Residual Soil Moisture Content Research Articles

Combined Use of Sentinel-1 SAR and Landsat Sensors Products for Residual Soil Moisture Retrieval over Agricultural Fields in the Upper Blue Nile Basin, Ethiopia.

The objective of this paper is to investigate the potential of sentinel-1 SAR sensor products and the contribution of soil roughness parameters to estimate volumetric residual soil moisture (RSM) in the Upper Blue Nile (UBN) basin, Ethiopia. The backscatter contribution of crop residue water content was estimated using Landsat sensor product and the water cloud model (WCM). The surface roughness parameters were estimated from the Oh and Baghdadi models. A feed-forward artificial neural network (ANN) method was tested for its potential to translate SAR backscattering and surface roughness input variables to RSM values. The model was trained for three inversion configurations: (i) SAR backscattering from vertical transmit and vertical receive (SAR VV) polarization only; (ii) using SAR VV and the standard deviation of surface heights (), and (iii) SAR VV, , and optimal surface correlation length (). Field-measured volumetric RSM data were used to train and validate the method. The results showed that the ANN soil moisture estimation model performed reasonably well for the estimation of RSM using the single input variable of SAR VV data only. The ANN prediction accuracy was slightly improved when SAR VV and the surface roughness parameters ( and ) were incorporated into the prediction model. Consequently, the ANN’s prediction accuracy with root mean square error (RMSE) = 0.035 cm3/cm3, mean absolute error (MAE) = 0.026 cm3/cm3, and r = 0.73 was achieved using the third inversion configuration. The result implies the potential of Sentinel-1 SAR data to accurately retrieve RSM content over an agricultural site covered by stubbles. The soil roughness parameters are also potentially an important variable to soil moisture estimation using SAR data although their contribution to the accuracy of RSM prediction is slight in this study. In addition, the result highlights the importance of combining Sentinel-1 SAR and Landsat images based on an ANN approach for improving RSM content estimations over crop residue areas.

Interplays between State and Flux Hydrological Variables across Vadose Zones: A Numerical Investigation

Knowledge of both state (e.g., soil moisture) and flux (e.g., actual evapotranspiration (ETa) and groundwater recharge (GR)) hydrological variables across vadose zones is critical for understanding ecohydrological and land-surface processes. In this study, a one-dimensional process-based vadose zone model with generated soil hydraulic parameters was utilized to simulate soil moisture, ETa, and GR. Daily hydrometeorological data were obtained from different climate zones to drive the vadose zone model. On the basis of the field phenomenon of soil moisture temporal stability, reasonable soil moisture spatiotemporal structures were reproduced from the model. The modeling results further showed that the dependence of ETa and GR on soil hydraulic properties varied considerably with climatic conditions. In particular, the controls of soil hydraulic properties on ETa and GR greatly weakened at the site with an arid climate. In contrast, the distribution of mean relative difference (MRD) of soil moisture was still significantly correlated with soil hydraulic properties (most notably residual soil moisture content) under arid climatic conditions. As such, the correlations of MRD with ETa and GR differed across different climate regimes. In addition, the simulation results revealed that samples with average moisture conditions did not necessarily produce average values of ETa and GR (and vice versa), especially under wet climatic conditions. The loose connection between average state and flux hydrological variables across vadose zones is partly because of the high non-linearity of subsurface processes, which leads to the complex interactions of soil moisture, ETa, and GR with soil hydraulic properties. This study underscores the importance of using soil moisture information from multiple sites for inferring areal average values of ETa and GR, even with the knowledge of representative sites that can be used to monitor areal average moisture conditions.

