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1.
Abstract

Soil tests are used to predict fertilizer and liming needs of legumes being introduced into permanent pastures. However, the routine drying of soil samples may change the soil characteristics so much that recommendations based on test results may be poorly related to actual plant needs in the field.

Test results from four soils, based on dried and moist samples, were related through stepwise multiple regression to percent nodulation and dry weight of white clover (Trifolium repens L. ) seedlings grown on soil cores in the greenhouse. Highly variable test results were obtained for Al, Mn, and P, depending on if a sample was dried or maintained moist. These discrepancies have implications for making P fertilizer and liming recommendations. Test results for other elements also varied widely.

Extractable Mn and P accounted for most of the variation observed in percent nodulation, whether soil samples were dried or not. There was a significant interaction of P, Al, and Mn extracted from dried soils with plant weight. This contrasted with the significant interaction of extractable P, Ca, K, and Mg with plant weight observed when soil samples were not dried before analysis.

Drying soil samples before analysis improved, rather than harmed, the ability of soil tests to predict white clover growtl responses on these soils. However, the soil tests explained only 40 percent of the variation in plant growth.  相似文献   

2.
Abstract

A greenhouse experiment was conducted to investigate the effect of root growth and exudation of 3 crop species on soil aggregation. Two plant populations for each of 3 crops (corn, soybeans, and wheat) were grown in a Fincastle silt loam for 5 time periods (7, 14, 21, 28, and 41 days) and compared with fallow controls. Aggregate stability was estimated by the wet‐sieve method on both initially moist and air‐dry samples.

Soil water content of initially moist soil samples varied widely among replicates, crops, and sampling dates. Wet‐sieving using initially moist soil showed that samples with higher initial soil water content had greater aggregate stability. Wet‐sieving performed on initially air‐dry soil samples was used for subsequent interpretation because the water content variable was removed.

The presence of any crop and its roots in the planted soils versus the fallow controls was associated with increases in aggregate stability. No differences in aggregate stability were found among the different crops or over the established range of root length densities. Aggregate stability decreased from the original level during the first 14 to 21 days of the experiment, possibly due to daily watering. After 21 days, as root growth continued to increase, restabilization occurred until the original aggregate stability of the soil was exceeded for all crops. The observed increase in aggregate stability may be due in part to the physical entanglement of aggregates by roots and to the increased production of root exudates resulting from increased root growth.  相似文献   

3.
Abstract

On air‐drying, the ATP contents of two moist soils fell to about one quarter of their original values. When a freshly‐sampled soil (field temperature 5.5°C) was stored moist (43% water holding capacity) for 7 days at 25°C the ATP content increased from 4.54 to 7.84 μg ATP g‐1 soil. Storage at 10°C caused a smaller increase; to 5.39 μg g‐1 soil. Microbial biomass C also increased on storage but the relative increase was less than that of ATP. Thus the biomass C/ATP ratio fell from 234 in the freshly sampled soil to 168 in the soil stored moist for 7 days at 25°C. The ATP content declined to less than half its starting value if storage was under waterlogged conditions.

The ATP method for determining microbial biomass in soil depends on the use of a constant factor (5.85 mg ATP g‐1 biomass C) for converting ATP content to biomass C. This factor came from work on soils that had been stored moist at 25°C for several days before biomass C and ATP measurements were made: it is only applicable to soils that have been stored in this way.  相似文献   

