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1.
This study was carried out with the objective of evaluating the effect of citrate concentration on the extraction efficiency of some micronutrients from soil. Composite surface soil samples (0–20 cm) were collected from Eastern Harage Zone (Babile and Haramaya Districts), Wolaita Zone (Damot Sore, Boloso Bombe, Damot Pulasa and Humbo Districts) and Dire Dawa Administrative Council in purposive sampling. The treatments were arranged in completely randomized design (CRD) with three replications. A greenhouse pot experiment with soybean plant was conducted to determine the correlation between soil test methods and the selected micronutrients, such as iron (Fe), copper (Cu), manganese (Mn) and zinc (Zn) in the leaves of the plant. The results showed that, among the different citrate concentrations with strontium chloride (SrCl2) tested for the determination of available Fe, Mn and Zn, the highest correlation coefficients (r = 0.82, p < 0.05), (r = 0.96, p < 0.001) and (r = 0.98, p < 0.001) were found between the diethylenetriamine pentaacetic acid (DTPA) method and 0.02 M strontium chloride (SrCl2)-0.025 M citric acid extractant, respectively. Therefore, 0.02 M SrCl2-0.025 M citric acid extractant is considered to be the most effective for the determination of Fe, Mn and Zn in soils of the studied areas. Similarly, high correlation coefficients (r = 0.97, p < 0.001) were found between DTPA and 0.02 M SrCl2-0.05 M citric acid and (r = 0.88, p < 0.01) between DTPA and 0.02 M SrCl2-0.025 M citric acid extractants for the determination of available Cu from soils. Hence, the 0.02 M SrCl2-0.05 M citric acid extractant was shown to be the best for the determination of Cu in soils of the studied areas. However, considering the use of universal extractant, the 0.02 M SrCl2-0.025 M citric acid extractant could easily be adopted as a procedure for the determination of Fe, Cu, Mn and Zn for both agricultural and environmental purposes. The greenhouse experiment confirmed the result.  相似文献   

2.
Abstract

Evaluation of nutrient status in soil is important for nutritional, environmental, and economical aspects. This research was carried out to determine the potassium (K) available to corn (Zea mays) in 15 soils from the Hamedan province in the west of Iran. The treatments included two K levels [0 and 200 mg K kg?1 as potassium sulfate (K2So4)] and 15 soils in a factorial experiment in a randomized block design with three replications. The results indicated that K application increased yield, K concentration, and K uptake of corn. According to the mechanism of the extraction, these extractants can be classified into four groups. The first group of extractants, acidic extractants, includes 0.02 M strontium chloride (SrCl2)+0.05 M citric acid, 0.1 M hydrochloric acid (HCl), and Mehlich 1. The second group includes 0.1 M barium chloride (BaCl2), 0.01 M calcium chloride (CaCl2), and 1 M sodium acetate (NaOAc). The third group includes 1 M ammonium acetate (NH4OAc), ammonium bicarbonate–diethylenetriamine tetraacetic acid (AB‐DTPA), and finally distilled water. The results showed that correlation between extractants in each groups were significantly high. Correlation studies showed that NH4OAc and AB‐DTPA cannot be used as available K extractants. The correlation of other extractants with relative yield, plant response, and K uptake were significantly high. Therefore, these extracting solutions can be used as available K extractants.

Potassium critical levels by extractants were also determined using the method by Cate and Nelson (1971) Cate, R. B. and Nelson, L. A. 1971. A simple statistical procedure for partitioning soil test correlation into two classes. Soil Science Society of America Proceeding, 35: 658–660. [Crossref], [Web of Science ®] , [Google Scholar]. Potassium critical levels for 90% relative yield were 29, 27, 82, 84, 45, 145, and 272 mg kg?1 for 0.002 M SrCl2, distilled water, 0.02 M SrCl2+0.05 M citric acid, 0.1 M HCl, Mehlich 1, 1 M NaOAC, and 0.1 M BaCl2, respectively.  相似文献   