Development of a steady-state model to predict daily water table depth and root zone soil matric potential of a cranberry field with a subirrigation system

Maintaining a steady water table depth (WTD) to ensure an optimal soil matric potential in the root zone (RMAP) is vital when growing cranberry under a subirrigation system; owing to losses and other hydrological processes. The excessive rising or falling of the WTD may threaten the plant transpiration either by saturation or lack of moisture in the root soil. A steady-state model was developed for a uniform soil column to predict WTD and RMAP under different weather conditions. The model is based on van Genuchten (VG) and Brooks and Corey (BC) analytical soil water retention functions coupled with Mualem, Brooks and Corey, and Gardner hydraulic conductivity models. The results show that the model is capable of predicting satisfactorily both WTD and RMAP. The VG model performed with a 78.13% accuracy for the WTD and an 88.59% precision according to the Kling Gupta Efficiency coefficient (r2 = 0.90, β = 1.00, and γ = 0.99) for the field storage. Meanwhile for the RMAP the Mualem and Gardner hydraulic conductivity models, predictions were successful 71.87% and 75.00% of the time, respectively. The BC model had a 78.13% success for the WTD, 86.93% accuracy in estimating the field water storage according to Kling-Gupta efficiency coefficient (r2 = 0.89, β = 1.00, and γ = 1.00) and the BC and Gardner hydraulic conductivity models had 65.63% and 71.88% success, respectively. A sensitivity analysis of the model, by means of the Morris method, reveals that for both models, the lower boundary condition impacts significantly both variables which are, however, less affected by the field capacity and the residual soil moisture content. The lower boundary condition interacts with the slope of the soil water retention functions, the height of the capillary fringe, the saturated conductivity, and the saturation moisture content which have non-linear effects. An uncertainty analysis shows that both variables for both models are normally distributed.

Agroecological integration of shade- and drought-tolerant food/feed crops for year-round productivity in banana-based systems under rain-fed conditions in Central Africa

Yield gaps in banana-based production systems have increased in the past two decades due to declining soil fertility, drought and biotic stresses. Sustainable, environmentally sound and economically viable strategies for intensification in these systems are urgently needed. Agroecological practices, such as the integration of shade- and drought-tolerant crops, nitrogen-fixing and cover crops could potentially improve soil fertility and moisture retention, reduce the weed burden, narrow yield gaps and increase overall plot/farm productivity in these systems. In Malaysia, leguminous crops like Pueraria phaseoloides, Calopogonium caeruleum and Centrosema pubescens are often cultivated as cover crops (to suppress weeds, and reduce moisture loss and soil erosion) in young rubber and oil palm plantations with low shade levels. Even in mature oil palm plantations with less than 30% light intensity, various shade-tolerant crops are grown, e.g., elephant foot yam, turmeric and arrow root. In humid tropical Africa, Colocasia (taro) and Xanthosoma (cocoyam) are reported to tolerate shade conditions and hence often planted under perennial banana/plantain plantations. Drought tolerance is a less common feature of most annual crops grown in the humid tropics. A few root and tuber crops (e.g., cassava, taro, yam and sweetpotato) remain in the field during the dry season in Central Africa and are then harvested according to household needs. This paper also reports on crops (Mucuna, lablab and chickpea) with potential for integration into banana-based systems during the dry season, if planted during the last month of the rainy season. These crops are reported to use the residual soil moisture content for continued growth during the dry season months. The paper concludes with detailed descriptions (from a literature review) on drought- and shade-tolerance characteristics of various crops which have long been integrated in Central African banana-based cropping systems, crops with a more recent cultivation history and crops with potential for system integration.

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This study evaluates the capability of soil water content predicted from remote sensing to indicate the soil/canopy water content at short time and space scale, through comparisons with daily soil moisture data determined in situ, using dielectric devices. Daily aqua moderate resolution imaging spectroradiometer (MODIS) normalized difference vegetation index (NDVI) and the diurnal (daytime and night time) land surface temperature difference (DLST) are employed to retrieving daily volumetric soil moisture content (θ) at Sparta experimental station, during the period June-August, of the years 2010, 2011, 2012 and 2014. Using the concept of apparent thermal inertia (ATI) in the remotely sensed topsoil moisture saturation index, daily θ is obtained from DLST and the volumetric saturated and residual soil moisture content and is compared with the experimental values of volumetric soil moisture content (SM) measured at various depths (10, 20, 30, 40, 60, 80 and 100 cm). Simple relationships are also calibrated between SM and ATI or DLST or NDVI during the years 2010, 2011 and 2014 and are tested for predicting θ, during the year 2012. Especially the three first models predict θ satisfactorily as compared with the measured SM and hence they can offer a considerable guidance in irrigated agriculture and other related fields.

