Measurement of biological dinitrogen fixation in grassland: Comparison of the enriched 15N dilution and the natural 15N abundance methods at different nitrogen application rates and defoliation frequencies

1994 ◽  
Vol 166 (2) ◽  
pp. 153-163 ◽  
Author(s):  
H. H�gh-Jensen ◽  
J. K. Schjoerring
Keyword(s):  
Dinitrogen Fixation ◽  
Nitrogen Application ◽  
Natural 15N Abundance ◽  
15N Dilution ◽  
Application Rates ◽  
15N Abundance

scholarly journals 111 Metsulfuron and variable nitrogen application rates on infected tall fescue: effects on stocker performance, forage yield, nutritive value, ergovaline concentration and botanical composition

2020 ◽  
Vol 98 (Supplement_2) ◽  
pp. 31-31
Author(s):  
Kevin R Meng ◽  
Eric Bailey ◽  
Josh Zeltwanger ◽  
Hannah Allen ◽  
Mikaela Adams ◽  
...  
Keyword(s):  
Species Composition ◽  
Tall Fescue ◽  
Nutritive Value ◽  
Ergot Alkaloids ◽  
Fertilization Rate ◽  
Forage Yield ◽  
Nitrogen Application ◽  
Forage Production ◽  
Seed Head ◽  
Application Rates

Abstract Chemical seed-head suppression of endophyte infected tall fescue (Lolium arundinaceum) improves stocker cattle performance but may decrease forage yield. Spring nitrogen application increases tall fescue growth with a concomitant increase in ergot alkaloids, produced by the symbiotic endophyte Epichloë coenophiala. We hypothesized that greater amounts of nitrogen applied to tall fescue would increase forage yield and offset losses in forage production from chemical suppression of seed-heads with metsulfuron without effect on alkaloid concentration. Ninety-six steers (270 ± 20 kg) were randomly assigned to one of sixteen paddocks (1.8 ha) on April 18 and continuously grazed for 57 d. Paddocks were blocked by previous use (n = 4) and randomly assigned to one of four treatments; no metsulfuron, no nitrogen (NEGCON), metsulfuron with 0 (MET0), 67 (MET67), or 134 (MET134) kg/ha of ammonium nitrate, applied March 11. Steers grazing MET0 paddocks were removed 17 d early due to insufficient forage availability. Steer weight, forage yield, forage nutritive value and ergot alkaloids in forage samples were measured monthly. Seed-head frequency and species composition were determined in June. Metsulfuron application reduced (P < 0.01) tall fescue seed-heads by 80%. Metsulfuron decreased (P = 0.03) ergovaline but ergovaline increased (P < 0.01) at each monthly sampling across treatments. Nitrogen had no impact on ergovaline concentration (P = 0.50). Forage yield tended to be least (P = 0.07) for MET0, intermediate for NEGCON and MET67, and tended to be greatest for MET134 (P = 0.08). Steer ADG was not affected by treatment (P < 0.80). Metsulfuron decreased NDF (P=0.02) regardless of fertilization rate. Forage CP increased with fertilization (P < 0.01) and no differences were detected between NEGCON and MET0 (P = 0.45). Species composition was not impacted (P >0.07) by treatment. Metsulfuron decreased seed-head growth and ergovaline concentration in tall fescue. Additional nitrogen fertilizer ameliorated forage yield lost to metsulfuron application but did not impact steer gain.

scholarly journals Estimation of Leaf Nitrogen Content from Spectral Characteristics of Rice Canopy

2001 ◽  
Vol 1 ◽  
pp. 81-89 ◽  
Author(s):  
Chwen-Ming Yang
Keyword(s):  
Nitrogen Content ◽  
Linear Relationship ◽  
Spectral Reflectance ◽  
Spectral Characteristics ◽  
Leaf Nitrogen ◽  
Leaf Nitrogen Content ◽  
Nitrogen Application ◽  
Spectral Signatures ◽  
Growing Period ◽  
Application Rates

Ground-based remotely sensed reflectance spectra of hyperspectral resolution were monitored during the growing period of rice under various nitrogen application rates. It was found that reflectance spectrum of rice canopy changed in both wavelength and reflectance as the plants developed. Fifteen characteristic wavebands were identified from the apparent peaks and valleys of spectral reflectance curves, in accordance with the results of the first-order differentiation, measured over the growing season of rice. The bandwidths and center wavelengths of these characteristic wavebands were different among nitrogen treatments. The simplified features by connecting these 15 characteristic wavelengths may be considered as spectral signatures of rice canopy, but spectral signatures varied with developmental age and nitrogen application rates. Among these characteristic wavebands, the changes of the wavelength in band 11 showed a positive linear relationship with application rates of nitrogen fertilizer, while it was a negative linear relationship in band 5. Mean reflectance of wavelengths in bands 1, 2, 3, 5, 11, and 15 was significantly correlated with application rates. Reflectance of these six wavelengths changed nonlinearly after transplanting and could be used in combination to distinguish rice plants subjected to different nitrogen application rates. From the correlation analyses, there are a variety of correlation coefficients for spectral reflectance to leaf nitrogen content in the range of 350-2400 nm. Reflectance of most wavelengths exhibited an inverse correlation with leaf nitrogen content, with the largest negative value (r = �0.581) located at about 1376 nm. Changes in reflectance at 1376 nm to leaf nitrogen content during the growing period were closely related and were best fitted to a nonlinear function. This relationship may be used to estimate and to monitor nitrogen content of rice leaves during rice growth. Reflectance of red light minimum and near-infrared peak and leaf nitrogen content were correlated nonlinearly.

Pattern of natural 15N abundance in lakeside forest ecosystem affected by cormorant-derived nitrogen

2006 ◽  
pp. 69-86 ◽  
Author(s):  
Kayoko Kameda ◽  
Keisuke Koba ◽  
Satoru Hobara ◽  
Takashi Osono ◽  
Masakazu Terai
Keyword(s):  
Forest Ecosystem ◽  
Natural 15N Abundance ◽  
15N Abundance
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