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1.
This investigation was done to determine the release of potassium (K) from five calcareous soils of southern Iran using 0.025 M CaCl2, HCl and citric acid during six successive extractions and to study the K fixation capacity of the soils after K release experiment. Mineralogical study indicated that Vertisols and Mollisols were dominated with smectites; while other soils had illite, chlorite, palygorskite and smectite. Results indicated that citric acid extracted more K than CaCl2 and HCl (137 vs. 111 and 113 mg kg?1, respectively). The analysis of calcium (Ca), magnesium (Mg) and K concentrations in the solutions suggests that the exchange of K with soluble Ca and Mg (originated from dissolution of carbonates by acidic solutions) is the main mechanism of K release, but citrate is able to dissolve K-bearing minerals and release K in slightly calcareous soils. Soils with more illite released more K. Potassium fixation capacity of soils increased after extractions of soils with different extractants from 324 to 471 mg kg?1, with no significant difference. It is suggested to apply more K fertilizers in K-depleted calcareous soils and use of different solutions for extracting K from soil minerals may be a temporary and short term solution.  相似文献   

2.
对 3种可变电荷土壤和 4种恒电荷土壤在不同 pH、不同浓度、不同相伴阴阳离子下混合体系中Cl-和NO3-的吸附进行了测定。结果表明 ,在Cl-和NO3- 共存体系中 ,Cl-比例增大使可变电荷土壤Na+吸附量及OH-释放量增加 ,而对恒电荷土壤影响不大。Cl-和NO3-吸附量随平衡Cl-和NO3-浓度增加而增大 ,随pH升高而减少。但恒电荷土壤在上述各种条件下对Cl-和NO3-吸附均相同 ,而可变电荷土壤对Cl-吸附量大于NO3-的吸附量 ;NO3-、Cl-的选择系数为 0.51～0.78,Cl-和NO3-的相对吸附量分别为56.9%和 43.1%。在不同相伴阳离子下 ,可变电荷土壤平衡溶液Cl-/NO3-比值均小于 1,且为Na+K+Ca2+Mg2+Fe3+;而恒电荷土壤Cl-/NO3-比值为 1左右 ,且不受阳离子类型的影响。由此认为 ,Cl-和NO3-在两类土壤中均以电性吸附为主 ,恒电荷土壤对Cl-和NO3-的亲合力及吸附机理相同 ;而可变电荷土壤对Cl-的亲合力 NO3- ,Cl-存在着专性吸附  相似文献   

3.
The objective of this study was to investigate possible ways of mobilizing residual fertilizer P as a result of local pH elevation caused by urea hydrolysis. The response of water-soluble P (Pw) and dissolved organic C (DOC) to urea hydrolysis was monitored in three cultivated soils and at two P levels for up to 127–135 d and compared with corresponding changes in soils limed with Ca(OH)2. Hydrolysis of urea was complete in 8–15d during which soil pH increased by 1–1.5 units at the maximum. Subsequently, the pH decreased to or below the original level owing to nitrification. Mobilization of soil P was enhanced substantially in parallel with the increase in pH, the peak Pw occurring simultaneously with the highest pH value. In all urea-treated soils, Pw remained at an elevated level for at least 60d. As compared to urea, elevation of soil pH with Ca(OH)2 had only a minor and inconsistent influence on Pw. In mobilization of soil P, the urea-induced increase in pH and a simultaneous production of NH4+ ions proved to be superior to liming with Ca(OH)2. It was hypothesized that when an acid soil is amended with urea, phosphate is first displaced by OH? ions, resulting in elevated solution P concentrations. A simultaneous dissolution of organic matter contributes to the persistence of high P concentration by competition for sorption sites on Fe and Al oxides, and thus retards the resorption of P.  相似文献   

