摘要:

Microbial biomass is determined from the excess of extractable organic N released from fumigated soil samples. In the presence of relatively high contents of labeled mineral N, small differences in organic N and N may not be detectable. Two approaches were tested to determine organic N content and its N enrichment in the presence of considerably greater concentrations of labeled mineral N: (i) Removal of mineral N from mixed solutions of alanine and NH4or NO3by reduction and boiling under alkaline conditions, prior to Kjeldahl digestion. (ii) Including mineral N in Kjeldahl N analysis, by reduction under acidic conditions prior to digestion and calculating organic N and N content by subtracting mineral N and N. The removal of mineral N was either incomplete‐ particularly regarding labeled mineral N, or partly destroyed organic N as well. When mineral N was included in the digest, the recovery of N and15N was sufficiently accurate to obtain good results of organic N and15N by subtracting the known quantities of mineral N, even when organic N was only 20% of the total Kjeldahl N. This procedure was used to determine the flush of Kjeldahl N in fumigated soils that were incubated with labeled mineral N and cellulose.

ISSN:0010-3624    

DOI:10.1080/00103628909368126

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

An automated method for the simultaneous analysis of total N, total C,15N and14C in small plant and soil samples is described. A commercial C‐N analyser ‐ continuous flow isotope ratio mass spectrometer (ANCA‐MS) has been extended to also measure CO2and collect14CO2produced by sample combustion. Samples containing 20 ‐ 200 μg N and up to 5 mg C can be analysed directly with no sample preparation other than drying and fine grinding. The precision of total elemental analysis is comparable to that by conventional methods. The average standard deviation of15N analyses of plant material at natural abundance was ±1 ‰. This is accurate enough for all15N studies except those using natural abundance and possibly long term studies of soil organic matter. Recovery of14C in test samples was 100%. The instrument can be operated by graduate students under supervision and operating costs are primarily for sample cups, combustion catalyst and quartz tubes.

ISSN:0010-3624    

DOI:10.1080/00103628909368127

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Availability of labor and laboratory instrumentation has frequently limited use of isotopes in N management research. Recent innovations in laboratory instrumentation have made it possible to simultaneously determine total C, total N, and15N concentrations in plant, soil, and water samples. An automatic C and N analyzer was interfaced with a continuous‐flow mass spectrometer for purposes of routine analytical determinations. Compared to manual procedures, the automated procedure was rapid, accurate, and gave reproducable results both over time and between adjacent samples. Ball‐mill preparation of samples greatly increased precision of determinations and is recommended to improve sample homogeneity.

ISSN:0010-3624    

DOI:10.1080/00103628909368128

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The measurement of NH4+‐N in soil, and plant digests is one of the greatest needs in laboratories conducting agricultural and environmental research. Many laboratories do not have access to automated equipment for colorimetric analysis of soil and plant digests. The objective of this research was to modify an automated colorimetric analysis procedure for determining NH4+‐N in soil and plant digests for manual use, and compare the proposed technique with the standard distillation‐titration technique. The modified procedure is based on the color reaction between NH4+‐ and a weakly alkaline mixture of Na salicylate and a chlorine source in the presence of Na nitroprusside. Wavelength scans indicated a very well defined peak for determinations at 650 nm. Time scans showed that color development in the manual procedure was rapid, 12 to 40 minutes depending on temperature, and that the color development remained stable for at least 120 minutes. Regression analysis of the results from 18 soil and 20 plant tissue sample determinations by distillation‐titration and the proposed method indicated NH4+‐N recoveries of 99% or higher. The results obtained using the colorimetric procedure were very similar to the values obtained by distil ling and titrating the digests for both soil and plant samples as indicated by the large coefficients of determination (R2= 0.99).

ISSN:0010-3624    

DOI:10.1080/00103628909368129

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Zinc solubility in soils can be affected by both pH and pyrophosphate (PP), yet the reaction of PP is influenced by pH, thus there is a need to evaluate pH effect on Zn transformation in soils treated with PP. Samples of three autoclaved soils, a Dalhousie (DT) clay, a St. Bernard (ST) loam, and an Uplands (UT) sand were equilibrated first with PP (0.0 and 9.0 P mM), then with Zn (0.0, 0.5, 1.0 Zn mM) and followed by 0.03 M KC104solutions at the initial pH of 4.5, 6.0, and 7.5 with constant ionic strength. The first equilibration was for PP sorption, the second for Zn sorption and PP desorption, and the third for Zn desorption and further PP desorption. And finally, Zn of selected samples were extracted with 0.5 M KNO3(exchangeable Zn, ZnKNO3), 0.5 M NaOH (organic and Fe oxides associated Zn, ZnNaOH) solutions, and concentrated HNO3+H2O2(residual Zn, ZnHNO3).

