Gravimetric Soil Water Content Research Articles

Soil organic matter, texture, and drying temperature effects on water content

AbstractA balance between soil water and air is needed to optimize soil microbial activity in laboratory incubations. Some fraction of water holding capacity (WHC) is often used to optimize water during controlled laboratory incubations, and yet this level may differ among soils. This study was undertaken to develop relationships among gravimetric and volumetric water content, WHC, and water‐filled pore space (WFPS) among a variety of soils, representing eight soil orders, 46 subgroups, total soil N from 0.46 to 4.68 g kg–1, and clay concentration from .072 to .491 kg kg–1 (5–95% range). Gravimetric soil water content was determined for each sample under the following sequence of conditions: (a) from dry storage, (b) when dried at 55 °C, (c) near saturation, and (d) when drained to WHC. Gravimetric water content was calculated at 50% WFPS (.50 m3 m–3). Like that of WFPS, WHC varied strongly with soil clay and total N concentrations. To achieve 50% WFPS, water content was 69 ± 10% of WHC and 58 ± 3% of near saturation. Although drying soil to only 55 °C for routine soil microbial processing led to overestimation of soil bulk density by 0.012 ± 0.006 Mg m–3, it was a bias. Soil water content calculations are important for obtaining best estimates of soil‐test biological activity and other soil C and N fractions to assess soil health, and this research demonstrated that using drying temperature of 55 °C was practical but created a small and consistent bias.

Quantification and mitigation of nitrogen leaching in a maize silage cropping system

Nitrogen (N) leaching is a major source of groundwater contamination. We used a series of lysimeters and suction cups to measure total N leaching losses in a high N maize crop system on a long-term maize paddock in the Waikato.
 The goal of the study was to 1) quantify N leaching losses under maize silage, 2) determine the effectiveness of a cut-and-carry annual ryegrass catch crop (RG) in mitigating N leaching losses and 3) determine an appropriate depth for measuring N leaching losses under maize.
 At least 200 kg/ha more fertiliser N than calculated plant requirements was applied to the maize crop to ensure surplus soil N after maize.
 Nitrogen leaching losses were measured in a maize-RG and maize-fallow rotation over two seasons (October 2018 - September 2020). Less than 10 % of N leaching losses occurred during the maize growing season. This is likely due to evapotranspiration exceeding rainfall in summer.
 The greatest leaching losses were observed in the maize-fallow rotation, averaging 60 kg N/ha and 88 kg N/ha for the 2018/19 and 2019/20 seasons. This was despite 2020 winter being drier than 2019. The greater 2019/20 leaching losses can be attributed to a greater soil N concentration (+15 mg N/L) in 2020.
 The importance of catch crops as a N leaching mitigation tool after maize was evident over the two years, resulting in leaching reductions >85% in the maize-RG than the maize–fallow plots. The catch crop removed >200 kg N/ha from the soil, significantly reducing the soil N concentration, which appear to be the main driver of leaching losses in our study. Additionally, RG also increased gravimetric soil water content by 7.3 % in the top 30 cm.
 When N leaching was measured at 70 cm, losses in fallow plots were almost three times higher than the 41.6 kg N/ha recorded at the 120 cm soil depth, our default maize rooting depth. 
 A similar amount of isotopic 15N (1.2 %) was observed in maize grain at maturity when 15N was inserted to 60 cm or 120 cm soil depth. This was greater than the background values obtained when standard urea was applied to the plots (0.37 %), indicating 15N interception at depth. 
 It is speculated that provided fertiliser rates match crop N demand and catch crops are used, N leaching losses in maize crops should be much lower than values reported here, irrespective of soil type and season.