3.
Abstract

Eight methods to determine exchangeable cations and cation exchange capacity (CEC) were compared for some highly weathered benchmark soils of Alabama. The methods were: (1) 1N NH4OAc at pH 7.0 by replacement (for CEC only), (2) 1N NH4OAc at pH 7.0 (summation of basic cations plus 1N KCl extractable Al), (3) 1N NH4OAc at pH 7.0 (summation of basic cations plus exchangeable H+), (4) 0.1M BaCl2 (summation of basic cations plus exchangeable Mn, Fe and Al), (5) Mehlich 1 (summation of basic cations plus 1N KCl extractable Al), (6) Mehlich 1 (summation of basic cations plus exchangeable H+), (7) Mehlich 3 (summation of basic cations plus 1N KCl extractable Al), and (8) Mehlich 3 (summation of basic cations plus exchangeable H+). The 0.1M BaCl2 was chosen as the standard method for the highly weathered soils and the other methods compared to it. The results indicated that the 1N NH4OAc replacement method gave significantly higher CEC values compared to the summation methods. This was probably due to the overestimation of the field CEC caused by measurement of pH dependent cation exchange sites in these soils. There was, however, close agreement between the BaCl2 method and the summation methods that included extractable Al. The generally good agreement between these summation methods suggests that the Mehlich 1 and Mehlich 3 extractants, commonly used to determine available nutrients in the southeastem USA, may also be used to measure effective CEC of some acid‐rich sesquioxide benchmark soils of Alabama. However, 1N KCl extractable Al as opposed to exchangeable H+ should be included in the computation.  相似文献   

4.
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   

5.
Abstract

The proportion of copper (Cu) that can be extracted by soil test extractants varied with the soil matrix. The plant‐available forms of Cu and the efficiency of various soil test extractants [(0.01 M Ca(NO3)2, 0.1 M NaNO3, 0.01 M CaCl2, 1.0 M NH4NO3, 0.1 M HCl, 0.02 M SrCl2, Mehlich‐1 (M1), Mehlich‐3 (M3), and TEA‐DTPA.)] to predict the availability of Cu for two contrasting pasture soils were treated with two sources of Cu fertilizers (CuSO4 and CuO). The efficiency of various chemical reagents in extracting the Cu from the soil followed this order: TEA‐DTPA>Mehlich‐3>Mehlich‐1>0.02 M SrCl2>0.1 M HCl>1.0 M NH4NO3>0.01 M CaCl2>0.1 M NaNO3>0.01 M Ca(NO3)2. The ratios of exchangeable: organic: oxide bound: residual forms of Cu in M1, M3, and TEA‐DTPA for the Manawatu soil are 1:20:25:4, 1:14:8:2, and 1:56:35:8, respectively, and for the Ngamoka soil are 1:14:6:4, 1:9:5:2, and 1:55:26:17, respectively. The ratios of different forms of Cu suggest that the Cu is residing mainly in the organic form, and it decreases in the order: organic>oxide>residual>exchangeable. There was a highly significant relationship between the concentrations of Cu extracted by the three soil test extractants. The determination of the coefficients obtained from the regression relationship between the amounts of Cu extracted by M1, M3, and TEA‐DTPA reagents suggests that the behavior of extractants was similar. But M3 demonstrated a greater increase of Cu from the exchangeable form and organic complexes due to the dual activity of EDTA and acids for the different fractions and is best suited for predicting the available Cu in pasture soils.  相似文献   

6.
Abstract

A new soil extractant (H3A) with the ability to extract NH4, NO3, and P from soil was developed and tested against 32 soils, which varied greatly in clay content, organic carbon (C), and soil pH. The extractant (H3A) eliminates the need for separate phosphorus (P) extractants for acid and calcareous soils and maintains the extract pH, on average, within one unit of the soil pH. The extractant is composed of organic root exudates, lithium citrate, and two synthetic chelators (DTPA, EDTA). The new soil extractant was tested against Mehlich 3, Olsen, and water for extractable P, and 1 M KCl and water‐extractable NH4 and NO2/NO3. The pH of the extractant after adding soil, shaking, and filtration was measured for each soil sample (5 extractants×2 reps×32 soils=320 samples) and was shown to be highly influential on extractable P but has no effect on extractable NH4 or NO2/NO3. H3A was highly correlated with soil‐extractable inorganic N (NH4, NO2/NO3) from both water (r=0.98) and 1 M KCl (r=0.97), as well as being significantly correlated with water (r=0.71), Mehlich 3 (r=0.83), and Olsen (r=0.84) for extractable P.  相似文献   