Prediction of Soil Moisture from Remote Sensing Data

This study evaluates the capability of soil water content predicted from remote sensing to indicate the soil/canopy water content at short time and space scale, through comparisons with daily soil moisture data determined in situ, using dielectric devices. Daily aqua moderate resolution imaging spectroradiometer (MODIS) normalized difference vegetation index (NDVI) and the diurnal (daytime and night time) land surface temperature difference (DLST) are employed to retrieving daily volumetric soil moisture content (θ) at Sparta experimental station, during the period June-August, of the years 2010, 2011, 2012 and 2014. Using the concept of apparent thermal inertia (ATI) in the remotely sensed topsoil moisture saturation index, daily θ is obtained from DLST and the volumetric saturated and residual soil moisture content and is compared with the experimental values of volumetric soil moisture content (SM) measured at various depths (10, 20, 30, 40, 60, 80 and 100cm). Simple relationships are also calibrated between SM and ATI or DLST or NDVI during the years 2010, 2011 and 2014 and are tested for predicting θ, during the year 2012. Especially the three first models predict θ satisfactorily as compared with the measured SM and hence they can offer a considerable guidance in irrigated agriculture and other related fields.

Assessing effects of soil hydraulic properties on the temporal stability of absolute soil moisture content and soil moisture anomaly under different climatic conditions

Due to the complex interactions of soil moisture with its controlling factors, numerical models are more suitable for quantifying different controls on the temporal pattern of soil moisture. Here, the effects of soil hydraulic properties on the temporal stability of absolute soil moisture content (TS SMC) and soil moisture anomaly (TS SMA) under different climatic conditions were assessed using a vadose zone model. To run the model, two soil datasets with van Genuchten parameters were generated and hydrometeorological data from four study sites with a significant precipitation gradient were obtained. The TS SMC analysis revealed that the patterns of mean relative difference (MRD) and standard deviation of relative difference (SDRD) of soil moisture partly depended on climatic conditions. With increasing precipitation, the range of MRD generally decreased; whereas, the range and mean value of SDRD increased, indicating that soil moisture was temporally more stable under drier climatic conditions. Based on the Spearman rank correlation coefficient, the results showed that the dependence of MRD on soil hydraulic parameters was partly determined by climatic conditions. With decreasing precipitation, the effects of residual soil moisture content, saturated hydraulic conductivity, and the parameter l that accounts for pore tortuosity and connectivity strengthened, while the effects of saturated soil moisture content and the parameter n that is a measure of pore size distribution weakened. Finally, according to the Pearson correlation coefficient, the results revealed that the control of soil hydraulic properties was shown to be reduced in the TS SMA analysis, thus confirming the previously made conjecture that the use of soil moisture anomalies in the temporal stability analysis reduces the impacts of static soil properties.

Field Observations of Regional Controls of Soil Hydraulic Properties on Soil Moisture Spatial Variability in Different Climate Zones

Knowledge of soil moisture spatial variability (SMSP) is important for many practical reasons. However, a significant gap still exists in our understanding of different controls on SMSP, especially the roles of soil hydraulic parameters due to their limited availability. Although modeling approaches have been used to assess the impacts of those parameters on SMSP, they have led to inconsistent findings. In this study, soil moisture data from Utah (5 yr) and the US Southeast (2 yr) were obtained from the Soil Climate Analysis Network (SCAN), along with estimated van Genuchten parameters. The method of mean relative difference (MRD) of soil moisture was used as a diagnostic tool for assessing different climate and soil controls on SMSP. The results show that instead of being controlled by climate variables (e.g., precipitation and potential evapotranspiration) as traditionally believed at regional scales (∼105 km2), MRD is mainly dependent on soil hydraulic properties. In Utah with a drier climate, the residual soil moisture content (θr) is the dominant control on MRD, followed by the saturated soil moisture content (θs). With wetter climates in the US Southeast, the impacts of θr and θs on MRD become comparable, mostly due to the high correlation between θr and θs in this region, and there exists a nonlinear negative relationship between MRD and the parameter n for coarser soils, indicated by larger n values tending to have lower MRDs. The findings of this study have important implications for verifying remotely sensed moisture data and initializing and parameterizing regional land surface and climate models.

