首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 251 毫秒
1.
Knowledge of soil potassium (K) dynamics and quantification of plant-available K reserves are essential for the correct management of this nutrient. The objectives of this study, conducted in six Uruguayan mollisols, were to (i) determine the contribution of plant-available nonexchangeable K to plant nutrition, (ii) compare the ability of the ammonium acetate (NH4OAc) method and the sodium tetraphenylboron (NaBPh4) method to determine plant-available K, and (iii) quantify the effect of K fixation and release processes on the ability of both methods to estimate changes in K availability due to different K balances. In a greenhouse experiment, perennial ryegrass (Lolium perenne, cv. Horizon) was grown over a period of 320 days in six soils fertilized with 0, 100, 200, and 400 mg K kg–1. We measured plant K uptake and the changes in soil K status related to different K balances using NH4OAc and NaBPh4. Use of NaBPh4 resulted in a more accurate determination of plant-available K (R2 = 0.97 vs. 0.78) and soil K balance (R2 = 0.73 vs. 0.63), but neither of the methods was suitable for identifying positive K balances. However, when positive balances were established by K addition and incubation without plant growth, both methods related well with K balances. Again, NaBPh4 was better than NH4OAc (R2 = 0.98 and 0.88, respectively). The more accurate determination of plant K uptake and the strongest relationship with K balance of NaBPh4 was due to the extraction of exchangeable K plus a proportion of plant-available nonexchangeable K. Soil–plant interactions enhance soil K fixation in forms that are available to plant absorption but are not extractable by the chemical methods considered in this study.  相似文献   

2.
ABSTRACT

Quantity-Intensity (Q/I) parameters were used for elucidating the role of buffering properties of soils through K depletion. Winter wheat was sown in a greenhouse pot experiment until K-depletion and soils were analyzed with NH4OAc and NaBPh4 (1 min incubation period). Q/I isotherms (partitioned in exchangeable and non-exchangeable form) were constructed for the soils before and at the end of the K-exhaustion experiment. Results showed that NaBPh4-K correlated better than NH4OAc-K with intensity parameter (AReK) or labile K (-ΔΚ0) in K-depleted soils (r = 0.41 and 0.70), indicating the importance of non-exchangeable K in K dynamics. The latter was confirmed from the comparison of buffering characteristics between initial and K-depleted soils which showed that among the soils studied there was a group whose increase in buffering capacity (PBCKt) was due to non-exchangeable K fixation. Furthermore, NaBPh4-K was well predicted by the sum of exchangeable K and the quantity of K that has to be applied to achieve K balance as derived from Q/I isotherms (EK0 + CK0). Finally, relationships were found between Q/I parameters of the initial soils (-ΔΚ0i, ΕΚ0i, ΕΚri, CK0i) and the K-depleted ones (ΕΚrd, ΕΚ0d, CK0d, CKrd) which allowed corresponding prediction of the initial parameters (r2 = 0.78–0.87).  相似文献   

3.
Abstract

Potassium (K) fixation and release in soil are important issues in long‐term sustainability of a cropping system. Fixation and release behavior of potassium were studied in the surface and subsurface horizons in five benchmark soil series, viz. Dhar, Gurdaspur, Naura, Ladowal, and Nabha, under rice–wheat cropping system in the Indo‐Gangetic plains of India. Potassium fixation was noted by adding six rates of K varying from 0 to 500 mg kg?1 soil in plastic beakers while K release characteristics were studied by repeated extractions with 1 M HNO3 and 1 M NH4OAc extractants. The initial status of K was satisfactory to adequate. Potassium fixation of added K increased with the rate of added K irrespective of soil mineralogy and soil depth. Soils rich in K (Ladowal and Nabha) fixed lower amounts (18–42%) of added K as compared to Gurdaspur, Dhar, and Naura (44.6–86.4%) soils low in K. The unit fertilizer requirement for unit increase in available K was more in low‐K soils. The study highlights the need for more studies on K fixation in relation to the associated minerals in a particular soil. Potassium‐release parameters such as total extractable K, total step K, and CR‐K varied widely in different soil series, indicating wide variation in the K‐supplying capacity of these soils. K released with 1 M NH4OAc extractant was 20–33% of that obtained with 1 M HNO3. Total extractable K using 1 M HNO3 varied from 213 to 528 mg kg?1 and NH4OAc‐extractable K ranged from 71 to 312 mg kg?1 soil in surface and subsurface layers of different soil series. The Ladowal and Nabha series showed higher rates of K release than Gurdaspur, Dhar, and Naura series, indicating their greater K‐supplying capacity.  相似文献   