7.
Abstract

Five soil extractants, namely, 0.005 M diethylene triamine pentaacetic acid (DTPA) (pH 7.3), 0.005 M DTPA+1 M ammonium bicarbonate (pH 7.6), Mehlich 3, 0.01 M ethylene diamine tetraacetic acid (EDTA)+0.05 M ammonium carbonate (pH 8.6), and 1 M magnesium chloride (MgCl2) (pH 6.0), were evaluated to predict the response of wheat to zinc (Zn) application in Mollisols. These extractants could be arranged in the following decreasing order of their Zn extracting power: Mehlich 3>0.005 M DTPA+1 M ammonium bicarbonate>0.01 M EDTA+0.05 M ammonium carbonate>0.005 M DTPA>1 M MgCl2. The critical limits of Zn in soil, below which the yield response to late sown wheat (var. UP‐2338) to Zn application could be expected, were 0.57 mg 0.005 M DTPA (pH 7.3) extractable and 1.72 mg Mehlich 3–extractable Zn kg?1 soil. The critical limit of Zn in whole shoot at 60 days after emergence was found to be 26.1 mg Zn kg?1 plant tissue. The DTPA and Mehlich 3–extractable soil Zn also correlated significantly and positively with Zn concentration in whole shoot at 60 days after emergence and total Zn uptake by wheat at harvest.  相似文献   

8.
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   

9.
Abstract

Various soil tests are used to estimate phosphorus (P) availability for both crop uptake and potential loss to water. Conversion equations may provide a basis for comparison between different tests and regions, although the extent to which information can be interchanged is uncertain. The objective was to determine and quantify relationships between specific soil test extractants for samples taken annually in October and February over 4 years from four sites in each of eight soil series under grassland. The extractants comprised Mehlich‐3, Morgan, Olsen, Bray‐1, lactate–acetate, CaCl2 (1∶2 and 1∶10 soil–solution ratios), and resin. The results showed distinct relationships for each soil series, for which individual lines regression models (different intercepts and slopes) were superior to a single conversion equation across all soils. The ensuing difference between soils was large and ranged from 1.9 to 8.0 and 9.2 to 15.6 mg kg?1 P for Morgan and Olsen, respectively, at 20 mg kg?1 Mehlich‐3 P. Generally, the environmentally oriented tests CaCl2 and resin correlated best with Morgan. Some soil‐specific limitations were also observed. CaCl2 was less efficient than Morgan, and Morgan less efficient than Mehlich‐3 on a high Fe–P soil derived from Ordovician‐shale diamicton, compared with the general trend for other soils. This finding suggests that further disparity may arise where evaluation of critical, or other, limits across regions involves even a limited sequence of tests.  相似文献   

10.
Abstract

In this experiment, when the strontium chloride–citrate acid extractant (0.02 M SrCl2–0.05 M citrate) was used for extraction of calcareous soils with calcium carbonate greater than 70 g kg?1, the filtrate was turbid. Furthermore, white precipitation appeared when this extract was used for phosphorus determination with the Murphy and Riley method. As the concentration of citrate in strontium chloride–citrate acid extractant decreased to 0.025 or 0 M, the filtrate became clean. Further experiments indicated that the 0.02 M SrCl2 extractant could be used as a universal extractant for soil nitrate+nitrite and potassium; the extracted nitrate+nitrite and potassium significantly correlated with nitrogen and potassium phytoavailability, respectively, determined with ryegrass pot experiment (P<0.05). Thus, the 0.02 M SrCl2 was recommended as a universal extractant for soil nitrate+nitrite and potassium.  相似文献   

11.
Twenty surface (0–15 cm) samples of acidic soils were analyzed for water soluble (WS), exchangeable (EX), lead displaceable (Pb-disp.), acid soluble (AS), manganese (Mn) oxide occluded (MnOX), organically bound (OB), amorphous Fe oxide occluded (AFeOX), crystalline iron (Fe) oxide occluded (CFeOX) and residual (RES) fractions of Mn, and also for extractable Mn in some common soil extractants: (diethylenetriaminepentaacetic acid (DTPA) (pH 7.3), DTPA (pH 5.3), AB-DTPA (pH 7.6), Mehlich-3 (pH 2.0), Modified Olsen, 0.005 M calcium chloride (CaCl2), 1 M magnesium chloride (MgCl2) and ion exchange resins. The WS-Mn fraction showed a significant and positive correlation with Mn extractable in DTPA (pH 5.3) and AB-DTPA (pH 7.6), while both WS-Mn and EX-Mn fractions correlated significantly and positively with Mn concentration and uptake by maize plants grown in these soils. The AB-DTPA (pH 7.6) and DTPA (pH 5.3) appeared suitable to assess the availability of Mn in acidic soils.  相似文献   

