Search

【Objective】 Study on the spatial and temporal variability in water demand of processing tomato in the Northwest Arid Region of China is very essential for local agricultural water management and optimal allocation. 【Method】 Based on the meteorological data measured from 40 weather stations in 1985—2014 within the study region, the evapotranspiration (ETc) and irrigation water demand (Ic) were calculated for the processing tomato, using the modified crop coefficients and water balance equation. 【Result】 Spatially from the west to the east, the ETc and Ic of the processing tomato during different growing stages increased first and then decreased, with its value peaking in eastern Xinjiang, Gansu and Northwestern Ningxia and Inner Mongolia. The annual average ETc during the growing period of the tomato in Xinjiang, Gansu, Ningxia and Inner Mongolia were 460.98-1 202.69 mm, 591.14-749.92 mm, and 530.63-878.66 mm, respectively. Meanwhile, the annual average Ic in these three regions were 187.21-1 180.98 mm, 508.69-702.97 mm, and 354.94-851.14 mm, respectively. On the time scale of 30 years, the ETc and Ic in tomato growing period increased at a rate ranging from 0 to 30.0 mm/10 a. In particular, the ETc in Xinjiang and Gansu showed a significant increase, while the ETc in Ningxia and Inner Mongolia increased insignificantly. Additionally, the trend of average Ic in Ningxia and Inner Mongolia was not obvious. 【Conclusion】 The ETc and Ic over whole growing period of processing tomato in the study region showed strong spatial and temporal variability, and there is an urgent need to implement water-saving irrigation technology and strengthen the optimal allocation of water resources under the environment of climate change.

【Objective】 Tracking the change in cultivation areas of different crops in a basin or catchment is essential for agricultural management but challenging. The objective of this paper is to investigate the feasibility of threshold feature - random forest classification model for extracting crop structure from remote sensing imageries of irrigation district. We took Qingtongxia irrigation as an example. 【Method】 Using field survey and visual interpretation, the threshold feature-random forest classification method in the Google Earth Engine platform was used to delineate the planting areas of spring wheat, spring maize, and rice within the Qingtongxia irrigation district from 2013 to 2020. 【Result】 The threshold feature-random forest classification method is effective for extracting planting structure in the Qingtongxia irrigation district in the seven years, with an overall accuracy of 0.88 and a Kappa coefficient of 0.76. The linear fitting between the extracted areas from the remote sense images and areas obtained from survey gave a R2 which was 0.80, 0.93 and 0.86, for spring wheat, spring maize and rice, respectively. Data analysis revealed that the planting area of spring maize surpassed that of rice and spring wheat in 2013 to 2020. Spring maize cultivation had notably increased, while spring wheat cultivation initially increased and then declined; rice cultivation also decreased. Spring maize was mainly grown in the North and South of the irrigation district, while the overall irrigation area increased from the North to the South. Spring wheat was primarily cultivated in central and Southern parts of the irrigation district, and rice was in the central region. Spring wheat and rice cultivation areas increased from the South to the North. 【Conclusion】 The threshold feature-random forest classification model is effective and accurate for extracting annual change in planting structures in irrigation districts in arid regions. It is novel and perspective for understanding long-term evolution in planting structure in a region.

At present, almost all the definitions of hypertension in pediatric hypertension guidelines issued by countries and organizations are based on blood pressure percentile of 95% (P95). However, a large number of research data have shown that high normal blood pressure has a higher risk of progression to hypertension and cause similar target organ damage as hypertension. The review summarized the classification methods of blood pressure of children and adolescents in different countries and organizations, the prevalence of hypertension and high normal blood pressure, the rate of progression from high normal blood pressure to hypertension, and target organ damage caused by high normal blood pressure in children and adolescents, emphasizing that pediatricians should pay greater attention to the definition of high normal blood pressure and hypertension for children and adolescents.

A compound control strategy is proposed in order to solve the low control accuracy and poor anti-disturbance of deadbeat control. In this method, the repetitive control is embedded into the deadbeat control to improve the robustness of the control system and the variation of inductance parameters. According to the mathematical model of three-phase four-leg inverter, the deadbeat control algorithm applied to the current loop is deduced and modified, then the repetitive control algorithm is added. Finally, the strategy is simulated and verified by experiments to verify the effectiveness of the strategy.

In order to study the torsional vibration of gear transmission system under slippage in high-speed train.A parametric vibration model of the gear transmission system is developed when the time-varying stiffness and the transmission error are considered.The nonlinear characteristic of selfexcited torsional vibration caused by wheel-rail creepage is analyzed.Numerical simulation results show that the time-varying mesh stiffness of meshing teeth pairs is the main cause of harmonic vibration of gear transmission system,when the wheel-rail creepage is over the best value,the self-excited vibration occurred and gear transmission system have the phenomenon of limited cycle in the same time,the self-excited vibration has no effect on the change of main frequency of the gear transmission system,but the harmonic response become more obvious,cause a strong vibration on the gear transmission system.