4.
Abstract

Rhizosphere soils had higher amounts of ‘readily soluble’, ‘weakly adsorbed’, ‘carbonate bound’ and ‘specifically adsorbed’ Mn, but had lower amounts of ‘oxide‐Mn’, than did bulk soils. This observation was true regardless of whether the comparison was based on values within moist or air‐dried treatments. Observed trends in Mn distribution between different soil fractions were qualitatively similar regardless of method of sample preparation. However, there were substantial quantitative differences depending on the method of sample preparation. Air‐dried samples increased significantly in the ‘oxide‐Mn’ fraction and decreased in its soluble and adsorbed fractions relative to moist soil samples. There was a significant effect of method of air‐drying on the distribution of Mn in rhizosphere samples. Samples that were extracted moist at first and then air‐dried accumulated more adsorbed Mn and were depleted in ‘oxide‐Mn’ relative to samples that were air‐dried initially. There was a significant rhizosphere x air‐drying interaction. Air‐drying of some rhizosphere samples resulted in a significant underestimation of the ‘readily soluble’, ‘specifically adsorbed’, and ‘oxide‐Mn’ fractions beyond the overall effect of air‐drying. The results of this study suggested that soil samples used for Mn analyses be extracted immediately in a moist condition rather than air‐dried, particularly for analyses of rhizosphere soil samples.  相似文献   

5.
Abstract

Most soil testing laboratories require soil samples collected for the pre‐sidedress soil nitrate test (PSNT) to be dried before shipment. Shipment of field‐moist samples would make it easier to use the test. The objective of this study was to measure the effect of bag type on changes in soil nitrate in samples collected for the PSNT. Soil samples were collected from the surface foot of soil when corn (Zea mays L.) plants were 15‐ to 30‐cm tall. Four fields with a history of manure applications were sampled. The bulk sample was subsampled in the field and the subsamples were kept cool during transport to the laboratory and were immediately air dried after arrival at the laboratory. Field‐moist subsamples from each bulk sample were placed into either cloth bags or plastic‐lined paper bags after arrival at the laboratory. Four replications of the subsamples were incubated at 30°C for 1, 2, 3, and 4 days. After removal from the incubator, the subsamples were immediately spread to air dry. The soils incubated in the plastic‐lined paper bags did not significantly increase in nitrate after one day of incubation. There was a significant increase, however, in nitrate each day after the second, third and fourth day of incubation. The soils incubated in the cloth bags did not significantly increase in nitrate until the fourth day of incubation. The average increase in nitrate‐N concentration in the cloth bags between day 3 and day 4 was 1.5 mg kg L‐1soil. The results suggest that cloth bags could be used to ship field‐moist soil samples for the PSNT without significant changes in soil nitrate concentrations.  相似文献   

6.
Abstract

The extraction of a field‐moist soil with DTPA will result in a level of extractable iron (Fe) lower than that of the air‐dried soil. Soil gas‐phase carbon dioxide (CO2) levels may be considerably higher than ambient atmospheric levels, especially in wet soils in the field. This study was undertaken to determine whether gas‐phase CO2 level influences the quantity of Fe extracted by DTPA. Three moist calcareous soils were incubated for 21 days, each at three different partial pressures of CO2, after which the moist soils were extracted with DTPA. A sample of each soil was also air dried, and was subsequently extracted with DTPA. In each case, DTPA‐extractable Fe from the moist sample was lower than that from the air‐dried sample; however, DTPA‐extractable Fe increased with increasing CO2 partial pressure of in the moist soils. DTPA‐extractable Fe concentration for a given soil following air drying was not significantly influenced by the CO2 partial pressure during incubation of the originally field‐moist soil. DTPA‐extract pH of the moist soils followed the same trend as soil‐solution pH (i.e., as CO2 concentration of the soil gas‐phase increased, soil solution pH and DTPA extract pH both decreased); however, the slope of the pH versus log PCO2 curve was less pronounced in the DTPA extract due to the buffering capacity of the triethanolamine. From this study, it is concluded that elevated soil gas‐phase CO2 partial pressure does not contribute to the lower level of DTPA‐extractable Fe observed when the extraction is performed on a field‐moist versus an air‐dried soil; increased CO2 partial pressure actually resulted in a slight increase in concentration of DTPA‐extractable Fe obtained from a field‐moist soil.  相似文献   

7.
Abstract

The effect of drying on the cation (CEC) and anion (AEC) exchange capacity, and on potassium (K) and magnesium (Mg) adsorption by three New Zealand soils was investigated. Air‐drying resulted in no significant changes in these properties compared with the field‐moist samples. Oven‐drying at 105°C significantly decreased the CEC and increased the AEC of most soils compared with air‐dried samples. The decrease in CEC was related to increased solubility of organic matter and a decrease in surface area on which charge could be developed. The increase in AEC was attributed to a decrease in soil pH.