4.
Surface and subsurface horizons of 16 representative sugarcane growing soils with varying soil properties in the eastern region of Thailand were collected to determine the potassium (K) fertility status and its availability by using the quantity/intensity relationship (potential buffering capacity of K (PBCk)). The results showed that most soils had a low K fertility status and lack of reserved K from K-bearing minerals. The PBCk values of the studied soils ranged from 3.75 to 168 cmol kg?1/(mol L?1)1/2, and the coarse-textured soil group showed much lower PBCk values; these results suggested a low capability of these soils to replenish K removal by plant uptake compared with that of the fine-textured soil group. The negative delta K (ΔK°) values of the coarse-textured soil group also indicated a large quantity of readily available K for plant uptake that easily leaches at the same time. The higher K activity ratio (ARke) of the coarse-textured soil group (>0.001 mol L?1)1/2) than that of the fine-textured soil group (<0.001 mol L?1)1/2) suggested that readily available K was desorbed from the non-specific sites of 1:1 clay minerals and specific sites of 2:1 clay minerals, respectively. The ΔK° value of the studied soils was more significantly correlated to K concentration in sugarcane stalks (R2 = 0.64) than that of readily available K content (R2 = 0.54). Therefore, the results of this study suggested that ΔK° represents a better parameter to estimate K availability in these soils compared to conventional ammonium acetate (NH4OAc)-extractable K content.  相似文献   

5.
Surface soil (0–15 cm) and foliar samples of wheat, rice, sugarcane, and cotton crops growing in eight intensively cultivated soil series of India were collected from farmers' fields during 2004 and 2005. Analysis of soil and leaf samples indicated widespread potassium (K) deficiency in soils and crops. Potassium deficiency in wheat growing in Lukhi series (Udic Ustocrept) and Akbarpur series (Udic Haplustulf) and in cotton growing in Typic Torrifluvent were comparable to 1N ammonium acetate (NH4OAc)–K (available K) soil test values. Rice cultivated on Udic Ustocrept soils in summer monsoon season showed relatively less K deficiency in comparison to winter wheat, and K deficiency in growing rice did not match 1N NH4OAc‐K soil test values. In the Khatki series, K deficiency in sugarcane was much less than 1N NH4OAc‐K soil test values. In the Arsia series (Typic Haplustert), despite the high 1N NH4OAc‐K status of soils, K deficiency in growing wheat was observed.  相似文献   

6.
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   

7.
Berpura alluvial soil series of the Indo‐Gangetic Plains is situated in the Ambala District of the Haryana State of India. Soils of this series had medium concentrations of both potassium (K) and phosphorus (P) and large concentrations of sulfur (S) before 1970. To study different fractions of K, Olsen P, and 0.15% calcium chloride (CaCl2)–extractable (available) S of soils of the Berpura series and to create nutrient indexing of rice crops growing on this series, surface soil samples were collected from 100 farmers' fields after the harvest of the wheat crop in 2005. During kharif season of same year, samples of upper two leaves at anthesis growth stage of rice crop were also collected from the same 100 farmers' fields that had earlier been sampled for soil analysis. Analysis of soil samples showed more K depletion in soils of this series, of which 86% of farmers' fields were deficient in ammonium acetate (NH4OAc) K (available K). Thirty and 62% of leaf samples of the rice crop growing on the 100 fields of this series were extremely and moderately deficient in K, respectively. The mean values of water‐soluble, exchangeable, nonexchangeable, lattice, and total K were 10.6, 30.3, 390.0, 8204, and 8635 mg kg?1, respectively. In soils of this series, 0.123, 0.351, 4.517, and 95.009% of total K were found in water‐soluble, exchangeable, nonexchangeable, and lattice K forms, respectively. On the other hand, long‐term farmers' practice of more application of P fertilizer in wheat crop has resulted in P buildup in the soils of the Berpura series. Olsen P in soils of farmers' fields of this series ranged from 9.0 to 153.0 mg kg?1, with the mean value of 41.8 mg kg?1. Eighty‐two percent of leaf samples of rice crops grown on this series without application of P fertilizer were sufficient in P. The analysis of soil and rice crops for P and K proved the suitability of 0.5 M sodium bicarbonate (NaHCO3) and 1 N NH4OAc for extracting available P and K, respectively, in alluvial soils of the Indo‐Gangetic Plains. The 0.15% CaCl2–extractable S in this soil ranged from 9.6 to 307 mg kg?1 with a mean value of 34.6 mg kg?1. Four and 26% of soil samples had low and medium, respectively, in 0.15% CaCl2–extractable S. S deficiency was recorded in rice crops, as 29% of the leaf samples were extremely deficient in S and 58% were moderately deficient in S. This indicated the unsuitability of the 0.15% CaCl2 to extract available S from the Udic ustochrept utilized for cultivation of rice crops.  相似文献   

