Range Of Soil Moisture Research Articles

Effect of soil moisture content on the suppression of Rhizoctonia stem canker on potato by the nematode Aphelenchus avenae and the springtail Folsomia fimetaria

The effect of soil moisture content on the suppression of Rhizoctonia stem canker on potato by mycophagous soil animals was studied in growth chambers. Three soil moisture levels were established in two bioassays, in which potato sprouts grew through a 15‐cm soil layer inoculated with sclerotia of Rhizoctonia solani (AG‐3). In one experiment two levels of R. solani inoculum were applied. The effect on plant disease of mycophagous soil fauna was assessed by adding the springtail Folsomia fimetaria and/or the nematode Aphelenchus avenae to the soil. In the absence of mycophagous organisms, Rhizoctonia disease severity on potato stems was highest in dry soil. A. avenae and F. fimetaria reduced Rhizoctonia stem canker when applied at populations found in the field. They were effective over a broad range of soil moistures. The stimulatory effect of dry soil conditions on Rhizoctonia stem canker was counteracted by a greater efficacy of the mycophagous soil fauna under these conditions. Mild drought stress did not seem to be a limiting factor in the biological control of stem canker by these two organisms.

Estimation of bare surface soil moisture and surface roughness parameter using L-band SAR image data

An algorithm based on a fit of the single-scattering integral equation method (IEM) was developed to provide estimation of soil moisture and surface roughness parameter (a combination of rms roughness height and surface power spectrum) from quad-polarized synthetic aperture radar (SAR) measurements. This algorithm was applied to a series of measurements acquired at L-band (1.25 GHz) from both AIRSAR (Airborne Synthetic Aperture Radar operated by the Jet Propulsion Laboratory) and SIR-C (Spaceborne Imaging Radar-C) over a well-managed watershed in southwest Oklahoma. Prior to its application for soil moisture inversion, a good agreement was found between the single-scattering IEM simulations and the L-band measurements of SIR-C and AIRSAR over a wide range of soil moisture and surface roughness conditions. The sensitivity of soil moisture variation to the co-polarized signals were then examined under the consideration of the calibration accuracy of various components of SAR measurements. It was found that the two co-polarized backscattering coefficients and their combinations would provide the best input to the algorithm for estimation of soil moisture and roughness parameter. Application of the inversion algorithm to the co-polarized measurements of both AIRSAR and SIR-C resulted in estimated values of soil moisture and roughness parameter for bare and short-vegetated fields that compared favorably with those sampled on the ground. The root-mean-square (rms) errors of the comparison were found to be 3.4% and 1.9 dB for soil moisture and surface roughness parameter, respectively.

Seasonal variation of carbon dioxide exchange rates above and below a boreal jack pine forest

Fluxes of carbon dioxide were measured above and below a boreal jack pine stand with the eddy covariance method. Our goal was to examine the seasonal variation of the net carbon dioxide exchange between the ecosystem and the atmosphere and to understand the relative contributions of the vegetation and rhizosphere to these fluxes. Over the course of the growing season the jack pine stand was a small, net sink of carbon dioxide—47 g C m −2 were assimilated during a 115 day period between spring (day 144) and autumn (day 259). On a daily basis, the magnitude of the net uptake of CO 2 by the forest was relatively small, less than 4 g C m −1 day −1. We also observed many days when carbon dioxide was lost from the forest stand (up to 2 g C m −2 day −1). Day to day sums of net carbon dioxide exchange exhibited little seasonality, despite the seasonality experienced by controlling environmental and biological variables. The aseasonality of net canopy CO 2 exchange occurred because temporal variations associated with canopy photosynthesis and plant and microbial respiration offset one another over the growing season. Canopy photosynthesis rates of the jack pine stand were evaluated using CO 2 flux measurements made above and below the canopy. Daily totals of canopy photosynthesis were a linear function of available solar energy and exhibited a quadratic dependence on temperature, with optimum photosynthesis occurring between 15 and 25°C. We also observed that the net daily uptake of carbon dioxide was independent of soil moisture in the upper 0.15 m of the soil profile, despite the wide range of soil moisture that was experienced. Finally, the net gain of carbon by a jack pine canopy came with a relatively large respiratory expense. On average, 68% of the carbon gained by photosynthesis was consumed by plant respiration, over the course of a day.

