摘要:

Although the compulsive method for measuring the cation exchange properties of soils is being widely accepted particularly for highly weathered soils, part of the procedure is rather tedious involving the addition of water in a stepwise fashion to attain the specific conductance of a standard ionic strength which approximates that of many soil solutions. A modification, which estimates this quantity of water by measuring the specific conductance of the solution before addition of water, is proposed. This estimate was based on calibrations conducted on thirty‐one top‐ and sub‐soils comprising examples from six soil orders. Results obtained by both the original and modified methods were compared over 118 top‐ and sub‐soils and were highly correlated (R2= 0.99) with a slope of 1.02. The proposed modification is accurate as well as time and labor saving.

ISSN:0010-3624    

DOI:10.1080/00103629409369063

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A reliable, rapid procedure for estimating native soil nitrogen (N) mineralization potential in paddy rice (Orysa sativaL.) has eluded researchers. While several have been proposed, no technique has been sufficiently reproducible to be implemented in any soil testing program. Therefore, the objective was to develop a chemical extraction procedure as an index to estimate N mineralization in silt.loam rice soils of the Southern United States Rice Belt. Samples of silt loam soils were collected from strategic locations throughout the rice‐growing region of Arkansas during 1990 and 1991. Anaerobic incubations were performed as an index of potentially mineralisable N. Extraction with acidified potassium permanganate (KMnO4), acidified potassium dichromate (K2Cr2O7), hydrochloric acid (HCl), and oxalic acid [(COOH)2], were evaluated at extractant:soil ratios ranging from 5:1 to 1:1. Also, distillation of centrifuged extracts (SUP) was compared to distilling the entire soil‐solution suspension (TOT). The acidified KMnO4and acidified K2CnO7extractions gave the best overall indices of N availability. The acidifed KMnO4and acidified K2Cr2O7sucessfully predicted N mineralization at all ratios evaluated. A significant relationship with anaerobic incubation was observed for all HCl TOT ratios evaluated, except the 3:1 in 1991. The HCl SUP methods were not significant for all soils evaluated. The oxalic acid TOT extractable ammonium‐nitrogen (NH4+‐N) was significantly related to anaerobic incubation. More N was extracted with the TOT methods than SUP methods, probably due to alkaline hydrolysis during distillation of TOT methods. Oxidation with KMnO4released the most N, while HCl and oxalic acid extracted the least.

ISSN:0010-3624    

DOI:10.1080/00103629409369064

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A simple nitrogen (N) availability index is needed to improve fertilizer recommendations and, thus, reduce the opportunity for over‐ or under‐fertilization of rice (Oryza sativaL.). Consequently, a study was conducted to develop a chemical extraction procedure that will estimate the potentially mineralizable N made available to rice during the growing season. The ammonium‐nitrogen (NH4+‐N) extracted with 0.05M KMnO4(potassium permanganate) + 0.5M H2SO4(sulfuric acid) (acidified KMnO4), 0.05M K2Cr2O7 (potassium dichromate) + 0.5M H2SO4 (acidified K2Cr2O7), 1.0M HC1 (hydrochloric acid), and 0.5M C2H2O4(oxalic acid) was compared to total N uptake (TNU) by ‘Newbonnet’ rice grown under greenhouse conditions. Comparisons were also made between distillation of the entire soil‐extractant suspension (TOT) and distillation of the supernatant after centrifugation (SUP). Anaerobic incubation for 7, 14, and 21 d was also included for comparison. The indices evaluated decreased in ability to predict TNU in the order: anaerobic incubation > acidified KMnO4> acidified K2Cr2O7= HC1 > oxalic acid. Anaerobic incubation was the best index of N availability for rice. The 14‐d incubation predicted TNU (r2= 0.82**) better than the 7‐ or 21‐d incubation (r2= 0.71 and 0.65**, respectively). The best chemical index of N availability was oxidation with acidified KMnO4(r2= 0.75**). Extraction with HC1 (TOT) and acidified K2Cr2O7(TOT) were similar and extraction with oxalic acid was the least effective method. Pre‐incubation of each soil for 30 d prior to anaerobic incubation did not improve the relationship with TNU by rice in the greenhouse.