8.
Potassium fixation capacity and mineralogical analysis of 24 representative soils, collected from southern Iran, were studied. Potassium fixation analysis was performed by adding six rates of K from 0 to 1000 mg kg?1 soil in a plastic beaker and shaking for 24 h. Mineralogical analysis showed that the clay fractions were dominated by smectite, chlorite, mica, palygorskite, vermiculite and quartz. In general, the studied soils fixed 8.5–55% of the added K. The potassium fixation capacity of the studied soils was significantly correlated with smectite content (r 2 = 0.87), clay content (r 2 = 0.60), cation-exchange capacity (r 2 = 0.79) and NH4OAc-K. Wetting and drying treatment and incubation time had significant effects on K fixation. The average percentage increase in K fixation following the wetting and drying treatment was 24 and 30% for surface and subsurface soils, respectively. The average percentage increase in K fixation with increasing residence time was 79 and 56% for surface and subsurface soils, respectively. Because K fixation is a diffusion process, time and increased concentration of soluble K (because of soil drying) are factors affecting the rate of K diffusion from a soil solution to the interlayer positions of the expansible 2:1 clay minerals.  相似文献   

9.
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   

10.
土壤非交换态钾与结构态钾能够区分吗？   总被引：2，自引：0，他引：2  
Nonexchangeable K (NEK) is the major portion of the reserve of available K in soil and a primary factor in determining soil K fertility. The questions of how much NEK is in soils and how to quantify total NEK in soils are so far still unclear due to the complicated effects of various minerals on K fixation. In this study, the NEK in 9 soils was extracted with sodium tetraphenylboron (NaBPh4) for various time periods longer than 1 d. The results showed that the NEK extracted by NaBPh4 gradually increased with time, but showed no more increase after the duration of extraction exceeded 10--20 d. As the temperature increased from 25 to 45 oC, the duration to obtain the maximum extraction of NEK was reduced from 20 to 10 d, and the maximum values of NEK released at both temperatures was almost the same for each soil. The maximum NEK (MNEK) of the 9 soils extracted by NaBPh4 varied from 3 074 to 10 081 mg kg-1, accounting for 21%--56% of the total soil K. There was no significant correlation between MNEK released by NaBPh4 and other forms of K, such as NH4OAc-extracted K, HNO3-extracted K and total K in soils, which indicates that NEK is a special form of K that has no inevitable relationship to the other forms of K in soils. The MNEK extraction by NaBPh4 in this study indicated that the total NEK in the soils could be differentiated from soil structural K and quantified with the modified NaBPh4 method. The high MNEK in soils made NEK much more important in the role of the plant-available K pool. How to fractionate NEK into different fractions and establish the methods to quantify each NEK fraction according to their bioavailability is of great importance for future research.  相似文献   

11.
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   

12.
Most Brazilian soil-testing laboratories use Mehlich 1 and 1.0 M potassium chloride (KCl) solutions as extractants for the determination of phosphorus (P), potassium (K), and sodium (Na) and for exchangeable calcium (Ca), magnesium (Mg), manganese (Mn), and aluminum (Al) in agricultural soil samples. Other laboratories use a combination of exchangeable ionic resin and KCl procedures. With recent adoption of the inductively coupled plasma (ICP-OES) in routine soil-testing laboratories, soil extraction with 1.0 M ammonium chloride (NH4Cl) became an alternative due to the possibility of determining all exchangeable elements in one run (Ca, Mg, K, Mn, Na, and Al), leaving determination of phosphorus (P) with Mehlich 1 or exchangeable ionic resin. To evaluate the performance of the NH4Cl solution, an experiment was carried out with thirty-seven samples of soils representative of the southernmost state of Brazil, Rio Grande do Sul. Four extraction solutions [Mehlich 1 at soil/solution ratio of 1:10 and 1.0 M ammonium acetate (NH4OAc), 1.0 M KCl, and 1.0 M NH4Cl at soil/solution ratio 1:20] were used with three different shaking times (5, 30, and 60 min). Correlation coefficients among all methods were high. Mehlich 1 did not perform well against NH4OAc and NH4Cl, despite the high correlation coefficients, with values consistently lower for K, even when the time of extraction was increased from 5 to 30 or 60 min. However, for concentrations less than 0.30 cmol kg?1 (i.e., in the range of K deficiency), both solutions performed similarly. Calcium and Mg increased with time of shaking. Comparable values of exchangeable Ca, Mg, and K, as well as of Al and Mn, were obtained with 1.0 M NH4Cl with 60 min shaking and the standard procedures of 1.0 M NH4OAc and 1.0 M KCl. The determination of Al by traditional titration/back-titration of the 1.0 M KCl solution gave slightly greater results compared to ICP-OES obtained using extraction with 1.0 M NH4Cl. The results indicate that for Ca, Mg, Mn, and Al, it is possible to replace the traditional 1.0 M KCl extraction with 1.0 M NH4Cl solution, with 60 min shaking time and a soil/solution ratio of 1:20.  相似文献   