The Interplay between Transpiration and Runoff Formulations in Land Surface Schemes Used with Atmospheric Models

Abstract The Project for Intercomparison of Land-surface Parameterization Schemes (PILPS) has shown that different land surface models (LSMs) driven by the same meteorological forcing can produce markedly different surface energy and water budgets, even when certain critical aspects of the LSMs (vegetation cover, albedo, turbulent drag coefficient, and snowcover) are carefully controlled. To help explain these differences, the authors devised a monthly water balance model that successfully reproduces the annual and seasonal water balances of the different PILPS schemes. Analysis of this model leads to the identification of two quantities that characterize an LSM’s formulation of soil water balance dynamics: 1) the efficiency of the soil’s evaporation sink integrated over the active soil moisture range, and 2) the fraction of this range over which runoff is generated. Regardless of the LSM’s complexity, the combination of these two derived parameters with rates of interception loss, potential evaporation, ...

Soil Moisture Measurement using Active Microwave Remote Sensing

Ground-base verification experiments for the soil moisture detection by spaceborne SARs (E ERS-1 and J ERS-1) were carried out. Backscattering coefficients obtained from satellite SARs were compared with those measured by ground-base scatterometer system and ground truth data of soil moisture, and the relationship between backscattering coefficients measured by SARs and soil moisture content was examined. Major results obtained from the study are as follows; (i) Backscattering coefficients measured by E ERS-1 AMI are not more sensitive to surface conditions than those by the scatterometer and have a high correlation with soil moisture content for the soil moisture range of less than 40 correlation with the saturation degree of soil moisture, but low sensitivity to it. (iii) Each land cover has its own seasonal change, which shows the possibility to classify land cover types from multitemporal SAR data. (iv) Using SAR data with visible satellite data, soil moisture distribution maps are made up and validated with qualitative observations.

能動型マイクロ波リモートセンシングによる表層土壌水分計測 Ｉ． 室内実験

全球スケールでの合成開口レーダ(SAR)によるモニタリングが実用化段階に入り,水文学の領域では表層土壌水分量と積雪内水分量の定量的把握が期待されている.本研究では能動型マイクロ波リモートセンシングによる表層土壌水分量に焦点を当て,地上計測用マイクロ波Cバンド散乱計を製作し,これを用いて重要な各種特性について室内実験を行なった.まずアンテナ特性などのシステム特性を電波暗室で調べる実験を行なった.さらに,この実験システムを用いて,マイクロ波土壌侵入深,土壌水分感度,入射角依存性,地表面粗度の影響について室内実験を行ない,以下の点が明らかとなった.(i)Cバンドマイクロ波の土壌への侵入深は,それが最も大きくなる乾燥時の鉛直入射状態でも10cm程度であり,SARの様なサイドルッキングレーダーでは土壌侵入深はより浅くなる.(ii)散乱計で観測される後方散乱係数と表層土壌水分量の関係を定式化する場合に実用的な表層土壌深は2.5cmである.(iii)後方散乱係数の入射角依存性は入射角が小さいほど顕著である.ただし,本室内実験システムでは30°以上の入射角については良い実験結果が得られなかった.(iv)HV偏波よりもHH偏波の方が後方散乱係数の土壌水分感度が高い.(v)対象土壌面が滑面と粗面とでは,後方散乱係数に非常に大きな差が生じる.