Potassium and Mg adsorption by two soils decreased following oven‐drying. This was consistent with the effect of drying on CEC. For the remaining soil, K adsorption increased following oven‐drying. This was attributed to K fixation.  相似文献   

8.
Abstract

Tests were made to determine the effects of grinding, type of extraction vessel, type of shaker, speed of shaking, time of shaking, time of filtering, soil to solution ratio and other variables on DTPA‐extractable Zn, Fe, Mn, and Cu from soils.

Time of grinding, force of grinding, and the quantity of soil being ground greatly affected the amount of extractable Fe. At the lower grinding force, the quantity of soil being ground only slightly affected extractable Fe, but at the higher grinding force, more Fe was extracted from the smaller sized samples especially at the longer grinding period. Extractable Zn was also increased by longer grinding time and greater grinding force, but increases were much less than increases for Fe. Increasing grinding time tended to increase extractable Mn. The effects of grinding on Cu was inconclusive. Increasing the ratio of extractant to soil increased the amount of extractable Fe from soils and tended to increase Zn, Mn, and Cu but to a lesser extent. Both shaker speed and type of extracting vessel affected the ex‐tractability of all nutrients except Cu. Greatest differences between extracting vessels occurred at the lowest shaker speed, while these differences were smaller or disappeared at the higher shaker speeds. The more thorough the mixing of soil and extracting solution, the higher were the levels of extractable Fe and Mn. A reciprocal shaker extracted more Fe and Mn from soils than a rotary shaker. The rate of dissolution of all four nutrients by DTPA was greatest during the first 5 minutes of extraction. There were large and significant correlation coefficients between levels of nutrients extracted after 15 or 30 minutes of shaking and those extracted after 120 minutes. The findings indicate that the levels of micronutrients extracted under one set of conditions can be related to levels extracted under other conditions by use of a simple linear regression equation for each nutrient.

The results of this study demonstrate the importance of standardizing the methods of preparation and extraction of soils used in the DTPA micronutrient soil test. A standard method for soil grinding and extraction is proposed for DTPA soil test.  相似文献   

9.
Abstract

We compared sequential and separate extraction procedures for estimating non‐crystalline and crystalline aluminum (Al) and iron (Fe) in a floodplain forest soil. We used 0.2M acid ammonium oxalate (pH 3.0) to estimate non‐crystalline Al and Fe, dithionite‐citrate‐bicarbonate to estimate crystalline Fe, and 0.1M sodium hydroxide (NaOH) to estimate crystalline Al. Both separate and various combinations of sequential extractions were compared, as well as variations in soil:solution ratio, extraction time, extraction temperature, and the use of field‐moist versus dried soils. A sequential oxalate/NaOH extraction, using 0.4 g dry weight equivalent of field‐moist soil and a soil:solution ratio of 1:100, gave the best estimate of non‐crystalline Al and Fe and crystalline Al, while a separate 16 hour DCB extraction at room temperature, using 0.8 g dry weight equivalent of field‐moist soil and a soil:solution ratio of 1:50, gave the best estimate for non‐crystalline plus crystalline Fe. A sequential oxalate/NaOH extraction followed by a separate DCB extraction is a relatively simple procedure for estimating amounts of non‐crystalline and crystalline Al and Fe in large numbers of soil samples.  相似文献   

10.
Abstract

A buffer is generally a mixture of a weak acid and a salt of the same weak acid. Hence it can neutralize both acids and bases, and thus resists marked changes in pH of a system. Yet systematic change in pH of a buffer caused by addition of an acidic substance can be used to indicate the total acidity represented by the change in buffer pH. Since acid soil is itself a buffer, when it is added to a buffer mixture for the purpose of measuring its acidity or lime requirement (LR), the resulting double‐buffer suspension (soil‐buffer) is a relatively complex system. Much of the complication in interpreting the changes in buffer pH brought about by mixing soil and buffer stems from the facts: i) that much of the acidity is pH‐dependent, and ii) that quick‐test methodology involves reaction of only a fraction of the total soil acidity with the buffer. Marked change in relative amounts of H ions dissociating from the soil‐SMP‐buffer system at soil‐buffer pH 6.9 and above accounts for relatively wide variations between buffer‐indicated and CaCO3 incubation‐measured LR of low LR soils. Similarly, decreased reactivity of H+ in high organic matter soils and increased reactivity of H in acid‐leached soils cause errors in buffer‐indicated LR. Awareness of these principles helps avoid pitfalls of existing buffer methods, and has led to incorporation of the double‐buffer feature for improving the SMP method.  相似文献   

11.
Abstract

The Mehlich‐3 method extracts a quantity of phosphorus (PM3) well correlated with crop yield in acid soils, and a quantity of aluminum (AlM3) well correlated with P sorption capacity of mineral soils. Phosphorus fertility levels in soils are generally determined on a volume basis, while soil sorption capacity for P and P saturation of the soil sorption capacity are assessed on a weight basis. However, scooped weights vary widely among tested soils. The purpose of this paper was to test the stability of a constructed ratio of PM3/AlM3 across a range of soil:solution ratios using 24 soils. Twenty‐four surface soils of different genetical and textural groups were extracted for PM3 and AlM3 without replication. Scooped weights varied between 3.21 and 4.17 g per 3‐mL scooped volume. Reproducibility of volumetric test (3 mL of soil per 30 mL of Mehlich‐3 solution) was within 3% for PM3, AlM3, and 100PM3/AlM3 using two contrasting soils with two replications. Extracted PM3 and AlM3 expressed on a weight basis decreased across the 24 soils as sample weight increased between 1.50 and 5.00 g, by steps of 0.50 g, per 30 mL of extracting solution. The 100PM3/AlM3 ratio was less variable than PM3 or AlM3 taken alone using a wide range of sample weights. In contrast with PM3 and AlM3 values taken alone, the 100PM3/AlM3 ratio produced stable data across the entire range of sample weights corresponding to scooped weights between 0.50 and 1.67 g mL‐1, as shown by a power test. The 100PM3/AlM3 ratio could be used simultaneously as a P saturation index for assessing environmental risk, and as a P fertility index for making fertilizer recommendations.  相似文献   

12.
Abstract

Single buffer‐two pH and two‐buffer adaptations were compared as double buffer features of the SMP method using a group of 54 soils of wide range in lime requirement (LR). Data from both methods were highly correlated both with each other and with Ca(OH)2‐titrated acidity.

Formulas for LR based on the schematics of similar triangles relating differences in measured pH vs corresponding acidities for the double buffer system were developed. A regression equation relating buffer‐indicated LR and Ca(OH)2 titrated acidity was used to adjust the quick‐test double buffer‐indicated values to levels nearer the actual ones. A recommended SMP double buffer procedure, and a formula for computing LR from soil‐buffer pH's measured by the double buffer, quick‐test method are presented.  相似文献   

13.
Abstract

Sloping and eroding soils are often avoided by many agronomists when selecting a site for long term crop or soils research due to concerns about the impact of soil variability on experimental results. The extent of soil loss and erosion phase was determined by comparisons of soil properties at the cultivated site with a forest site having similar soil, slope and landscape characteristics. The cultivated site was dominated by the moderately eroded phase of the Grantsburg soil with approximately 7.5 cm of soil (38% of upper 20 cm of original soil) eroded during the previous 80 years. Prior to the establishment of the tillage treatments of no‐tillage (NT); chisel‐plow (CP); and moldboard plow (MP), a number of selected soil property parameters were examined to measure the inherent soil conditions that existed within the experimental area, and to test the precision of the experimental design. An experimental design was selected which fit within the field boundaries, landscape position, soil and slope constraints. The experimental design was a Youden Type III, and Incomplete Latin Square, that allowed for randomization of treatments to the plots by both row (block) and column (replication) to control random variability in the two directions. Overall, the experimental design selected to control random variability that existed within the experimental area was effective. This was evidenced by the lack of significant differences among most of the tillage treatment locations with respect to the background data collected.  相似文献   