Soil moisture and salinity are two key factors for crop production in arid irrigation districts. It is critical to modify soil water-salt dynamics and crop growth on a regional scale for the sustainable agriculture. In this paper, a distributed agro-hydrological model that well considers the spatial variability of soil and hydrological factors was developed to simulate soil water movement, solute transport and crop growth process on the regional scale. Jiefangzha Irrigation System (JIS) of the Hetao Irrigation District was selected as the study area. The JIS was divided into 201 homogeneous simulation units based on the combinations of weather-soil-crop-irrigation. In this way, the one-dimensional agro-hydrological model--HYDRUS-EPIC (HYDRUS-1D coupled with EPIC crop growth module), was used and expanded to the regional scale. Field experiments were conducted in 2012 and 2013. The dataset of soil moisture, soil solute concentration, leaf area index (LAI) and crop yield were collected at 40 monitoring points, and used for model calibration and validation. Simulated soil moisture and salinity concentration in the root zone showed good agreement with the measured values. During the calibration process, root mean square error (RMSE), mean relative error (MRE) and coefficient of determination (R²) for soil moisture were 0.03 cm³/cm³, 0.3% and 0.67, respectively. For salinity concentration, RMSE, MRE and R² were 2.72 g/L, -13.5% and 0.53. LAI and crop yields were fitted well with the observations. MRE values for the estimated and measured LAI and crop yields were 1.0% and 1.1%, and R² were both larger than 0.90 for these two items. During the validation process, RMSE, MRE, and R² were 0.04 cm³/cm³, 2.6%, 0.57 for soil moisture, and 2.62 g/L, -4.5%, 0.51 for salinity concentration, respectively. And MRE and R² were 9.1%, 0.88 for LAI, and -1.9%, 0.92 for crop yields. These results showed that the distributed agro-hydrological model was able to simulate the soil water flow, salt transport, and crop growth process in JIS with accuracy. The calibrated and validated model was then applied to predict spatial distribution of soil moisture, salinity concentration, crop evaporation and crop yields of the study area in present irrigation water management practices. Effective saturation and salinity concentration in the root zone were chosen to represent soil water and salinity stress on crop growth. Results showed that effective saturation ranged from 0.44 to 0.90 with an average of 0.7 for the JIS. In most areas, soil water could meet crop water consumption needs. In the areas where groundwater depth (GWD) was less than 1.3 m, root water uptake was limited due to waterlogging. The average salinity concentration in the root zone varied from 3.1 g/L in the northwest to 13.5 g/L in the northeast with an average of 6.4 g/L for the whole district. High soil salinity concentration limited crop production seriously. Corresponding to the spatial distribution of salinity concentration in the root zone, crop relative yield (ratio of actual yield and average yield of JIS) ranged from 0.33 to 1.33. The results suggested that for the northeastern part, where GWDs were larger than 2.0 m, more irrigation was needed for leaching salt. It was also better to plant more salt tolerant crops in these areas. In northwestern and southwestern parts, shallow groundwater levels intensified waterlogging or salinity accumulation problems. The study indicated that it is better to keep the groundwater depth not shallower than 1.3 m for maintaining the crop yields. [ABSTRACT FROM AUTHOR]

Evapotranspiration is the main way of soil water depletion in field, and soil evaporation is an important part of evapotranspiration, and it may account for 32%-50% of the total evapotranspiration during the whole crop growth period. Soil evaporation does little effect on the formation of crop biomass and yield, so reducing soil evaporation is important for improving water use efficiency and agricultural water saving management. In recent years, straw mulching has been used widely due to its capability of improving soil structure, increasing soil organic matter, reducing soil evaporation and maintaining soil water content. Mulching affects exchange of energy and heat between soil surface and free air, so the mechanism for soil evaporation under mulching condition may be different from that without mulching. Considering the fast development of straw mulching, therefore modeling soil evaporation under straw mulching is of important for making agricultural water management. In this paper, the factors (soil water content and mulching amount) that affect soil evaporation had been analyzed, the values of mulching resistance were calculated, the equations for calculating resistance of mulching and the resistances of soil evaporation and soil evaporation under straw mulching had been established, the parameters for the equation had been determined. The experiment was carried out from late July to middle August in 2010 and from middle July to middle August in 2011, respectively. The undisturbed soil with winter wheat plants was prepared and put into plastic buckets when winter wheat was maturity, two main treatments (stubble and stubble+mulch treatments) were set up, there were five sub-treatments for each of the two main treatments. The stubble heights for stubble treatments were 0, 5, 15, 25, 35cm. Stubble heights were 0, 5, 15, 25, 35 cm with mulching amounts of 0.47, 0.43, 0.348, 0.267, 0.187 kg/m2 in stubble+mulch treatment, respectively. The total biomass (stubble biomass) for each stubble treatment was 0, 0.04, 0.122, 0.203, 0.283 kg/m2, respectively; the total biomass (stubble biomass and mulching amount) in each stubble+mulch treatment was 0.47 kg/m2. During the prepared period, water was applied to the soil until all the soil in the plastic bucket was saturated, and then the excessive water was discharged out off plastic bucket through small hole at the bottom of plastic bucket to make sure soil water content was about field capacity at the beginning of the experiment. The soil evaporation and soil temperature were measured daily and soil water content in 0-2 cm depth was measured every 2 ~ 5 days according to the soil evaporation. Meteorological data, including relative humidity, hourly mean air temperature, and wind speed were measured with an automatic weather station. Results showed that the relative soil evaporation (the ratio of soil evaporation to water evaporation from 20 cm diameter pan) kept relatively stable when soil water content was higher than 0.23 cm3/cm3 (60% field capacity), the ratio declined linear with the decreasing of soil water content when soil water content was higher than 0.05 cm3/cm3 (wilting point) and less than 0.23 cm3/cm3. Mulching affected soil evaporation, reducing stubble height and increasing mulching amount could reduce soil evaporation when the total biomass was the same. The total amount of soil evaporation during experiment period reduced by 8%-51% under stubble+mulch treatment with mulching amount of 0.348-0.47 kg/m2 compared with stubble treatment when stubble height was 0-15 cm. Mulching resistance was 158-600 s/m in this study and it was exponentially increasing with the mulching amount, and the resistance of soil layer decreased linearly with the soil water content increasing when soil water was less than 0.23 cm3/cm3 and higher than 0. 05 cm3/cm3. The validation processes showed that the developed method and related parameters (mulching resistance and the resistance of soil layer) performed well for modeling soil evaporation under mulching condition. [ABSTRACT FROM AUTHOR]

Reduction of water diversion from the Yellow River will intensify water shortage problems in the Yinbei Irrigation District (YID). Reasonable use of groundwater for irrigation is helpful to maintain the agricultural production. Groundwater exploitation may cause groundwater level declines in local areas. This helps to reduce the salinity accumulation in the root zone but decreases the capillary rise. Thus, it is important to figure out the responses of soil water-salt dynamics and crop yields to groundwater table fluctuations for salinity control and stable yields. In this study, HYDRUS-1D model was modified by coupling with the EPIC (erosion-productivity impact calculator) crop growth module for simulating agro-hydrological processes. The new crop module could simulate crop height, leaf area index (LAI), above-ground biomass and crop yield. The information between HYDRUS-1D and EPIC was exchanged by daily step. Root water uptake under water and salt stress was calculated with HYDRUS-1D and imported to EPIC to limit crop growth. EPIC module estimated crop height, LAI and root depth for HYDRUS-1D to calculate soil water-solute dynamics. HYDRUS-1D assumed that soil evaporation remained at the potential rate unless pressure head of the soil surface decreased to a prescribed value. After then this prescribed value was set as a constant head to renew the top boundary condition. However, it cannot reasonably reflect the decrease stage of soil evaporation when using the constant head boundary. This may overestimate soil evaporation. Therefore, a new soil evaporation module, estimating soil evaporation reduction coefficient using soil water content of the top layer (0-10 cm), was added for better describing the soil evaporation under shallow water tables. With the experimental data collected from the maize field in 2008, the model was calibrated by the data of groundwater irrigation treatment and validated by the data of canal irrigation treatment. Simulated soil water content and solute concentration in the root zone (0-90 cm) showed good agreement with the measured values. Root mean square error (RMSE), mean relative error (MRE) and coefficient of determination for soil moisture were 0.03 cm3/cm3, 3.4% and 0.78, respectively. For solute concentration, RMSE, MRE, coefficient of determination were 1.6 g/L, 1.3% and 0.29, respectively. LAI and above-ground biomass values were fitted well with the observations. MRE values for estimated and measured LAI and above-ground biomass were 5.9% and 10.6%, and R2 were both larger than 0.95 for these two items. The model was then used to assess the impacts of groundwater table and irrigation changes on soil water-salt dynamics and maize yields. Nine groundwater depth (GWD) scenarios (100, 110, 125, 140, 155, 170, 185, 200 and 250 cm) and 6 irrigation treatments (0.6, 0.8, 1.0, 1.2, 1.4 and 1.6 times of the present irrigation) were considered. The results showed that soil water content and salt storage in the root zone declined with the reduction of groundwater level and irrigation amount. Due to the decrease of groundwater contribution and soil moisture, lowering groundwater depth resulted in a gradual increase of the average solute concentration in the root zone. Maize yields increased first and then decreased as the groundwater table declined. Generally, the maximum yields were achieved when GWD was between 140 and 155 cm. The maize yields may decrease with reducing the irrigation amount, therefore water-saving strategies were not recommended for local farmers with low incomes. Finally, the optimum groundwater depth of 140-155 cm was suggested, and three irrigations with an amount of 900 m3/hm2 for each will be applied during maize growing period. [ABSTRACT FROM AUTHOR]