Soil environmental variables affecting the flux of methane from a range of forest, moorland and agricultural soils

Measurements of the net methane exchange over a range of forest, moorland, and agricultural soils in Scotland were made during the period April to June 1994 and 1995. Fluxes of CH4 ranged from oxidation –12.3 to an emission of 6.8 ng m–2 s–1. The balance between CH4 oxidation and emission depended on the physical conditions of the soil, primarily soil moisture. The largest oxidation rates were found in the mineral forest soils, and CH4 emission was observed in several peat soils. The smallest oxidation rate was observed in an agricultural soil. The relationship between CH4 flux and soil moisture observed in peats (FluxCH 4 = 0.023 × %H2O (dry weight) – 7.44, p > 0.05) was such that CH4 oxidation was observed at soil moistures less than 325%( ± 80%). CH4 emission was found at soil moistures exceeding this value. A large range of CH4 oxidation rates were observed over a small soil moisture range in the mineral soils. CH4 oxidation in mineral soils was negatively correlated with soil bulk density (FluxCH 4 = –37.35 × bulk density (g cm–3) + 48.83, p > 0.05). Increased nitrogen loading of the soil due to N fixation, atmospheric deposition of N, and fertilisation, were consistently associated with decreases in the soil sink for CH4, typically in the range 50 to 80%, on a range of soil types and land uses.

Soil moisture simulation: Achievements of the RICE and PILPS intercomparison workshop and future directions

Soil moisture simulation in current landsurface schemes is diverse: in terms of the realism (and complexity) of the parameterizations and in terms of the resulting predictions. Even after careful adjustment, the range in soil moisture among the results from the 14 schemes compared for the HAPEX-MOBILHY (S. France) site's 1.6 m soil layer remains around 100 mm (the annual precipitation for HAPEX-MOBILHY being 856 mm). Results show that the partitioning of surface available energy into sensible and latent heat fluxes is closely coupled to the partition of precipitation into evaporation and runoff plus drainage. Runoff seems to be grossly (30–40%) underestimated by 13 of the 14 participating schemes but incomplete observations do not allow a full evaluation. Runoff from the nearly saturated soil outside the main growing season differs significantly among landsurface schemes although these differences do not greatly affect soil moisture values themselves. Transpiration operates at different rates depending upon the initial soil water content as well as the scheme formulation. The implications are far-reaching: (l) landsurface schemes forced by the same atmospheric conditions reached different equilibrium states; and (2) response times differ for schemes with different structures and different parameterizations. In combination, these two conclusions mean that observational data limited to a few weeks or months cannot be used for validation unless the initial conditions are known very precisely. Soil moisture remains an ill-defined, and inconsistently and, generally, inaccurately predicted quantity.

Issues related to low resolution modeling of soil moisture: experience with the PLACE model

This study documents the new PLACE soil hydrology model, and examines the effects of various parameterization schemes on the solution of the Richards equation. Richards equation is the basis upon which many of the land surface schemes participating in the PILPS experiments model soil water transport. Generally, the integration is carried out using a coarse model grid, which makes the solution more sensitive to particulars of the parameterization scheme. Parameterization schemes for the lower boundary condition, lateral interflow, and for moisture fluxes between model layers are tested in PLACE using both high and low resolution grids. Simulations were made using PILPS-HAPEX forcing data and soil and vegetation parameters. The soil hydrology model is validated against the annual observed HAPEX soil moisture profiles. The predicted evapotranspiration is also compared to a value computed from the PILPS-HAPEX forcing data using the Penman-Monteith equation. When testing a low-resolution soil grid typical of land surface schemes, predicted soil moisture was found to be highly sensitive to the interpolation method for computing vertical moisture fluxes between model layers. A new interpolation method for low resolution models is proposed and tested. It reproduces the high resolution model results more faithfully, over the entire range of soil moisture, than two methods commonly applied in the literature. Further tests demonstrate that by varying the parameterizations for lower boundary condition and the treatment of lateral flow (collectively called drainage), the predicted total annual evapotranspiration may range between 74% and 97% of the incident precipitation in this case. Both of these parameterizations involve one free parameter, and both are largely unconstrained by the available observations. Good overall agreement between the PLACE predicted and HAPEX observed soil moisture profiles was attained by varying these two PLACE drainage parameters over their respective ranges for a series of model simulations. Root-mean square error tests were then used to determine the set of parameters which corresponded to the best predicted soil moisture profile. However, the best predicted soil moisture profiles do not correspond with the best predicted evapotranspiration. This inconsistency occurs not only for PLACE, but, to varying degrees, for all of the land-surface schemes participating in PILPS-HAPEX.