Single midseason drainage events decrease global warming potential without sacrificing grain yield in flooded rice systems

Rice (Oryza sativa L.) cultivation is an important part of global food security, yet it is also responsible for a significant portion of agricultural greenhouse gas (GHG) emissions, particularly methane (CH4). Midseason drainage of flooded rice fields can decrease CH4 emissions, but the magnitude of CH4 reduction and its effect on grain yield are variable due to variation in the timing and soil-drying severity of drainage across studies. Therefore, in this two-year study, we aimed to quantify the effect of timing and severity of a single midseason drainage event on seasonal GHG emissions and grain yields, compared to a continuously flooded (CF) control. Treatments varied in terms of soil-drying severity (low, medium, and high, corresponding to approximately 5, 8, and 12 days of drying, respectively) and the timing of when drainage events occurred (between 34–49 and 45–59 days after seeding, or roughly between tillering and panicle initiation). Soil moisture parameters (perched water table, volumetric water content, gravimetric water content (GWC), and soil water potential), soil mineral nitrogen, CH4 and nitrous oxide (N2O) emissions, grain yield, and yield components were all quantified. Midseason drainage reduced seasonal CH4 emissions by 38–66%, compared to the CF control. Seasonal CH4 emissions decreased with increasing drain severity, and for every 1% reduction in soil GWC during the drainage period, seasonal CH4 emissions were reduced by 2.5%. The timing of drainage had no significant impact on CH4 emissions. Emissions of N2O were low (average = 0.035 kg N2O-N ha−1) and accounted for only 0.5% of the seasonal global warming potential (GWP) across all drainage treatments. Within each year, drainage did not significantly affect grain yield compared to the CF control. Additionally, midseason drainage reduced both GWP and yield-scaled GWP by approximately the same amount as seasonal CH4 emissions, as N2O emissions were minimal and yields were similar across treatments. These results indicate that midseason drainage may be a viable GHG mitigation practice in flooded rice systems with limited risk for yield reduction, however, this practice should also be further tested under a broad range of soil types and different environments to determine its widespread adoptability.

Performance of field‐scale lab vs in situ visible/near‐ and mid‐infrared spectroscopy for estimation of soil properties

AbstractComparison of laboratory versus in situ visible/near‐ (visNIR) and mid‐infrared (MIR) spectroscopy for prediction of various soil properties is required to demonstrate trade‐offs between accuracy and efficiency. Field measurements were made on an arable field in Germany (silt loam Haplic Luvisol) using visNIR (ASD FieldSpec 3 Hi‐Res) and MIR (Agilent Technologies 4300 Handheld FTIR) and material was collected for lab visNIR (Foss XDS Rapid Content Analyzer) and MIR (Bruker‐TENSOR 27) measurements on dried and ground soil and determination of total, labile (>63 μm light), stabilized (>63 μm heavy + <63 μm oxidizable) and resistant organic carbon (OC) content, total nitrogen (Nt), pH and texture. Partial least squares regression models were calculated for five repeated partitions of the dataset (n = 238) into training (75%) and test (25%) sets. Lab spectral models outperformed in situ models for total OC (root mean squared error [RMSE] = 0.24–1.0 g kg−1), Nt (RMSE = 0.026–0.088 g kg−1), pH (RMSE = 0.12–0.28) and texture (RMSE = 0.53–1.5%). For both lab and field spectra, the accuracy of visNIR models was comparable or slightly better than MIR for sand, silt and clay. Spectral estimations for labile (RMSE = 0.34–0.47 g kg−1) and stabilized OC (RMSE = 0.41–0.85 g kg−1) were slightly (lab spectra) to substantially (field spectra) inferior to estimations from multiple linear regressions using total OC, Nt, clay and pH as predictors. Variable importance in the projection scores elucidated differences in spectral prediction mechanisms by spectrometer and OC fraction, and found mineral spectral signatures were highly important. For this field‐scale study with 14% median soil gravimetric water content (GWC), the loss of accuracy from lab to field measurement was lower for visNIR than MIR. Analysis of the driest soils (<9% GWC) found field MIR outperformed field visNIR for OC and Nt estimation and vice versa for the wettest soils (>18%), demonstrating the moisture dependence of performance rankings.Highlights Lab vs field visible/near‐ (visNIRS) and mid‐infrared (MIRS) spectroscopy require comparison for prediction of soil C fractions, N, pH and texture. Lab MIRS prediction of C, N and pH were superior, while texture estimations were comparable or slightly inferior to lab visNIRS. At 14% median soil water content, the loss of accuracy from lab to field measurement was lower for visNIRS than MIRS. The ranking of field visNIRS vs MIRS performance for C and N estimation is moisture dependent.

