Two-year field experiments were conducted at Tamil Nadu Rice Research Institute, Aduthurai, Tamil Nadu, India, to evaluate the effect of continuous flooding (CF) and alternate wetting and drying (AWD) irrigation strategies on rice grain yield and greenhouse gas emissions from double-cropping paddy rice. Field observation results showed that AWD irrigation was found to reduce the total seasonal methane (CH4) emission by 22.3% to 56.2% compared with CF while maintaining rice yield. By using the observed two-year field data, validation of the DNDC-Rice model was conducted for CF and AWD practices. The model overestimated rice grain yield by 24% and 29% in CF and AWD, respectively, averaged over the rice-growing seasons compared to observed values. The simulated seasonal CH4 emissions for CF were 6.4% lower and 4.2% higher than observed values and for AWD were 9.3% and 12.7% lower in the summer and monsoon season, respectively. The relative deviation of simulated seasonal nitrous oxide (N2O) emissions from observed emissions in CF were 27% and −35% and in AWD were 267% and 234% in the summer and monsoon season, respectively. Although the DNDC-Rice model reasonably estimated the total CH4 emission in CF and reproduced the mitigation effect of AWD treatment on CH4 emissions well, the model did not adequately predict the total N2O emission under water-saving irrigation. In terms of global warming potential (GWP), nevertheless there was a good agreement between the simulated and observed values for both CF and AWD irrigations due to smaller contributions of N2O to the GWP compared with that of CH4. This study showed that the DNDC-Rice model could be used for the estimation of CH4 emissions, the primary source of GWP from double-cropping paddy rice under different water management conditions in the tropical regions.

Direct seeded rice is a boon to farmers where the water release from the reservoir is delayed. Nitrogen fertiliser management is one of the strategies bto rectify the nutrient-related issue in Direct seeded rice. The present study aimed to optimize the nitrogen dose for direct-seeded rice in the new and old Cauvery delta zone of Tamil Nadu. Field experiments were conducted during kuruvai and samba seasons at Tamil Nadu Rice Research Institute, Aduthurai and Agricultural research station Thanjavur representing old and new Cauvery delta regions during 2019-20 and 2020-21. Totally from eight experiments, the results of four field experiments in each location revealed the highest grain yield in the treatment T6 -application of 150 kg Nha-1 (5596kg/ha) which was statistically on par with treatment T5 -125kg N/ha (5326 kg/ha) in old delta and new delta. The higher grain yield was recorded in the T6 (5140 kg/ha), statistically on par with T5 (4550 kg/ha). The higher available nitrogen content of 312 kg/ ha,292 kg/ha was recorded for N application @ 150kg/ha, which was statistically on par with  309 kg/ha and 289 kg/ha, respectively, both the kuruvai and samba seasons for N application of 125 kg/ha. In the new CDZ, the same trend was followed as that of the old delta. Based on economics, N applied @125 kg/ha recorded a higher BC ratio for direct-seeded rice. For the benefit of farmers of both deltaic regions, the nitrogen application of 125 kg ha-1 for direct-seeded rice is recommended.

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Soil organic carbon (SOC) is a potential indicator of soil quality and ecosystem sustainability. The present study aimed to evaluate SOC pools under major cropping systems of Mayiladuthurai district of Tamil Nadu. The composite samples were collected from two depths (0-15 and 15-30 cm) by stratified random sampling and were analysed for pH, EC (Electrical conductivity), C fractions, inorganic carbon and permanganate oxidisable carbon by standard procedures. The SOC content under different land use was in the order of Forestry > Rice – pulses > Rice – cotton > Sugarcane > Uncultivated. The mean SOC content of the study area was 12.58 Mg ha-1, where the majority of the area falls under low to medium rating of SOC. Hence, cultivation practices should incorporate activities that increase SOC to maintain soil quality. SOC was positively correlated with fractions of carbon – CVL (r = 0.37**), CL (r = 0.65**) and CLL (r = 0.58**), indicating changes in land use would affect the carbon dynamics of the ecosystem. The root biomass, aeration status, microbial activity, nutrient reserves and inherent soil characteristics influenced SOC to decrease with depth. The PCA analysis revealed that the variation in carbon dynamics of the study area was influenced by SOC, CLC, CLL and non-labile carbon due to differences in land management practices. Therefore, such soil management practices will be a powerful tool to sequester carbon, which supplements climate change mitigation.

Aim: To study the effect of rice husk biochar and rice straw compost on Rabi season rice cultivation. Study Design: The randomized block design was used. The treatments of different doses of soil amendments like rice husk biochar, rice straw compost and recommended fertilizer doses are applied. Place and Duration of Study: The experimental trial was conducted during the Rabi season (January - April) of 2022 at Tamil Nadu Rice Research Institute, Aduthurai, Tamil Nadu, India. Methodology: The study consisted of 11 sets of RBD design treatments replicated thrice. The rice variety of ADT57 Short duration variety was used for this study. The observation has been recorded during the crop growing period at regular intervals. Results: The study results revealed that application of PSB @ 2kg/ha + RSC @ 5 t/ha + 75% RDF (T10) treatment showed the highest plant growth parameters like plant height (27.88, 74.22 and 108.89 cm), number of tillers m-2 (122, 620 and 642), leaf area index (2.62, 6.53 and 8.47), SPAD reading (47.22, 43.64 and 40.46), root length (18.86, 37.45 and 56.31 cm) and root volume (17.85, 26.01 and 37.77 ml) at 30, 60 and 90 DAT respectively and yield parameters like grain yield (5133 kg/ha), straw yield (7090 kg/ha), panicle length (25.28cm) and number of productive tillers m-2 (571.6) and was significantly on par with application of PSB @ 2kg/ha + Rice Husk Biochar (RHB) @ 5 t/ha + 75% RDF (T6) and superior over the other all treatments. Plant growth parameters of application of PSB @ 2kg/ha + Rice Husk Biochar (RHB) @ 5 t/ha + 75% RDF (T6) recorded the plant height (27.41, 73.76 and 108.29 cm), number of tillers m-2 (118, 613 and 630), leaf area index (2.54, 6.42 and 8.38), SPAD reading (46.26, 43.10 and 40.20), root length (18.35, 37.05 and 55.40 cm) and root volume (17.42, 25.44 and 37.33 ml) at 30, 60 and 90 DAT respectively and yield parameters like grain yield (4953 kg/ha), straw yield (7077 kg/ha), panicle length (25.07 cm) and number of productive tillers m-2 (555). So, the application of PSB @ 2 kg/ha + RSC @ 5 t/ha + 75% RDF has recorded the best results than all other treatments. With respect to soil properties, application of Rice husk Biochar (RHB) @ 5t/ha + 75% RDF (T4) has reduced the soil bulk density (from 1.52 to 1.47) and application of rice straw compost @ 5t/ha has increased the soil pH (from 6.58 to 7.14) as compared to other treatments whereas the nutrient status (nitrogen (from 212 to 266 kg ha-1); phosphorus (from 45.41 to 61.59 kg ha-1) and potassium (from 192 to 218.4 kg ha-1) has increased by application of PSB @ 2kg/ha + RSC @ 5t/ha + 100% RDF (T11) than other treatments.