Numerical Simulations of the Effect of Soil Moisture and Vegetation Cover on the Development of Deep Convection

Abstract A one-dimensional (column) version of a primitive equations model has been used to study the impact of soil moisture and vegetation cover on the development of deep cumulus convection in the absence of dynamical forcing. The model includes parameterizations of radiation, turbulent exchange, deep convection, shallow boundary layer convective clouds, vegetation, and soil temperature and moisture. Multiple one-dimensional experiments were performed using the average July sounding for Topeka, Kansas, as the initial condition. A range of volumetric soil moisture from one-half of the wilting point to saturation and vegetation cover ranging from bare soil to full cover were considered. Vegetation cover was found to promote convection, both by extraction of soil moisture and by shading the soil so that conduction of heat into the soil was reduced (thereby increasing the available energy). The larger values of initial soil moisture were found to delay the onset of precipitation and to increase the precipi...

Soil evaporation monitoring: a possible synergism of microwave and infrared remote sensing

Microwave remote sensing allows the measurement of the water content ( θ s) at the soil surface within a layer of a few centimetres. When combined with climatic data, θ s is a relevant quantity to estimate the evaporation of bare soils. The implementation of a simple daily evaporation ( E d) model on bare soils based on a knowledge of θ s is analysed. In order to cover a wide range of soil, soil moisture and climatic conditions, the analysis was carried out on a set of data simulated by a mechanistic model of heat and water flows in the soil. Propagation error analysis on the inputs ( θ s, daily potential evaporation and wind velocity) of the simple model shows that an accuracy of ± 1.5 mm day −1 (95% confidence interval) may be expected when θ s is observed from space-borne microwave sensors. This accuracy is significantly improved (±0.6 mm days) if E d is averaged over a 5 day period. With the simple evaporation model considered, the time interval between microwave observations should not exceed 3 days. However, if the precipitation amounts were known, this time interval could reach 5 days. The soil hydrodynamic properties are included in the simple evaporation model through empirical parameters, which depend strongly on the soil type. We show that the complementarity between thermal infrared and microwave observations could be used to infer the empirical parameters of the simple evaporation model. When microwave and infrared observations are available for the same day, we can inverse the simple evaporation to retrieve its parameters. Even with important errors on the input quantities, the proposed inversion method allows good discrimination between soils. Furthermore, the performances in the estimation of the evaporation are little affected when the simple model is implemented with the retrieved parameters.

Soil evaporation monitoring: a possible synergism of microwave and infrared remote sensing

Microwave remote sensing allows the measurement of the water content (θs) at the soil surface within a layer of a few centimetres. When combined with climatic data, θs is a relevant quantity to estimate the evaporation of bare soils. The implementation of a simple daily evaporation (Ed) model on bare soils based on a knowledge of θs is analysed. In order to cover a wide range of soil, soil moisture and climatic conditions, the analysis was carried out on a set of data simulated by a mechanistic model of heat and water flows in the soil. Propagation error analysis on the inputs (θs, daily potential evaporation and wind velocity) of the simple model shows that an accuracy of ± 1.5 mm day −1 (95% confidence interval) may be expected when θs is observed from space-borne microwave sensors. This accuracy is significantly improved (±0.6 mm days) if Ed is averaged over a 5 day period. With the simple evaporation model considered, the time interval between microwave observations should not exceed 3 days. However, if the precipitation amounts were known, this time interval could reach 5 days. The soil hydrodynamic properties are included in the simple evaporation model through empirical parameters, which depend strongly on the soil type. We show that the complementarity between thermal infrared and microwave observations could be used to infer the empirical parameters of the simple evaporation model. When microwave and infrared observations are available for the same day, we can inverse the simple evaporation to retrieve its parameters. Even with important errors on the input quantities, the proposed inversion method allows good discrimination between soils. Furthermore, the performances in the estimation of the evaporation are little affected when the simple model is implemented with the retrieved parameters.