Spatial Heterogeneity and Driving Factors of Soil Moisture in Alpine Desert Using the Geographical Detector Method

Soil moisture is a vital factor affecting the hydrological cycle and the evolution of soil and geomorphology, determining the formation and development of the vegetation ecosystem. The previous studies mainly focused on the effects of different land use patterns and vegetation types on soil hydrological changes worldwide. However, the spatial heterogeneity and driving factors of soil gravimetric water content in alpine regions are seldom studied. On the basis of soil sample collection, combined with geostatistical analysis and the geographical detector method, this study examines the spatial heterogeneity and driving factors of soil gravimetric water content in the typical alpine valley desert of the Qinghai–Tibet Plateau. Results show that the average value of soil gravimetric water content at different depths ranges from 3.68% to 7.84%. The optimal theoretical models of soil gravimetric water content in 0–50 cm layers of the dune are different. The nugget coefficient shows that the soil gravimetric water content in the dune has a strong spatial correlation at different depths, and the range of the optimal theoretical model of semi-variance function is 31.23–63.38 m, which is much larger than the 15 m spacing used for sampling. The ranking of the influence of each evaluation factor on the alpine dune is elevation > slope > location > vegetation > aspect. The interaction detection of factors indicates that an interaction exists among evaluation factors, and no factors are independent of one another. In each soil layer of 0–50 cm, the interaction among evaluation factors has a two-factor enhancement and a nonlinear enhancement effect on soil gravimetric water content. This study contributes to the understanding of spatial heterogeneity and driving factors of soil moisture in alpine deserts, and guidance of artificial vegetation restoration and soil structure analysis of different desert types in alpine cold desert regions.

Spatial distribution of argan tree influence on soil properties in southern Morocco

Abstract. The endemic argan tree (Argania spinosa) populations in southern Morocco are highly degraded due to overbrowsing, illegal firewood extraction and the expansion of intensive agriculture. Bare areas between the isolated trees increase due to limited regrowth; however, it is unknown if the trees influence the soil of the intertree areas. Hypothetically, spatial differences in soil parameters of the intertree area should result from the translocation of litter or soil particles (by runoff and erosion or wind drift) from canopy-covered areas to the intertree areas. In total, 385 soil samples were taken around the tree from the trunk along the tree drip line (within and outside the tree area) and the intertree area between two trees in four directions (upslope, downslope and in both directions parallel to the slope) up to 50 m distance from the tree. They were analysed for gravimetric soil water content, pH, electrical conductivity, percolation stability, total nitrogen content (TN), content of soil organic carbon (SOC) and C/N ratio. A total of 74 tension disc infiltrometer experiments were performed near the tree drip line, within and outside the tree area, to measure the unsaturated hydraulic conductivity. We found that the tree influence on its surrounding intertree area is limited, with, e.g., SOC and TN content decreasing significantly from tree trunk (4.4 % SOC and 0.3 % TN) to tree drip line (2.0 % SOC and 0.2 % TN). However, intertree areas near the tree drip line (1.3 % SOC and 0.2 % TN) differed significantly from intertree areas between two trees (1.0 % SOC and 0.1 % TN) yet only with a small effect. Trends for spatial patterns could be found in eastern and downslope directions due to wind drift and slope wash. Soil water content was highest in the north due to shade from the midday sun; the influence extended to the intertree areas. The unsaturated hydraulic conductivity also showed significant differences between areas within and outside the tree area near the tree drip line. This was the case on sites under different land usages (silvopastoral and agricultural), slope gradients or tree densities. Although only limited influence of the tree on its intertree area was found, the spatial pattern around the tree suggests that reforestation measures should be aimed around tree shelters in northern or eastern directions with higher soil water content or TN or SOC content to ensure seedling survival, along with measures to prevent overgrazing.