13.
  相似文献   

14.
ABSTRACT

The 1 M ammonium acetate (NH4OAc) (AA) is the most widely used method for soil-test potassium (K), but other methods have been also suggested to estimate crop available K. The accuracy of these extractants may be influenced by soil texture and clay mineralogy. This study evaluated the relationships among AA, Mehlich-3 (M3), and sodium tetraphenylboron (TPhB) methods using soils differing in texture and clay minerals from the agricultural area of Uruguay. The M3 and AA extractable K concentrations were highly correlated (R2 > 0.97) across soils, although AA extracted slightly higher amount of K than M3. The TPhB method extracted more K than AA and M3, indicating that extracted K from different pools. The slopes of the relationships between TPhB and AA or M3 varied among soils being higher in fine-textured and illitic soils than in coarse soils. These results would be useful for evaluating the feasibility of incorporating M3 into a test program using the existing calibrations of the AA method. In addition, TPhB could be considered a complementary tool to improve the interpretations of the extractants to estimate soil-test K along with other characteristics such as the texture and clay mineralogy.  相似文献   

15.
Knowledge of K-dynamics in soils can help devise practices for efficient K management in intensive rice-wheat systems. We studied the effect of long-term application of rice straw, farmyard manure (FYM) and inorganic fertilizer on total K and its distribution among different forms in 60-cm soil profile after 14 years of rice-wheat cropping. The exchangeable, the non-exchangeable and the lattice K respectively comprised 1%, 3–10% and 89–95% of total K in surface soil under different treatments. Application of rice straw and FYM positively impacted total K status of soil and its distribution among different forms. The greatest concentrations of total K, lattice K, exchangeable K and NH4OAc-extractable K were observed in plots receiving both rice straw and FYM together and the lowest in inorganic fertilizer treated plots. On the contrary, the non-exchangeable K was the highest in inorganically fertilized plots and the lowest in rice straw amended plots. The exchangeable, the water soluble and the NH4OAc-extractable K decreased with soil depth and did not indicate K movement beyond the rooting zone of the crops. The results showed that incorporation of rice residue in soil, instead of burning, besides reducing environmental pollution led to improved K-fertility of soils.  相似文献   

16.
Abstract

The enzyme arylamidase [EC 3.4.11.2] catalyzes the hydrolysis of N‐terminal amino acids from arylamides. Because it has been proposed that this enzyme may play a major role in nitrogen (N) mineralization in soils, studies were carried out using short‐term laboratory incubations under aerobic and anaerobic conditions and chemical hydrolysis of soil organic N to assess the N mineralization in a range of 51 soils from six agroecological zones of the North Central region of the United States. The enzyme activity was assayed at its optimal pH value. With the exception of the values obtained for field‐moist soils incubated under anaerobic conditions, the amounts of N mineralized by all the biological and chemical methods studied were significantly correlated with arylamidase activity, with r values of 0.54*** for the amounts of inorganic N produced under aerobic incubation, of 0.44** for anaerobic incubation of air‐dried soils, of 0.53*** and 0.55*** for the amounts of ammonium (NH4 +)‐N released by steam distillation with PO4‐B4O7 for 4 and 8 min, respectively; and of 0.49*** and 0.53*** for the amounts of NH4 +‐N released by steam distillation with disodium tetraborate (Na2B4O7) for 4 min or 8 min, respectively. The amounts of N extractable with hot potassium chloride (KCl) were most significantly correlated with arylamidase activity (r=0.56***). Arylamidase activity was significantly correlated with organic carbon (C) (r=0.49***), organic N (r=0.55***), and fixed ammonium (NH4 +)‐N (r =0.42**).  相似文献   

