UGC NET

Yes, you are eligible to apply for UGC NET after the PG Diploma course. UGC NET Eligibility Criteria:
UGC NET Age Limit:
Students should not be more than 31 years of age in order to be eligible for National Test Agency, National Eligibility Test, or Junior Research Fellow. There is no age limit to apply for the post of Assistant Professor. A relaxation of 5 years in age criteria is given to SC/ST (reserved) category students. UGC NET Educational Qualification:
Students should have completed their PG from a University Grants Commission-recognised college or university. A relaxation of 5% in educational qualification is given to SC/ST category students. Students who have cleared SET (State Eligibility Test) before June 1, 2002, are exempted from taking the University Grants Commission-National Eligibility Test exam. For more details, you may visit the Shiksha UGC NET exam page. (https://www.shiksha.com/exams/ugc-net-exam). I hope this will help you.

First and foremost, you need to understand that the vacancies are less in comparison to the number of candidates clearing UGC NET JRF every year. And more vacancies cannot be generated until or unless more institutions are constituted. Therefore, you will have to take it with a pinch of salt that clearing UGC NET JRF does not guarantee a job. It is not that you will sit idle after having a NET/JRF qualification or your hard work will go waste. Just understand that, when the Universities have a plethora of options to choose from then what is it that will make you stand out in the crowd? Nowadays only possessing a qualification does not REAP benefits, you need to possess some internal skills as well.

If you are a Post graduate in Commerce, your most natural choice of subject for UGC NET (now NTA NET) should be Commerce. People with Commerce stream don't specialise in any particular subject. You could also appear for NET in Management. But this is usually preferred by students doing MBA
Another choice could be NET in Economics, but again this is done by students pursuing Post graduation in Economics. It serves you well in the long run if youd keep your subjects same throughout your career. Educational Qualification
1. Post-Graduation in Commerce, Finance, Economics, Business Services, Accountancy or any other related subjects.
2. The candidates percentage in PG should be more than 55% for General Category & 50% for ST/SC/OBC/PWD/Transgenders.
3. Candidates who have secured at least 55% marks (without rounding off) in Masters Degree or equivalent examination from universities/institutions recognised by UGC in Humanities (including languages) and Social Science, Computer Science & Applications, Electronic Science etc. Are eligible for this Test. The Other Backward Classes (OBC) belonging to non-creamy layer / Scheduled Caste (SC) / Scheduled Tribe (ST) / Persons with disability (PWD) category candidates who have secured at least 50% marks (without rounding off) in Masters degree or equivalent examination are eligible for this Test.

The subject code for Environmental Science is 89 in UCG NET. To qualify for the NET exam in Environmental Science, you have to pass Papers 1 and 2. For Paper 1, any good aptitude book by either KVS Madan, Arihant Experts, or Harpreet Kaur will do. The books recommended for environmental Science are as follows:
1. Introduction to Environmental Engineering by Gilbert M. Masters
2. Statistical Method by S. P Gupta
3. Environment Chemistry by Stanley E. Manahan
4. Environment Ecology by E. P ODUM
5. Principles of Biochemistry Voet, Pratt and Voet
6. Non-conventional Energy Sources GD Rai
7. Any good publication that solves previous year's questions
You can prefer other books also, but your focus should be on covering the syllabus, which is as follows:
1. Fundamentals of Environmental Sciences
2. Environmental Chemistry
3. Environmental Biology
4. Environmental Geosciences
5. Energy and Environment
6. Environmental Pollution and Control
7. Solid and Hazardous Waste Management
8. Environmental Assessment, Management and Legislation
9. Statistical Approaches and Modelling in Environmental Sciences
10. Contemporary Environmental Issues.