INFLUENCE OF ANTHROPOGENIC FACTORS ON THE SOIL CONDITION OF THE N.V. TSITSIN MAIN BOTANICAL GARDEN OF RAS

The territory of the N.V. Tsitsin Main Botanical Garden of the Russian Academy of Sciences is subjected to significant anthropogenic stress, which has a negative effect on the state of valuable collections of tree and shrub species. Soil compaction is one of the most dangerous consequences of anthropogenic impact, expressed in increased recreational impact. In this context, the botanical garden was very concerned about the deterioration of the collection of elaeagnus species. Therefore, the soils on which these plants grow were chosen as the object of research. On this territory, three sampling plots with different degrees of anthropogenic impact were laid. Sampling plot No. 1 had the maximum anthropogenic impact. The area of medium anthropogenic impact was represented by the sampling plot No. 2. The sampling plot No. 3 where the anthropogenic impact was minimal was a reference plot. All the studied soils were classified as soddy-slightly podzolic medium loamy soils (Umbric Albeluvisols Abruptic). Fundamental differences in the morphological properties of the studied soils were that the soils located in the area of maximum anthropogenic impact, starting from a depth of 40 cm, showed gley spots, which were not found in other soils. Increased bulk density of soil in undisturbed state corresponded to increased anthropogenic impact. This led to a decrease in total pore space of soil. Soil compaction contributed to a noticeable decrease in gravimetric soil water content in upper horizons. At the same time, worsening of subsurface runoff contributed to gley-forming processes in the illuvial part of the profile. Cluster analysis revealed good grouping of the dependence of the studied indicators on the severity of anthropogenic impact. The studied indicators were separated depending on their type and position in the profile. The conducted study made it possible to assess the essential physical and hydrophysical properties of soils on the part of the territory of the Main Botanical garden of RAS that is occupied by the valuable collection of elaeagnus. Based on the results of the study, a set of measures is proposed that can significantly reduce the identified negative effects and improve the state of both the studied soils and stands growing on them in general.

Meta-analysis of green manure effects on soil properties and crop yield in northern China

• Evaluation of green manure application effect by meta-analysis. • Green manure can significantly improve soil nutrient content. • Green manures’ type affects succeeding crops yield. The application of green manure is a traditional and valuable practice for agroecosystem management. In northern China, the effects of green manure on production of the region’s major crops have been extensively investigated, but the inconsistent conclusions that these case studies have yielded cannot provide effective guidance for practical local agricultural production. Here, we conducted a meta-analysis to generate a comprehensive evaluation of the effects of green manure on soil properties and crop yield in this region. Our results shown that green manure improves soil quality effectively, decreasing soil bulk density by ∼ 5.6 %, increasing microbial biomass carbon by 28 %, and improving the activities of soil enzymes by 14 % ∼ 39 %. Among the different types of green manure, legume green manure more markedly increased both nitrate and hydrolysable nitrogen, while non-legume green manure more markedly increased available potassium. Soil gravimetric water content was decreased under green manure treatment. Maize yield was significantly increased under green manure by 11 % on the whole, while effects of green manure on wheat and potato were inconsistent. In summary, the application of green manure in northern China can improve soil quality significantly, and proper green manure use can improve cash crop yields.

Soil water content measurement using polymer optical fibre Bragg gratings

Measuring soil water content is crucially important and can affect soil strength, which is a key parameter in the analysis, design and monitoring of geo-structures. In this study, an optical fibre Bragg grating sensor inscribed in polymer optical fibre was developed, and for the first time, its ability to measure soil water content was investigated. The sensitivity of the sensor to different values of gravimetric soil water content under the different compaction conditions of loose and normal compaction was tested. The effect of soil temperature on the sensor’s performance was considered. To assess the sensor’s implementation, accuracy and reliability, a commercial soil water content probe (SM150), which measures volumetric soil water content was employed. The results indicate that the developed sensor, when calibrated correctly, is able to provide detailed data on any minor variation of soil water content (e.g. 0.5%) with high precision. The outcomes of this study define an additional capability of the polymer optical fibre Bragg grating sensors, which is significantly important for the long-term performance monitoring of geo-structures.