17.
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   

18.
The suitability of seven chemical extractants was evaluated on 24 Indian coastal soils for prediction of plant-available potassium (K) to rice (Oryza sativa L. var. NC 492) grown in modified Neubauer technique. Average amounts of soil K extracted were in descending order: 0.5 M NaHCO3 > neutral 1 N NH4OAc > 0.02 M CaCl2 > Bray and Kurtz No.1 > 1 N HNO3 > 0.1 N HNO3 > distilled water. The highest simple correlation with plant K uptake was obtained with 0.1 N HNO3-K (r = 0.848) and lowest with CaCl2-K (r = 0.805). Predictive models were developed using plant K uptake as the dependent variable and extractable soil K, sand, silt, soil pH, and electrical conductivity as the independent variables. Based on the final R2 and ease of measurement, distilled water, 1 N NH4OAc, and 0.1 N HNO3 models were the best predictors of plant-available K in coastal soils when used along with sand or soil pH.  相似文献   

19.
Abstract

The effect of sesquioxides on the mechanisms of chemical reactions that govern the transformation between exchangeable potassium (Kex) and non‐exchangeable K (Knex) was studied on acid tropical soils from Colombia: Caribia with predominantly 2∶1 clay minerals and High Terrace with predominantly 1∶1 clay minerals and sesquioxides. Illite and vermiculite are the main clay minerals in Caribia followed by kaolinite, gibbsite, and plagioclase, and kaolinite is the major clay mineral in High Terrace followed by hydroxyl‐Al interlayered vermiculite, quartz, and pyrophyllite. The soils have 1.8 and 0.5% of K2O, respectively. They were used either untreated or prepared by adding AlCl3 and NaOH, which produced aluminum hydroxide. The soils were percolated continuously with 10 mM NH4OAc at pH 7.0 and 10 mM CaCl2 at pH 5.8 for 120 h at 6 mL h?1 to examine the release of Kex and Knex. In the untreated soils, NH4 + and Ca2+ released the same amounts of Kex from Caribia, whereas NH4 + released about twice as much Kex as Ca2+ from High Terrace. This study proposes that the small ionic size of NH4 + (0.54 nm) enables it to enter more easily into the K sites at the broken edges of the kaolinite where Ca2+ (0.96 nm) cannot have access. As expected for a soil dominated by 2∶1 clay minerals, Ca2+ caused Knex to be released from Caribia with no release by NH4 +. No Knex was released by either ion from High Terrace. After treatment with aluminum hydroxide, K release from the exchangeable fraction was reduced in Caribia due to the blocking of the exchange sites but release of Knex was not affected. The treatment increased the amount of Kex released from the High Terrace soil and the release of Knex remained negligible although with Ca2+ the distinction between Kex and Knex was unclear. The increase in Kex was attributed to the initially acidic conditions produced by adding AlCl3 which may have dissolved interlayered aluminum hydroxide from the vermiculite present, thus exposing trapped K as exchangeable K. The subsequent precipitation of aluminum hydroxide when NaOH was added did not interfere with the release of this K, and so was probably formed mostly on the surface of the dominant kaolinite. Measurement of availability of K by standard methods using NH4 salts could result in overestimates in High Terrace and this may be a more general shortcoming of the methods in kaolinitic soils.  相似文献   

20.
Effect of potassium (K) fertilization (0, 20, 40, 60, 80 and 100 kg K ha?1) on yield, nitrogen (N) and K nutrition of Boro (dry season) rice and apparent soil K balance was studied. Experiment was conducted at Bangladesh Rice Research Institute (BRRI) regional station farm, Habiganj, Bangladesh during 2007–2008 to 2009–2010 in a wetland rice ecosystem under haor area. Cropping pattern was Boro–Fallow–Fallow. A popular rice variety BRRI dhan29 was tested in a randomized complete block design with three replications. Results indicated that BRRI dhan29 maintained an average grain yield of 5.19 t ha?1 year?1 without K fertilization. Potassium fertilization significantly increased the grain yield to 6.86 t ha?1 year?1. Quadratic equations best explained the progressive increase of rice yield with increasing K rates. Optimum dose of K in 3 years ranged from 78 to 93 kg ha?1. Internal N use efficiency of rice decreased with increasing K rates. However, K use efficiency was inconsistent. Apparent K balance study revealed that application of 100 kg K ha?1 was not able to maintain a positive K balance in soil under wetland ecosystem with Boro–Fallow–Fallow cropping system. However, K fertilization decreased the negativity of K balance in soil.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号