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Given that wetlands, especially man-made wetlands including paddy fields, are a major source of the greenhouse gases methane and nitrous oxide, a study of the present status of knowledge in this area was carried out with reference to India. Based on printed material, digital repositories, and personal correspondence an up-to-date assessment of all studies reported so far has been conducted. It is shown that despite India having 4.6% of its area covered by natural or man-made wetlands, being home to a very large number of wetlands, and being the second largest cultivator of paddy in the world, its wetlands—including paddy fields which are intermittently flooded as typical wetlands are—have been very poorly studied in terms of their GHG emissions. Even the reports that are available have been mostly confined to a few regions of India, and as many as seven of the most wetland-rich states—Bihar, Chhattisgarh, Jharkhand, Madhya Pradesh, Maharashtra, Himachal Pradesh, and Jammu & Kashmir—have not been studied in this respect at all. A major finding is that, contrary to a recent report published by authors based in USA, intermittently irrigated rice fields have not been found to emit exceptionally high quantities of nitrous oxide. The study brings out the urgent need for carrying out assessments of GHG emissions from wetlands throughout India with a view to finding strategies to minimize such emissions.

Vermicompost (VC) of different substrates, especially of animal manures, is known to be highly potent organic fertilizer but it is not known how beneficial VC is in paddy cultivation. Considering that rice is the world’s third most cultivated and consumed grain, it is important to assess the effect of VC on its productivity. Equally important is to see whether vermicompost application leads to higher or lower greenhouse gas (GHG) emissions compared to synthetic chemical fertilizers (SFs). The present mini-review has aimed to assess and summarize this state-of-the-art. It is seen that only 27 studies have been reported on this subject so far, and in 18 of them, it is possible to compare the performance of VC with SF and other organic fertilizers. Half of these studies reveal the VC to be superior to all the other fertilizers tested while 39% of the studies show VC to be the second best. With the exception of three papers—two from Bangladesh and one from Iran—all other publications have been from India, representing 89% of all work reported in this field. In respect of types of VC studied, 25 (93%) of all studies have been on VC derived from cow-dung. For the remaining two studies, the VC was obtained from the dung of other cattle and distillation waste respectively. As for GHG emissions occurring from VC-fertilized rice fields, only five reports are available. In four of these reports, no statistically significant difference has been reported in the GHG emissions from the VC and the SF-fertilized rice fields. Hence, the available information is too scanty to enable any generalization.

In separate treatments rice (Oryza sativa) of the Chinna Ponni variety was grown either with the application of synthetic fertilizer (SF) containing 120 kg/ha, 60 kg/ha, and 60 kg/ha of nitrogen, phosphorous, and potassium, respectively, or vermicompost (4 t/ha) with equivalent nitrogen content. The objective was to see whether vermicompost performs as well, or better, than the SF in terms of grain length, unit mass, and overall yield of rice. The relative contribution of the two fertilizer applications on the emission of the global warming gas methane was also studied. Direct sowing method was applied for the rice cultivation which spanned 140 days during which intermittent flooding of the plots was done. The average grain yield (2300 kg/ha), grain weight (21 mg), and grain length (6.3 mm) of the vermicompost-fertilized rice were all marginally higher than the corresponding values: 2060 kg/ha, 18 mg, and 6.1 mm, respectively, of the SF-fertilized rice. The overall hourly methane flux in vermicompost-fertilized plots was 111.3 ± 58.3 µg/m2 h in comparison with 71.0 ± 81.0 µg/m2 h emitted by the SF-fertilized plots, but the difference was not statistically significant.