Low-Cost Control and Measurement Circuit for the Implementation of Single Element Heat Dissipation Soil Water Matric Potential Sensor Based on a SnSe2 Thermosensitive Resistor.

A low-cost signal processing circuit developed to measure and drive a heat dissipation soil matric potential sensor based on a single thermosensitive resistor is demonstrated. The has a high thermal coefficient, from C in the 20 to 25 C to C in the 20 to 25 C. The thermosensitive resistor is encapsulated with a porous gypsum block and is used as both the heating and temperature sensing element. To control the power dissipated on the thermosensitive resistor and keep it constant during the heat pulse, a mixed analogue/digital circuit is used. The developed control circuit is able to maintain the dissipated power at mW when the resistor changes from to . When the gravimetric water content of the porous block changes from dry to saturated (), we measured a variation of in the thermosensitive resistor, which results in an end-point sensitivity of 130 m/%. The developed system can easily meet the standard requirement of measuring the gravimetric soil water content with a resolution of approximately , since the resistance is measured with a resolution of approximately , three orders of magnitude smaller than the sensitivity.

Tillage and its temporal effects on soil organic matter and microbial characteristics in the semi-arid central South Africa

Context Tillage has temporal effects on soil organic matter and microbial attributes. Aim Three tillage systems (NT, no-tillage; MT, mulch tillage; MP, mouldboard ploughing) were used to assess the impact on soil quality indicators such as gravimetric soil water content (GSWC), soil organic carbon (SOC), total nitrogen (TN), easily extractable-glomalin (G EE), dehydrogenase (DHA), β-glucosidase (β-glu), urease (URE), acid-(AcP) and alkaline-(AlP) phosphatase over time in a sandy-loam Plinthustalf cropped annually with winter wheat and occasionally oat in eastern Free State. Methods Samples were collected during oat (October 2010, November 2010), fallow (February 2011, April 2011, May 2011) and wheat (August 2011, September 2011, October 2011) phases at 0–5 and 5–10 cm depth. Results When averaged over sampling dates, GSWC, SOC, TN and enzyme activities were 6–85% higher under NT than in MT and MP in the upper 5 cm soil. Trends changed at the 5–10 cm depth, with 20–32% higher enzyme activities recorded under MT. Soil quality indicators exhibited different trends over time, with GSWC, TN, DHA, AcP and AlP generally increasing during the fallow period and decreasing during oat and wheat phases, while β-glu was higher during both crop phases than at fallowing. URE was 33.6–174.3% higher during the oat phase than at the fallow and wheat phases. The opposite was observed with SOC, C/N ratio and G EE. Conclusions Enzyme activities were sensitive indicators, but SOC and TN can be used to assess temporal changes in soil quality in resource-limited countries. Implications However, temporal effects on SOC and TN were probably built in the long-term, hence further research focusing on multiple seasons is required.

Differences in dehydration tolerance affect survival of white clover (

There is very little robust, experimentally based knowledge comparing drought tolerance of one legume species with another. Dehydration tolerance and plant survival of the perennial legumes white clover (Trifolium repens L., considered quite sensitive to drought) and lucerne (Medicago sativa L., considered drought tolerant) were compared in a drying cycle experiment conducted in pots in a glasshouse, with the deep rooting of lucerne constrained. White clover used more soil water, drying the pots to a final soil gravimetric water content (θg) of 4.7%, compared with 8.3% in lucerne pots. Rates of water use were also different: white clover used 0.47% of θg per day and lucerne 0.3%. The more conservative water use allowed lucerne to survive for longer into the drying cycle than white clover. Lucerne partitioned more of its total dry matter into root growth and had much higher root:shoot ratios than white clover. Leaf/stolon elongation is one of the first plant processes to cease as water deficit increases; however, elongation was greater in white clover than lucerne at the beginning of the drying cycle, and this trend continued until lower soil water contents were reached. Conversely, leaf senescence generally commenced at quite high levels of water stress and progressed more rapidly to complete senescence in white clover than in lucerne. Lucerne retained tissue relative water content at a higher level than white clover, with final minimum values of 25% and 13.6%, respectively. In lucerne, 50% mortality was observed at θg of 9%, compared with 6% in white clover, albeit with greater variability. In conclusion, lucerne maintained a higher relative water content than white clover even though it endured the drying cycle for longer and without access to water at depth, evidence of its superior dehydration avoidance and better adaptation to dry conditions. However, white clover was more able to extract water from surface soil layers. This study provides valuable insight into the adaptive traits of both species and identifies some traits that might be useful in the quest to improve white clover adaptation.