Characterization and crop planning of rabi fallows using remote sensing and GIS.

Rice is the principal crop during kharif (rainy) season in eastern India, which occupies 26.8 M ha accounting for 63.3% of the total rice-growing areas of the country. However, this area is not fully utilized for crop production in the subsequent rabi (post-rainy) season and kept fallow due to a number of biotic, abiotic and socio-economic constraints. If this rabi fallow area can be effectively utilized, it will help in improving the economy of this region, which is yet to be benefited from the green revolution. The objectives of the present study include: (i) delineation of rabi fallow areas of eastern India using remote sensing and GIS technique; (ii) characterization of soil resources of the rabi fallow regions, and (iii) suggesting site-specific crop planning for this region. It was estimated that about 12.54 M ha area in the rabi season is left fallow in eastern India. The soil properties like soil texture, soil moisture retention at field capacity and permanent wilting point, saturated hydraulic conductivity, soil pH, electrical conductivity, soil organic carbon, etc. were determined at the representative profiles distributed in different agro-ecological sub-regions (AESRs) of this region and mapped in a GIS environment. Using water balance studies, site-specific crop planning based on available residual soil moisture has been suggested. In most of the AESRs, pulses and oilseeds like green gram, black gram, Sesamum and mustard can be grown successfully on residual soil moisture content. Crops which suffer from water deficit during maturity stages can also be grown during rabi season with one or two supplemental irrigations, wherever possible. If the site-specific constraints to crop production can be alleviated and these fallow lands can be brought under cultivation through proper crop planning as suggested, poverty in this resourceful region can be eradicated to a great extent.

Investigating soil controls on soil moisture spatial variability: Numerical simulations and field observations

Due to its complex interactions with various processes and factors, soil moisture exhibits significant spatial variability across different spatial scales. In this study, a modeling approach and field observations were used to examine the soil control on the relationship between mean (θ¯) and standard deviation (σθ) of soil moisture content. For the numerical experiments, a 1-D vadose zone model along with van Genuchten parameters generated by pedotransfer functions was used for simulating soil moisture dynamics under different climate and surface conditions. To force the model, hydrometeorological and physiological data that spanned over three years from five research sites within the continental US were used. The modeling results showed that under bare surface conditions, different forms of the θ¯–σθ relationship as observed in experimental studies were produced. For finer soils, a positive θ¯–σθ relationship gradually changed to an upward convex and a negative one from arid to humid conditions; whereas, a positive relationship existed for coarser soils, regardless of climatic conditions. The maximum σθ for finer soils was larger under semiarid conditions than under arid and humid conditions, while the maximum σθ for coarser soils increased with increasing precipitation. Moreover, vegetation tended to reduce θ¯ and σθ, and thus affected the θ¯–σθ relationship. A sensitivity analysis was also conducted to examine the controls of different van Genuchten parameters on the θ¯–σθ relationship under bare surface conditions. It was found that the residual soil moisture content mainly affected σθ under dry conditions, while the saturated soil moisture content and the saturated hydraulic conductivity largely controlled σθ under wet conditions. Importantly, the upward convex θ¯–σθ relationship was mostly caused by the shape factor n that accounts for pore size distribution. Finally, measured soil moisture data from a semiarid region were retrieved from the Automated Weather Data Network. The observed moisture data showed that based on soil texture, a positive θ¯–σθ relationship existed for sandy soils, while an upward convex one was observed for silty soils. The difference in the observed θ¯–sigmaθ relationship can be attributed to the differences in water holding capacities between sand and silt, which is consistent with the modeling results. The field data also revealed that increasing spatial variability in soil texture led to increased variability in soil moisture (e.g., the maximum σθ). Therefore, the effect of soil texture for verifying remotely sensed soil moisture products should be considered.

