性及POD 同功酶数量表达增强。喷施La(NO3)3 处理可降低盐胁迫下黑麦草幼苗叶片的O2- 和H2O2 含量, 提高SOD、CAT、POD、APX 和质膜H+-ATP 酶的活性及POD 同功酶的表达, 使AsA、GSH、可溶性蛋白质、可溶性糖和游离脯氨酸含量及幼苗生物量增加, Na+/K+比降低。表明La(NO3)3 可通过提高抗氧化系统的活性和积累渗透溶质减轻盐胁迫伤害, 从而提高黑麦草的耐盐性。  相似文献   

20.
Understanding the photosynthetic carbon (C) dynamics in the plant–soil–microbe continuum is critical to the C sequestration in soils. However, such information is limited in maize (Zea mays L.) in Mollisols. Pot-grown maize was labelled with 13CO2 at the 10-leaf, 15-leaf, heading, milk and dent stages to investigate the photosynthetic C flow in a maize–soil system and its contribution to soil organic carbon (SOC) in Mollisols. The majority of fixed 13C was recovered in shoots, ranging from 44.7% to 78.6%. The allocation of 13C fixed at different growth stages to belowground (roots and soil) gradually decreased over the growing period, indicating that the strength of root C sink is stronger at the early stages. However, the proportion of 13C in dissolved organic C and microbial biomass C to that in SOC significantly increased as the growth stages advanced. Over the entire growth period, the contribution of root-derived C to SOC was estimated to be 5461 mg C plant?1 growth period?1, of which approximately 79% was synthesized during the vegetative stages. Therefore, the input of photosynthetic C by maize plants into SOC mainly occurred during the younger stages of the plant, favouring the storage of SOC in Mollisols.  相似文献   

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