ISSN:0010-3624    

DOI:10.1080/00103628909368130

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Current nitrogen (N) fertilizer recommendations for Kentucky bluegrass (Poa pratensisL.) seed production in northern Idaho are based on potential yield and annual precipitation. Soil test correlation information collected for other northern Idaho crops provide the basis for P, S and B recommendations. The objective of this paper is to assess the current recommendations with a series of forty field trials conducted on ten sites during four seed production seasons. All field trials were conducted on Alfisols and Mollisols initially containing less than 60 kg N/ha, 3.5 μg/g NaOAc extractable P, 40 kg extractable SO4‐S/ha and 0.5 μg/g extractable B. Fertilization rates evaluated included: 0, 50, 75, 100, 125, 150 and 200 kg N/ha; 0, 30 and 60 kg P2O5/ha; 0, 25, and 50 kg SO4‐S/ha, and 0 and 1.5 kg B/ha. Five field sites contained the cultivar ‘Argyle’ Kentucky bluegrass seed, while the other five sites contained the cultivar ‘South Dakota’.

ISSN:0010-3624    

DOI:10.1080/00103628909368131

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Research data are limited on K andWgrequirements of peanuts (Arachis hypogaeaL.) grown on sandy soils either with or without irrigation. Purposes of this study were (1) to determine Mg, K, and irrigation effects on yield, sound mature kernels (SMK's), and diseases of ‘Florunner’ peanuts grown on two sandy soils and (2) to determine sufficient amounts of Mg and K in peanut leaves and soils. Field experiments were conducted for three years on a Lakeland sand (thermic, coated Typic Quartzipsainments) and a Fuquay loamy sand (siliceous, thermic, Arenic Plinthic Paleudults). Both soils initially tested low in Mehlich 1 extractable K and Mg, but Lakeland was lower than Fuquay in both K and Mg. Factorial treatments were 0, 67, 67 (split into three applications), and 134 kg Mg/ha as MgS04and 0, 56, 112, and 224 kg K/haas KC1.

ISSN:0010-3624    

DOI:10.1080/00103628909368132

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

This study was designed to identify strains ofBradyrhizobium sp. (lespedeza)which could improve the plant performance and N status ofLespedeza cuneata(Dumont) G. Don (sericea lespedeza). Based upon preliminary screening for nodulation capability and acetylene reducing activity (ARA), six strains of rhizobia were chosen to be evaluated in the greenhouse for plant growth effects and N2‐fixing ability.

ISSN:0010-3624    

DOI:10.1080/00103628909368133

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

When fertilization capital is limited, the maximum economic rate which gives the greatest profit per unit area cannot be applied to all crops, therefore, a predicting method for the most profitable fertilizer rates for each crop is needed. This work describes a graphical method for sharing the available fertilizer between two different crops, or else the same crop in two different soils or crop sequences where the fertilizer needs are not the same. The method can also be used in the case of irrigation when the capital or the amount of the available water are limited.

ISSN:0010-3624    

DOI:10.1080/00103628909368134

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Since soil test based N recommendations are not practiced in Morocco, this study was conducted to develop a N recommendation model based on soil nitrate level and other parameters for dryland wheat (Triticum aestivumL.) grown in common rotations in shallow (Rendolls), moderately deep (Calcixerolls) and deep (Chromoxererts) soils of Settat Province in Morocco. Sixteen N‐P Factorial experiments were conducted. Significant grain yield increases due to N fertilization averaged 76% over the check plot yields in all sites and in both seasons. Uptake of N was highly related to soil nitrates only in deeper soils with r2values of 0.89, 0.76, and 0.64 for 20‐, 40‐ and 60‐cm deep profiles. Apparent uptake efficiency of fertilizer N averaged 34% in the drier year and 50% in the wet year. Relative yield was a linear function of initial soil nitrate content in 20‐, 40‐ and 60‐cm profiles with r2values of 0.87, 0.94, and 0.89, respectively. For maximum grain yield 18, 31, and 50 kg of nitrate N/ha were required in 20‐, 40‐ and 60‐cm profiles, respectively. Nitrogen mineralization potentials were 144, 164, and 179 mg/kg for the above soils, respectively. A model based on critical level of soil nitrates, initial level of soil nitrates and apparent uptake efficiencies of soil and fertilizer N was developed to predict the fertilizer N requirement of wheat in deeper soils. If legume or mixed volunteer pastures preceded the wheat crop, the N fertilizer requirement was lower.

ISSN:0010-3624    

DOI:10.1080/00103628909368135

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor