Status and sustainability challenges of agricultural water usage in Bangladesh

Maintaining sustainability in agricultural water usage is a critical concern particularly when the burgeoning population demands more food while adverse climate change impacts water availability. Despite this, the climate-water-crop nexus is still poorly understood in many regions throughout the globe. This study was conducted to quantify current agricultural water use in Bangladesh, one of the most climate-vulnerable countries, and to assess its sustainability challenges. The number of crops, cropping area, yield, water use, long-term daily rainfall, daily river stage and weekly groundwater level data were collected and statistically analyzed. This study revealed that the two most drought-prone northwest divisions export virtual water embedded in agricultural produce at 14086 Mm3/yr, whereas two urbanized divisions import 18477 m3/yr, to or from the national water-use budget. Only rice production consumed ~88% of the total water used in agriculture, and the dry season rice had higher water demand than the wet season rice. The water use sustainability in the two most water-exporting divisions is at great stake because total rainfall in July is decreasing significantly (2.90 mm/yr) in one division and the number of rainless days in August is significantly increasing (0.033 day/yr) in other division. Irrigated rice production will also face water scarcity because the dry season water level in both rivers (63%) and observation wells (92%) shows a declining trend. The ratio of green (rainfed) to blue (irrigation) water use in the country was estimated at 2.5, which needs to be increased

Transport of Cryptosporidium parvum oocysts in soil columns following applications of raw and separated liquid slurry

The potential for the transport of viable Cryptosporidium parvum oocysts through soil to land drains and groundwater was studied using simulated rainfall and intact soil columns which were applied raw slurry or separated liquid slurry. Following irrigation and weekly samplings over a 4-week period, C. parvum oocysts were detected from all soil columns regardless of slurry type and application method, although recovery rates were low (<1%). Soil columns with injected liquid slurry leached 73 and 90% more oocysts compared to columns with injected and surface-applied raw slurries, respectively. Among leachate samples containing oocysts, 44/72 samples yielded viable oocysts as determined by a dye permeability assay (DAPI [4′,6′-diamidino-2-phenylindole]/propidium iodide) with the majority (41%) of viable oocysts found in leachate from soil columns with added liquid slurry. The number of viable oocysts was positively correlated (r = 0.63) with the total number of oocysts found. Destructively sampling of the soil columns showed that type of slurry and irrigation played a role in the vertical distribution of oocysts, with more oocysts recovered from soil columns added liquid slurry irrespective of the irrigation status. Further studies are needed to determine the effectiveness of different slurry separation technologies to remove oocysts and other pathogens, as well as whether the application of separated liquid slurry to agricultural land may represent higher risks for groundwater contamination compared to application of raw slurry