Soil fertility assessment plays a vital role in improving fertilizer efficiency by indicating the nutrients available in the soil. A research was conducted in 4 districts (Banke, Dang, Kapilvastu, and Rupandehi) at the western Terai of Nepal to study the fertility status at different soil depths (0-20, 20-40, and 40-60cm) in the paddy harvested fields. 10 samples each were collected from each district to study the nutrients available in different soil depths so that the necessary amendments could be made for the sustainable and scientific production of rice wheat. Four districts were taken as blocks and 3 different depths as the main plot. Composite soil samples were collected in each study site at 0-20,20-40 and 40-60cm soil depth. Soil physical and chemical properties like soil texture, pH, total nitrogen, available potassium, and available phosphorus were tested in the Soil laboratory at HICAST. GenSTAT, MS-Excel, and SPSS were used for data analysis. All the soil fertility parameters analyzed were significantly affected (P<0.05) by the variation in soil depth. The soil organic matter and nitrogen level were significantly higher in Kapilvastu district (1.2767% & 0.075%) and in the upper surface of the soil (1.45% & 0.86%) while lowest soil organic matter and nitrogen levels were recorded from Rupandehi district (0.669%) and in Dang district (0.052%) respectively. In contrast, the available Phosphorus was highest in Banke district (80.02 kg/ha) and in the top depth of 0-20cm (55.32kg/ha), lowest in Kapilbastu district (35.97 kg/ha) and in the depth of 40-60cm (37.26kg/ha). The available K content followed the order: Kapilbastu (177.0kg/ha) > Dang (120.8kg/ha) > Banke &Rupendehi (81.4kg/ha) and 0-20cm depth (168.3kg/ha) > 20-40cm depth (157.7 kg/ha) >40-60cm depth (151.7kg/ha). There was no significant difference in available K levels in different depths of soil. The lowest pH was recorded in Kapilbastu district at the depth of 20-40cm (5.5). The pH of 0-20cm depth (7.147), 20-40cm depth (7.52) and 40-60 cm depth (7.449) were not significantly different as determined by DMRT. The results obtained from the study indicated that the land under rice-wheat cropping system in the western terai of Nepal has poor soil health, therefore future research strategy should be built based on the soil fertility status of the research to judge the nutrient requirement and application of nutrients for the sustainable management of crop and soil health.

Atmospheric dust deposition supplies a significant amount of macro-and micronutrients to surface ocean water, thus playing a vital role in modulating phytoplankton growth. In this context, we measured soluble and total bioactive trace elements (TEs; Fe, Mn, and Cu) along with eolian dust concentration in aerosol samples collected over a wide area of the Arabian Sea during the southwest monsoon (SWM) month of two consecutive years (2017 and 2018). Our objective in this study is to assess the spatial variability of TEs and quantify their fluxes over the Arabian Sea. Relatively higher mineral dust concentrations were observed during the campaign period compared to earlier studies over the Arabian Sea. A large spatial variability in total Fe (91−2830 ng m −3 ) and soluble Fe (0.3−32.7 ng m −3 ) concentrations was observed in contrast to Mn and Cu. However, the operational fractional solubility (defined as the fraction of soluble metal leached using ultrapure deionized water out of the total metal) is relatively low (less than 3.6%) for Fe as compared to Mn (range: 6−87%) and Cu (4−79%). Higher enrichment factors were observed for Mn (range: 1−37) and Cu (range: 6−96), particularly in the northern sector, suggesting the partial contribution of TEs from the anthropogenic emissions that is further corroborated by air-mass back trajectory analyses. An inverse hyperbolic relationship between fractional solubility and total metal concentration is observed for Fe (similar to previous observations); however, no such association is found in case of Mn and Cu. The dry deposition fluxes of Fe, Mn, and Cu to surface water of the Arabian Sea were estimated as 757, 38.8, and 1.4 μg m −2 day −1 , respectively. These fluxes are on the higher side compared to those reported from other oceanic regions of the globe.