Soil organic carbon dynamics in the agricultural soils of Bangladesh following more than 20 years of land use intensification.

Soil organic carbon (SOC) is a key soil quality indicator, as it is a source and storage of plant nutrients and plays a vital role in soil fertility and productivity maintenance. Intensification of agriculture is known to cause SOC decline; however, much of the evidence stems from field-scale experimental trials. The primary aim of this study is to investigate how more than 20 years of agricultural land use intensification in Bangladesh has influenced SOC levels at landscape levels. This was achieved by revisiting in 2012 four sub-sites from the Brahmaputra and Ganges alluviums which were previously sampled (1989-92) by the Soil Resource Development Institute and collecting 190 new samples. These were located at different elevations and subjected to differing amounts of inundation. The SOC was determined using the same method, potassium dichromate wet oxidation, used in the 1989-92 campaign. A comparison of the SOC in the 2012 samples with their historic levels (1989-92) revealed that overall SOC declined significantly across both alluviums as well at their four sub-sites. Further analysis, however, showed that SOC has declined more at higher sites. The higher sites are inundated to a limited level, which makes them suitable for growing multiple crops. Among the land types considered here, the low land sites (because of their topographical position) remain inundated for a greater part of the year, allowing a maximum of only one crop of submerged rice. As a result of reduced biomass decomposition due to anaerobic conditions when inundated, and lower land use/cropping intensity, SOC accretion has occurred in the lower land sites. The SOC levels in South Asian countries are inherently low and agricultural land use intensification fuelled by growing food production demand is causing further SOC loss, which has the potential to jeopardise food security and increase the environmental impact of agriculture.

Preoperative discrimination of benign and malignant ovarian tumors using color Doppler sonography and its correlation with histopathology.

A total of forty clinically diagnosed ovarian tumors were studied over a period of one year. The study aimed at evaluating the efficacy of trans-vaginal color Doppler sonography (TV-CDS) in preoperative discrimination of benign and malignant ovarian tumors and to correlate the imaging findings with postoperative histopathological findings. The pulsatility Index (PI) and Resistive Index (RI) were studied as primary effecacy variables of TV-CDS. In the present study, using TV-CDS, 72.5% of the ovarian tumors were found benign and 22.8% were malignant which were significantly correlated with postoperative histopathological findings. The average PI for benign and malignant tumors were 1.98 and 0.77 respectively and RI for benign and malignant tumors were 0.62 and 0.41 respectively. The low PI and RI values in malignant tumors as compared to benign ones were statistically highly significant (p < 0.001). The validity tests for TV-CDS were found to be 90% sensitive, 100% specific and 97% accurate. The study concludes that TV-CDS is a useful imaging diagnostic modality in preoperative discrimination of benign and malignant ovarian tumors due to its excellent characterization of tumors neo-vascularization.