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Soil Properties, Greenhouse Gas Emissions, and Nutrient Availability in Rainfed Lowland Rice as Affected by Biochar Application
Dissertation Abstract:
Two consecutive greenhouse experiments were conducted to investigate the effects of corn cob and rice straw biochars on soil properties, microbial activity, rice yield, and greenhouse gas (methane and nitrous oxide) emissions in rainfed rice cultivation. The experiments were conducted at the International Rice Research Institute (IRRI), Los Baños, Philippines. In wet season (WS 2016), biochar addition increased soil pH and decreased soil bulk density with or without chemical fertilizer and cow manure. The lowest soil bulk density was observed in rice straw biochar (40 t/ha) together with cow manure and chemical fertilizer. All treatments with added biochar, chemical fertilizer, and cow manure significantly enhanced total nitrogen, soil organic carbon, available phosphorus, exchangeable potassium, and nitrogen uptake by rice plants, when compared to the control treatment. The highest total nitrogen was exhibited in rice straw biochar (40 t/ha) with chemical fertilizer treatment. Soil organic carbon and exchangeable potassium were highest in rice straw biochar (40 t/ha) together with cow manure and chemical fertilizer, while corn cob biochar (40 t/ha) with cow manure and chemical fertilizer showed highest available phosphorus and nitrogen uptake in WS 2016. Fluorescein diacetate microbial activity was measured at flowering and harvesting stages and the results indicated that 40 t/ha of corn cob and rice straw biochar combinations with cow manure and chemical fertilizer stimulated higher microbial activity, while the treatments with only chemical fertilizer and cow manure incorporation showed lower activity in WS 2016. Emissions of methane and nitrous oxide were monitored in a closed chamber method throughout the whole rice growing season at two weeks intervals. Chemical fertilizer alone, single cow manure addition, and combination of them favored CH4 emission and showed higher rate of emission compared to all biochar containing treatments. The emission rate was lowest in rice straw biochar (40 t/ha) application alone. In contrast, higher N2O emission occurred in rice straw biochar (10 t/ha) with cow manure and chemical fertilizer applications compared to chemical and cow manure containing treatments, while the lowest emission was found in corn cob biochar (40 t/ha) alone applied treatment in wet season. Rice straw and corn cob biochar combination at the rate of 40 t/ha with chemical fertilizer and cow manure gave the highest grain yield and no significant differences with the grain yield of other biochar containing combinations. In dry season (DS 2016), soil pH increased with rice straw and corn cob biochar application. Lower soil bulk density was observed in all biochar containing treatments in comparison with other treatments and corn cob biochar (40 t/ha) together with cow manure and chemical fertilizer showed lowest bulk density. Soil total nitrogen and available phosphorus were also highest in corn cob biochar (40 t/ha) together with cow manure and chemical fertilizer. Mixed application of rice straw biochar (40 t/ha) with cow manure and chemical fertilizer showed highest soil organic carbon and exchangeable potassium. The highest nitrogen uptake was observed in the treatment of corn cob biochar (40 t/ha) together with cow manure and chemical fertilizer. Fluorescein diacetate microbial activity was highest in treatments with corn cob biochar (40 t/ha) with chemical fertilizer at flowering stage. Similarly, application of rice straw biochar (40 t/ha) added with cow manure and chemical fertilizer demonstrated similar effect at harvesting stage. Single chemical fertilizer, cow manure alone, and their combination showed higher methane emission rate than biochar containing treatments. The combination of rice straw biochar (40 t/ha) with cow manure and chemical fertilizer showed the lowest emission rate of methane. For N2O emission, the highest emission rate was observed in corn cob biochar (10 t/ha) together with cow manure and chemical fertilizer, followed by rice straw biochar (10 t/ha) together with cow manure and chemical fertilizer. On the other hand, the lowest N2O emission rate was found in rice straw biochar alone with the rate of 40 t/ha in DS 2016. The highest grain production resulted from rice straw biochar (40 t/ha) combination with cow manure and chemical fertilizer and corn cob biochar (40 t/ha) together with cow manure and chemical fertilizer. Thus, this study suggested that biochar was more efficient in improving rice production when added with organic and inorganic amendment to.