12.
Optimal fertilizer nitrogen (N) rates result in economic yield levels and reduced pollution. A soil test for determining optimal fertilizer N rates for wheat has not been developed for Quebec, Canada, or many other parts of the world. Therefore, the objectives were to determine: 1) the relationship among soil nitrate (NO? 3)- N, soil ammonium (NH + 4)- N and N fertilizer on wheat yields; and 2) the soil sampling times and depths most highly correlated with yield response to soil NO? 3-N and NH + 4-N. In a three year research work, wet and dried soil samples of 0- to 30- and 30- to 60-cm depths from 20 wheat fields that received four rates of N fertilizer at seeding and postseeding (plants 15 cm tall) were analyzed for NH + 4-N and NO? 3 -N using a quick-test (N-Trak) and a standard laboratory method. Wheat yield response to N fertilizer was limited, but strong to soil NO? 3-N.  相似文献   

13.
Ammonium and nitrate are the major forms of nitrogen (N) present in tropical soils. An experiment was conducted to assess the influence of nitrate and ammonium forms (NO3?, NH4+, and mix of NO3? + NH4+), and levels (1.5–12.0 mM) of N on the growth and nutrition of cacao (Theobroma cacao L). Growth parameters were significantly influenced by N forms, and nitrogen supplied as NH4+ proved better for the growth of cacao compared with NO3? form and mixtures of these two forms. Irrespective of the forms of N, levels of N had no significant effect on plant growth parameters. Nutrient efficiency ratios (NERs) (shoot dry matter produced per unit of nutrient uptake) for macronutrients were sulfur>phosphorus>calcium>magnesium>nitrogen>potassium (S>P>Ca>Mg>N>K) and for micronutrients NERs were in the order of copper>boron>zinc>iron>manganese (Cu>B>Zn>Fe>Mn).  相似文献   

14.
Seventeen Mollisols having pH(1:2) in the range of 6.00 to 8.42 were analyzed with five extractants, and the extractable zinc (Zn) ranges were 0.84 to 2.75 mg Zn kg?1 soil for diethylenetriaminepentaacetic acid (DTPA) (pH 7.3), 0.91 to 2.72 mg Zn kg?1 soil for DTPA + ammonium bicarbonate (pH 7.6), 1.82 to 7.18 mg Zn kg?1 soil for Mehlich 3, 1.22 to 3.83 mg Zn kg?1 soil for ethylenediaminetetraacetic acid (EDTA) + ammonium carbonate, and 0.88 to 1.18 mg Zn kg?1 soil for 1 mol L?1 magnesium chloride (MgCl2) (pH 6.0). Zinc extracted by DTPA (pH 7.3) and Mehlich 3 showed significant positive correlation with sand content, whereas only Mehlich 3 showed negative correlation with soil pH. All extractants showed significant positive correlation with each other except for 1 mol L?1 MgCl2‐extractable Zn, which had significant positive correlation with only Mehlich 3– and EDTA + ammonium carbonate–extractable Zn. A greenhouse experiment showed that Bray's percentage yield of rice was poorly correlated to extractable soil Zn but had a significant and negative linear correlation with soil pH (r = ?0.662, significant at p = 0.01). Total Zn uptake by rice had a significant positive correlation with 1 mol L?1 MgCl2– and Mehlich 3–extractable Zn. A proposed parameter (p extractable Zn + p OH?) involving both soil extractable Zn and pH terms together showed significant and positive correlation with Bray's percentage yield and total Zn uptake of rice. The calculated values of critical limits of soil Zn in terms of the proposed parameter were 14.1699 for DTPA (pH 7.3), 13.9587 for DTPA + ammonium bicarbonate, 13.7016 for Mehlich 3, 13.9402 for EDTA + ammonium carbonate, and 14.1810 for 1 mol L?1 MgCl2 (pH 6.0). The critical limits of Zn in rice grain and straw were 17.32 and 22.95 mg Zn kg?1 plant tissue, respectively.  相似文献   

15.
A flow injection analysis (FIA) method capable of automation for molybdate reactive phosphorus (P) determination in soil extracts is described. Results obtained using this method in three soil extracts [calcium chloride (CaCl2), Olsen, and Mehlich I] were the same as those provided by the manual molybdate blue colorimetric method. Linear range extending to 2 mg P L?1, detection limits ranging from 6 to 26 µg L?1 depending on the soil extract, and accurate recoveries from P‐spiked samples were achieved. The sensitivity of the system was around 0.3 absorbance units per mg P L?1, and the sampling frequency was 72 samples h?1, higher than those described for most of the flow injection methods.  相似文献   

