Phosphorus (P) is the limiting factor for eutrophication in most freshwater ecosystems. In China, Ptransported from intensively cultivated land has been reported as an important source of P in surface waters.In this s...Phosphorus (P) is the limiting factor for eutrophication in most freshwater ecosystems. In China, Ptransported from intensively cultivated land has been reported as an important source of P in surface waters.In this study, we investigated P concentration and forms in surface and subsurface drainage from wetland ricefields in the Shaoxing plain, Zhejiang Province, China. From selected rice fields, surface drainage sampleswere collected at rice-growing, non-growing and fertilization periods, and subsurface drainage samples atdrought and rewetting (irrigation or precipitation after 5～10 d drought period in the surface soils) and wet(drainage under long-term wet soil condition) periods. Water samples were characterized for their totalreactive P (TRP), dissolved reactive P (DRP) and particulate reactive P (PRP). Concentrations of the TRPand DRP in the surface drainage ranged from 0.08 to 1.50 and 0.06 to 1.27 mg L-1, respectively. The TRPand DRP were dependent on field operation activities, and decreased in the order of fertilization period ＞rice-growing period ＞ non-growing period. Phosphorus concentration of runoff receiving P fertilizer can bean environmental concern. The PRP concentration in the surface drainage, ranging from 0.01 to 0.57 mgL-1, accounted for 8%～78% of the TRP. Concentration of the TRP in the subsurface drainage was from0.026 to 0.090 mg L-1, consisting of 29%～90 % of the DRP and 10%～71% of the PRP. In the droughtand rewetting period, the PRP accounted for, on average, 63% of the TRP, much higher than in the wetperiod (23%), suggesting that there was transport of P in preferential flow during drainage events after ashort-term drought period in the surface soils. Therefore, P losses in particulate form may be importantin the subsurface drainage from rice fields when surface soils form cracks and favor rapid flow downwardthrough the soil profiles, suggesting the important role of water-dispersible colloid particles in mediating andco-transporting P in the subsurface drainage of rice fields.展开更多
Wetlands have immense poverty-fighting potentials and in Nigeria, more and more people are dependent on wetlands for their livelihoods. To examine the social factors affecting the current status of the wetlands utiliz...Wetlands have immense poverty-fighting potentials and in Nigeria, more and more people are dependent on wetlands for their livelihoods. To examine the social factors affecting the current status of the wetlands utilization for agriculture in Nigeda, a simple random sampling technique was used to select 200 farmers cultivating wetlands and a structured questionnaire was applied to elicit the information on the social factors. Data collected were described using frequency and percentage and a multiple regression analysis was used to identify significant variables that are determinants of wetland utilization. The results of the analysis showed that significant variables included crop preferences, farming system, culture, taste, land tenure, knowledge of wetland cultivation, perceived suitability, farmers＇ tribe, location of wetland, and farmers＇ age. it was concluded with suggestions for the right combination of policies, public awareness, and appropriate farming methods in order to improve wetland utilization in Nigeria.展开更多
Agriculture is one of the biggest sources of greenhouse gases. Rice production has been identified as one of the major sources of greenhouse gases, especially methane. However, data on the contributions of rice toward...Agriculture is one of the biggest sources of greenhouse gases. Rice production has been identified as one of the major sources of greenhouse gases, especially methane. However, data on the contributions of rice towards greenhouse gas emissions in tropical Africa are limited. In Zimbabwe, as in most of Sub-Saharan Africa, there are very few studies that have explored greenhouse gas emissions from agricultural lands. This study reports the first dataset on greenhouse gas emissions from intermittently flooded rice paddies in Zimbabwe. The objective of this study was to quantify greenhouse gas emissions from dambo rice under different tillage treatments, which were conventional tillage, no tillage, tied ridges, tied fallows, and mulching. Average soil nitrous oxide emissions were 5.9, 0.2, 5.4, 5.2 and 7.8 μg·m-2·hr-1 for tied fallows, conventional tillage, tied ridges, mulching and no tillage respectively. Average methane emission was 0.35 mg·m-2·hr-1 and maximum as 1.62 mg·m-2·hr-1. Average methane emissions for the different tillage systems were 0.20, 0.18, 0.45, 0.52 and 0.38 mg·m-2·hr-1 for tied fallows, conventional tillage, tied ridges, mulching and no tillage respectively. Carbon dioxide emissions were 98.1, 56.0, 69.9, 94.8 and 95.5 mg·m-2·hr-1 for tied fallows, conventional tillage, tied ridges, mulching and no tillage respectively. The estimated emissions per 150 day cropping season were 1.4, 3.6 and 0.6 kg·ha-1 for methane, carbon dioxide and nitrous oxide respectively. We concluded that intermittently saturated dambo rice Paddys are a potential source of greenhouse gases which is important to global greenhouse gas budgets, thus, they deserve more careful study.展开更多
The functions of and services from wetlands are seriously compromised due land and water scarcity coupled with the inability of poor people to adopt sound management strategies. The expansion of rice irrigation into t...The functions of and services from wetlands are seriously compromised due land and water scarcity coupled with the inability of poor people to adopt sound management strategies. The expansion of rice irrigation into the Ombeyi wetland ecosystem is likely to reduce their long-term ecological functionality. Using field observations and measurements, stakeholder analysis framework and consultative fora, this study investigated the growth in irrigated agriculture, irrigation practices and existing and potential trade-offs between the various uses of the wetland and their ecological functions. The objective was to identify the equilibrium between expansion of area under rice and restoration of the Ombeyi wetland ecosystem. Issues affecting wetland use and management were identified and used to derive possible solutions that could lead to sustainable use of the wetlands. The study showed that the area under rice cultivation increased by up to 760% as compared to the 1970s, most of it into the wetlands. There was a huge dependency on irrigation for food and income generation. However, there was observed low efficiency in water use and management. Recent emerging crops, especially arrow roots, would pose more threats to the wetland ecosystem because of their tolerance to waterlogged soils, low labour input, continuous harvesting and fewer pests and diseases. The fast exhaustion of soil fertility by arrow roots is also likely to motivate expansion into new areas, predominantly the wetlands. It was established that transplanting rice by mid May as opposed to the current practice in which farmers transplant in mid July saves water. The impact could further be reduced if the farmers adopted an optimized seasonal calendar. The study concluded that the solutions to wetland encroachment and over exploitation of resources lie in capacity building of farmers, improving efficiency in resource use and seeking for alternative livelihood options.展开更多
A study on the effect of Pb-Cd interaction on plant growth and on the chemistry of elements in plants was conducted under greenhouse condition with red soil-wetland rice system in different growth stage. The results s...A study on the effect of Pb-Cd interaction on plant growth and on the chemistry of elements in plants was conducted under greenhouse condition with red soil-wetland rice system in different growth stage. The results showed that Pb-Cd interactions on growth and metal uptake varied with different growth stageS and chemical compounds added. The plant height and the root weight were markedly affected by Pb-Cd interiction in the young stage but not in the ripening stage of rice at the treatments of PbCl_2 and CdCl_2 added. However, the weight of rice straw in the ripening stage was significantly effected by Pb-Cd interaction with the treatments of Pb(OAc)_2 and CdCl_2. The chemistry of elements in plants also depended on Pb-Cd interaction in varying degrees on account of different plant parts and growth stage. It seems that Pb-Cd interaction occurred not only in roots but also in other parts of wetland rice.展开更多
基金Project supported by the National Natural Science Foundation of China (No.49601013).
文摘Phosphorus (P) is the limiting factor for eutrophication in most freshwater ecosystems. In China, Ptransported from intensively cultivated land has been reported as an important source of P in surface waters.In this study, we investigated P concentration and forms in surface and subsurface drainage from wetland ricefields in the Shaoxing plain, Zhejiang Province, China. From selected rice fields, surface drainage sampleswere collected at rice-growing, non-growing and fertilization periods, and subsurface drainage samples atdrought and rewetting (irrigation or precipitation after 5～10 d drought period in the surface soils) and wet(drainage under long-term wet soil condition) periods. Water samples were characterized for their totalreactive P (TRP), dissolved reactive P (DRP) and particulate reactive P (PRP). Concentrations of the TRPand DRP in the surface drainage ranged from 0.08 to 1.50 and 0.06 to 1.27 mg L-1, respectively. The TRPand DRP were dependent on field operation activities, and decreased in the order of fertilization period ＞rice-growing period ＞ non-growing period. Phosphorus concentration of runoff receiving P fertilizer can bean environmental concern. The PRP concentration in the surface drainage, ranging from 0.01 to 0.57 mgL-1, accounted for 8%～78% of the TRP. Concentration of the TRP in the subsurface drainage was from0.026 to 0.090 mg L-1, consisting of 29%～90 % of the DRP and 10%～71% of the PRP. In the droughtand rewetting period, the PRP accounted for, on average, 63% of the TRP, much higher than in the wetperiod (23%), suggesting that there was transport of P in preferential flow during drainage events after ashort-term drought period in the surface soils. Therefore, P losses in particulate form may be importantin the subsurface drainage from rice fields when surface soils form cracks and favor rapid flow downwardthrough the soil profiles, suggesting the important role of water-dispersible colloid particles in mediating andco-transporting P in the subsurface drainage of rice fields.