Development and Validation of a New Calibration Model for Diviner 2000® Probe Based on Soil Physical Attributes

This study aimed to develop a new model, valid for soil with and without expandable characters, to estimate volumetric soil water content (θ) from readings of scaled frequency (SF) acquired with the Diviner 2000® sensor. The analysis was carried out on six soils collected in western Sicily, sieved at 5 mm, and repacked to obtain the maximum and minimum bulk density (ρb). During an air-drying process SF values, the corresponding gravimetric soil water content (U) and ρb were monitored. In shrinking/swelling clay soils, due to the contraction process, the variation of dielectric permittivity was affected by the combination of the mutual proportions between the water volumes and the air present in the soil. Thus, to account for the changes of ρb with U, the proposed model assumed θ as the dependent variable being SF and ρb the independent variables; then the model’s parameters were estimated based on the sand and clay fractions. The model validation was finally carried out based on data acquired in undisturbed monoliths sampled in the same areas. The estimated θ, θestim, was generally close to the corresponding measured, θmeas, with Root Mean Square Errors (RMSE) generally lower than 0.049 cm3 cm−3, quite low Mean Bias Errors (MBE), ranging between −0.028 and 0.045 cm3 cm−3, and always positive Nash-Sutcliffe Efficiency index (NSE), confirming the good performance of the model.

Spatial cross-correlation between physicochemical and microbiological variables at superficial soil with different levels of degradation

Best soil management practices can be achieved by evaluating the spatial cross-correlation variability ofsoil microbiological and physicochemical indicators, in order to comprehend the underlying relations between these mutually dependent properties, being valuable indicators for prospective evaluation of soil resources.The purposes of this study were to measure microbiological and physicochemical variables in superficial soil, spatially cross-correlate and determine spatial causalities between these two families of variables.The spatial variability of pH, gravimetric soil water content, 238U, 232Th, 40K, 137Cs, acid phosphatase, dehydrogenase activity, microbial biomass carbon, mesophilic aerobic bacteria and filamentous fungi was studied at a 13 ha field located in Uruguay.238U and 232Th were both negatively lineally correlated with gravimetric soil water content (−0.42), 137Cs (-0.45 and −0.48 respectively) and dehydrogenase activity (-0.44 and −0.48 respectively). A semivariogram analysis revealed that the best fit model for soil variables was spherical, with moderate to strong spatial dependence. Cross-correlation results suggest that there is an influence factor from spatial interaction. In this sense, gravimetric soil water content connects physicochemical variables with soil biodiversity. Spatially, soil water content is inversely influenced by 232Th and 238U (as indicators of sub-superficial soil), and directly influenced by dehydrogenase activity (indicator of soil microbial activity), revealing soil microbial activity as a possible indicator of water retention in drying soils. The combination of spatial patterns of environmental radionuclides with microbiological indicators of soil quality could represent a valuable integrated approach to assess soil conservation status and further explain the impact of anthropogenic disturbance.

A comparative study of soil processes in depletion and accumulation zones of permafrost landslides in Siberia

