5. Quality standards for Rhizobium and Azotobacter

Several quality standards have been formulated for Rhizobium and Azotobacter inoculants. These specifications are shown in Table 2.

Table 2: general standards specified for Rhizobium and Azotobacter biofertilizers

Parameters	Rhizobium Biofertilizer	Azotobacter Biofertilizer
Cell no. at the time of manufacture	108/g carrier within 15 days of manufacture	107/g carrier within 15 days of manufacture
Cell no. at the time of expiry date	107/g carrier within 15 days before expiry date	106/g carrier within 15 days before expiry date
Expiry date	6 months from the date of manufacture	6 months from the date of manufacture
Permissible contamination level	No contamination at 108 dilution	No contamination at 107 dilution
pH	6.0–7.5	6.5–7.5
Strain	Should be checked serologically	Nothing specific. But A. chroococcum species is mentioned
Carrier	Should pass through 150–212 microns IS sieve	Should pass through 160 microns IS sieve
Nodulation test	Should be positive	––
Nitrogen fixation	Above 20 mg/g of glucose	Not less than 10 mg/g of sucrose

The variability in quality standards specified for Rhizobium in various countries are as follows (Table 3).

Table 3: Quality standards of commercial Rhizobium culture in different countries

Country	Cells/gm of culture (total viable count on Congo-red agar)
	Very satisfactory	Satisfactory	Doubtful
U. S. A.	109	–	106 – 107
Australia	–	2 × 108	106 – 107
Russia	109	–	–
India	More than 109	107–109	Less than 107

Although quality control standards for biofertilizer Azospirillum and PSM has not been in force, the proposed standard specification of PSM and Azospirillum are given in Table 4.

Table 4: Proposed standard specifications of PSM and Azospirillum

No.	Parameter	PSM	Azospirillum
1.	Base	Carrier (Lignite/ Charcoal)	Carrier (Lignite/ Charcoal)
2.	Carrier	>100 micron	>100 micron
3.	pH	6.5–7.5	7.0–8.0
4.	Moisture	35–40%	35–40%
5.	Viable count at manufacture	107/g carrier	107/g carrier
6.	Viable count at expiry	107/g carrier	107/g carrier
7.	Level of contaminant	No at 104 dilution	No at 104 dilution
8.	Growth in Pikovskaya medium	+ve	–
9.	Growth in S. S. Malate medium	–	+ve
10.	P Solubilization zone	1mm	–
11.	Pellicle formation	–	+ve
12.	Shelf life	6 months	6 months
13.	P Solubilization	30–50%	–
14.	N-fixation	–	15 mg/g of malic acid