4.
We determined proton budgets of surface soils in a deciduous forest (Df) and a coniferous forest (Cf) of Volcanogenous Regosols in Tomakomai, Hokkaido of northern Japan. The total H+ source was 12.9 and 11.6 kmolc ha?1 y?1 at Df and Cf respectively, and the external H+ was 1% at Df and 2% at Cf. The primary H+ sources were vegetation uptake of base cations and nitrification, while the major H+ sinks were release of base cations and NO3 + uptake by vegetation. Leaching incubation experiments using A horizon soils including Df and Cf with NH4 + solutions (5.3, 15.9 mg N L?1) showed that H+ from nitrification was generally higher in the Df soil than Cf soil, and nitrification of Tomakomai Df soil was the highest in both treatments. Results of multiple regression analyses suggested that pHkCl and exchangeable Ca2+ contributed to the H+ generation via nitrification. Leaching experiments with dilute HCl (pH 3.3) revealed that cation release (mainly Ca2+) occurred, and the proportion of release by decrease of exchangeable cations was higher than that by mineral weathering. Mineral weathering in the Tomakomai soil was higher than the other soils.  相似文献   

5.
Sulphate sorption by variable charge soils   总被引：2，自引：0，他引：2  
The sorption of sulphate (SO2?4) by three variable charge soils from the Canary Islands (Spain) was studied. Sulphate sorption decreased with increasing pH. Only negligible amounts of SO2?4 were sorbed above pH 6.5. When the soils were washed with an indifferent electrolyte (0.01 M KCl), more SO2?4 was recovered than had been sorbed. This indicated a release of native SO2?4 Sulphate replaced hydroxyl ions (OH) and co-ordinated H2O molecules, as well as very small amounts of silicate (Si). No measurable amount of phosphate (P) was released. On average hydroxyl release accounted for 50% of SO2?4 sorbed, the rest being accounted for by the increase in negative charge as measured by K+ adsorption. The results presented here are consistent with the sorption of SO2?4 through a ligand exchange mechanism, but in a different plane of sorption to that of phosphate.  相似文献   

6.
Abstract

Nonexchangeable potassium (K) release kinetics of six major benchmark soil series of India as affected by mineralogy of clay and silt fractions, soil depth and extraction media was investigated. The cumulative release of nonexchangeable K was greater in smectitic soils (353 mg K kg?1 at 0‐ to 15‐cm depth and 296 mg K kg?1 at 15‐ to 30‐cm depth, averaged for 2 soils and 3 extractants) than in illitic (151 mg K kg?1 at 0‐ to 15‐cm depth and 112 mg K kg?1 at 15‐ to 30‐cm depth) and kaolinitic (194 mg K kg?1 at 0‐ to 15‐cm depth and 167 mg K kg?1 at 15‐ to 30‐cm depth) soils. Surface soils exhibited larger cumulative K release in smectitic and illitic soils, whereas subsurface soils had larger K release in kaolinitic soils. Among the extractants, 0.01 M citric acid extracted a larger amount of nonexchangeable K followed by 0.01 M CaCl2 and 0.01 M HCl. The efficiency of citric acid extractant was greater in illitic soils than in smectitic and kaolinitic soils. Release kinetics of nonexchangeable K conformed fairly well to parabolic and first‐order kinetic models. The curve pattern of parabolic diffusion model suggested diffusion controlled kinetics in all the soils, with a characteristic initial fast rate up to 7 h followed by a slower rate. Greater nonexchangeable K release rates in smectitic soils, calculated from the first‐order equation (b=91.13×10?4 h?1), suggested that the layer edge and wedge zones and swelling nature of clay facilitated the easier exchange. In contrast to smectitic soils, higher release rate constants obtained from parabolic diffusion equation (b=39.23×10?3 h?1) in illitic soils revealed that the low amount of exchangeable K on clay surface and larger amount of interlayer K allowed greater diffusion gradients, thus justifying the better fit of first‐order kinetic equation in smectitic soils and parabolic diffusion equation in illitic soils.  相似文献   