Modeling the impacts of soil hydraulic properties on temporal stability of soil moisture under a semi-arid climate

Summary Despite the significant spatiotemporal variability of soil moisture, the phenomenon of temporal stability of soil moisture ( TS SM ) has been widely observed in field studies. However, the lack of understandings of the factors that control TS SM has led to some contradictory findings about TS SM . To resolve this issue, numerical models may offer an alternative way to complement field studies by quantifying different controls on TS SM . In this study, a 1-D vadose zone model was adopted to simulate daily soil moisture contents, which were used to compute the mean relative difference ( MRD ) and standard deviation of relative difference ( SDRD ) of soil moisture. Different from recent modeling studies, a soil dataset was employed with 200 samples of correlated soil hydraulic parameters for sandy soils. Compared to the results of previous modeling studies, more reasonable patterns of MRD and SDRD that resembled field observations were produced. By varying soil hydraulic parameter values, different patterns of MRD and SDRD could also be generated, implying variations in soil hydraulic properties could partly control the patterns of MRD and SDRD . More specifically, the residual soil moisture content ( θ r ) was found to be the primary control on MRD , mainly due to the semi-arid climate that was simulated. By fixing θ r , however, a highly nonlinear relationship emerged between MRD and the shape factor n in the van Genuchten model, which resulted in the positively skewed distributions of MRD widely observed for sandy soils in field experiments. Moreover, both the range and skewness of the distributions of MRD were affected by the range of n . In addition, with increasing n , a positive correlation between MRD and the shape factor l in the van Genuchten model was also found. The simulation results suggested that the control of soil hydraulic properties on MRD might weaken for areas under bare surface conditions or for regions with more humid climates due to elevated soil moisture contents. Therefore, the impacts of soil hydraulic properties on TS SM may vary under different climate regimes.

Soil carbon sequestration as affected by slope aspect under restoration treatments of a degraded alfisol in the Indian sub-tropics

Rehabilitation of degraded lands needs appropriate mix of land use and erosion control measures, and is often associated with carbon (C) sequestration in the soil profile. However, topographic attributes play a deterministic role in the rate of C accretion in degraded sloping lands. This study was carried out to assess the effect of slope aspect on soil C sequestration, soil aggregation and soil moisture retention in aggradation phase of a denuded land in eastern India. Eight treatments of horti-silvi-pastural system integrated with in-situ moisture conservation were taken in randomized block design during 2000 to 2006. Indigofera teysmanni was taken as the silviculture component and hedgerows of the species were used uniformly for all the treatments. A significant interaction effect of the rehabilitation system and slope aspect was observed for residual soil moisture content, soil organic C (SOC) content, SOC stock, size distribution of aggregates and C content in aggregate fractions. Treatments with trenches of 0.45×0.45×1.0m dimension at 0.5mu/s of fruit plants conserved significantly higher soil moisture even at 87mm of evaporativity. On an average, the north facing (NF) aspect had 1.13 and 0.75g 100g−1 higher soil moisture than the east facing (EF) aspect in the 0–15cm and 15–30cm soil depths, respectively. The SOC concentration was higher by 11–12% in the NF than the EF aspect. In the 0–30cm soil profile, the SOC stock varied from 31.55 to 37.91Mgha−1 in the EF aspect and from 35.01 to 41.28Mgha−1 in the NF aspect, as compared to the initial stock of 18.19 and 19.06Mgha−1 in the two aspects, respectively. The NF aspect had 0.35 to 3.17Mgha−1 higher SOC stock in the 0–15cm soil, 0.64 to 3.03Mgha−1 in the 15–30cm soil and 1.85 to 4.59Mgha−1 in the whole 0–30cm soil profile. Averaged over all the rehabilitation systems, the NF aspect accumulated extra C to the tune of 0.19, 0.18 and 0.36Mgha−1yr−1 than the EF aspect in the 0–15, 15–30 and 0–30cm soil layers, respectively. Under all the systems and slope aspects, small macroaggregates (>250μm) constituted the highest proportion, with values varying from 50.4–65.4% in the EF to 61.7–71.7% in the NF aspect. The C content in small macroaggregates was also higher than that in microaggregates and silt+clay size fractions. The study indicates slope aspect to be a significant factor in soil C sequestration, which also affects the aggregation pattern of soils under recovery.

One-Dimensional Soil Moisture Profile Retrieval by Assimilation of Near-Surface Measurements: A Simplified Soil Moisture Model and Field Application

The Kalman filter assimilation technique is applied to a simplified soil moisture model for retrieval of the soil moisture profile from near-surface soil moisture measurements. First, the simplified soil moisture model is developed, based on an approximation to the Buckingham‐Darcy equation. This model is then used in a 12month one-dimensional field application, with updating at 1-, 5-, 10-, and 20-day intervals. The data used are for the Nerrigundah field site, New South Wales, Australia. This study has identified (i) the importance of knowing the depth over which the near-surface soil moisture measurements are representative (i.e., observation depth), (ii) soil porosity and residual soil moisture content as the most important soil parameters for correct retrieval of the soil moisture profile, (iii) the importance of a soil moisture model that represents the dominant soil physical processes correctly, and (iv) an appropriate forecasting model as far more important than the temporal resolution of near-surface soil moisture measurements. Although the soil moisture model developed here is a good approximation to the Richards equation, it requires a root water uptake term or calibration to an extreme drying event to model extremely dry periods at the field site correctly.

896. Investigation of the metallurgical prepation and properties of high purity nickel and NiWZr-alloys: G Pupke and K Mund, Neue Hütte, 12 (11), Nov 1967, 661–666 ( in German)

Rehabilitation of degraded lands needs appropriate mix of land use and erosion control measures, and is often associated with carbon (C) sequestration in the soil profile. However, topographic attributes play a deterministic role in the rate of C accretion in degraded sloping lands. This study was carried out to assess the effect of slope aspect on soil C sequestration, soil aggregation and soil moisture retention in aggradation phase of a denuded land in eastern India. Eight treatments of horti-silvi-pastural system integrated with in-situ moisture conservation were taken in randomized block design during 2000 to 2006. Indigofera teysmanni was taken as the silviculture component and hedgerows of the species were used uniformly for all the treatments. A significant interaction effect of the rehabilitation system and slope aspect was observed for residual soil moisture content, soil organic C (SOC) content, SOC stock, size distribution of aggregates and C content in aggregate fractions. Treatments with trenches of 0.45 × 0.45 × 1.0 m dimension at 0.5 m u/s of fruit plants conserved significantly higher soil moisture even at 87 mm of evaporativity. On an average, the north facing (NF) aspect had 1.13 and 0.75 g 100 g− 1 higher soil moisture than the east facing (EF) aspect in the 0–15 cm and 15–30 cm soil depths, respectively. The SOC concentration was higher by 11–12% in the NF than the EF aspect. In the 0–30 cm soil profile, the SOC stock varied from 31.55 to 37.91 Mg ha− 1 in the EF aspect and from 35.01 to 41.28 Mg ha− 1 in the NF aspect, as compared to the initial stock of 18.19 and 19.06 Mg ha− 1 in the two aspects, respectively. The NF aspect had 0.35 to 3.17 Mg ha− 1 higher SOC stock in the 0–15 cm soil, 0.64 to 3.03 Mg ha− 1 in the 15–30 cm soil and 1.85 to 4.59 Mg ha− 1 in the whole 0–30 cm soil profile. Averaged over all the rehabilitation systems, the NF aspect accumulated extra C to the tune of 0.19, 0.18 and 0.36 Mg ha− 1 yr− 1 than the EF aspect in the 0–15, 15–30 and 0–30 cm soil layers, respectively. Under all the systems and slope aspects, small macroaggregates (> 250 μm) constituted the highest proportion, with values varying from 50.4–65.4% in the EF to 61.7–71.7% in the NF aspect. The C content in small macroaggregates was also higher than that in microaggregates and silt + clay size fractions. The study indicates slope aspect to be a significant factor in soil C sequestration, which also affects the aggregation pattern of soils under recovery.