16.
Abstract

Phosphorus extractants have not been tested extensively in the Southeast. An experiment was carried out to compare four P extractant methods using samples from a field P‐K factorial experiment with soybeans (Glycine max (L.) Merr.) at three locations in Georgia over four years. There were five P rates ranging from none to 80 kg ha‐1. Soils and plant tissue were sampled at mid‐summer and yields were recorded. The four P extractants compared were Olsen, Mehlich 1, Mehlich 2, and Bray 1. Quadratic regressions for soil P versus plant P and P rates were not significant compared to linear regressions. There were no significant yield responses to P. All extractants except Olsen were similar in their response to added fertilizer P as measured by linear r2 values. Olsen P gave lower linear r2 values both with P rate and with plant P. Mehlich 1 values were highly correlated with Mehlich 2 (0.94**) and Bray 1 (0.96**). Mehlich 2 and Bray 1 gave nearly the same soil P values with linear regressions of slope of 1.0 and low intercepts. Results from these experiments show that Mehlich 1, Mehlich 2, or Bray 1 could be used successfully on these soils, but that Olsen should be avoided.  相似文献   

17.
Abstract

Extractants employed for routine soil analysis vary from one laboratory to another. Lack of a universal soil extractant is a serious limitation for interpretation of analytical results from various laboratories on nutritional status of a given soil. This limitation can be overcome by developing functional relationships for concentrations of a given nutrient extractable by various extradants. In this study, extractability of Ca, Mg, P, and K in a wide range of soils (0–15 cm) from citrus groves in Florida representing 21 soil series, with varying cultural operations, were compared using Mehlich 3 (M3), Mehlich 1 (M1), ammonium acetate (NH4AOc), pH = 7.0 (AA), 0.2M ammonium chloride (NH4Cl), and ammonium bicarbonate‐DTPA (AB‐DTPA) extractants. Soil pH (0.01M CaCl2) varied from 3.57 to 7.28. The concentrations of Ca or Mg extractable by M3, M1, AA, and NH4Cl were strongly correlated with soil pH (r2 = 0.381–0.482). Weak but significant correlations were also found between AB‐DTPA extractable Ca or Mg and soil pH (r2 = 0.235–0.278). Soil pH relationships with extractable K were rather weak (r2 = < 0.131) for M1 and NH4Cl but non‐significant for M3, AB‐DTPA, and AA. Concentrations of Ca, Mg, and K extractable by M3 were significantly correlated with those by either M1, AA, or NH4Cl extractants. Mehlich 3‐P was significantly correlated with P extractable by M1 extractant only. Mehlich 3 versus AB‐DTPA relationship was strong for K (r2 = 0.964), weaker for Mg and P (r2 = 0.180–0.319), and non‐significant for Ca. With the increasing emphasis on possible use of M3 as an universal soil extractant, data from this study support the hypothesis that M3 can be adapted as a suitable extractant for routine soil analysis.  相似文献   

18.
This trial was carried out to study the evolution of the nutrient parameters of the nutrient solution applied to tomato plants (Lycopersicum sculentum Mill. Forteza) cultivated in Mediterranean greenhouse conditions under different fertigation management models. The dynamic model is based on soil water content, which was measured by tensiometers, and on soil solutions obtained with suction cups (porous ceramic cup water samplers). The local traditional method consists of following technical recommendations, and the classical model requires the estimation of Crop Factor (Kc) and knowing the nutrient extraction. Nutrient solution and water applied are functions of the fertigation management criteria. The water used for fertigation was classified as C4-S3 according to the Riverside classification system. The cultivation period lasted from 15 August to 20 April. The nutrient parameters studied in nutrient and soil solution were pH, electrical conductivity (EC), nitrate (NO3 ?), phosphate (H2PO4 ?), potassium (K+), calcium (Ca2+), magnesium (Mg2+), sodium (Na+), and chloride (Cl?). The pH shows similar trends under the different treatments. Electrical conductivity is in the range of 2.8–4.5 dS m?1. Chloride, sodium, magnesium, and sulfate are exclusively modified by the salt concentration in the irrigation water, so it can be assumed that the three treatments vary equally. Nitrate, potassium, phosphate, and calcium are modified depending on each fertigation management method. Soil solution is modified by the nutrient solution applied. Dynamic management allows low nutrient concentration in the nutrient solution to be maintained and keeps soil nutrient concentration low, reducing fertilizer losses and therefore aquifer contamination.  相似文献   

19.
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   

20.
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   

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