7.
Measurements of pH and A1 concentration were made on 10-2 M CaCl2, suspensions of a number of acid soils that had been limed to give 3 range of pH values, and exchangeable A1 and Ca+Mg were determined in 1.0 M NH4Cl extracts. The variation of pH with A1 concentration did not support the theory that pH is controlled by the solubility of Al(OH)3. For some of the soils, proton release on hydrolysis of A13+ions in solution accounted for the pH values, and explained quantitatively the variation of pH with the Ca:Al balance of the exchange complex, taking account of the selectivity coefficient for exchange, Kca→A1 Although Kca→A1 was smaller for soils containing more humus, their pH values were also less than those predicted by the hydrolysis of A13+ in solution, indicating that they contained other sources of protons, presumably the carboxyl groups in humus.  相似文献   

8.
Drainage of peatlands affects the fluxes of greenhouse gases (GHGs). Organic soils used for agriculture contribute a large proportion of anthropogenic GHG emissions, and on-farm mitigation options are important. This field study investigated whether choice of a cropping system can be used to mitigate emissions of N2O and influence CH4 fluxes from cultivated organic and carbon-rich soils during the growing season. Ten different sites in southern Sweden representing peat soils, peaty marl and gyttja clay, with a range of different soil properties, were used for on-site measurements of N2O and CH4 fluxes. The fluxes during the growing season from soils under two different crops grown in the same field and same environmental conditions were monitored. Crop intensities varied from grasslands to intensive potato cultivation. The results showed no difference in median seasonal N2O emissions between the two crops compared. Median seasonal emissions ranged from 0 to 919?µg?N2O?m?2?h?1, with peaks on individual sampling occasions of up to 3317?µg?N2O?m?2?h?1. Nitrous oxide emissions differed widely between sites, indicating that soil properties are a regulating factor. However, pH was the only soil factor that correlated with N2O emissions (negative exponential correlation). The type of crop grown on the soil did not influence CH4 fluxes. Median seasonal CH4 flux from the different sites ranged from uptake of 36?µg CH4?m?2?h?1 to release of 4.5?µg?CH4?m?2?h?1. From our results, it was concluded that farmers cannot mitigate N2O emissions during the growing season or influence CH4 fluxes by changing the cropping system in the field.  相似文献   

9.
Dissolved organic carbon (DOC) in acid‐sensitive upland waters is dominated by allochthonous inputs from organic‐rich soils, yet inter‐site variability in soil DOC release to changes in acidity has received scant attention in spite of the reported differences between locations in surface water DOC trends over the last few decades. In a previous paper, we demonstrated that pH‐related retention of DOC in O horizon soils was influenced by acid‐base status, particularly the exchangeable Al content. In the present paper, we investigate the effect of sulphate additions (0–437 µeq l?1) on DOC release in the mineral B horizon soils from the same locations. Dissolved organic carbon release decreased with declining pH in all soils, although the shape of the pH‐DOC relationships differed between locations, reflecting the multiple factors controlling DOC mobility. The release of DOC decreased by 32–91% in the treatment with the largest acid input (437 µeq l?1), with the greatest decreases occurring in soils with very small % base saturation (BS, < 3%) and/or large capacity for sulphate (SO42?) retention (up to 35% of added SO42?). The greatest DOC release occurred in the soil with the largest initial base status (12% BS). These results support our earlier conclusions that differences in acid‐base status between soils alter the sensitivity of DOC release to similar sulphur deposition declines. However, superimposed on this is the capacity of mineral soils to sorb DOC and SO42?, and more work is needed to determine the fate of sorbed DOC under conditions of increasing pH and decreasing SO42?.  相似文献   

10.
The long-term fertilization results in accumulation of phosphorus especially in the top layer of the soils. Inundation of agricultural lands leads to a switch to anaerobic soil condition, causing reduction of iron and leaching of phosphate simultaneously. From the ecological and environmental perspective, high nutrients flux especially phosphorus will increase the possibility of eutrophication in aquatic system. The fern Azolla had a good potential to adsorb phosphorus, it also has distinctive nitrogen-fixing capacity. We conducted a 10-week aquarium experiment to investigate the phosphorus release capacity from two agricultural soils in the Netherlands with different Fe and P concentrations but comparable Fe/P ratios. Besides, the research questions rose to whether Azolla could use the mobilized phosphate released from the soils for growth. We also tried to find an effective indicator to estimate the actually phosphate mobilization from sediment to water layer. Results showed that the soils with high Fe and P concentrations had higher phosphate release rate compared with the soil with low Fe and P concentrations. Pore water Fe: PO43? ratios were valid to identify P release to surface water, when the Fe: PO43? ratios less than 8 mol mol?1 substantial phosphorus mobilization occurred. The conclusions showed that the actual mobilization of phosphate is more important than the phosphorus retained in the sediments for the internal PO43? fluxes. From 10-week experimental results, we found that Azolla can reuse the phosphate retained in soils thus removed the mobilized phosphate in a moderately low surface water nutrient loading.  相似文献   

