High nitrate (NO₃⁻) in vegetables, especially in leaf vegetables poses threaten to human health.  Selenium (Se) is an important element for maintaining human health, and exogenous Se application during vegetable and crop production is an effective way to prevent Se deficiency in human bodies.  Exogenous Se shows positive function on plant growth and nutrition uptake under abiotic and/or biotic stresses.  However, the influence of exogenous Se on NO₃⁻ accumulation in hydroponic vegetables is still not clear.  In the present study, hydroponic lettuce plants were subjected to six different concentrations (0, 0.1, 0.5, 5, 10 and 50 µmol L^–1) of Se as Na₂SeO₃.  The effects of Se on NO₃⁻ content, plant growth, and photosynthetic capacity of lettuce (Lactuca sativa L.) were investigated.  The results showed that exogenous Se positively decreased NO₃⁻ content and this effect was concentration-dependent.  The lowest NO₃⁻ content was obtained under 0.5 µmol L^–1 Se treatment.  The application of Se enhanced photosynthetic capacity by increasing the photosynthesis rate (P_n), stomatal conductance (Cs) and the transpiration efficiency (T_r) of lettuce.  The transportation and assimilation of NO₃⁻ and activities of nitrogen metabolism enzymes in lettuce were also analysed.  The NO₃⁻ efflux in the lettuce roots was markedly increased, but the efflux of NO₃⁻ from the root to the shoot was decreased after treated with exogenous Se.  Moreover, Se application stimulated NO₃⁻ assimilation by enhancing nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS) and glutamate synthase enzyme (GOGAT) activities.  These results provide direct evidence that exogenous Se shows positive function on decreasing NO₃⁻ accumulation via regulating the transport and enhancing activities of nitrogen metabolism enzyme in lettuce.  We suggested that 0.5 µmol L^–1 Se can be used to reduce NO₃⁻ content and increase hydroponic lettuce yield. 

    Following a rice or wheat harvest, a large amount of crop residue (straw) is retained in fields. The straw is often incorporated into the soil in order to increase the soil organic carbon storage and to reduce soil erosion. However, it has become apparent that the incorporated straw can significantly alter soil shear properties, which can dramatically affect energy inputs for tilling and other soil management practices. In this study, laboratory-remolded wheat straw-soil samples were compared with field-collected straw-soil samples; we found high correlations for the cohesion (R²=0.9084) and internal friction angle (R²=0.9548) properties of the samples. Shear tests on rice and wheat straw with different moisture content levels clearly demonstrated the relatively higher shear strength of wheat straw compared to rice straw. The cohesion of remolded rice and wheat straw-soil samples exhibited an increasing linear trend with an increase in densities, whereas the internal friction angle data for these samples exhibited a quadratic trend. Overlapping the cohesion curves revealed that the wheat straw-soil and rice straw-soil samples had the same cohesion at a straw density of 0.63%. Similar results were obtained when the internal fraction angle curves overlapped; the resultant point of intersection was observed at a straw density of 0.46%. As a whole, the remolded sample methodology was found suitable to simulate the shear properties of soils sampled directly from fields.