Effect of pasture age on the efficiency of nitrogen fixation by 10 accessions of Stylosanthes spp

1985 ◽  
Vol 25 (1) ◽  
pp. 70 ◽  
Author(s):  
I Vallis ◽  
CJ Gardener
Keyword(s):  
Nitrogen Fixation ◽  
Age Differences ◽  
Soil Nitrogen ◽  
Nitrogen Uptake ◽  
Isotope Dilution ◽  
Symbiotic Nitrogen Fixation ◽  
Isotope Dilution Method ◽  
Dilution Method ◽  
Total Uptake ◽  
Pasture Age

The proportion of legume nitrogen that had been symbiotically fixed in 10 accessions of Stylosanthes spp. was determined by an isotope dilution method in microplots within grazed pastures 1, 4 and 6 years after the legumes were sown in association with buffel grass at Lansdown, near Townsville, Queensland. The proportion, averaged over all accessions, varied between years from 0.79 to 0.83, but was not related to pasture age, differences in legume yield, or total uptake of soil nitrogen. Within years, the proportion in individual plots was weakly and negatively correlated with legume yield and soil nitrogen uptake 4 years after sowing, but not at other times. No significant differences in proportions between the 10 accessions of Stylosanthes were demonstrated. It is concluded that, in these pastures, the efficiency of nitrogen fixation by the legume is not greatly affected by changes in the availability of soil nitrogen as the pasture ages. Consequently, the rate of symbiotic nitrogen fixation will depend mainly on the growth of the legume.

Seasonal variation in the suitability of different methods for estimating biological nitrogen fixation by grain legumes under rainfed conditions

1996 ◽  
Vol 47 (7) ◽  
pp. 1061 ◽  
Author(s):  
AM McNeill ◽  
CJ Pilbeam ◽  
HC Harris ◽  
RS Swift
Keyword(s):  
Nitrogen Fixation ◽  
Isotope Dilution ◽  
Biological Nitrogen Fixation ◽  
N Uptake ◽  
Isotope Dilution Method ◽  
Dilution Method ◽  
First Year ◽  
Soil N ◽  
A Value ◽  
Biological Nitrogen

Biological nitrogen fixation (BNF) by legume crops was estimated in a Mediterranean environment at ICARDA in northern Syria for 3 consecutive seasons beginning in 1991-92. Using the classical isotope dilution technique (NID), estimates ranged from 32 to 82 kg N/ha for chickpea and from 18 to 82 kg N/ha for lentil. In comparison the simple N-difference method gave lower, sometimes negative, estimates for BNF by both crops in the latter 2 seasons but a higher estimate for chickpea in the first year. Discrepancies in the estimates from N-difference were correlated with differences in the amount of soil N taken up by the legume and the non-fixing wheat reference crop. Since soil N uptake by lentil in the first year was similar to wheat, the estimates of BNF from the 2 methods for that season were similar. The indirect effects of an interaction of added N fertiliser on N derived from the soil and thus on N uptake and estimated BNF are discussed in relation to the use of the isotope dilution method with A-value modification (NAV). Despite some significant differences in A-value for soils receiving different amounts of fertiliser it is demonstrated that the A-value method used in this study, with fertiliser rates of 10 kg N/ha to the legume and 30 kg N/ha to the non-legume, resulted in BNF estimates for lentil similar to those obtained using classical isotope dilution. However, this was not the case for chickpea where a direct inhibitory effect of fertiliser N at 30 kg N/ha resulted in lower estimates of BNF from NID than NAV. Since the reference crops derived as much as 90% of their N from the soil, it is recommended that future BNF studies using isotope dilution techniques for lentil and chickpea crops at ICARDA use a fertiliser rate lower than that used in this study. An isotope dilution method utilising a slow-release source of 15N or the natural abundance technique for estimating BNF are suggested as potentially useful alternatives. The need for a basic understanding of the soil N dynamics pertinent to each site as a prerequisite for choosing an appropriate method for estimating BNF is highlighted.

ON THE VALUE OF SOME PARAMETERS OF ADRENOCORTICAL GLUCOCORTICOID FUNCTION

1963 ◽  
Vol 44 (4) ◽  
pp. 499-504 ◽  
Author(s):  
M. Van Der Straeten ◽  
A. Vermeulen ◽  
N. Orie ◽  
P. Regniers
Keyword(s):  
Urinary Excretion ◽  
Adrenal Cortex ◽  
Isotope Dilution ◽  
Isotope Dilution Method ◽  
Dilution Method ◽  
Steroid Excretion ◽  
Colorimetric Methods

ABSTRACT The authors studied the correlation between cortisol production, as measured by an isotope dilution method, and the urinary excretion of total and free Porter-Silber chromogens, as well as of 17-ketogenic steroids. Although a significant correlation exists between total Porter-Silber chromogens, 17-ketogenic steroid excretion and cortisol production, discrepancies are occasionally observed. Hence, different colorimetric methods should be used to assess the glucocorticoid activity of the adrenal cortex.

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