11.
Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L?1 nitric acid (HNO3) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L?1 ammonium acetate (NH4OAc) and 1.0 mol L?1 HNO3 extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.  相似文献   

12.
The acid- and base-buffering properties of 84 non-calcareous surface soil samples were studied by batch titration with HCI or KOH at a constant ionic strength of I = 0.1. The soil samples were classified according to their pH of zero point of titration (ZPT). Differential buffer values, dB(H) or dB(OH) (H+ or OH? as meq kg?1 needed to reduce or increase the soil pH sequentially by 0.5 units, respectively), were introduced to describe the course of titration curve and the intensity of buffer action. In all soils, the first acid-buffer value, dB(H)0→0.5, varied from 8 to 78 meq kg?1 and the second one, dB(H)0.5→1, from 10 to 138 meq kg?1. The corresponding base-buffer values, dB(OH)0→0.5 and dB(OH)0.5→1, ranged from 10 to 48 and from 14 to 44 meq kg?1, respectively. The most acid soils were most strongly buffered against acid, and the soils with the highest initial pH against base. The results reveal the acid-buffering by exchange reactions to be very important. In the soils with ZPT≦5.4, the first acid-buffer value was dependent on the content of organic matter and oxalate-soluble Al, whereas in the more acid soils the role of clay became significant. Thus, it was concluded that at higher pHs the foremost inactivation of H+ is attributable to soil components of pH-dependent charges, and the significance of constituents of permanent charges to increase with proceeding acidification. In strongly acid soils (ZPT≦4.8) the very effective buffering seemed to be primarily due to the dissolution of Al-hydroxides and, thus, to exert detrimental effects on the edaphic environment. The general rank of soil factors explaining the variation in the base-buffer values was in accord with the neutralization sequence, i.e. the strongest acid in the soil being neutralized first. In the strongly acid soils (ZPT≦4.8) the base-buffer values seemed to depend on the clay as well as KCl- and NH4OAc-extractable Al, whereas in the soils with higher initial pH mostly on organic C.  相似文献   

13.
The study aimed at evaluating whether salt-induced mobilization of acidity may be modified by the type of anion. For this purpose, the effects of different neutral salts on the solution composition of acid soils were investigated. The results were compared with those of the addition of acids. Two topsoil (E and A) and two subsoil horizons (Bs and Bw) were treated with NaCl, Na2SO4, MgCl2, MgSO4, HCl, and H2SO4 at concentrations ranging from 0 to 10 mmol dm?3. With increasing inputs of Cl? the pH of the equilibrium soil solution dropped, the concentrations of Al and Ca increased, and the molar Ca/(Al3+ + AlOH2+ + Al(OH)2+) ratios decreased. These effects were the least pronounced when NaCl was added and the most at the HCl treatments. According to the release of acidity, the topsoils were more sensitive for salt-induced soil solution acidification whereas on base of the molar Ca/(Al3+ + AlOH2+ + Al(OH)2+) ratios, the salt effect seems to be more important for the subsoils. Addition of S042? salts and H2SO4 induced higher pH and lower Al concentrations than the corresponding Cl? treatments due to the SO42? sorption, especially in the subsoils. The Ca/(Al3+ + AlOH2+ + Al(OH)2+) ratios were higher than those of the corresponding Cl? treatments. In subsoils even after H2SO4 additions these ratios were not higher than those of the NaCl treatments. The results indicate (I) that speculation about the effects of episodic salt concentrations enhancement on soil solution acidification not only need to consider the ionic strength and the cation type but also the anion type, (II) that salt-induced soil solution composition may be more crucial in subsoils than in topsoils, and (III) that in acid soils ongoing input of HNO3 due to the precipitation load may induce an even more acidic soil solution than the inputs of H2SO4 of the last decade.  相似文献   

14.