14.
Abstract

A procedure for extraction and measurement of nitrate‐nitrogen (NO3‐N) in soil is described. Extracting solution [0.025M Al2(SO4)3] and field‐moist soil are measured volumetrically, with NO3‐N concentration measured by nitrate‐sensitive colorometric test strips or nitrate‐selective electrode. Across a range of soil texture, moisture content, and NO3‐N concentration, the procedure was well correlated with conventional laboratory analysis of 2N KC1 soil extracts (r2 = 0.94). This quick test procedure is proposed as an on‐farm monitoring technique to improve N management.  相似文献   

15.
Abstract

Samples of four soils having a wide range of volume weights (0.65, 1.02, 1.25, 1.62 g/cm3) were either weighed or measured by volume and extracted with: (a) the Bray P1 extractant, (b) the Mehlich double acid extractant for P, K, Ca, Mg, Mn, Zn and (c) neutral N NH4OAc for K, Ca, Mg all at a soil/extracting solution ratio of 1:10. The soil test results were recorded on a volume basis in mg/dm3 and on a weight basis in mg/kg.

The test values for all macronutrients obtained with all extractants decreased, relative to a constant volume, with increasing VW of soil when analyzed and expressed on a weight basis. Results based on the use of a volume sample (scooped) but calculated on an assumed weight of soil changed the values in direct ratio of 1/assumed VW. The use of an assumed VW has no justification, since uniform soil test results can be obtained when expressed on a volume basis by either using a scooped sample of known volume or a weighed sample followed by multiplication with the VW of each soil.  相似文献   

16.
Abstract

Problems are invariably encountered when attempts are made to explain the variability in Bray percent yields or plant response in terms of soil or plant iron (Fe). To resolve this inconsistency, the present investigation was initiated to identify a combination of soil extractable Fe, soil properties and form of plant Fe that may be used as a measure of Fe deficiency. The study involved 16 diverse soils, using upland rice (Oryza sativa L.) as the test crop and Fe‐EDDHA [ferric ethylenediamine di (o‐hydroxyl‐phenyl acetic acid)] as source of Fe. The results showed that Bray percent yields were neither related to DTPA (diethylenetriamine pentaacetic acid) or EDTA (ethylenediamine tetraacetic acid) extractable Fe nor with total plant Fe. Even the inclusion of pH, lime, organic carbon and clay data in the regression equations was of no value. However, Bray percent yields were significantly and positively (r = 0.57* ) associated with ferrous Fe (Fe2+) in 40‐day‐old rice plants. The explanation concerning variability in Bray percent yields obtained on diverse soils could be increased about one and half 2 times (R2= 0.59*) if the contribution of lime and soil pH was also incorporated in the stepwise regression analysis. The individual contribution to R of lime, pi respectively. Thus, it appears that Fe2+ concentration in plants (along with soil pH) may identify Fe deficiency. The critical limit to separate Fe deficient from green rice plants was set at 45 ug Fe2+/g in the leaves.  相似文献   

17.
Abstract

In Western Australia soil samples to measure soil‐test phosphorus (P) are collected November to March when soils are usually dry. Most of the soils are hard‐setting when dry and it is difficult to penetrate and collect soil samples to 10 cm using the traditional sampler, which is a 2.5 cm diameter tube that is pushed into the soil by foot. Farmers collect too few soil samples at shallow depths to measure soil‐test P. In Part 1 of this paper, it was shown that soil‐test P can vary markedly for individual soil samples collected from uniform areas in paddocks. Consequently, an adequate number of soil samples needs to be collected and bulked from defined areas to measure soil‐test P. Phopshorus accumulates near the top of the soil of (i) pastures since P fertilisers are applied to the surface of pastures, and (ii) crops sown by minimum (conservation) tillage. Crops are increasingly being sown using conservation tillage methods. Collecting too few soil samples to a shallow depth can result in large errors when estimating the current P status of soils and determining optimum fertiliser application levels. A new rotating blade method of collecting soil samples to the standard 10 cm depth for measuring soil‐test P was compared with the traditional sampler. The new sampler successfully penetrated hard‐setting soils to the standard depth and the soil samples it collected produced similar soil‐test P as the traditional sampler. Consequently, the same soil‐test P calibrations determined using the traditional sampler can also be used for the new sampler. The new sampler is, therefore, recommended for collecting soil samples to measure soil‐test P. It should have application wherever hard‐setting soils pose a problem for soil P testing.  相似文献   