文摘Wetlands have immense poverty-fighting potentials and in Nigeria, more and more people are dependent on wetlands for their livelihoods. To examine the social factors affecting the current status of the wetlands utilization for agriculture in Nigeda, a simple random sampling technique was used to select 200 farmers cultivating wetlands and a structured questionnaire was applied to elicit the information on the social factors. Data collected were described using frequency and percentage and a multiple regression analysis was used to identify significant variables that are determinants of wetland utilization. The results of the analysis showed that significant variables included crop preferences, farming system, culture, taste, land tenure, knowledge of wetland cultivation, perceived suitability, farmers＇ tribe, location of wetland, and farmers＇ age. it was concluded with suggestions for the right combination of policies, public awareness, and appropriate farming methods in order to improve wetland utilization in Nigeria.
文摘Agriculture is one of the biggest sources of greenhouse gases. Rice production has been identified as one of the major sources of greenhouse gases, especially methane. However, data on the contributions of rice towards greenhouse gas emissions in tropical Africa are limited. In Zimbabwe, as in most of Sub-Saharan Africa, there are very few studies that have explored greenhouse gas emissions from agricultural lands. This study reports the first dataset on greenhouse gas emissions from intermittently flooded rice paddies in Zimbabwe. The objective of this study was to quantify greenhouse gas emissions from dambo rice under different tillage treatments, which were conventional tillage, no tillage, tied ridges, tied fallows, and mulching. Average soil nitrous oxide emissions were 5.9, 0.2, 5.4, 5.2 and 7.8 μg·m-2·hr-1 for tied fallows, conventional tillage, tied ridges, mulching and no tillage respectively. Average methane emission was 0.35 mg·m-2·hr-1 and maximum as 1.62 mg·m-2·hr-1. Average methane emissions for the different tillage systems were 0.20, 0.18, 0.45, 0.52 and 0.38 mg·m-2·hr-1 for tied fallows, conventional tillage, tied ridges, mulching and no tillage respectively. Carbon dioxide emissions were 98.1, 56.0, 69.9, 94.8 and 95.5 mg·m-2·hr-1 for tied fallows, conventional tillage, tied ridges, mulching and no tillage respectively. The estimated emissions per 150 day cropping season were 1.4, 3.6 and 0.6 kg·ha-1 for methane, carbon dioxide and nitrous oxide respectively. We concluded that intermittently saturated dambo rice Paddys are a potential source of greenhouse gases which is important to global greenhouse gas budgets, thus, they deserve more careful study.
文摘The functions of and services from wetlands are seriously compromised due land and water scarcity coupled with the inability of poor people to adopt sound management strategies. The expansion of rice irrigation into the Ombeyi wetland ecosystem is likely to reduce their long-term ecological functionality. Using field observations and measurements, stakeholder analysis framework and consultative fora, this study investigated the growth in irrigated agriculture, irrigation practices and existing and potential trade-offs between the various uses of the wetland and their ecological functions. The objective was to identify the equilibrium between expansion of area under rice and restoration of the Ombeyi wetland ecosystem. Issues affecting wetland use and management were identified and used to derive possible solutions that could lead to sustainable use of the wetlands. The study showed that the area under rice cultivation increased by up to 760% as compared to the 1970s, most of it into the wetlands. There was a huge dependency on irrigation for food and income generation. However, there was observed low efficiency in water use and management. Recent emerging crops, especially arrow roots, would pose more threats to the wetland ecosystem because of their tolerance to waterlogged soils, low labour input, continuous harvesting and fewer pests and diseases. The fast exhaustion of soil fertility by arrow roots is also likely to motivate expansion into new areas, predominantly the wetlands. It was established that transplanting rice by mid May as opposed to the current practice in which farmers transplant in mid July saves water. The impact could further be reduced if the farmers adopted an optimized seasonal calendar. The study concluded that the solutions to wetland encroachment and over exploitation of resources lie in capacity building of farmers, improving efficiency in resource use and seeking for alternative livelihood options.
文摘A study on the effect of Pb-Cd interaction on plant growth and on the chemistry of elements in plants was conducted under greenhouse condition with red soil-wetland rice system in different growth stage. The results showed that Pb-Cd interactions on growth and metal uptake varied with different growth stageS and chemical compounds added. The plant height and the root weight were markedly affected by Pb-Cd interiction in the young stage but not in the ripening stage of rice at the treatments of PbCl_2 and CdCl_2 added. However, the weight of rice straw in the ripening stage was significantly effected by Pb-Cd interaction with the treatments of Pb(OAc)_2 and CdCl_2. The chemistry of elements in plants also depended on Pb-Cd interaction in varying degrees on account of different plant parts and growth stage. It seems that Pb-Cd interaction occurred not only in roots but also in other parts of wetland rice.