Purpose

Hydroxyl ion release by maize (Zea mays L.) roots under acidic conditions was investigated with a view to develop a bioremediation method for ameliorating acid soils in tropical and subtropical regions.

Materials and methods

Two hydroponic culture experiments and one pot experiment were conducted: pH, nitrogen state, and rhizobox condition, which investigated the effects of different nitrogen forms on hydroxyl release by maize roots under acidic conditions.

Results and discussion

The pH of the culture solution increased as culture time rose. The gradient of change increased with rising NO3 ?/NH4 + molar ratios. Maize roots released more hydroxyl ions at pH 4.0 than at pH 5.0. The amount of hydroxyl ions released by maize roots at a constant pH was greater than those at a nonconstant pH. Application of calcium nitrate reduced exchangeable acidity and increased the pH in an Ultisol rhizosphere, compared with bulk soil. The increasing magnitude of soil pH was greater at higher doses of N. The absorption of NO3 ?–N increased as the NO3 ?/NH4 + molar ratios rose, which was responsible for hydroxyl ion release and pH increases in culture solutions and rhizosphere.

Conclusions

Root-induced alkalization in the rhizosphere resulting from nitrate absorption by maize plants can be used to ameliorate acidic Ultisols.  相似文献   

15.
Employing four mathematical models (first-order, parabolic-diffusion, Elovich and zero-order), kinetics of potassium desorption from eight soils with and without cropping were studied to evaluate their ability in explaining K release from soils. The decline in the soil test K in cropped soils over original soils was drastic in easily desorbable forms compared to that of strongly held forms like 3 M H2SO4 K. Results showed that parabolic diffusion as well as first-order kinetic equation explained the K release data well for both original and K depleted (cropped) soils. Elovich and zero-order equations were not suitable to describe the kinetic data. However, zero-order equation explained K release data better in case of K-depleted soils as compared to original soils. Soils with higher initial K contents registered higher release rate constants. Over the entire period of cropping the range of release rate (b) decreased from 1.26 to 1.53 × 10?2 to values ranging from 1.12 to 1.30 × 10?2 h?1. In contrast, the first-order equation, parabolic diffusion showed higher b values for cropped soils as they represent the diffusion gradient. Mica and its biotite content in both silt and clay fractions showed significant correlation (r) with b values. Similarly with the rate of K release, clay content of soils maintained significant r whereas the silt content did not.  相似文献   

16.
Potassium (K) fixation and release in soil are important factors affecting K availability to plants and the utilization efficiency of K fertilizer. Three typical soils (red soil, yellow cinnamon soil, and alluvial soil) were collected from the middle and lower reaches of Yangtse River, China, to study the K-fixation and K-release characteristics of the normal and K-exhausted soil. Results showed that K fixation of added K in K-exhausted soils were significantly (P < 0.05) greater than that of the normal soils. There were significantly (P < 0.05) negative correlations among K-fixation capacity, concentration of soil-available K, and K+ saturation. Irrespective of soil K exhaustion, K fixation of added K was in the order of red soil > yellow cinnamon soil > alluvial soil, but the cumulative amount of K released from the three soils during successive extractions with 1.0 mol L?1 nitric acid (HNO3) was in the opposite order. The cumulative amounts of K released with 1.0 mol L?1 ammonium acetate (NH4OAc) and 1.0 mol L?1 HNO3 extraction increased with the increasing numbers of extractions. The K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was lower in K-exhausted soil than in normal soil. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.  相似文献   