18.
Abstract

Studies with 42 soils selected to obtain a wide range in properties showed that air‐dry and moist soils have substantial capacities for sorption of H2S from air (averages, 9.8 and 12.5 g S kg‐1 soil, respectively). Soil properties influencing the capacities of air‐dry soils for sorption of H2S included sand and clay contents, DCB‐soluble Mn, exchangeable Na, DCB‐soluble Fe, and total DCB‐soluble metals. The corresponding capacities of moist soils were influenced by sand and clay contents, DCB‐soluble Mn, and surface area. It was possible to closely predict the H2S sorption capacities of both air‐dry and moist soils (R2 = 0.804 and 0.918, respectively) from consideration of their properties.  相似文献   

19.
Abstract

This study was carried out to determine if ammonium bicarbonate‐DTPA soil test (AB‐DTPA) of Soltanpour and Schwab for simultaneous extraction of P, K, Zn, Fe, Cu and Mn can be used to determine the availability index for Se. Five Mollisols from North Dakota were treated with sodium selenate and were subjected to several wetting and drying cycles. These soils were extracted with hot water and with ammonium bicarbonate‐DTPA (AB‐DTPA) solution for Se analysis. Alfalfa plants were grown in these soils in a growth chamber to determine plant uptake of Se. In addition to the above experiment, coal mine soil and overburden materials from Western Colorado were extracted and analyzed as mentioned above.

It was found that hot water and AB‐DTPA extracted approximately equal amounts of Se from Mollisols. A high degree of correlation (r =0.96) was found between Se uptake by plants and AB‐DTPA extractable Se. Extractable level of Se in treated soils was decreased with time due to change of selenate to less soluble Se forms and plant uptake of Se. An AB‐DTPA extractable Se level of over 100 ppb produced alfalfa plants containing 5 ppm or higher levels of Se that can be considered toxic to animals. Soils with about 2000 ppb of extractable Se were highly toxic to alfalfa plants and resulted in plant concentrations of over 1000 ppm of Se. The high rate of selenate (4ppm Se) was less toxic to alfalfa plants in soils of high organic matter content. This lower toxicity was accompanied with lower extractable levels of Se.

The AB‐DTPA solution extracted on the average about 31% more Se than hot water from the mine and overburden samples and was highly correlated with the latter (r =0.92). The results indicated the presence of bicarbonate‐exchangeable Se in these materials.  相似文献   

20.
Abstract

Since only one extraction is required to determine a large number of nutrients, many laboratories employ universal extractants to determine the available nutrients in a soil sample. This paper compares the universal ammonium bicarbonate‐DTPA (AB‐DTPA) method developed by Soltanpour and Schwab (1977) with the traditional methods, ammonium acetate (NH4OAc) test for exchangeable cations and the Lindsay and Norwell (1969) test for the micronutrients. Results from the analysis of 28 soils by these methods were compared. Most soils were selected from those used by the Spanish Working Group for the Standardization of Analytical Methods. In most cases, statistical correlations between methods presented good agreement for each element, but depending on the soil pH range, some elements needed two correlations. Also, when results for wet and dry soils were compared, variability was lower when the AB‐DTPA extraction method was used. We concluded that, besides being faster, the AB‐DTPA method is valid for Spanish soils, even for calcium (Ca) extraction in calcareous soils, where the ammonium acetate method fails due to excessive Ca solubilization.  相似文献   

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