Paddy and Water Environment最新文献

Joint cracks are a type of characteristic crack that occurs in the side walls of cast-in-place reinforced concrete open channels. In this study, thermal stress analysis was performed to analyze the cause and timing of joint cracks in the side walls of such channels. The distribution of maximum principal stress indicated that previously placed spans restrain subsequently placed spans, increasing the risk of generating joint cracks. This suggests that the waterstops buried in the previously placed spans restrain the deformation of the subsequently placed spans due to the difference in strength caused by the material ages. In addition, the risk of generating joint cracks increased with the increase in the casting intervals. The maximum principal stresses exceeded the tensile strength of the concrete around the joint sections for both summer and winter construction. Thus, joint cracks may occur at both early and long-term material ages, regardless of construction season. To obtain a more realistic thermal stress analysis, outside temperature models capturing the features of temperature data in Japan were proposed, and these models gave appropriate analysis results.

Alternate wetting and drying (AWD) irrigation practice requires an appropriate threshold value for which, maximum water savings and minimum water and nutrient loss can be achieved without affecting the grain yield significantly. Determining the appropriate AWD threshold value experimentally is a challenging task. Mathematical models with optimization can be substitute tools for determining appropriate AWD threshold value. In this study, field studies were carried out using the non-weighing lysimeters with three levels of irrigation treatment (no soil water stress: NS, mild soil water stress/400 cm: MS and severe soil water stress/750 cm: SS) along with three levels of nitrogen application rate (high nitrogen: HN/150 kg/ha; medium nitrogen: MN/120 kg N/ha; low nitrogen: LN/60 kg N/ha). Each treatment was replicated three times. The field experimental data were used to determine the crop production function and simulate water flow and nutrient transport with the help of the Hydrus-1D model. Finally, the simulated results were optimized with the help of Design Expert software and appropriate irrigation (ponding water depth, soil matric potential head) and nutrient management (nutrient application rate) practice determined. The simulated results indicate that, the change in ponding water depth, soil matric potential head and nutrient application rates affect the water flow, nutrient transport and grain yield significantly. Overall, the 4.5 cm ponding water depth with the recommended dose of fertilizer (N: P: K-120: 50:60 kg/ha) and soil matric potential head of 400 cm was considered as an appropriate irrigation and nutrient management practice, which resulted a maximum grain yield of 5 t/ha and net profit of approx. Rs.20595.

Water scarcity has widely affected agricultural production and food security, particularly in arid regions. There is little information available on the concurrent effects of water stress and organic amendment application on the water holding capacity of soil as well as the growth and yield responses of quinoa as a drought-resistant plant. In addition, there are limited reports on the optimum levels of deficit irrigation as a promising strategy for enhancing the water use efficiency and production of quinoa plant. Therefore, the aim of this study is to investigate the moisture holding capacity of soil as well as the morphological and physiological responses of quinoa to the interactive effects of drought and organic amendment under field conditions. Three levels of water stress (full-irrigation, moderate drought, and severe drought) and four treatments of organic amendment including control (without the use of organic matter), vermicompost (20 t ha⁻¹), biochar (20 t ha⁻¹), and the composition of vermicompost and biochar (at an equal rate of 10 t ha⁻¹ each) were applied as the subsidiary factor. Result indicated that severe drought reduced the plant yield significantly (21.7%) as compared to control, whereas moderate drought showed no significant effect. Drought increased the proline content, whereas reduced all other traits including crop growth rate, 1000-seeds weight, bush height, panicle length, leaf area index, chlorophyll, proline, carotenoids, protein, and relative water content. However, the application of biochar, vermicompost, and Bvrm relative to the control treatment increased WUE by 12.3, 36.8, and 45.6%, soil moisture content by 2.0, 20.1 and 28.9%, and the quinoa yield by 1.0, 21.9, and 28.6%, respectively. There was an inverse relationship between water use efficiency and the grain yield of quinoa. The simultaneous effect of drought and biofertilizer on the quinoa grain yield (Y) was demonstrated based on soil moisture content (θ) using a linear relationship (Y = 168.5(θ) − 4.74; R² = 0.994, p < 0.01). The results also indicated that WUE was reduced linearly with increasing soil moisture content. Among different relationships, logarithmic function exhibited the best performance for predicting the yield of quinoa based on the amount of irrigation water. The findings of this study revealed the important role of soil moisture as a manageable characteristic in facing environmental stresses such as drought and achieving the sustainability of crop production.

This research examined the impact of extreme drought on rice planting dates in the Vietnamese Mekong Delta (VMD) region from 2014 to 2018 using the time series of Normalized Difference Vegetation Index (NDVI). The Savitzky–Golay filter method was applied to remove noises and smooth the NDVI time series. Rice planting dates were determined by using the threshold of increasing NDVI to 20% of the amplitude for each season using TIMESAT. The research findings show that the remotely sensed-based sowing batches and the cultivation areas matched the official statistics with an estimated error of less than 12%. In the 2015/2016 extreme drought, the rice planting dates were delayed compared to the neutral years, especially in the winter–spring (WS) and summer–autumn (SA) crops. In general, the WS crop was more affected in the double rice crops than the SA crop in the triple rice crops. The results also pointed out various ecoregions facing different problems that should be addressed to ensure farmers' livelihood, primarily water management. Further research is necessary to understand the combined impacts of drought and changes in sowing dates on rice yield and the vulnerability of different farming models in the VMD.