Water and salt movement in different soil textures under various negative irrigating pressures

This study examined the effect of different negative pressures and soil textures on water and salt movement to improve the efficiency of negative pressure irrigation(NPI).Four soil textures of varying fineness(Loamy Sand,Loam,Silty Loam,and Sandy Loam) and three negative pressure values(0,-5,and-10 kPa) were used.As irrigation time increased,wetting front movement speeds decreased,and as negative pressure increased,wetting front size decreased.Coarse soils had the smallest wetting front under greater negative pressure.Next,water infiltration rate decreased as irrigation time increased,and coarse soils had the lowest average infiltration rate under greater negative pressure.Finally,salt content increased with distance from the irrigation emitter and with increased negative pressure.Further,coarse soils were found to have decreased desalination under greater negative pressure.Thus,soil texture has a strong effect on NPI efficiency.However,by adjusting pressure values in accordance with soil texture,soil water content can be controlled and maintained.These findings are important to the improvement of NPI systems,increasing their practicality for agricultural use.

Influence of vegetation type and topographic position on volumetric soil water content dynamics and similarity among surface and deep soil layers

Clarifying the mechanisms governing volumetric soil water content(VSWC)dynamics in soil profiles is essential,as it can help to elucidate soil water transport processes and improve the prediction accuracy of soil hydrological processes.Using Spearman's rank correlation and wavelet coherence analysis methods,similarity in soil profile VSWC dynamics and factors governing VSWC soil profile dynamics in upslopes and downslopes under three vegetation types(evergreen forest[EG],secondary deciduous forest mixed with shrubs[SDFS],and deforested pasture[DP])at different time scales(hourly,daily,weekly,and monthly)and in different seasons were analyzed.The results revealed significant similarity in the VSWC of different soil depths(P<0.01),with the similarity decreasing in accordance with the increment in soil depth.Greater VSWC similarity was found in EG than SDFS and DP sites and in upslope than downslope areas at both forest sites.The average significant coherence area(SCA)of VSWC similarity among surface and deep soil layers varied with the time scale,which was in the order of monthly(58.6%)>weekly(42.8%)>daily(21.8%).The effects of soil properties(e.g.,texture,saturated hydraulic conductivity),rainfall,and potential evapotranspiration(ET_(p))on VSWC similarity were related to the time scale and season in which VSWC monitoring took place.Soil properties had apparent effects on VSWC similarity at longer time scales(i.e.,monthly),with a high SCA.In contrast,the effects of rainfall and ET_(p) on VSWC similarity were concentrated at weekly and daily scales,with a relatively low SCA.Rainfall and ET_(p) dominated VSWC dynamics in the summer and fall,respectively.These results imply the use of measured VSWC at one soil depth to predict the VSWC at other soil depths was a reliable method.While the in-fluence of time scale effects and seasonal variations on prediction accuracy of VSWC should be considered.

Flow-slide characteristics and failure mechanism of shallow landslides in granite residual soil under heavy rainfall

Affected by typhoons over years, Fujian Province in Southeast China has developed a large number of shallow landslides, causing a long-term concern for the local government. The study on shallow landslide is not only helpful to the local government in disaster prevention, but also the theoretical basis of regional early warning technology. To determine the whole-process characteristics and failure mechanisms of flow-slide failure of granite residual soil slopes, we conducted a detailed hazard investigation in Minqing County, Fujian Province, which was impacted by Typhoon Lupit-induced heavy rainfall in August 2021. Based on the investigation and preliminary analysis results, we conducted indoor artificial rainfall physical model tests and obtained the whole-process characteristics of flow-slide failure of granite residual soil landslides. Under the action of heavy rainfall, a granite residual soil slope experiences initial deformation at the slope toe and exhibits development characteristics of continuous traction deformation toward the middle and upper parts of the slope. The critical volumetric water content during slope failure is approximately 53%. Granite residual soil is in a state of high volumetric water content under heavy rainfall conditions, and the shear strength decreases, resulting in a decrease in stability and finally failure occurrence. The new free face generated after failure constitutes an adverse condition for continued traction deformation and failure. As the soil permeability(cm/h) is less than the rainfall intensity(mm/h), and it is difficult for rainwater to continuously infiltrate in short-term rainfall, the influence depth of heavy rainfall is limited. The load of loose deposits at the slope foot also limits the development of deep deformation and failure. With the continuous effect of heavy rainfall, the surface runoff increases gradually, and the influence mode changes from instability failure caused by rainfall infiltration to erosion and scouring of surface runoff on slope surface. Transportation of loose materials by surface runoff is an important reason for prominent siltation in disaster-prone areas.

Natural consolidation characteristics of viscous debris flow deposition

Pore water pressure and water content are important indicators to both deposition and consolidation of debris flows, enabling a direct assessment of consolidation degree. This article gained a more comprehensive understanding about the entire consolidation process and focused on exploring pore water pressure and volumetric water content variations of the deposit body during natural consolidation under different conditions taking the viscous debris flow mass as a study subject and by flume experiments. The results indicate that, as the color of the debris changed from initial dark green to grayish-white color, the initial deposit thickness declined by 3% and 2.8% over a permeable and impermeable sand bed, respectively. A positive correlation was observed between pore water pressure and depth in the deposit for both scenarios, with deeper depths being related to greater pore water pressure. For the permeable environment, the average dissipation rate of pore water pressure measured at depths of 0.10 m and 0.05 m were 0.0172 Pa/d and 0.0144 Pa/d, respectively, showing a positivechanging trend with increasing depth. Under impermeable conditions, the average dissipation rates at different depths were similar, while the volumetric water content in the deposit had a positive correlation with depth. The reduction of water content in the deposit accelerated with depth under impermeable sand bed boundary conditions, but was not considerably correlated with depth under permeable sand bed boundary conditions. However, the amount of discharged water from the deposit was greater and consolidation occurred faster in permeable conditions. This indicates that the permeability of the boundary sand bed has a significant impact on the progress of consolidation. This research demonstrates that pore water and pressure dissipations are present during the entire viscous debris consolidation process. Contrasting with dilute flows, pore pressure dissipation in viscous flows cannot be completed in a matter of minutes or even hours, requiring longer completion time — 3 to 5 days and even more. Additionally, the dissipation of the pore water pressure lagged the reduction of the water content. During the experiment, the dissipation rate fluctuated substantially, indicating a close relationship betweenthe dissipation process and the physical properties of broadly graded soils.

Construction of Forecast and Early Warning System of Meteorological and Geological Disasters in Qinghai Province

Based on the meteorological and geological disaster data, ground observation data set, CLDAS grid point data set, and EC, BJ and other model product data during 2008-2020, the temporal and spatial distribution characteristics of meteorological and geological disasters and precipitation were analyzed, and the causes of the occurrence of meteorological geological disasters and the deviation of model precipitation forecast were revealed. Besides, an objective precipitation forecast system and a forecast and early warning system of meteorological and geological disasters were established. The results show that meteorological and geological disasters and precipitation were mainly concentrated from May to October, of which continuous precipitation appeared frequently in June and September, and convective precipitation was mainly distributed in July-August;the occurrence frequency of meteorological and geological disasters was basically consistent with the distribution of accumulated precipitation and short-term heavy precipitation, and they were mainly concentrated in the southern and eastern parts of Qinghai. Meteorological and geological disasters were basically caused by heavy rain and above, and meteorological and geological disasters were divided into three types: continuous precipitation(type I), short-term heavy precipitation(type II) and mixed precipitation(type III). For type I, the early warning conditions of meteorological and geological disasters in Qinghai are as follows: if the soil volumetric water content difference between 0-10 and 10-40 cm is ≤0.03 mm^(3)/mm^(3), or the soil volumetric water content at one of the depths is ≥0.25 mm^(3)/mm^(3), the future effective precipitation reaches 8.4 mm in 1 h, 10.2 mm in 2 h, 11.5 mm in 3 h, 14.2 mm in 6 h, 17.7 mm in 12 h, and 18.2 mm in 24 h, and such warning conditions are mainly used in Yushu, Guoluo, southern Hainan, southern Huangnan and other places. For type II, when the future effective precipitation is up to 11.5 mm in 1 h, 14.9 mm in 2 h, 16.2 mm in 3 h, 19.9 mm in 6 h, 25.3 mm in 12 h, and 26.3 mm in 24 h, such precipitation thresholds are mainly used in Hainan, Huangnan, and eastern Guoluo;as it is up to 13.3 mm in 1 h, 15.5 mm in 2 h, 16.6 mm in 3 h, 19.9 mm in 6 h, 31.1 mm in 12 h, and 34.0 mm in 24 h, such precipitation thresholds are mainly used in Hehuang valley. The precipitation thresholds of type III are between type I and type II, and closer to that of type II;such precipitation thresholds are mainly used in Hainan, Huangnan, and northern Guoluo. The forecasting ability of global models for heavy rain and above was not as good as that of mesoscale numerical prediction model, and global models had a wet bias for small-scale precipitation and a dry bias for large-scale precipitation;meso-scale models had a significantly larger precipitation bias. The forecast ability of precipitation objective forecast system constructed by frequency matching and multi-model integration has improved. At the same time, the constructed grid forecast and early warning system of meteorological and geological disasters is more precise and accurate, and is of instructive significance for the forecast and early warning of meteorological and geological disasters.

How precipitation and grazing influence the ecological functions of drought-prone grasslands on the northern slopes of the Tianshan Mountains, China?

Drought-prone grasslands provide a critical resource for the millions of people who are dependent on livestock for food security.However,this ecosystem is potentially vulnerable to climate change(e.g.,precipitation)and human activity(e.g.,grazing).Despite this,the influences of precipitation and grazing on ecological functions of drought-prone grasslands in the Tianshan Mountains remain relatively unexplored.Therefore,we conducted a systematic field investigation and a clipping experiment(simulating different intensities of grazing)in a drought-prone grassland on the northern slopes of the Tianshan Mountains in China to examine the influences of precipitation and grazing on aboveground biomass(AGB),soil volumetric water content(SVWC),and precipitation use efficiency(PUE)during the period of 2014–2017.We obtained the meteorological and SVWC data using an HL20 Bowen ratio system and a PR2 soil profile hydrometer,respectively.We found that AGB was clearly affected by both the amount and seasonal pattern of precipitation,and that PUE may be relatively low in years with either low or excessive precipitation.The PUE values were generally higher in the rapid growing season(April–July)than in the entire growing season(April–October).Overall,moderate grazing can promote plant growth under water stress conditions.The SVWC value was higher in the clipped plots than in the unclipped plots in the rapid growing season(April–July),but it was lower in the clipped plots than in the unclipped plots in the slow growing season(August–October).Our findings can enhance the understanding of the ecological effects of precipitation and grazing in drought-prone grasslands and provide data that will support the effective local grassland management.

Evaluating Reflected GPS Signal as a Potential Tool for Cotton Irrigation Scheduling

Accurate soil moisture content measurements are vital to precision irrigation management. Remote sensing using the microwave spectrum (such as GPS signals) has been used for measuring large area soil moisture contents. In our previous work, we estimated surface soil moisture contents for bare soil using a GPS Delay Mapping Receiver (DMR) developed by NASA. However, the effect of vegetation was not considered in these studies. Hence the objectives of this study were to: 1) investigate the feasibility of using DMR to determine soil moisture content in cotton production fields;2) evaluate the attenuation effect of vegetation (cotton) on reflected GPS signal. Field experiments were conducted during the 2013 and 2014 growing seasons in South Carolina. GPS antennas were mounted at three heights (1.6, 2.7, and 4.2 m) over cotton fields to measure reflected GPS signals (DMR readings). DMR readings, soil core samples, and plant measurements were collected about once a week and attenuation effect of plant canopy was calculated. Results showed that DMR was able to detect soil moisture changes within one week after precipitation events that were larger than 25 mm per day. However, the DMR readings were poorly correlated with soil volumetric water content during dry periods. Attenuation effect of plant canopy was not significant. For irrigation purpose, the results suggested that the sensitivity of reflected GPS signals to soil moisture changes needed to be further studied before this technology could be utilized for irrigation scheduling in cotton production. Refinement of this technology will expand the use of advanced remote sensing technology for site-specific and timely irrigation scheduling. This would eliminate the need to install moisture sensors in production fields, which can interfere with farming operations and increase production costs.

Influence of mulch and poultry manure application on soil temperature,evapotranspiration and water use efficiency of dry season cultivated okra

Sustainable vegetable production especially during the dry season requires adequate conservation of soil water.This study was conducted to evaluate the sole and interactive effects of mulching(M)and poultry manure(PM)application on soil temperature(ST),crop evapotranspiration(ETc)and water use efficiency(WUE)of okra.The experiment was a Randomized Complete Block Design(RCBD)with three replicates.The treatments were M at 0 and 6t ha^(-1)and PM at 0,10 and 20t ha^(-1).Soil temperature was measured using digital thermometer while ETc was determined by water depletion method using a Time Domain Reflectometer.Irrigation at field capacity was applied manually at 2-day intervals.Independent appli-cation of mulch significantly lowered ST while joint application of 20t ha^(-1)PM(PM20)and M signifi-cantly(p≤0.05)reduced ST at 5 cm and 10 cm soil depth compared with the unmulched plots in both seasons.Application of 10t ha^(-1)PM(PM10)without M recorded the highest ETc(43.7 mm),while joint application of PM20 and M reduced ETc by about 93%compared with PM10 only.Okra used water most efficiently when PM20 was applied under mulched plot.There was 62.2%increase in WUE under mulched plots compared with the control while the residual effect of PM10 and M significantly increased WUE by 65.5%.It was evident that M alongside application of PM is a good strategy for regulating ST,moderating ETc and increasing okra WUE,especially during dry season farming.

Performance evaluation and calibration of capacitance sensor for estimating the salinity of reclaimed land

Generally,soil moisture and salinity in reclaimed land are monitored using soil dielectric sensors such as time domain reflectometry,frequency domain reflectometry,and capacitance.The soil dielectric sensor measures apparent dielectric permittivity.However,apparent dielectric permittivity is affected by soil moisture,salinity,and texture.In this study,performance evaluation and calibration of a dielectric sensor(5TE;METER Group,Inc.,Pullman,WA,USA)for monitoring soil salinity were performed.Laboratory calibration tests were completed,incorporating various levels of dry density,water content,and salinity.The soil salinity was determined by the electrical conductivity(EC)1:5 method.The volumetric water content as measured by the sensor was affected by dry density and water content.Generally,it linearly increased as dry density and water content increased.However,when dry density or water content was high,the measured value of the sensor increased nonlinearly.The bulk EC measured by sensor had no specific correlation with EC 1:5.The EC 1:5 measurement had a linear relationship with the gradient ofθandθs.Therefore,it can be estimated with a simple linear equation usingθfrom the soil test andθs from the capacitance sensor.The R 2 value of the EC 1:5 estimation equation was 0.98.The proposed equation requiresθfrom the gravimetric sample andθs from the sensor.Therefore,in the case of monitoring salinity using a sensor,it is recommended to measure the water content with a tensiometer.