摘要:

Soluble polyphenol concentrations of tropical leaves are believed to affect nitrogen (N) mineralization potential during decomposition. However, polyphenol concentrations reported for the same species have varied several‐fold among studies. Testing potential explanations for these discrepancies, we found high tissue‐to‐solvent ratios, as specified in one of two popular extraction procedures, led to reduced estimates. Use of aqueous methanol rather than water increased recovered polyphenols somewhat, but was not adequate to explain differences among studies. Elevated drying temperatures decreased recovery of soluble polyphenols. Folin‐Ciocalteu reagent produced less precipitate and was more reproducible than Folin‐Denis reagent.

ISSN:0010-3624    

DOI:10.1080/00103629409369260

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Adsorption of cobalt (Co), copper (Cu), and manganese (Mn) by synthetic aluminium oxide, ferrihydrite, goethite, extracted humic acid, and a sandy soil sample were determined as a function of metals concentration (0–1.2 mM) and pH (3.8–8.2). For each pH and adsorbent, the Langmuir adsorption maximum (adsorption capacity) was calculated. The position of the adsorption curves for Co, Cu, and Mn as a function of pH has been shown to be related to the first hydrolysis constant of the cations in solution (pK1). The sequence of preference of the three metals to the studied adsorbents decreased in order Cu >> Co > Mn. The results obtained from this study showed that the Co, Cu, and Mn adsorption characteristics of soils are probably controlled to large extent by their organic matter and oxides contents.

ISSN:0010-3624    

DOI:10.1080/00103629409369261

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A flow injection analysis (FIA) procedure for the determination of dissolved silica (0.04–20 mg/L Si) in aqueous solution has been optimized to reduce phosphate interference. Determinations are based on measurement of absorbance at 790 nm of heteropoly molybdenum blue formed by reduction with ascorbic acid at room temperature. Phosphate did not interfere in a 15‐fold excess. The optimized procedure was tested on soil solutions isolated by centrifugation of various horizons from a Typic Haplohumod. Si concentrations of 1.3–4.8 mg/L Si were found with a variation coefficient of about 2. Results obtained compared well with those obtained by a manual reference method and a proprietary FIA method except in solutions high in dissolved humic material where slightly higher values were obtained by the optimized method. In a standard addition mode the optimized method yielded 5–15% lower values than in the ordinary mode. This difference was reduced by persulfate oxidation of organic matter. Soil solutions investigated were very low in phosphate but phosphate spiking experiments demonstrated that phosphate interference was less than in model solutions matched in metal ion concentrations and insignificant in solutions low in humic material and with less than 10 mg/L P. Dissolved silica was unstable in a solution isolated from an organic horizon of high biological activity.

ISSN:0010-3624    

DOI:10.1080/00103629409369262

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An electrolytic method for the copperization of cadmium as a reducing agent for nitrate‐nitrogen (NO3‐‐N) determination is described. The conditions, medium, and time of copperization as well as the length of the cadmium reducing column has been studied in detail. This column was placed in a flow injection analyzer for the online determination of NO3‐‐N in soil extracts. The results obtained show that 1% copper sulfate (CuSO4), 30 min and 55 mm are the optimal medium, time, and column length, respectively. With this reducing column, the method is linear between 0 and 12 ppm NO3‐‐N with a precision of 0.29% and a sampling frequency of 80 determinations per hour. The proposed method has been applied to the determination of NO3‐‐N in soil extracts and the results agree with those obtained by the reference method (r = 0.9998). The optimized electrolytic procedure for the copperization of cadmium permits more than 3000 determinations without any significant loss of sensitivity.

ISSN:0010-3624    

DOI:10.1080/00103629409369263

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

As in other areas of the world, in the Middle East, phosphorus (P) is also a vital element in agricultural production. Laboratory studies have shown how inorganic P changes with time after application. With increased interest in the use of organic wastes, the extent to which seasonal change, characteristic of the Mediterranean climate, affects transformation of organic P alone and in combination with fertilizer P has been given attention. This preliminary pot experiment, conducted under outdoor conditions, examined changes in sodium bicarbonate (NaHCO3)‐extractable P over a 19‐month period in soil amended with organic matter as farmyard manure (5%) and superphosphate (100 mg/kg P). During the initial cool winter season's incubation, there was no change in available P. With the onset of the warmer dry season, NaHCO3‐extractable P declined rapidly. The rate of decrease was greater, and the onset earlier with inorganic P alone. Organic matter reduced the P Sorption maxima and increased desorption. Thus, organic matter, whether added or as accumulated root biomass, enhances the longevity and potential plant availability of P in soils of a xeric moisture regime. Future field research should focus on monitoring, with time, the various organic and inorganic P fractions as well as detailed moisture and temperature measurements.