Soil physical properties as influenced by induced compaction under laboratory and field conditions

Soil compaction changes the ability of soil to hold water, decreases infiltration rate and saturated hydraulic conductivity, and increases penetration resistance. The compaction characteristics of a clay loam were studied under various compaction loads and antecedent soil water contents. Soil water content had a more pronounced effect than load. The penetration resistance varied with water content, whereas saturated hydraulic conductivity decreased with increase in the bulk density. The compaction effects were more pronounced in the surface 0.1 m, but were negligible at 0.1-0.2 m depth when compaction was employed at available water levels up to 40%. The narrow range of suitable soil moisture for tillage operations requires the use of appropriate practices to reduce spatial variability in surface soil moisture.

Modeling the thermal conductivity of frozen soils

This paper describes the computerized extended version of the De Vries model for predicting the thermal properties of frozen field soils. The extended model generally requires a limited data input and can be applied to a full range of soil moisture (dryness to saturation) and a wide range of soil temperatures (from −30 to 90°C). Predicted results are in good agreement with published experimental data provided that default data of mineral composition closely follow the experimental results. A user-friendly computer program has been developed to calculate thermal properties of soils below and above 0°C. The program offers two modes of input data, default and self-entered. The latter requires the following data: grain size distribution, bulk density or porosity, mineral composition including semi-quantitative analysis of clay mineral composition, shape of minerals. The model can be used for the quick estimation of thermal conductivity of practically any soil having lognormal grain size distribution and for computer simulation of heat transfer in soils above and below the freezing point.

Effects of soil moisture, temperature, and inorganic nitrogen on nitric oxide emissions from acidic tropical savannah soils

NO fluxes from soils with a wide range of soil moistures, soil inorganic‐N concentrations, and soil temperatures were measured during the wet and the dry season at a Venezuelan savannah site. Maximum NO emissions (∼12 ngN m−2 s−1) were observed at soil gravimetric moistures between 10% and 18%. Deviation from this optimum range results in decreased NO fluxes; very low emissions ( < 2 ngN m−2 s−1 ) were recorded at low ( < 2% ) and high ( > 25% ) soil moistures. Both NO production in soil and its transport within the soil play important roles in the emission of NO to the atmosphere. Under most conditions no temperature effect was observed. NO emission was strongly stimulated by the addition of NO3− and only very weakly by the addition of NH4+; at low and moderate soil moistures, soil nitrate and the NO flux were positively correlated. At low (natural) soil nitrate content and comparable soil moisture and temperature, NO emissions were greater during the dry season than during the rainy season, suggesting that other factors (i.e., soil physical structure) may also govern NO flux from savannah soil.

Influence of rainfall, temperature and somes oil physico-chemical variables on seasonal population structure and vertical distribution of earthworms in two semi-arid tropical grassland soils

Two semi-arid tropical grasslands, one of an alfisol and the other on vertisol were sampled for earthworm populations during July 1985 to July 1987. The soil of the alfisol grassland was slightly acidic while that of the vertisol was slightly alkaline. The alfisol grassland has a lower range of soil moisture, soil temperature, electrical conductivity, organic carbon, available nitrogen and potassium, and a higher range of phosphorus compared to the vertisol. The alfisol grassland was inhabited byOctochaetona phillotti (Michaelsen) with rare occurrence ofBarogaster annandalei (Stephenson) whereas the vertisol grassland was inhabited only byB. annandalei. The total population ofO. phillotti ranged between 16 and 96/m2 while its juvenile population ranged between 3.2 and 25.6/m2, pre-adult population between 5.3 and 53.6/m2 and adult population between 0 and 28.8/m2. The total population ofB. annandalei ranged between 3.2 and 58.3/m2 and its juvenile population between 0 and 26.6/m2, pre-adult population 0 and 10.6/m2 and adult population between 0 and 22.4/m2. The earthworms migrated to deeper layers during winter and summer,O. phillotti reaching a maximum depth of 40 cm andB. annandalei reaching a depth of 45 cm, and seen in quiescent stage. Their seasonal population structure was significantly influenced by the seasonal patterns in rainfall, soil temperature, pH, electrical conductivity and phosphorus. These variables along with organic carbon, available nitrogen and potassium together accounted for 32–63% and 79–91% respectively, of the variation in seasonal population fluctuation of differentO. phillotti andB. annandalei age groups. The physical factors of the soil were collectively more effective in causing the seasonal variation in their population size than the chemical factors.