Landslides are one of the main reasons for permafrost degradation in high latitudes. Any landslides consist of different top-down slope zones: removal, transit-depletion, and accumulation zones. These slope parts can demonstrate different successional behavior of plant community and carbon (C) cycling during post-sliding seral stages. To address this issue, soil respiration (SR), hydrothermal conditions (mineral soil temperature at a depth of 5 cm (ST5, °C), and gravimetric soil water content at a depth of 0–5 cm in mineral soil horizon (SWC5, %)), total soil C (TC) and nitrogen (TN) contents, and soil microbial activity at the middle (depletion zone) and lower (accumulation zone) slope parts of the landslides with different history have been studied. The most significant differences between the middle and lower slope positions were found at the ground microsites (or G-plots) of the L2001 landslide. Thus, here, a midslope part occurred to be a high source of C compared to the lower part. Midslope of L2001 was characterized by significantly higher SR at G-plots as well because of better hydrothermal conditions and more intensive vegetation regeneration. The accumulation zone of L2001 characterized by the lower SR despite significantly higher microbial activity due to the high nutrient level of the soil moved from the top, likely favored to promotion of the soil C stabilization processes. Despite the registered ST5 differences in the E-plots and the G-plots between middle and lower slope positions of the L1972 landslide, SR, TC, TN, and soil microbial activity did not differ significantly.

Tree fine roots productivity and turnover rates estimation in alpine sandy land

Sequential coring method was used to collect the data of fine roots from June to August in alpine sandy land. Turnover rates were calculated by maximum or mean biomass during the growing season in 2015 using Decision Matrix (DM) or Maximum-Minimum (MM) method. Results show that biomass in June is lower than that in July and August. Turnover rates of Artemisia desertorum are higher than that of Caragana intermedia and Caragana korshinskii. Turnover rates of mixed forest are higher than that of pure forest. Soil gravimetric water content is highly related to root biomass/ length in the depth of 40 - 60 cm for Caragana intermedia and Caragana korshinskii. But soil gravimetric water content and root biomass/ length have no obvious regularity in the depth of 40 ~ 60 cm for Artemisia desertorum. The minimum water requirement threshold of around 0.02 can be acquired for Caragana intermedia and Caragana korshinskii in the arid region. In alpine sandy land, it is suitable to plant Artemisia desertorum compared to Caragana intermedia and Caragana korshinskii; mixed forest has more advantages compared to pure forest.

Multi-scale drivers of soil resistance predict vulnerability of seasonally wet meadows to trampling by pack stock animals in the Sierra Nevada, USA

BackgroundMeadow ecosystems have important ecological functions and support socioeconomic services, yet are subject to multiple stressors that can lead to rapid degradation. In the Sierra Nevada of the western USA, recreational pack stock (horses and mules) use in seasonally wet mountain meadows may lead to soil trampling and meadow degradation, especially when soil water content is high and vegetation is developing.MethodsIn order to improve the ability to predict meadow vulnerability to soil disturbance from pack stock use, we measured soil resistance (SR), which is an index of vulnerability to trampling disturbance, at two spatial scales using a stratified-random sampling design. We then compared SR to several soil and vegetation explanatory variables that were also measured at the two spatial scales: plant community type (local scale) and topographic gradient class (meadow scale).ResultsWe found that local-scale differences in drivers of SR were contingent on the meadow scale, which is important because multiple spatial scale evaluation of ecological metrics provides a broader understanding of the potential controls on ecological processes than assessments conducted at a single spatial scale. We also found two contrasting explanatory models for drivers of SR at the local scale: (1) soil gravimetric water content effects on soil disaggregation and (2) soil bulk density and root mass influence on soil cohesion. Soil resistance was insufficient to sustain pack stock use without incurring soil deformation in wet plant communities, even when plant cover was maximal during a major drought.ConclusionsOur study provides new information on seasonally wet meadow vulnerability to trampling by pack stock animals using multi-scale drivers of SR, including the contrasting roles of soil disaggregation, friction, and cohesion. Our work aims to inform meadow management efforts in the Sierra Nevada and herbaceous ecosystems in similar regions that are subject to seasonal soil saturation and livestock use.

