The ascorbic acid concentration (vitamin C) was determined by the Tillmans method, which is based on the reduction of 2.6-dichlorophenol sodium indophenol
(DCFI) by ascorbic acid, according to Benassi and Antunes (1988).
Urease (EC 188.8.131.52) activity was measured by the indophenol
colourimetric method, and illustrated by the amount of N[H.sub.3]-N (mg) produced from 1 g soil after being cultured at 37[degrees]C for 24 h (Huang et al.
The N-N[H4.sup.+] and N-N[O2.sup.-] levels were measured weekly with indophenol
blue and sulphanilamide methods, respectively.
100 [mL.sup.-1] (IAL, 2008); and ascorbic acid according to the Tillmans method (2.6 dichlorophenol indophenol
) and the results expressed as mg ascorbic acid.
(34) Ascorbic acid was determined by titration against 2,6-dichlorophenol indophenol
Ammonia was analyzed using the indophenol
reaction noted by Cheney and Marbach .
method with some modifications was used to measure the urease inhibitory activity of the extracts (9).
The dye solution was prepared by dissolving 0.5 g 2, 6-dichlorophenol indophenol
and 0.42 g sodium bicarbonate in 200 ml hot distilled water.
The 4-hydroxylation of aniline hydrochloride results in the formation of 4-aminophenol, which is determined spectorphotometrically by indophenol
Kiyota, "Estimation of L-glutaminase and L-asparaginase activities in soils by the indophenol
method," Soil Science and Plant Nutrition, vol.
method was used to determine the urease activity by measuring the production of ammonia .
The water quality of the culture tanks was monitored by regular observations of the following variables: (1) pH (pH meter mPA210 - MS Tecnopon), (2) temperature and specific conductance at 0900 and 1500 (conductivity meter CD-4303-Lutron), (3) dissolved oxygen (0800; dissolved oxygen meter YSI 55), (4) total ammonia nitrogen (TAN; indophenol
method), (5) nitrite (sulfanilamide method), (6) free C[O.sub.2] (titration with standard [Na.sub.2]C[O.sub.3] solution), (7) reactive phosphorus (molybdenum blue method), (8) total alkalinity (titration with [H.sub.2]S[O.sub.4] standard solution), (9) total hardness (titration with EDTA standard solution), (10) soluble iron (colorimetric Herapath method) and (11) total dissolved sulfide (titration with standard [Na.sub.2][S.sub.2][O.sub.3] solution).