Estimation of soil moisture and surface roughness parameters from backscattering coefficient

A statistical inversion technique was implemented to estimate soil moisture and surface roughness parameters from the remotely sensed multifrequency backscattering coefficients. Both two- and three-frequency approaches were examined and tested in detail for the inversion technique. Initially the technique was tested with a simulated data set generated from various scattering models. Later it was applied to an experimental data set that provided, for a wide range of surface roughness and soil moisture, backscattering coefficients at many incidence angles and frequencies. It was found that, in general, the three-frequency approach produces more accurate results. However, under a favorable combination of frequencies and incidence angles, both approaches give results with a comparable accuracy. There is a potential that soil moisture could be estimated to an accuracy of about 2%. In the mean time the surface roughness parameters could be estimated to an accuracy of better than 10%. >

VEGETABLE AMARANTH PERFORMANCE AT DIFFERENT SOIL MOISTURE LEVELS

The effects of differing soil moisture levels on the vegetative components of vegetable amaranth, Amaranthus tricolor RRC no. 241, were evaluated. A completely randomized design with 10 replications and 4 treatments (3,6,13, & 18% soil moisture) was followed. Leaf, stem, plant, root fresh weight and leaf area (LFW, SFW, PFW, RFW, and LA, respectively)—were recorded 48 days after planting. For each of the vegetative components the only significant difference (P ≤ 0.05) occurred between 3% versus 6-18% soil moistures, with moisture level of 6-18% showing no significant variation among themselves. The mean ranges for LFW (28.3-32.7 g), STW (6.9-9.2 g), PFW (41.3-48.2 g), RFW (8.6-12.8 g), and LA (1049-1222 cm2) across 6-18% soil moisture were approximately four times greater than the vegetative components of 3% soil moisture. From these preliminary results, it appears that vegetable amaranth has the ability to grow and perform well over a 6-18% soil moisture range, indicating an ability to better adjust and adapt to changing soil moisture environments.

GROWTH, WATER RELATIONS, AND PHOTOSYMTHESIS ARE REDUCED BY DECREASING SOIL MOISTURE IN 'MARY WASHINGTON ' AND 'SYN 4-56' ASPARAGUS SEEDLINGS

Seedlings of the asparagus cvs Mary Washington (MW) and Syn 4-56 (4-56) were grown at minimum soil matric potentials (SMP) of -0.05, -0.10, and -0.30, -0.50 or -1.5 MPa. Decreases in shoot dry weight leaf area, storage and fibrous root dry weights, and total root and plant dry weight were an exponential function of soil moisture in both cvs. Most of the growth inhibition occurred between the -0.05 and the -0.30 MPa levels of soil moisture, with little further response to SMP drier than -0.30 MPa. Consistent differences between the two cvs, regardless of SMP were apparent in leaf area, shoot dry weight, storage and fibrous root dry weights and root/shoot ratios. MW produced greater leaf area and shoot dry weights than did 4-56 at high SMP and exhibited greater inhibition of shoot dry weight by low SMP than did 4-56. Conversely, 4-56 produced greater storage root dry weight than MW at all SMP., although in mature field-grown plants, 4-56 produced greater fern weight, crown weight and number and stem numbers than MW. Root/shoot ratios generally increased with decreasing SMP. However, the root/shoot ratio of 4-56 was greater than that of MW over the entire range of soil moisture and increased more with decreasing SMP than did MW. Stomatal conductance (gs), fern xylem potential (), and net C02 assimilation rates decreased with decreasing SMP in a similar manner in both cvs. were

Effects of Soil Moisture and Temperature on the Survival ofColletotrichum acutatum

Sections of strawberry inoculated with Colletotrichum acutatum were buried in unsterilized soil and subjected to range of soil temperatures (10, 25, and 40 C) and soil moistures (flooded, moist [10.6%], and dry). Sections were recovered weekly and assayed for the presence of C. acutatum. Survival of C. acutatum was highest under cool, dry soil conditions. Survival decreased with increases in both soil temperature and moisture