Straw mulch and irrigation affect solute potential and sunflower yield in a heavy textured soil in the Ganges Delta

Since soil water depletion and salinity are major constraints for crop production, rice straw mulch could be beneficial for increasing yield and water productivity due to its role in conserving soil water and decreasing soil salinity. Two field experiments were conducted on a saline, silty clay soil to determine the effects of mulch and irrigation on the dynamics of soil water content and soil salinity, and on the growth and yield of sunflower sown by strip planting. In 2017, the mulching treatments were: no mulch (NM), rice straw mulch (RS) and retaining 15–20% of the crop residue of the previous rice crop (RR). In 2018 three irrigation treatments: one (I1), two (I2) and three irrigation events (I3), and two mulching treatments (NM and RS) were tested. In both years, the average gravimetric soil water content (SWC) was higher and topsoil salinity (EC1:5) was lower under RS treatment at 0−7 and 7−15 cm depth than with the NM treatment. The substantially higher solute potential of the soil solution in the surface soil with the RS treatment at 0−7 and 7−15 cm (−644 and −588 kPa in 2017, and -649 and −558 kPa in 2018) than with NM treatment (−925 and −728 kPa in 2017, and -801 and −641 kPa in 2018) was associated with increased grain yield (2.7 and 2.5 t ha−1 in 2017 and 2018, respectively). In the second year, the increasing number of irrigation events also increased yield, but the effects were additive to those of mulch. We conclude that the application of a rice straw mulch to the surface of saline-clay soils under strip planting can increase the solute potential of the soil solution thereby improving the growth and yield of sunflower.

Laboratory characterization of sandy soil water content during drying process using electrical resistivity/resistance method (ERM)

Drought-induced evaporation can reduce soil water content and significantly alter soil hydro-mechanical behavior. Understanding the temporal and spatial distribution characteristics of soil water content during evaporation is of great significance for evaluating the encountered geotechnical and geo-environmental problems in arid or semi-arid regions. In this study, an electrical resistivity/resistance method (ERM) with a high spatial resolution of centimeter-level was developed for a small-scale laboratory test and applied to quantitatively characterize the evaporation-induced water content variations along a depth gradient. A total of 8 groups of initially saturated sandy soil columns (84 mm in diameter and 290 mm in height) were prepared, and eight pairs of mini electrodes (3.5 mm in diameter) were installed in each soil sample with a vertical distance of 30 mm. The soil columns were subjected to continuous drying. The changes in soil electrical resistance at different depths were monitored by the electrode couples. The gravimetric water contents at different depths were also measured at the end of drying. It is found that soil water content decreases exponentially with increasing electrical resistance. Based on the obtained data, a calibration relationship between soil gravimetric water content and corrected electrical resistance was well established with consideration of temperature effect. This relationship was validated successfully by the experimental results, indicating the feasibility of the developed ERM to characterize the soil water content dynamics during the drying process. Besides, the drying process with the movement of the evaporation front was discussed. The results of this study demonstrate the good performance of ERM in the estimation of temporal and spatial variations of soil water content and its potential application in arid or semi-arid regions with frequent droughts.

Manure Consistency and Weathering Affect the Removal of Fecal Indicator Bacteria from Grass-Covered Soil

Animal manures contain bacteria which may be used to indicate the potential microbial pollution of irrigation and recreation water sources. The objective of this work was to research how the release of these indicators to runoff is affected by the concurrent influence of the manure consistency and the duration of manure weathering between rainfall events. Liquid and solid dairy manure was applied on grassed soil boxes. The percentage of manure-borne bacteria removed in runoff over 1 hour was determined after the initial rainfall immediately after manure application and after rainfalls that occurred 1 week and 2 weeks after the initial rainfall. The runoff delay was linearly related to the time between rainfalls and was significantly affected by both weathering duration and manure consistency (P = 0.017 and 0.038, respectively). The runoff delay was dependent on the antecedent gravimetric soil water content (R2 = 0.92 and 0.99 for liquid and solid manure treatments, respectively). Manure weathering caused a substantial decrease in the removal of fecal bacteria with runoff in the 2-week weathering compared with the 1-week weathering treatments for both of E. coli and enterococci (P = 0.063 and 0.049, respectively). Every day of weathering decreased the percentage of the released E. coli and enterococci by about 1.2 and 1.5 times, respectively, for both manure consistencies. Manure consistency was not found to significantly affect the percentages of E. coli or enterococci removed with runoff for any level of weathering. Results indicate the need of correcting existing manure bacteria removal models by accounting for manure consistency and weathering duration.