17.
The predicted activity of Al in the soil solutions of acid forest soils often differs from that observed in the field. We have investigated the influence of soil structure and flow rate of the soil solution on the aluminum release to explain this divergence. Disturbed and undisturbed samples of soil were collected from the A and B horizons of a dystric cambisol at Waldstein (Fichtelgebirge, Germany). The samples were irrigated with solutions mixed according to field data on throughfall or soil solution composition with pH 3.5 with flow rates of 4 mm d?1, 12 mm d?1 and 36 mm d?1. The percolates were analysed for major ions. Resulting relations between pH and pAl were compared with batch experiments. In neither the A horizon nor in the B horizon did soil structure influence the relation between pH and pAl. The apparent equilibrium between pH and pAl was described as the pKapp value with pKapp= pAl—a pH (where a is an empirical constant). It was found that the pKapp values for the column percolates were in the range of variation of those found in batch experiments. Flow rate had no influence on pKapp at 4 and 12 mm d?1. At 36 mm d?1 a significant increase of pKapp was observed. This relative undersaturation of Al was more pronounced in the A horizon than in the B horizon. When flow is fast Al release into the percolating soil solution might be limited by diffusion.  相似文献   

18.
The evolution of C2H4 from soils was stimulated by air-drying, and still more by oven-drying at 105°C. The quantities evolved were closely correlated with organic matter content, with no significant difference in this relationship between grassland and arable soils, or between topsoil and subsoil. In arable soils only, the quantities of C2H4 also increased significantly with decreasing pH. No significant relationship could be found between NO3? concentrations in fresh soils and the quantities of C2H4 evolved, but for air-dried soils (arable only) there was a significant decrease with increasing NO3?. Artificial addition of NO3? only partially inhibited the evolution of C2H4, even at concentrations an order of magnitude higher than those found in the field. At normal soil concentrations the only effect of NO3? seems likely to be a short delay in the achievement of the maximum C2H4 concentrations.  相似文献   

19.
Amending soils with glucose (5 mg g?1) resulted in an immediate increase in microbial activity and within 30 min the rates of heat output and respiration at 22° C were increased by up to 17.8 and 23.4 times, respectively. The increased rate of heat output remained stable for up to 6 h and there was good correlation with the amount of CO2 respired. The soil biomass was calculated by the method of Anderson and Domsch (1978). The rate of heat output of the biomass varied in different soils and ranged from 11.5 to 83.7 Jh?1 g?1 biomass C. In glucose-amended soils, however, the rate of heat output was much more consistent; the soils were in two groups having between 169–265 Jh?1g?1 biomass C or 454–482 J h?1 g?1 biomass C, both the latter two soils were from pasture. The increased rate of heat output from the amended soils was lower than expected from the respiration rate and the heat of oxidation of glucose, suggesting that a proportion of the CO2 respired was from catabolism of substrates other than glucose. Use of 14C-glucose confirmed that between 57–91% of the CO2 was derived from the glucose substrate.  相似文献   

20.
Rate of zinc (Zn) release from solid to solution phase by organic acids can influence Zn availability in calcareous soils. The objective of the present study was to investigate the effect of different concentrations (1.1, 2.2, and 3.3 mM) of oxalic acid and citric acid on the kinetic release of Zn from two calcareous soils from Eastern Iran. The two organic acids showed significant difference in Zn release from studied soils. Cumulative Zn release during 72 h ranged from 5.85 to 10.4 mg kg?1 in soil 1 and ranged from 8.7 to 16.9 mg kg?1 in soil 2 using different concentrations of oxalic acid. The amount of cumulative Zn release after 72 h in soil 1 ranged from 13.65 to 28.77 mg kg?1 and from 17.63 to 23.13 mg kg?1 when different concentrations of citric acid was used. In general, Citric acid released 38% more Zn from soils than oxalic acid. The release of Zn from soils increased with citric acid concentration but decreased with increasing of oxalic acid concentrations in the solution. The simplified Elovich equation best described Zn release as a function of time (r2 = 0.93 and SE = 0.78). From the present study, Zn release from soils can be limited by the higher concentration of oxalic acid, while citric acid is suitable for enhancing soil lability of Zn.  相似文献   

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