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The study of the micro-physical characteristics of spray droplets provides crucial insights into the impact of sprinkler water on soil erosion, leaf impact, and the microclimate of agricultural environments. However, the variability in measurement outcomes across different technologies due to their distinct measurement principles is a significant challenge. This research aims to evaluate and compare the droplet diameter, velocity, application rate, and kinetic energy rate using four distinct measurement technologies: the paper stain method (PS), flour pellet method (FP), laser precipitation monitor (LPM), and two-dimensional video disdrometer (2DVD), alongside a rain gauge (RG) in the context of sprinkler irrigation conditions. The results reveal that: (1) The FP method struggled to capture small droplets under the same spray conditions, while the PS method recorded a maximum droplet diameter exceeding 7 mm. The LPM registered the highest droplet count per unit area and time, notably capturing a significant number of small droplets (< 1 mm). Conversely, the 2DVD provided a more uniform distribution of droplet sizes, with the LPM's mean equivalent droplet diameter (dv) being 0.86 times that of the 2DVD. (2) Although droplet diameters and velocities measured by the 2DVD, LPM, FP, and PS, decreased with increased working pressure, these technologies concurred when assessing low-velocity and small-diameter droplet. (3) The 2DVD's larger sampling area compared to other methods enables the acquisition of more representative droplet characteristics, including their irregular shapes, suggesting its utility in measuring the micro-physical properties of sprayed droplets. (4) Based on the kinetic energy rate measured by the 2DVD under identical conditions, kinetic energy rate calibration factors of 0.88, 1.15, and 1.10 are suggested for the LPM, FP, and PS, respectively. This study provides essential data for calibrating and applying various droplet measurement technologies. [ABSTRACT FROM AUTHOR]

Aim: Assessing water consumption in intercropping systems relative to sole crop systems is important for planting system planning. Methods: This study focused on wheat/maize (Triticum aestivum L./Zea mays L.) relay intercropping to evaluate water use advantage of relay intercropping system based on the same period. Field experiments were conducted from 2014 to 2016, and three cropping patterns were designed: sole wheat, sole maize, wheat/maize intercrops. Method for evaluating water use advantage in intercropping was revised by considering water consumption of sole crops during the fallow period (periods where no plants are grown). Results: Intercropping grain yield was higher than sole cropping yield. Based on the existing method, the intercropping system had 20.4% greater water use than the sole cropping system and the water equivalent ratio (WER) was lower than 1; after revision, intercropping had 7.7% less water use than sole cropping, and the WER was greater than 1. Before revision, intercropped wheat used 3.1% more water than sole wheat, and the intercropped maize used 38.8% more water than sole maize; after revision, intercropped wheat used 24.4% less water than sole wheat, and intercropped maize used 11.0% more water than sole maize. Conclusion: These results indicated that the revised method can be better used to evaluate water use advantage of relay intercropping system. This study implied that wheat/maize intercropping increased both yield and water use based on revised method, and relay intercropping can be a suitable production practice employed in fallow policy, especially in areas with limited water. [ABSTRACT FROM AUTHOR]

The implementation of large-scale vegetation restoration over the Chinese Loess Plateau has achieved clear improvements in vegetation fraction, as evidenced by large areas of slopes and plains being restored to grassland or forest. However, such large-scale vegetation restoration has altered land-atmosphere exchanges of water and energy, as the land surface characteristics have changed. These variations could affect regional climate, especially local precipitation. Quantitatively evaluating this feedback is an important scientific question in hydrometeorology. This study constructs a coupled land-atmosphere model incorporating vegetation dynamics, and analyzes the spatio-temporal changes of different land use types and land surface parameters over the Loess Plateau. By considering the impacts of vegetation restoration on the water-energy cycle and on land-atmosphere interactions, we quantified the feedback effect of vegetation restoration on local precipitation across the Loess Plateau, and discussed the important underlying processes. To achieve a quantitative evaluation, we designed two simulation experiments, comprising a real scenario with vegetation restoration and a hypothetical scenario without vegetation restoration. These enabled a comparison and analysis of the net impact of vegetation restoration on local precipitation. The results show that vegetation restoration had a positive effect on local precipitation over the Loess Plateau. Observations show that precipitation on the Loess Plateau increased significantly, at a rate of 7.84 mm yr−2, from 2000 to 2015. The simulations show that the contribution of large-scale vegetation restoration to the precipitation increase was about 37.4%, while external atmospheric circulation changes beyond the Loess Plateau contributed the other 62.6%. The average annual precipitation under the vegetation restoration scenario over the Loess Plateau was 12.4% higher than that under the scenario without vegetation restoration. The above research results have important theoretical and practical significance for the ecological protection and optimal development of the Loess Plateau, as well as the sustainable management of vegetation restoration. [ABSTRACT FROM AUTHOR]

Background and aims: Understanding the variability in water availability in agroforestry systems in rain-fed orchards is vital for optimizing orchard management in semiarid areas. However, few studies have examined the soil capacity of water stock and supply in these systems over multiple years. We aim at (i) characterizing several soil physical properties related to water availability and inter-annual dynamics of soil water content and (ii) exploring their response to meteorological conditions and root distribution. Methods: Jujube (Ziziphus jujuba Mill.) intercropped with the fodder species canola (Brassica napus L.) (JFCS), jujube intercropped with daylily (Hemerocallis fulva L.) (JDLS), and a jujube orchard with clean tillage (JCS) were established on the Loess Plateau, China. Soil physical properties (including soil bulk density, soil hydraulic conductivity, soil field capacity, and soil porosity), soil water content and fine root data were collected over the period 2014–2017. Results: Compared to JCS-Tree, the field capacity was significantly increased both in the JFCS-Tree and JDLS-Tree treatments, while soil capillary porosity increased significantly only in the JFCS-Tree. Compared to JCS-Inter-row, the JFCS-Inter-row and JDLS-Inter-row exhibited significantly decreased soil bulk density, and increased field capacity, saturated hydraulic conductivity, and improved soil porosity, but the non-capillary porosity in the JDLS-Inter-row treatment were not significantly modified. Compare to JCS-Tree treatment, the soil water at 0–60 cm significantly increased under JFCS-Tree and JDLS-Tree in four years. However, due to the deeper fine root distribution for both tree and crop under JDLS-Inter-row, the soil water content at 60–180 cm in JDLS-Inter-row significantly decreased more than JFCS-Inter-row and JCS-Inter-row. Conclusions: The introduced crop modified the soil physical properties and soil water content, indirectly under trees and directly between inter-rows through the role of fine roots, thereby changing the orchard environment in semiarid areas. Agroforests can generally improve water condition at shallow soil layers compared to monocultural plantations, although such an effect may be accompanied with lower water stock at deeper soil layers in inter-rows, depending on crop species chosen. [ABSTRACT FROM AUTHOR]

This study is intended to simulate and better understand mean and extreme precipitation over the Loess Plateau (LP) in China using the Weather Research and Forecasting (WRF) model. We performed a long-term (1980–2011) simulation with the WRF model at a 10 km horizontal resolution, forced by the ERA-Interim reanalysis. A series of sensitivity experiments were conducted to investigate the influence of resolution and physical parameterization schemes on the simulation ability of the WRF model over the LP. The region has a dominant semi-arid climate and is adversely affected by extreme precipitation. Results show that the WRF model produced better simulations at a 10 km resolution for the LP with complex terrain than it did at coarser resolutions. WRF simulations for precipitation over the LP were most sensitive to cumulus schemes, moderately sensitive to planetary boundary layer schemes, and less sensitive to microphysics schemes. The WRF model not only adequately captured the spatial distribution of precipitation in the LP but also reproduced its magnitude and variability at different time scales. Moreover, the WRF model captured 73% of the observed extreme precipitation events with an intensity of more than 12 mm day− 1, which cause substantial soil erosion in the LP. Although it was unable to capture 27% of the observed events, the WRF model reasonably reproduced ERA-Interim extreme precipitation and its dynamic processes. These analyses strongly suggest that the biased extreme precipitation generated with the WRF model most likely resulted from inaccurate ERA-Interim forcing data. This study provides a better understanding of extreme precipitation simulations as well as insight into predictions of soil erosion in the LP. [ABSTRACT FROM AUTHOR]

An introduction to the journal is presented that focuses on the significance of root traits in genetics and breeding, adaptation to water and nutrient deficits, root trait variation and plasticity in response to agronomic practices and interaction with soil microbiome.

Background and Aims: Understanding the characteristics of root system is important for optimization of intercropping systems and increased utilization efficiency of limited resources. However, few studies have examined root development and water uptake in wheat/maize intercropping system under different water conditions. Methods: A two-year field experiment of sole wheat, sole maize, and intercropped wheat/maize was carried out under rainfed conditions and supplementary irrigation. Roots of wheat and maize were sampled seven times over the two growing seasons (2014–2015 and 2015–2016) using auger and monolith methods. Results: Root growth and distribution were promoted in intercropped wheat, while in intercropped maize roots both were suppressed. The maximum lateral extension distance of intercropped wheat under rainfed conditions varied from 40 to 50 cm during the co-growth period, which was significantly (p < 0.05) greater than that under supplementary irrigation conditions (25–30 cm), allowing intercropped wheat to access soil water in the area between the wheat and maize strips. Meanwhile, after wheat harvest, intercropped maize roots grown under supplementary irrigation showed growth recovery mainly in a horizontal direction with maximum lateral distance of 50 cm. Conclusions: Intercropping boosted the capacity of wheat roots but suppressed root growth in maize, and rainfed conditions encouraged the lateral distribution of intercropped wheat roots. [ABSTRACT FROM AUTHOR]

Emitter clogging has a direct impact on the performance and service life of a drip irrigation system. A study of labyrinth emitter clogging was conducted to determine the effects of pulsating versus constant pressure on average emitter flow rate ( $$\overline{q}$$ ), the Christiansen uniformity coefficient (Cu), and the location of clogged emitters. Under constant pressure, emitters in this study began to be clogged after the 8th irrigation, whereby 15 emitters eventually became clogged; the average emitter flow rate decreased to 75% of the original emitter flow rate ( $${{q}_{0}}$$ ) after the 15th irrigation, and Cu decreased rapidly by 68.2%. For pulsating pressure, emitters began to be clogged after the 14th irrigation, only 5 emitters became clogged, and $$\overline{q}$$ only decreased to 85.3% of $${{q}_{0}}$$ , and Cu declined by only 22.6%. These results demonstrate that the anti-clogging performance of emitters with pulsating pressure is better than with constant pressure. Emitter clogging at a constant pressure generally occurred at the inlet and front of labyrinth channels, mainly due to deposition of sediment particles. Emitter clogging with pulsating pressure is due to other impurities (e.g., debris of Teflon tape) besides sediment particles plugging the labyrinth channel. Pulsating pressure is recommended for use in drip irrigation to prevent emitter clogging. [ABSTRACT FROM AUTHOR]

Recognizing the need for a comprehensive review of the tools and metrics for the quantification and assessment of water footprints, and allowing for the opportunity for open discussion on the challenges and future of water footprinting methodology, an international symposium on water footprint was organized. The Water Footprint Symposium was held in December 2013 at the University of Leeds, UK. In particular, four areas were highlighted for discussion: water footprint and agriculture, quantification of water footprint, industrial water footprint, and from theory to practice. Discussion was organized to focus on the 'prioritization of water footprint research & applications to practical sectors'. The concept of water footprinting has helped to better communicate water management and assessment among different research and user communities. Significant research progress has been made in the relations between water footprint and agriculture, quantification of water footprint, industrial water footprint, and the transition from theory to practice. Future water footprint research needs to further enhance assessment accuracy, improve sustainability assessment methodology, develop databases, address uncertainties, and prioritize application by government and in practical sectors. More information on the symposium can be found on the water@leeds website: . [ABSTRACT FROM AUTHOR]

China faces the dual challenge of grain production pressure and water scarcity. It is significant to reduce water footprint of grain product ( WFGP, m/t) in irrigated farmland. The focus of grain production and agricultural water use, and the precondition is to determine the WFGP and its composition. This paper estimates the WFGP in irrigated farmland of 31 provinces (including municipalities, autonomous regions) a by collecting actual data of 443 typical irrigation districts in 1998, 2005 and 2010, and analyses its temporal and spatial variation in irrigated farmland of China. The result shows that the WFGP in each province decreases with time except in Jiangxi and Hunan, and the average value of all provinces reduced from 1494 m/t in 1998 to 1243 m/t in 2010. The WFGP decreases faster in more developed municipal cities and major grain production provinces. The annual average WFGP in irrigated farmland is 1339 m/t and the blue and green water account for 63.5 % and 36.5 % of the total, respectively. The WFGP and its composition are significantly different between provinces. Generally, provinces distributed inside and beyond Huang-Huai-Hai Plain, have a higher water productivity, lower WFGP and blue water footprint of grain product, while most provinces located in northwest, northeast, southeast and south China have a higher WFGP and lower proportion of green water in the WFGP as a whole. Portion of the blue water footprint ( BWFGP) is not consumed for crop evapotranspiration ( BWFGP) but conveyance loss (B WFGP). The national averaged BWFGP decreases with time and but still remains up to 466 m/t in 2010, making up 34.8 % of the WFGP. In order to safeguard grain security and ease the water resource pressure, the Chinese government should increase investment and apply advanced technology for developing water-saving agriculture, improve the efficiency of water use and further reduce the WFGP. Considering also the contribution of grain output and the relatively high WFGP, the government should give priority to developing water-saving agriculture in the Northeast of China. [ABSTRACT FROM AUTHOR]

Soil moisture variability and controls are little known in large gullies of the Loess Plateau which represent complex topography with steep slopes. This study analyzed spatial-temporal variability of soil moisture at the 0-20, 20-40, 40-60, and 60-80 cm depths in a large gully of the Loess Plateau based on root-zone soil moisture measurements for 3 years (2009-2011). The result showed that mean soil moisture, standard deviation (SD), and coefficient of variation, were highly dependent on depth; the highest mean value was observed at the 20-40 cm depth, while the lowest one was at the 0-20 cm depth. The SD increased with mean soil moisture for various depths as soil moisture was relatively wet; however, a transition that SD decreased with mean soil moisture occurred when soil moisture was relatively dry. Positive correlations exist between moisture contents over different depths, and that the relationships of the neighboring layers are relatively high with R from 0.70 to 0.76. Correlation analysis, principle component analysis, and stepwise multiple regression analysis showed that soil particle size distribution and topography (slope and elevation) were the main environmental factors controlling soil moisture variability in the large gully. [ABSTRACT FROM AUTHOR]

Accurate estimation of reference evapotranspiration (ET) becomes imperative for better managing the more and more limited agricultural water resources. This study examined the feasibility of developing generalized artificial neural network (GANN) models for ET estimation using weather data from four locations representing different climatic patterns. Four GANN models with different combinations of meteorological variables as inputs were examined. The developed models were directly tested with climatic data from other four distinct stations. The results showed that the GANN model with five inputs, maximum temperature, minimum temperature, relative humidity, solar radiation, and wind speed, performed the best, while that considering only maximum temperature and minimum temperature resulted in the lowest accuracy. All the GANN models exhibited high accuracy under both arid and humid conditions. The GANN models were also compared with multivariate linear regression (MLR) models and three conventional methods: Hargreaves, Priestley-Taylor, and Penman equations. All the GANN models showed better performance than the corresponding MLR models. Although Hargreaves and Priestley-Taylor equations performed slightly better than the GANN models considering the same inputs at arid and semiarid stations, they showed worse performance at humid and subhumid stations, and GANN models performed better on average. The results of this study demonstrated the great generalization potential of artificial neural techniques in ET modeling. [ABSTRACT FROM AUTHOR]

The article focuses on a study which discusses role of climate variability and vegetation restoration on soil erosion at the Hekou-Longment in the Middle Yellow River Basin, China. The study used linear regression and Mann–Kendall (MK) test to analyze the streamflow and sediment yield, and two multiscalar drought indices including standardized precipitation index (SPI) and standardized precipitation evapotranspiration (SPEI) to measure climate changes.

Drought is a complex natural hazard that is poorly understood and difficult to assess. This paper describes a VIC-PDSI model approach to understanding drought in which the Variable Infiltration Capacity (VIC) Model was combined with the Palmer Drought Severity Index (PDSI). Simulated results obtained using the VIC model were used to replace the output of the more conventional two-layer bucket-type model for hydrological accounting, and a two-class-based procedure for calibrating the characteristic climate coefficient ( K) was introduced to allow for a more reliable computation of the PDSI. The VIC-PDSI model was used in conjunction with GIS technology to create a new drought assessment index (DAI) that provides a comprehensive overview of drought duration, intensity, frequency, and spatial extent. This new index was applied to drought hazard assessment across six subregions of the whole Loess Plateau. The results show that the DAI over the whole Loess Plateau ranged between 11 and 26 (the greater value of the DAI means the more severe of the drought hazard level). The drought hazards in the upper reaches of Yellow River were more severe than that in the middle reaches. The drought prone regions over the study area were mainly concentrated in Inner Mongolian small rivers, Zuli and Qingshui Rivers basin, while the drought hazards in the drainage area between Hekouzhen-Longmen and Weihe River basin were relatively mild during 1971-2010. The most serious drought vulnerabilities were associated with the area around Lanzhou, Zhongning, and Yinchuan, where the development of water-saving irrigation is the most direct and effective way to defend against and reduce losses from drought. For the relatively humid regions, it will be necessary to establish the rainwater harvesting systems, which could help to relieve the risk of water shortage and guarantee regional food security. Due to the DAI considers the multiple characteristic of drought duration, intensity, frequency, and spatial extent, and because it is based on the VIC-PDSI model and GIS technologies, the DAI could provide some new way on directly comparing the drought hazards over different regions during a long-term period. The result of this study may be useful to decision makers when formulating drought management policies to alleviate the risk of water shortages and guarantee regional food security. [ABSTRACT FROM AUTHOR]

The combined effects of hydraulic variation and manufacturing variation on the relative flow difference in drip emitters were analyzed for a drip irrigation submain unit. Emitter manufacturing variation is a random variable and follows a normal distribution, which can be expressed by emitter coefficient of manufacturing variation ( v) and a random variable ( u) following a standardized normal distribution. Emitter flow rate equation can be expressed by two parts: (1) emitter discharge coefficient ( k) and discharge exponent ( x) determine the flow rate ( kh) from an emitter at pressure head ( h) and (2) the unknown random term ( uvkh), taking into account emitter manufacturing variation. Next, the formula for relative flow difference in a drip irrigation submain unit is derived based on (1) hydraulic variations due to head loss and elevation differences and (2) emitter manufacturing variation. A new hydraulic design procedure for drip irrigation submain unit is proposed based on the formula. [ABSTRACT FROM AUTHOR]

In this study, the Variable Infiltration Capacity model and Palmer Drought Severity Index (PDSI) were combined for drought identification on the Loess Plateau. The calibration method of climatic characteristic ( K) in PDSI was improved. Land cover datasets in 1980 and 2005 were used to drive the model. The driest periods over the past four decades of the study region emerged in 1976-1982, 1997-2001 and 2003-2008. Regardless of ranking by duration, spatial extent or severity, most of the prominent droughts occurred in the detected driest periods. The drought severity and area over the upper reaches of the Yellow River were higher than other domains. A total of 53 droughts with area greater than the 25,000 km threshold were identified with durations longer than 3 months using clustering algorithm. Most regions of the study area exhibited spatially increasing trends in drought severity and frequency, indicating that the Loess Plateau has experienced apparent drying and warming processes between 1971 and 2010. [ABSTRACT FROM AUTHOR]

This study characterized and compared changes in vegetation condition in areas with different gradients during the past three decades across the entire Loess Plateau. For this purpose, changes in vegetation type and vegetation coverage at sites with 0 - 15° and >15° slope gradients were determined by analyzing land use data and Normalized Difference Vegetation Index (NDVI) data, respectively. The software Arc/Info 9.3, land use transformation matrix, linear regression analysis, and Mann-Kendall test were used for the data processing and analysis. Policy influences, human impacts, and climate variability were also taken into account to find the reasons for vegetation condition change. The results indicated that the 'Grain-For-Green' project achieved initial success. Areas of farmland and grassland changed most extensively, and far greater areas of farmland were transformed into forest and grassland than vice versa. Moreover, the conversion of farmland to forest and grassland mainly occurred in areas where slopes exceeded 15°, while grassland was mainly changed to farmland in areas with gentle slopes. Vegetation coverage on the Loess Plateau exhibited overall increases after the implementation of 'Grain-For-Green' project. Regions with sparse vegetation have declined sharply, mostly in steeply sloped areas. Vegetation coverage has increased significantly in most regions, particularly in the parts traversed by the principal sediment source of the Yellow River, which could help to control the severe soil and water losses. However, regions with sparse vegetation on the Loess Plateau still covered 71.1 % of the total area in 2010. Therefore, it is important to further increase vegetation coverage in the future. [ABSTRACT FROM AUTHOR]

n evaluation of the interactions between vegetation, overland and soil erosion can provide valuable insight for the conservation of soil and water. An experiment was conducted to study water infiltration, runoff generation process, rate of sediment erosion, and hydrodynamic characteristics of overland flow from a sloping hillside with different draw-off discharges from alfalfa and control plots with 20° slope. The effect of alfalfa on runoff and sediment transport reduction was quantitatively analyzed. Alfalfa was discussed for its ability to reduce the overland flow scouring force or change the runoff movement. Compared to the bare-soil plots, alfalfa plots generated a 1.77 times increase in infiltration rate. Furthermore, the down-slope water infiltration rate for the bare soil plots was higher than in the up-slope, while the opposite was found in the alfalfa plots. In addition, alfalfa had a significant effect on runoff and sediment yield. In comparison to the control, the runoff coefficient and sediment transportation rate decreased by 28.3% and 78.4% in the grass slope, respectively. The runoff generated from the alfalfa and bare-soil plots had similar trends with an initial increase and subsequent leveling to a steady-state rate. The transport of sediment reduced with time as a consequence of the depletion of loose surface materials. The maximum sediment concentration was recorded within the first few minutes of each event. The alfalfa plots had subcritical flow while the baresoil plots had supercritical flow, which indicate that the capability of the alfalfa slope for resisting soil erosion and sediment movement was greater than for bare soil plots. Moreover, the flow resistance coefficient and roughness coefficient for the alfalfa plots were both higher than for the bare-soil plots, which indicate that overland flow in alfalfa plots had retarded and was blocked, and the flow energy along the runoff path had gradually dissipated. Finally, the ability to erode and transport sediment had decreased. [ABSTRACT FROM AUTHOR]

Water and food safety are two major challenges which the world faces today. Traditional water management focuses on the reduction of water use through improvements in water saving technologies. However, quantitative research is needed to evaluate the effects of changing food consumption patterns on water resources. Here we report the water saving effects of changing diet pattern of the major crops and animal products in mainland China. By using the concepts of water footprint (WF) per weight unit and per calorie unit, provided by 13 primary crop and animal products, the WFs of the 13 agricultural products in each province are compared, and their water/energy conversion efficiencies are analyzed. Then, impacts of different scenarios of changing diet pattern on water consumption were explored. Results show that there are obvious differences between the WF per weight and calorie unit provided by crop and animal products due to the nutritional properties of the agricultural products. Promoting water savings from the food consumption side could give a positive feedback on water consumption. Scenario analysis of adjustments to the diet pattern proves that it is potentially feasible to reach the objective of alleviating stress on water resources while guaranteeing nutritional value of the residents. [ABSTRACT FROM AUTHOR]