ISSN:0010-3624    

DOI:10.1080/00103629409369264

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Beneficial uses of a yard‐waste compost as a soil amendment and plant‐growth medium were evaluated on a highly weathered, acid soil (Ustic Kanhaplohumult), using corn(Zea maysL.) seedlings as a test crop. First, factors responsible for the soil's infertility were identified in a greenhouse experiment consisting of five phosphorus (P) rates (0, 75, 150, 300, and 600 mg/kg) with or without 1.0 g calcium (Ca)/g (2 tons Ca/ha) as gypsum (CaSO4‐2H2O) or calcium hydroxide [Ca(OH)2]. At no or low P additions, severe growth restrictions (low dry matter production and shoot P concentration <0.10%) irrespective of the Ca amendments indicated that P deficiency was the most growth limiting factor in this tropical soil. Subsequently, P sorption isotherms were constructed for the soil, the compost, and soilxompost mixtures by equilibrating 1.0 g soil in 20 mL 0.001M calcium chloride (CaCl2) containing various P concentrations. The results showed that in the unamended state, the soil supported only 0.01 mg P/L, the compost 9.5 mg P/L, and the mixtures containing 25%, 50% or 75% compost by volume 0.04, 0.06, or 0.10 mg P/L in the soil solution, respectively. Approximately 300 mg P/kg must be added to the unamended soil to maintain 0.20 mg P/L in the soil solution. Finally, effects of the compost amendment were studied by growing corn in various volumetric mixtures containing 0, 25, 50, 75, and 100% compost. Best growth was obtained when compost fractions were >75%, corresponding to approximately 0.20% P in the plant shoots and 40 mg/kg Mehlich‐1‐extractable P.

ISSN:0010-3624    

DOI:10.1080/00103629409369265

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We measured the concentration and composition (sensuLeenheer, 1981) of dissolved organic carbon (DOC) in lysimeter solutions from the forest floor of a spruce stand in Maine and in laboratory extracts of organic (Oa horizon) and mineral soils collected from various forests in Maine, New Hampshire, and Vermont. All soils were acid Spodosols developed from glacial till. The effects of different storage, extraction and filtration methods were compared. Extracts from Oa horizons stored fresh at 3°C contained a larger fraction of hydrophobic neutrals than lysimeter forest floor solutions (31 and 4% of DOC in stored and lysimeter solutions, respectively), whereas extracts from Oa horizons which had been extracted, incubated at 10–15°C, and extracted again had DOC compositions similar to that in lysimeter solutions. Mechanical vacuum and batch extractions of Oa horizons yielded DOC similar in concentration and composition if the extracts were filtered through glass fiber filters. Nylon membrane filters, however, removed more hydrophobic acids from batch extracts. Dissolved organic carbon extracted from frozen, air‐dry, and oven‐dry Oa and Bh horizons was relatively rich in hydrophilic bases and neutrals and was similar to that released after chloroform fumigation, indicating that common soil‐storage methods disrupt microbial biomass.

ISSN:0010-3624    

DOI:10.1080/00103629409369266

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Extraction with hot water is the most widely used procedure to determine boron (B) in soils for the diagnosis of the nutrient availability for plants. However, this procedure is tedious for routine conditions and requires some special precautions. An alternative extraction procedure was developed, consisting in the extraction of B with a 1.25 g/L solution of barium chloride (BaCl2) or with water heated in a domestic microwave oven. Boron was determined either by inductively coupled argon plasma emission spectrometry (ICP‐AES) and by spectrophotometry with azomethine‐H. Good correlations were found between the extraction by boiling water under reflux and the extraction by the microwave heating for 13 Brazilian soils, and the contents of B obtained by spectrophotometry did not differ significantly from those obtained by ICP‐AES. Considering the calculated standard deviations, it can be concluded that microwave heating followed by ICP‐AES determination is an adequate procedure for the determination of hot water extractable B in soils.

ISSN:0010-3624    

DOI:10.1080/00103629409369267

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The interacting effects between topsoil water supply, nitrogen (N) placement and subsoil aluminum (Al) toxicity on wheat growth were studied in two split‐root pot experiments. The native nitrate‐N (NO3‐N) in the topsoil used in each experiment differed and were designated as high (3706 μM) and low (687 μM) for experiments one and two, respectively. Wheat was grown in pots that enabled the root system to be split so that half of the roots were in topsoil and the other half were in subsoils containing varying concentrations of soluble Al. Treatments were imposed which varied the supply of water to the topsoil (either ‘wet’ or ‘dry'). Placement of applied N in either the topsoil or subsoil had little effect on either shoot or root fresh weight, or on the length of roots produced in the subsoil section of the split pots. When water supply to the topsoil was decreased, both shoot and root growth of wheat declined and the yield decrease increased with subsoil Al. In the high‐N experiment, wheat grown in the low Al subsoil with the high native soluble subsoil (NO3(3002 μM) was able to exploit the N and subsoil water, hence both shoot and root growth increased considerably in comparison to shoot and root growth of wheat grown in soils containing higher concentrations of subsoil Al. When the native NO3was lower (i.e. the low‐N experiment) inadequate root proliferation restricted the ability of plants to use subsoil N and water irrespective of subsoil Al. The results from this study suggest that wheat, grown on yellow earths with Al‐toxic subsoils, will suffer yield reductions when the topsoil dries out (e.g. in the spring when winter rainfall ceases) because subsoil reserves of water and nitrogen are under utilised.

ISSN:0010-3624    

DOI:10.1080/00103629409369268

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Rapid determination of cation exchange capacity (CEC) of soils can be useful for soil testing to improve efficiency of fertilizer use. The methylene blue (MB) method of Wang et al. (1989) has been simplified for rapid determination of CEC of mineral soils in field. For the temperate and tropical soils used, the relationships between the CEC by the ammonium acetate (NH4OAc) method and the simplified MB method were linear (r2= 0.97) with a slope ranging from 0.84 to 1.02. These results suggest that the simplified MB method has the potential for a rapid determination of the CEC of mineral soils.

ISSN:0010-3624    

DOI:10.1080/00103629409369269

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor