21.12.2012 Views

Production Practices and Quality Assessment of Food Crops. Vol. 1

Production Practices and Quality Assessment of Food Crops. Vol. 1

Production Practices and Quality Assessment of Food Crops. Vol. 1

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

176 Chris A. Shisanya<br />

MPN = (m × d)/v (3)<br />

where: m is the most likely number, d is the lowest dilution, <strong>and</strong> v is the aliquot<br />

used for inoculation<br />

The plants in the glass growth tubes were harvested after 30 days. The plant material<br />

was separated into shoots, roots <strong>and</strong> nodules <strong>and</strong> dried to constant weight at<br />

70 °C. The dry weights were determined using a high precision digital Sartorius<br />

weighing balance (U6100-D2, Sartorius, Göttingen).<br />

2.7. Determination <strong>of</strong> nitrogen concentration in plant tissues<br />

Due to high cost <strong>of</strong> nitrogen analysis, final field harvest plant samples were analysed<br />

for nitrogen. The plants were dried to constant weight <strong>and</strong> the dry matter weights<br />

recorded. Thereafter, the dry matter was separated into above ground (shoot) <strong>and</strong><br />

below ground (root) tissues. The shoot, root <strong>and</strong> seeds were ground into powder<br />

using a grinding mill type 1029-A (Yoshida Seishakusho Co. Ltd., Japan). Nitrogen<br />

was analysed in the shoot, root <strong>and</strong> seeds using the highly sensitive automatic<br />

nitrogen-carbon analyzer (SUMIGRAPH NC-90 A). 10 mg <strong>of</strong> each sample were<br />

weighed into a boat <strong>and</strong> inserted into the reaction tube <strong>of</strong> the analyzer that was<br />

then sealed. The analyzer completely combusted the sample in a circulating oxygen<br />

current with an oxidation catalyst, converting the component nitrogen <strong>and</strong> carbon<br />

to N2 <strong>and</strong> CO2 gases, respectively for detection by a TCD gas chromatograph <strong>and</strong><br />

simultaneous quantification by the data processor. Nitrogen concentration <strong>of</strong> the<br />

sample was calculated as follows:<br />

a) Using equation (4) below, nitrogen coefficient FN was obtained per peak integral<br />

value <strong>of</strong> N2 for the known st<strong>and</strong>ard sample.<br />

b) The calculated coefficient FN was used in equation (5) to calculate the total<br />

nitrogen concentration, which was then recorded. The percentage N concentration<br />

was multiplied by the respective plant tissue dry weights to get the actual<br />

N concentrations as mg N/g dry matter.<br />

N ST<br />

F N = NPST – NP BL × 100<br />

TN (% N) = FN × (NPSA – NPBL) SA<br />

where:<br />

N ST = Nitrogen content <strong>of</strong> the st<strong>and</strong>ard sample<br />

NP ST = N 2 peak integral value <strong>of</strong> the st<strong>and</strong>ard sample<br />

NP BL = N 2 peak integral value <strong>of</strong> the operating blank<br />

NP SA = N 2 peak integral value <strong>of</strong> the unknown sample<br />

SA = weight <strong>of</strong> the unknown sample in mg.<br />

(4)<br />

(5)

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!