Effects of water and rice straw management practices on yield, water productivity, greenhouse gas emissions and soil organic carbon stocks in a double-cropped paddy fields in the central plain of Thailand | |
| Author | Sumana Maneepitak |
| Call Number | AIT Diss no.NR-19-01 |
| Subject(s) | Straw Water--Management Greenhouse gas mitigation |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Natural Resources Management, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. NR-19-01 |
| Abstract | Global food demand is rapidly increasing due to continuing population and consumption growth. Rice is one of the most important staple food crops to meet the ever-increasing demand for food. Irrigated lowland rice is the largest consumer of freshwater in the agricultural sector. Freshwater resources to farmland are declining due to climate change and heavy groundwater extraction. Rice cultivation techniques with less irrigation water input are crucial for global food security in the context of changing climate scenarios. Therefore, alternative approaches are needed to increase water productivity in irrigated lowland rice production system. Alternate wetting and drying (AWD) is among such watersaving techniques, which could potentially reduce irrigation water input for rice cultivation through alteration of soil submergence period with period of soil non-submergence (unsaturated soil conditions) during the growing season. Rice straw (RS) is often scattered in the field after harvest or burned in intensive rice cultivation systems. Response of irrigated lowland rice with respect to grain yield and water use under different water and RS management practices largely remains unknown. Field experiments were conducted at the Ayutthaya Rice Research Center, Ayutthaya, Thailand, in two consecutive rice-growing seasons (wet and dry) of 2016–2017 to evaluate the growth, yield and water productivity of irrigated lowland rice under different water and RS management practices. The treatments included were two water (continuous flooding [CF] and AWD [15 cm threshold water level below the soil surface for irrigation]) and three RS management practices (RS incorporation [RS-I], RS burning [RS-B] and without RS incorporation and burning [WRS]). AWD increased grain yield by 15% in the wet season and by 7% in the dry season compared with CF. Other yield components such as panicle number m–2, spikelet number panicle–1 and 1000-grain weight were also higher under AWD compared with CF depending on the growing season. AWD reduced total water input by 19% in the wet season and by 39% in the dry season resulting in an improvement in total water productivity by 46% in the wet season and by 77% in the dry season relative to CF. RS application either as soil incorporation or open-field burning had no effect on grain yield, water-saving potential and water productivity of the tested variety regardless of the growing seasons. Although its positive role in supplying plant nutrients and maintaining soil fertility, RS incorporation in the field or burning should be discouraged due to negative environmental impacts. AWD (15 cm threshold water level below the soil surface for irrigation or with soil water potential of ≥ −20 kPa [AWD15]) is recommended for irrigated lowland rice cultivation from a point of view of reducing total water input without jeopardizing yield. Rice-rice (double-rice) cropping in the Central Plain region of Thailand relies heavily on irrigation water inputs for cultivation under flooded conditions, which is increasingly constrained by water scarcity. In this production system, farmers often burn or incorporate rice straw (RS) in the field. The effects of the combined use of water and RS management on irrigated lowland double-rice cropping, with respect to irrigation water saving, grain yield, and greenhouse gas (GHG) emissions, remain largely unknown. Field experiments of two consecutive rice-growing seasons in 2016–2017 were conducted at the Ayutthaya Rice Research Center in Ayutthaya, Thailand, to investigate the effects of different water and RS management practices on irrigation water savings, rice grain yields, and GHG emissions. The treatments consisted of two water regimes (continuous flooding [CF], alternate wetting and drying [AWD; 15 cm threshold water level below the soil surface for irrigation]) and three RS management practices (RS incorporation [RS-I], RS burning [RS-B], without RS incorporation and burning [WRS]). Parameters such as irrigation water inputs, soil characteristics (pH, temperature, water content), above-ground biomass, and grain yields iv were measured. The static vented flux chamber technique was used to measure GHG emissions (CH4 and N2O fluxes). AWD irrigation significantly reduced water inputs compared to CF in both growing seasons; however, there were more water savings in the dry season. AWD also resulted in higher grain yields compared to CF in both growing seasons. The average CH4 emissions from WRS plots were significantly lower compared to both RS-I and RS-B plots, regardless of the growing seasons. However, RS-I and RS-B plots under AWD had 39% and 63% lower CH4 emissions, respectively, in the wet season, while the corresponding values were 37% and 36%, respectively, in the dry season compared to the average CH4 emissions from these RS treatments under CF. Water and RS management did not significantly influence the average flux of N2O emissions from paddy fields in the wet season; however, CF had a lower average N2O flux than AWD in the dry season. The average flux of N2O emissions were very low compared to the CH4 emissions flux in both seasons. Averaged across two seasons, the yield-scaled global warming potential (GWP) under AWD was reduced by 34% compared to CF, and under WRS it was reduced by 36% and 29% compared to RS-I and RS-B, respectively. RS application, either as soil incorporation or open-field burning, had little or no effect on irrigation water savings and grain yields; however, the yield-scaled GWP was significantly higher from plots with RS-I or RS-B than WRS plots. Among the water regime and RS management practices tested, AWD irrigation without any RS application (soil incorporation or burning) can be employed for maintaining the yield-scaled GWP of irrigated lowland double-rice cropping at a low level. Water and RS management practices can potentially affect the accumulation of soil organic carbon (SOC) in agricultural soils. Field experiments were conducted in two consecutive rice-growing seasons (wet and dry) to evaluate SOC stocks under different water (CF, AWD) and RS management practices (RS-I, RS-B, and WRS) in a double-cropped paddy field. RS-I under AWD had higher volumetric water content than the same RS management under CF at tillering in both growing seasons. Total SOC was significantly higher under AWD at tillering in both wet and dry seasons and after harvesting in the dry season compared with CF. The same trend was also observed for C:N ratio at tillering and after harvesting in the dry season. RS-B plots had lower SOC stocks than RS-I and WRS plots across most of the measuring periods regardless of the growing seasons. SOC stocks were 33.09 and 39.31 Mg/ha at RS-B and RS-I plots, respectively, in the wet season, whereas the respective values were 21.45 and 24.55 Mg/ha in the dry season. Incorporation of RS enhanced SOC stocks under AWD irrigation, especially in the dry season before planting. These management practices (RS-I under AWD irrigation) could be a viable option to increase SOC stocks in the double-cropped rice production region. However, the environmental consequences of RS incorporation in irrigated lowland rice production system should be taken into consideration before its recommendation for paddy field on a large scale. |
| Year | 2019 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. NR-19-01 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Development and Sustainability (DDS) |
| Academic Program/FoS | Natural Resources Management (NRM) |
| Chairperson(s) | Shrestha, Rajendra P.; |
| Examination Committee(s) | Datta, Avishek;Shrestha, Sangam;Kuwornu, John K.M.;Boonlue Kachenchart ; |
| Scholarship Donor(s) | Ministry of Agriculture and Cooperatives (MOAC), Thailand;Asian Institute of Technology Fellowship ; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2019 |