ISSN:0010-3624    

DOI:10.1080/00103629409369065

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Limited water resources and increased demands have triggered a nationwide campaign for water conservation and augmentation in the Sultanate of Oman. Renovated wastewater use is sought as part of the National Conservation Strategy being drafted by the authorities in the country. About 10 million cubic meters of wastewater is treated annually and primarily used for amenity along the main roads. Social, health, and environmental considerations have necessitated setting guidelines and regulations to accord with the most stringent international practices attaining at the time. Soil and water samples collected from different sites, using industrial and domestic treated effluent and potable underground water, and analysed for copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) revealed the effectiveness of such stringent but costly regulations, reflected by the low level of concentrations detected. No signs of toxicity to the plants were visible, some showing Zn‐deficiency symptoms, and a separate study disclosed insignificant levels in the plants as well. Using treated and regulated wastewater for agricultural production has proved to be chemically safe and poses as a partial solution for conserving significant amounts of water, at a time when every drop counts.

ISSN:0010-3624    

DOI:10.1080/00103629409369066

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A rapid method is described for the determination of total cadmium (Cd) in soils. The soil samples and standard sediment samples were digested in a microwave oven using concentrated HNO3and also by the conventional HF‐HC1O4digestion in platinum crucibles. The Cd content in the extracts was determined using graphite furnace atomic absorption spectro‐photometry (GFAAS). Both digestion methods produced comparable quantitative values for total Cd of standard reference materials obtained from the National Institute of Standards and Technology and a series of surface and subsurface soil samples. Thus, the microwave digestion technique was shown to be an accurate and rapid method for digesting soil samples prior to total Cd analysis.

ISSN:0010-3624    

DOI:10.1080/00103629409369067

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The objective of this study was to evaluate a new soil test for simultaneous extraction of available phosphorus (P) and potassium (K) in soils. The new soil test is a modification of the Kelowna extraction. The modified Kelowna (KM) extractant is composed of 0.025M HOAc and 0.25M NH4OAc as well as 0.015M NH4F with a measured pH of 4.9. The KM test was compared to the Olsen 0.5M sodium bicarbonate extraction. In order to provide maximum contrast in nutrient availability and soil properties, four hundred soil samples from all six soil zones in Saskatchewan were selected to be tested. Thirty eight of the samples were also used for growth chamber study to compare plant response to the new test. Results showed P and K extracted by the new method to be highly and significantly correlated with the Olsen‐extractable P and K (r2= 0.92*** and 0.85***). Results also showed higher correlations between test‐predicted P and K availability and actual plant uptake for the new method (r2= 0.76*** and 0.56***) compared to the Olsen test (r2= 0.67*** and 0.38***).

ISSN:0010-3624    

DOI:10.1080/00103629409369068

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

When peanut is grown under conservational tillage systems which leave residue on the surface, yields are lower than under conventional tillage. There is evidence that nutrition plays a roll in the lower yields. In this study, Virginia‐type peanuts were grown under conventional and conservational tillage to determine tillage influence on soil and leaf Ca levels and to evaluate yield response to extra gypsum. The Virginia‐type peanut cultivar NC 6 was grown under conventional till (CT) and conservational (NT) systems with three cultivation levels and two gypsum application levels applied to the NT system. Yields were lower in the NT system than in the CT system. Yields in the NT system did not respond to cultivation or gypsum rate. Seed and pod Ca increased with increased gypsum application as did soil Ca. Soil Ca increased with gypsum application. The lack of yield response to cultivation suggests that yield losses occur because of differences early in the growing season. Additional work is needed to overcome the peanut yield loss associated with tillage systems which leave residue on the soil surface.

ISSN:0010-3624    

DOI:10.1080/00103629409369069

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Soil samples for inorganic nitrogen (N) determination are usually deep‐frozen to prevent microbial transformations of N between sampling and analysis. For analysis, frozen soils are thawed, which may also lead to transformations of N. A specially manufactured mill for grinding frozen soil was tested to minimize these transformations. Whether the time of extraction of the samples could be extended to 20 hr to better accomondate routine work and to make the clay aggregates to disperse better during extraction was also investigated. Freezing of the samples did not produce different results to fresh soils from ammonium nitrogen (NH4+‐N) or nitrate nitrogen (NO3‐‐N) determination. Thawing of the samples increased the concentration of NO3‐‐N in the extracts and grinding increased that of NH4+‐N. When either thawing or grinding was applied, the total inorganic nitrogen concentration was about the same. Thawing of the ground samples increased concentrations of NO3’‐N and NH4+‐N in the extracts. Extending the time of extraction from 0.5 or 1 hr to 20 hr increased the concentration of NH4+‐N in the extracts, while NO3‐‐N content was also increased slightly. It was concluded that sample pretreatment may cause serious errors in the determination of inorganic N even by methods which have proven most successful to prevent microbial transformations of nitrogen, unless the soils are extracted immediately after sampling. The period of extraction should not exceed two hours.

ISSN:0010-3624    

DOI:10.1080/00103629409369070

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0010-3624    

DOI:10.1080/00103629409369052

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor