Variations In Soil Moisture Content Research Articles

Integration of electrical resistivity and soil analysis for Agricultural soil characterization—a case study

Integration of 2D electrical resistivity method and soil analysis was used to characterize the topsoil in the farmland of Federal University Oye-Ekiti, Nigeria, to determine its suitability for agricultural purposes. A 2D electrical resistivity survey was carried out along four traverses using Wenner array electrode configuration with electrode spacing ranging from 1 to 5 m and station interval of 1 m. The acquired 2D electrical resistivity data were processed and inverted using DIPRO version 4.01 software. Forty (40) soil samples were collected along the established traverses at depth intervals of 0.5 and 1.0 m to estimate the moisture contents and grain size distributions. The 2D inverted resistivity sections revealed three probable geologic materials namely clay, clayey sand, and sand. Grain size analysis showed that the farmland is made up of gravel, sand, and fines (silts and clay) with mean percentage distributions of 8.77%, 80.08%, and 11.15% respectively. The moisture content of the forty (40) soil samples analyzed ranges from 10.2 to 18.6%, with an average value of 11.91%. Areas of low electrical resistivity values were observed to coincide with zones of fine particles and high moisture content and are identified to be favorable for crops in the farmland. This study shows the effectiveness of the electrical resistivity method and soil analysis in determining the variability of soil moisture content at shallow depth and in selecting soil that can aid the optimum production of crops.

Spatial‐Temporal Simulations of Soil Moisture Content in a Large Basin of the Loess Plateau, China

Soil moisture is a crucial factor limiting the growth and survival of plants on the Loess Plateau. Its level has a severe impact on plants’ growth and development and the type and distribution characteristics of communities. This study area is the Jihe Basin in the Loess Plateau, China. Multiple linear regression models with different environmental variables (land use, topographic and meteorological factors, etc.) were developed to simulate soil moisture’s spatial and temporal changes by integrating field experiments, indoor analysis, and GIS spatial analysis. The model performances were evaluated in the Jihe Basin, with soil moisture content measurements. The result shows that soil moisture content is positively correlated with soil bulk density, monthly rainfall, topographic wetness index, land use coefficient, and slope aspect coefficient but negatively correlated with the monthly‐averaged temperature and the relative elevation coefficient. The selected variables are all related to the soil moisture content and can account for 75% of the variations of soil moisture content, and the remaining 25% of the variations are related to other factors. Comparing the simulated and measured values at all sampling points shows that the average error of all the simulated values is 0.09, indicating that the simulation has high accuracy. The spatial distribution of soil moisture content is significantly affected by land use and topographic factors, and seasonal variation is remarkable in the year. Seasonal variation of soil moisture content is determined by the seasonal variation of rainfall and the air temperature (determining evaporation) and vegetation growth cycle. Therefore, the proposed model can simulate the spatial and temporal variation of soil moisture content and support developing the soil and water loss model on a basin scale.

Comparison Quality of Interpolation Methods to Estimate Spatial Distribution of Soil Moisture Content

ABSTRACT Determining and predicting both the spatial and temporal variability of soil moisture content is a critical factor in crop production in semi-arid agricultural systems. The objective of this research was to predict the spatial distribution of soil moisture content using ordinary kriging (OK), regression kriging (RK) and cokriging (CK) models. For that purpose, the soil moisture was monitored in the wet period (March, April and May) and dry period (August, September and October) in Kadınhanı district of Konya Province, Turkey. In each monthly sampling period of the study, a total of 278 samples were collected from locations within an area of 29,608.6 ha. The coefficients of variation (CV) of the soil moisture in dry and wet soil conditions were 0.39 and 0.20, respectively. Soil texture, bulk density (BD) and land use were the most important factors influencing soil moisture. In addition, dry soil generally had a smaller nugget effect than wet soil. Overall, CK was able to better estimate the soil moisture content than OK and RK, as evidenced by the smaller mean absolute error (MAE) and mean square error (MSE). RK estimation is more vulnerable to error than CK and OK estimations because the low coefficients of determination in the regression equation lead to increased error and lower confidence in the estimates. The insights generated by the modeling utilized in this study can assist land use planners, land managers and farmers to more efficiently predict, manage and utilize soil moisture content and hence produce larger crops more sustainably.

Estimation of Surface Moisture Content using Sentinel-1 C-band SAR Data Through Machine Learning Models

Monitoring the spatio-temporal variation in soil moisture content (SMC) of the surface soil layer is essential for agriculture and water resource management activities, especially in regions where the socio-economic condition and livelihood depend upon agriculture and allied sectors. In the present study, we have compared different machine learning (ML) and linear regression models to estimate the SMC integrating field observed soil moisture and Sentinel-1 SAR data. Total 56 soil samples were collected from the surface soil layer (~ 5 cm) in correspondence with the passing date of the Sentinel-1 sensor over the study area. The surface SMC was estimated for bare soil areas, which was extracted by applying the threshold values on vegetation and water index maps derived from the Sentinel-2 multispectral data. The univariate linear regression with the co-polarized VV band provided higher accuracy compared to the cross-polarized VH band. However, the multiple linear regression with VV and VH bands indicated similar accuracy as obtained by the VV band alone. The random forest model was observed as the best performing ML model for soil moisture estimation (R2 = 0.87 and 0.93 during modeling and validation, respectively; RMSE: ~ 0.03). The obtained results indicate well accurate surface soil moisture verified with in-situ information collected during the dry rabi crop season (January to March 2019). The maximum SMC was observed for March, followed by February and January, that corroborated with the total monthly precipitation and irrigation activities. The study highlights the potentiality of ML models and Sentinel-1 SAR data for soil moisture estimation, which is useful for policy-level implications and decision making in agriculture and water resource management activities.

Effects of rainwater harvesting system on soil moisture in rain-fed orchards on the Chinese Loess Plateau

Rainwater is a primary water source for the hilly and gully region of the Loess Plateau where an improved efficiency of rainwater utilization is crucial for sustainable agricultural development. A new system, comprised of rainwater harvesting, concentrating infiltration with multi-holed pipe and mulching (RIM), was designed to sustain soil moisture at a proper level in rain-fed orchards in the hilly and gully loess region of China. This study monitored changes in soil moisture and distribution over soil profiles using four treatments: (a) RIM1 with two rainwater harvesting areas, two infiltration pipes and film mulching, (b) RIM2 with one rainwater harvesting area, one infiltration pipe and film mulching, (c) film mulching (FM) only and (d) traditional apple orchard as a control treatment (CK) as a baseline in this experiment. The results showed that mean soil moisture content (SMC) in a range of soil layer between 0 cm and 300 cm for RIM1 and RIM2 treatments increased by 43.01% and 34.78% in 2018 and 30.55% and 26.41% in 2019, respectively. Dividing the soil vertical profile into three layers, i.e., an easy-changing layer (0−60 cm), an increasing or decreasing layer (60−180 cm), and a relatively steady layer (180−300 cm), this study examined the vertical changes of soil moisture. The RIM1 and RIM2 treatments induced a large increase in the size and depth of wetted areas over the whole soil layers. The soil moisture was replenished to a horizontal distance of 1.5 m and 2.5 m apart from the trunk within the soil layer between 60 cm and 300 cm under the RIM1 treatment while only the horizontal distance of 1.5 m apart from the trunk under the RIM2 treatment. While the seasonal variation of SMC in the easy-changing soil layer (0−60 cm) corresponded to precipitation consistently, the SMC in the deep soil layers (60−300 cm) was not sensitive to precipitation. As a result, the treatments of RIM1, RIM2 and FM improved apple yield and crop water productivity compared with those under the control treatment. In particular, the RIM1 treatment performed the best among the treatments investigated in this study. The results highlighted the efficiency of the RIM system in enhancing the soil moisture, which may be useful to improve an orchard production for rain-fed orchards in the loess hilly and gully region of China.

Vertical variation in shallow and deep soil moisture in an apple orchard in the loess hilly–gully area of north China

AbstractDeep soil (>2 m) moisture is relatively stable water that supports tree growth and water management in the loess hilly–gully area of China. Characterizing the spatial variation of deep soil moisture is important for water management in apple orchards. Using a space‐for‐time substitution approach, we analysed the spatial variation of soil moisture content (θ) in 0–8 m soil profiles in a dry year (2015, precipitation: 392 mm) in rainfed apple (Malus pumila Mill.) orchards of various ages (mainly established in 2009, 2006, 2003, 1997 and 1994). The soil moisture surveys revealed: (a) four soil layers according to soil moisture distribution characteristics at 0–8.0 m depth: shallow rapidly changing layer (0–0.6 m), rainfall redistribution layer (0.6–2.0 m), transition layer (2.0–4.0 m) and stable layer (4.0–8.0 m); (b) the most critical zone for water consumption is the 0.6–2.0 m soil layer, with the lowest θ in the orchards, while water in the 4.0–8.0 m soil layer remained stable; and (c) significant (p < .01) positive correlations between θs in the 0.6–2.0 m, 2.0–4.0 m and 4.0–8.0 m layers. In addition, the θs showed a significant (p < .01) negative relationship with orchard age in the deep soil layers (>2 m), and especially in the 0.6–2.0 m soil layer. Therefore, effective water management through various water regulation measures at the 0.6–2.0 m soil layer is essential for the sustainable development of apple orchards and reducing drought stress on the Loess Plateau and, potentially, other semi‐arid orchards.

Production and optimization of eco-bricks

Waste plastics are often indiscriminately disposed into the built environment and sometimes voyaged into the sea, constitute nuisance to the built environment and disturb aquatic life. These threats have birthed researches for the promotion of circular economy in plastic waste management. However, few studies have investigated the use of waste plastic in the production of eco-bricks. This study examined the effect of moisture content and soil types on the characterisation of eco-bricks under compressive load. Samples of eco-bricks were produced using laterite, sharp sand and stone dust at 0%, 5%, 10%, 15% and 20% moisture contents as infill materials. The soil samples were tested of specific gravity, fineness modulus and uniformity coefficient computation to determine the suitability of the samples, while the eco-bricks produced with the soil samples were subjected to compressive load. The study found a positive relationship between soil moisture content and compressive strength of eco-bricks produced with sharp sand and stone dust while the compressive strength of laterite bottle bricks had a negative relationship with the moisture content. Also, the specific strength, Poisson’s ratio and bulk density of the eco-bricks were satisfactory at varying soil moisture contents. The study concludes that soil moisture content affects the performance of bottle bricks and adequate consideration for soil types in the production of eco-bricks is paramount.

Investigating the effectiveness of drain infiltration to minimize peat oxidation in agricultural fields in Flevoland, the Netherlands

Abstract. In the Province of Flevoland, the Netherlands, land subsidence poses a problem to agriculture and water management. The peat layers in the soil are susceptible to compression and oxidation causing further subsidence. Applying subirrigation through the tile drain system to maintain saturation of the peat may be a measure to slow down subsidence. A study was therefore carried out at two sites, Nagele and Zeewolde, to assess the impact of subirrigation in the peat on the seasonal variation in soil moisture content, and corresponding redox conditions. Bacterial community analysis was carried out to verify the hydrochemical observations. Subirrigation proved to be an efficient measure to maintain a high water level in the peat soil as long as the permeability in the upper part of the peat was sufficient to allow transmission of water into the inter-drain area and when the peat layer extended enough below the minimum regional water level to prevent drainage to the sand layer underneath. The peat showed dual porosity and water levels could well be maintained by subirrigation at the Nagele site. At the Zeewolde site, the variability in the thin peat layer allowed drainage to occur in the sand layer, preventing subirrigation to maintain high water levels. However, at both sites the peat layer remained close to saturation throughout the summer, which may be caused by the fine-grained mineral layer isolating the peat from water extraction via evapotranspiration. Nitrate concentrations of up to 100 mg L−1 were observed were high (>50 mg L−1) in the oxic mineral top layer but were low in the peat (0.3 mg L−1) at both Nagele and Zeewolde sites. Sulphate concentrations also showed a decrease with depth in the peat at Nagele, indicating a transition from sub-oxic above 1.5 m depth to anoxic conditions at 3.5 m depth. The hydrochemical observations in the soil moisture in the peat at Nagele confirmed that conditions were sub-oxic in the upper part of the peat (0.7 m below soil surface) to anoxic at greater depth (3.5 m). Soil microbe analyses showed few nitrification bacteria in the peat, whereas communities specialised in denitrification and ammonification were present, as well as sulphate reducing bacteria and methanogenic species. This confirmed the sub-oxic to anoxic conditions in the peat deduced from the hydrochemical observations. At Zeewolde, conditions remained sub-oxic throughout the profile.

Slope Stability from a Hydrological Perspective: Taking Typical Soil Slope as an Example

In the traditional research of slope stability, it is difficult to continuously obtain the moisture content of soil in long time sequences. In combination with the precipitation, temperature, and vegetation cover data in the study area, the variable infiltration capacity hydrological model is used to estimate the daily variation of soil moisture content, which is used as a calculation condition for the analysis of slope stability. The results show that, from 1970 to 2010, the spatial‐temporal distribution of soil moisture content in the Weihe River Basin showed an increasing trend. Moreover, the shear strength of soil decreased, but the range was stable at approximately 2%. The strength reduction method based on the M‐C inscribed circle criterion (DP3) shows that the slope stability factor k had an increasing trend for over 40 y. The portion of the period with a k value higher than 1.2 is more than 85% of the entire period, that with a k value between 1 and 1.2 is approximately 9%, and that with a k value less than 1 is approximately 5.5%. The R/S analysis results show that the Hurst coefficients of the τ‐t curve and the k‐t curve are 0.5568 and 0.5888, respectively, and that the slope is in a state of no variation. Based on these factors, the present and future of the slope is in a stable state. This scheme is a method of studying slope stability based on hydrology, and it provides a modern alternative for soil shear strength calculation and geological hazard assessment.

WATER FRONT ADVANCE UNDER VARIABLE BORDER WIDTH AND INITIAL SOIL MOISTURE CONTENTS UNDER WHEAT (Triticum aestuivium L.) CROP – I: HYDRAULICS AND IRRIGATION EFFICIENCIES

Border irrigation experiments were conducted on wheat ( Triticum aestivum L.) crop at Water Technology Centre, Indian Agricultural Research Institute (IARI) New Delhi in winter season (October-April) of 2013-2014 to study the border hydraulics (cutoff ratio, border width and stream discharge), irrigation efficiencies, grain and biomass yields for 4 border sizes (2, 3, 4 and 5 m widths) to economize the water use. Optimizing the border width under varying soil moisture contents prior to irrigation was attempted. The border of length 25 m required 30.2 minutes (min) to 78.1 min for irrigation for a fixed cutoff length of 15 m. The water front advance time up to cutoff length was 10 min and 27.3 min for border widths varying from 2 to 5 m; respectively corresponding to the selected stream discharge of 1.5 l/s. The water front advance time was inversely proportional to the initial soil moisture contents. The travel time to cutoff point of 15 m for three soil moisture contents namely q 1:14.2, q 2:16.5 and q 3:17.2%; varied from 10.0-11.7 min for the border size (width) of 2.0 m, 14.0-15.6 min for the border size of 3 m; 20.0-23.4 min for the border size of 4 m whereas, it took 24.5- 27.3 min for 5 m border size. The best border size was identified as 4 m without any yield penalty. The effect of the stream discharge was not pronounced based on yields. Due to uniform cutoff ratio there was no significant difference in the amount of water use. Hence, the border size of 4 m was rated the best.

Spatio-temporal variation of soil moisture in a fixed dune at the southern edge of the Gurbantunggut Desert in Xinjiang, China

Soil moisture is critical for vegetation growth in deserts. However, detailed data regarding the soil moisture distribution in space and time in the Gurbantunggut Desert of China have not yet been reported. In this study, we conducted a series of in situ observation experiments in a fixed sand dune at the southern edge of the Gurbantunggut Desert from February 2014 to October 2016, to explore the spatio-temporal variation of soil moisture content, investigate the impact of Haloxylon ammodendron (C. A. Mey.) Bungeon soil moisture content in its root zone, and examine the factors influencing the soil moisture spatial pattern. One-way analysis of variance, least significant difference tests and correlation analysis were used to analyze the data. The results revealed that the soil moisture content exhibited annual periodicity and the temporal variation of soil moisture content throughout a year could be divided into three periods, namely, a moisture-gaining period, a moisture-losing period and a moisture-stable period. According to the temporal and spatial variability, the 0–400 cm soil profile could be divided into two layers: an active layer with moderate variability and a stable layer with weak variability. The temporal variability was larger than the spatial variability in the active layer, and the mean profile soil moisture content at different slope positions displayed the trend of decreasing with increasing relative height and mainly followed the order of interdune area>west and east slopes>slope top. The mean profile soil moisture content in the root zone of dead H. ammodendron individuals was significantly higher than that in the root zones of adult and young individuals, while the soil moisture content in the root zone of adult individuals was slightly higher than that in the root zone of young individuals with no significant difference. The spatial pattern of soil moisture was attributable to the combined effects of snowfall, vegetation and soil texture, whereas the effects of rainfall and evaporation were not significant. The findings may offer a foundation for the management of sandy soil moisture and vegetation restoration in arid areas.

High spatial density ground thermal measurements in a warming permafrost region, Beiluhe Basin, Qinghai-Tibet Plateau

Air, ground surface, and permafrost surface temperatures are important components of the permafrost thermal regime. However, ground temperatures from one or two boreholes are commonly considered representative of site conditions in permafrost studies despite significant variations in local surface conditions. This makes the evaluation of site-scale temperature variations important for improving the accuracy of permafrost modelling efforts. In this study we analyzed the variability in near-surface ground temperatures in a warming permafrost region using high spatial density borehole measurements to capture variations in surface conditions. Ground temperatures were collected from 72 boreholes drilled to 5 m depth at 8 sites in Beiluhe Basin, Qinghai-Tibet Plateau. Six sites straddled an alpine meadow ecotone between well- and sparsely-vegetated ground, and two sites were located on slopes with opposing aspects. Air temperatures at the 8 sites were similar with annual mean values ranging from −2.6 to −3.0 °C in 2016–18. In contrast, annual mean surface temperatures exhibited greater variation between sites, so that surface offsets were also variable. Ground surface temperatures were highest at a sloping sunny site, and lowest at a north-facing shady site. The results indicated that surface temperatures were strongly controlled by slope aspect. In contrast, the expected effect of vegetation cover shading was not distinguishable because of variations in soil moisture content between sites. Deeper temperatures at the permafrost surface and at 5 m depth exhibited a similar trend among sites except in an unusual warm transitional area where eolian erosion disturbed the surface vegetation cover. The detailed ground temperature records characterizing within- and between-site variations could be used in future to support the calibration and validation of numerical models of permafrost distribution.

Potential of thermal remote sensing techniques in monitoring waterlogged area based on surface soil moisture retrieval

The aim of this paper was to test the capability of thermal remote sensing in monitoring waterlogged areas in Ismailia governorate based on surface soil moisture retrieval. Three landsat satellite images 5, 7 and 8 (TM, ETM+ and TIRS) were used for this purpose during three different dates (1998, 2008 and 2015). Soil moisture index (SMI) was produced based on calculated Land surface temperature (LST). Fifty five soil profiles have been dug to measure the depth of water tables of the study area. SMI Validation was carried out in 2015 using surface soil samples from the upper 5 cm in which actual moisture content was estimated. Digital change detection techniques for SMI were applied in order to monitor the change in the surface soil moisture along two time periods (1998–2008), (2008–2015). The results indicated that the spatio-temporal variations of soil moisture content are associated with soil texture, landuse/landcover, soil elevation and water table levels. Correlation between actual and retrieved soil moisture revealed a moderate correlation relationship with R2 = 0.61. Furthermore, an increase of water table eastern the study area. Also the results illustrated the increasing of water table is a direct relation with soil moisture. In addition, an increase in the surface soil moisture (SSM) recognized in 22.06% of the study area from 1998 to 2008 while, 40.55% of the area showed an increased in the SSM from 2008 to 2015. This continuous increase in the SSM could be prone to the increasing agricultural expansion and water table levels which, led to conversion of sabkhas to water bodies and fish farms. SMI could be an effective tool in mapping waterlogged areas.

Responses of carbon, nitrogen and phosphorus to two consecutive drying–rewetting cycles in soils

AbstractDrying and rewetting cycles are known to be important for the dynamics of carbon (C), phosphorus (P), and nitrogen (N) in soils. This study reports the short‐term responses of these nutrients to consecutive drying and rewetting cycles and how varying soil moisture content affects microbial biomass C and P (MBC and MBP), as well as associated carbon dioxide (CO2) and nitrous oxide (N2O) emissions. The soil was incubated for 14 d during which two successive drying–rewetting episodes were imposed on the soils. Soils subjected to drying (DRW) were rewetted on the seventh day of each drying period to return them to 60% water holding capacity, whilst continually moist samples (M), with soil maintained at 60% water holding capacity, were used as control samples. During the first seven days, the DRW samples showed significant increases in extractable ammonium, total oxidized nitrogen, and bicarbonate extractable P concentrations. Rewetting after the first drying event produced significant increases only in CO2 flux (55.4 µg C g−1 d−1). The MBC and MBP concentrations fluctuated throughout the incubation in both treatments and only the second drying–rewetting event resulted in a significantly MBC decrease (416.2 and 366.8 mg kg−1 in M and DRW soils, respectively).The two drying–rewetting events impacted the microbial biomass, but distinguishing the different impacts of microbial versus physical impacts of the perturbation is difficult. However, this study, having a combined approach (C, N, and P), indicates the importance of understanding how soils will react to changing patterns of drying–rewetting under future climate change.

Influence of Variation in Moisture Content to Soil Bearing Capacity in Nairobi Area and Its Environs

The increasing human population in cities and urban areas continues to raise the demand for housing and other infrastructure in developing nations. Stability of structures is critical for sustainable development to ensure longer useful life of structures and reduction in the rate at which natural resources for construction purposes are extracted from the environment. Foundation of buildings infrastructure plays a key role of transferring the loading from the structure to the soil underneath. In foundation design, the ultimate bearing capacity of soil under normal circumstances assumes that the water table is located well below the foundation. Variation in soil moisture content during construction and during the structure’s lifespan affect the soil bearing capacity. Information on the extent to which variation in soil moisture content affect the soil bearing capacity was lacking. This paper presents findings of a research that sought to establish the extent to which variation in soil moisture content affects the soil bearing capacity. Seven soil samples collected from Nairobi area and its environs were subjected to 30%, 50% and 75% moisture content variation. The soil bearing capacity was tested using Direct Shear method and Undrained Triaxial method in accordance to British Standard 1377 of 1990 Part 7 and Part 8 respectively. Test results determined that the insitu moisture content for the collected 7 soil samples from Nairobi area and its environs varied from 21.9% to 55.4% implying the diverse characteristics of soil samples and sites studied. Increasing the soil moisture content from 30% to 50% and to 75% all other factors held constant contributed to reduction in soil bearing capacity as illustrated by a linear equation <i>y = -170.89x + 565.64</i> using direct shear method. <i>y</i> is the resultant soil bearing capacity (kN/mm²) while <i>x</i> is the soil moisture content in percentage. This shows that variation in soil moisture content contributes to a significant reduction in soil bearing capacity by a factor of <i>-170.89x</i>. To mitigate the negative effect of reduction in soil bearing capacity as a result of changes in soil moisture content, a factor of safety should be applied at design stage by adjusting the allowable soil bearing capacity to take cognisance of the contribution by changes in soil moisture content. This is critical to ensure that all structures are designed to withstand variation in moisture content at the foundation throughout their lifespan and avoid potential structural failure.

Soil thermal conductivity and its influencing factors at the Tanggula permafrost region on the Qinghai–Tibet Plateau

Soil thermal conductivity (λ) is one of the essential parameters relating to heat exchange, and it also plays a key role in verifying soil thermal hydrodynamics in permafrost regions. In this paper, the characteristic of in situ λ was analyzed based on data measured from June 2004 to December 2008 at Tanggula district on the Qinghai–Tibet Plateau. The result showed that diurnal λ strongly influenced by variation of soil moisture content. The daily λ exhibited distinct seasonal variation; on average, the largest value of λ occurred in summer, followed by the autumn and spring season, while the smallest value occurred in winter. As a whole, λ values in the unfrozen state were larger than those in the frozen state. Unsaturated soil and the huge difference in soil moisture content between the unfrozen state and initial freeze resulted in the lower λ in the frozen state. For the study area, the critical value of local soil saturation degree was about 0.37, the corresponding critical soil moisture content was about 0.195 m3 m−3. And soil moisture content was the main factor controlling in situ λ. Finally, an empirically-derived model was proposed for predicting daily λ, and which showed good performance in the study area.

Retrieval of land surface properties from an annual time series of Landsat TOA radiances during a drought episode using coupled radiative transfer models

The accurate retrieval of land surface vegetation properties under varying environmental conditions from time series of moderately high spatial resolution satellite observations is challenging. By coupling various Radiative Transfer (RT) models one can describe the soil, vegetation and atmosphere contributions in a “bottom-up” approach and, thereby, simulate top-of-atmosphere (TOA) spectral radiance data comparable to satellite-observed TOA radiances. This makes it possible to retrieve vegetation properties directly from TOA radiances rather than from atmospherically corrected top-of-canopy (TOC) reflectance data. The advantages of this approach are that a separate atmospheric correction of the satellite images is not necessary, and that the anisotropic surface reflection can also be taken into account effectively. In this study, we coupled various RT models, including the brightness – shape – moisture (BSM) reflectance model of the soil, the optical radiative transfer (RTMo) model of vegetation and the ‘MODerate resolution atmospheric TRANsmission’ (MODTRAN) model of the atmosphere, to simulate an annual time series of Landsat satellite TOA radiances observed during a drought episode in California Mediterranean grasslands in 2004. The inversion of this coupled system through an optimization technique against Landsat TOA radiances resulted in direct retrieval of vegetation properties. We accommodated the surface anisotropic reflection in our coupled modeling and also defined a novel anisotropy index to quantitatively express the importance of this phenomenon in satellite image analysis for the first time. Our study showed that the coupled use of RT models was able to accurately reproduce the time series of observed TOA radiances collected under varying soil moisture contents during an extended drought episode. The proposed coupling approach is useful for successful retrieval of vegetation properties from time series of satellite TOA radiance data to produce maps of land surface properties and to monitor vegetation properties variations in an operational straightforward way. The approach can also be easily adapted for conducting multi-sensor time series studies, creating a much denser temporal sampling than would be possible for separate single sensors.

A random survival forest illustrates the importance of natural enemies compared to host plant quality on leaf beetle survival rates

BackgroundWetlands are habitats where variation in soil moisture content and associated environmental conditions can strongly affect the survival of herbivorous insects by changing host plant quality and natural enemy densities. In this study, we combined natural enemy exclusion experiments with random survival forest analyses to study the importance of local variation in host plant quality and predation by natural enemies on the egg and larval survival of the leaf beetle Galerucella sagittariae along a soil moisture gradient.ResultsOur results showed that the exclusion of natural enemies substantially increased the survival probability of G. sagittariae eggs and larvae. Interestingly, the egg survival probability decreased with soil moisture content, while the larval survival probability instead increased with soil moisture content. For both the egg and larval survival, we found that host plant height, the number of eggs or larvae, and vegetation height explained more of the variation than the soil moisture gradient by itself. Moreover, host plant quality related variables, such as leaf nitrogen, carbon and phosphorus content did not influence the survival of G. sagittariae eggs and larvae.ConclusionOur results suggest that the soil moisture content is not an overarching factor that determines the interplay between factors related to host plant quality and factors relating to natural enemies on the survival of G. sagittariae in different microhabitats. Moreover, the natural enemy exclusion experiments and the random survival forest analysis suggest that natural enemies have a stronger indirect impact on the survival of G. sagittariae offspring than host plant quality.

Comparison of Different Methods for Assessing Chlorophyll Content in Citrus

The content of chlorophyll-Chl present in green vegetables is strongly associated with the momentary state of the plant photosynthesis. Conventionally, determination of chlorophyll is by extraction with organic solvents and determining a spectrophotometer, and this method expensive, laborious and moreover a destructive method. Thus, the use of portable equipment has been used instead, as they allow studies without destruction of leaf tissue and obtaining instantaneous measurements. Thus, the aim of correlating the chlorophyll results obtained in the laboratory with Falker Chlorophyll Index (FCI) obtained by the ClorofiLog in different citrus rootstocks, as well asits relationship to soil moisture content variation. Positive simple correlations (linear Pearson correlation) were obtained for chl a, b and total, with the lowest correlation values observed for chl β, which ranged from 0.470-788 among the analyzed rootstocks. The coefficients of determination for the three variables chl α, β and total α+β showed a better fit by the polynomial regression model in all analyzed rootstocks; in general, the best results were for chl α, ranging from 0.7093-0.8551. The results indicate the usefulness of the ChloroflLog apparatus in the indirect determination of chlorophyll content in citrus.

Spatial and temporal variations in surface soil moisture and vegetation cover in the Loess Plateau from 2000 to 2015

The “Grain for Green” project utilizes large-scale revegetation to improve the local environment in the Loess Plateau. Understanding the trends in the variations in soil moisture content (SMC) and vegetation after the implementation of this project is necessary. This study examined the spatial and temporal variations in SMC and vegetation cover in the Loess Plateau after 1999. Furthermore, interactions between SMC and vegetation cover (e.g., spatial distribution and temporal variation) were assessed. The results of this study showed that (1) the SMC and vegetation cover increased in most of the Loess Plateau from 2000 to 2015; (2) both SMC and vegetation cover are predicted to decrease after 2015; (3) the increase in precipitation promoted SMC in the northwestern region, but the impact on vegetation cover was not significant; (4) the spatial variation in SMC exhibited a positive correlation with the spatial variation in vegetation cover, however, the difference in their cycle of change indicated that the interaction between SMC and vegetation cover varied over time. The most important results indicated that SMC and vegetation cover have begun to decrease since 2015.