Increasing Soil Moisture Content Research Articles

Ecohydrology in a Brazilian tropical dry forest: thinned vegetation impact on hydrological functions and ecosystem services

Study regionThis study was developed in two paired catchments under a tropical dry climate with a tropical dry forest landcover subject to vegetation management in the Brazilian northeastern region. Water input is mostly from rainfall, concentrated in three to four months of the year and with a potential evaporation that is over twice the amount of rainfall that characterizes its hydric deficit. Study focusInteractions between hydrological functions, services and human actions to minimize environmental impacts, improve the availability of water of good quality and decrease degradation of the ecosystems; land use management effect on systems resilience, impact on surface runoff, soil loss, herbaceous and radicular biomass production, soil humidity and total organic carbon under altered vegetation cover. New hydrological insights for the regionStrategies to improve ecosystem services should rely on adequate management of vegetation to reduce surface flow. This reduction contributes to higher soil moisture contents, less intense erosive processes and resulting higher stocked soil carbon. The many techniques that improve resilience and ecosystem services in tropical dry forests lack an integrated view on how ecohydrological processes may be managed to favor the system. Vegetation thinning promotes underbrush development that dissipates rainfall and surface flow kinetic energy, increasing soil moisture content and carbon fixation and reducing soil loss.

Trade-offs of gaseous emissions from soils under vegetable, wheat-maize and apple orchard cropping systems applied with digestate: An incubation study

ABSTRACTLand application of digestate from anaerobic digestion causes various gaseous emissions. A soil core incubation experiment was carried out in the laboratory to investigate the trade-offs of NH3, N2O and CH4 emissions from soils collected from vegetable, arable and orchard cropping systems. Digestate derived from liquid cattle manure was applied to the soil cores through the surface (SA) and incorporation application (IA) methods under three soil moisture conditions (40%, 60%, and 80% water-filled pore space, WFPS). Gaseous emissions from vegetable soil were significantly greater (P< .05) than those from soils under the other two cropping systems under similar conditions, particularly under a high moisture condition. The greenhouse gas emissions (GHG, in term of CO2-equivalents) of all soils increased with the increasing soil moisture contents, mainly due to rapidly increasing N2O emissions. Trade-offs in the emissions of these three gases were observed between SA and IA. As expected, SA was characterized by greater NH3 and CH4 but lower N2O emissions compared to IA. The increase in GHG under IA could be offset only somewhat by the reduced NH3 (and this reduced indirect N2O) and CH4 emissions under lower moisture conditions (<60% WFPS), which indicates a requirement for other strategies to control gaseous emissions from wet soils applied with digestate. In conclusion, an environmentally friendly strategy for digestate application should consider the soil moisture, types of soils and application methods, and all the presented suggestions need to be verified in the field in the future.Implications: This study shows that digestate incorporation can decrease NH3 but increase GHG emissions verse the surface application method, where the increased GHG could only be offset by the NH3 reductions at relatively dry soil condition, indicating an urgent requirement to mitigating GHG emissions under moist soil condition.

Signals of Spring Thermal Contrast Related to the Interannual Variations in the Onset of the South China Sea Summer Monsoon

AbstractLand–sea thermal contrast is one of the key factors modulating the onset and strength of summer monsoons. This study investigates the precursory thermal-contrast signal of the onset of the South China Sea summer monsoon (SCSSM) and reveals that the land–sea thermal contrastDT(ToceanminusTlandat the surface) in March tracks the date of the monsoon onset very well. In an energy-balance framework, the monthly anomalies in this thermal contrast are decomposed into different components associated with the anomalies of various radiative and nonradiative dynamical processes over the South China Sea in early spring. It is found that the interannual variations ofDT, and thus the onset date of monsoon, are mainly tied to the anomalies in surface heat fluxes, ocean–land heat storage rate, and oceanic dynamical processes. The variation of ocean–land heat storage rate and ocean dynamics is the largest positive contributor to the change inDT. Specifically, an early SCSSM onset tends to be associated with an amplified “cold-land, warm-ocean” pattern that can be further attributed to increased soil moisture content in March, which enhances land surface cooling and weakens oceanic heat storage rate that benefits ocean surface warming. Furthermore, the variations ofDTand soil moisture content in March are positively related with the late-February precipitation over the Indochina Peninsula, which could therefore be regarded as a precursory signal for both the land–sea thermal contrast in March and the onset of the SCSSM.

Biotopic Association of Earthworms in Intact Forests of Teberda Nature Reserve

Contribution of micromosaic structure of high mountain forests to ecological diversity of earthworms have been assessed. Intact forests of Arkhyz section of Teberda Nature Reserve were studied. The dominant types of forests have been recognized for the first time based on eco-coenotic classification. The ecological conditions of their functioning have been studied. Earthworm numbers have been studied in the recognized forest types. Diversity of earthworms was studied in soils under crowns, under fallen trees, and in mosses growing on rocks. 16 species of Lumbricidae have been found, with 4 of them being discovered for the first time. Full complexes of Lumbricidae were associated with biotopes of forest types of increased soil moisture content, low acidity, availability of nitrogen and pronounced litter. The largest abundance, diversity and biomass of Lumbricidae have been found in nitrophilous tallgrass gray alder forests. The lowest have been found in xeromesophytic pine forests with fir, spruce and birch. The most widespread dark coniferous forest with beech were inhabited by seven species of Lumbricidae, dominated by the epigeic species. There were few epi-endogeic and anecic species. The endogeic group of earthworms was represented by Crimea and Caucasus subendemic Dendrobaena schmidti. Diversity and biomass of earthworms in dark coniferous forests with beech were higher than in spruce-fir forests. During summer, dead fallen trees served as a microsite preferential for epigeic and endogeic species, while mosses growing on rocks were preferred by endogeic species.

Effects of polymer materials on soil physicochemical properties and bacterial community structure under drip irrigation

Polymer materials have the effect of retaining water and increasing yield in irrigated agricultural systems. However, little is known about how polymer materials affect soil properties. The purpose of this study was to evaluate the effect of humic acid (H) (an alkaline extract of cottonseed meal), modified polymer (P) (a mixture of anionic polyacrylamide, polyvinyl alcohol, and manganese sulfate), and composite polymer (HP) (1:1 mixture of H and P) on soil physicochemical properties and structural diversity of bacterial community in soils with/without plants under drip irrigation. The results demonstrated that the application of polymer materials decreased soil bulk density, and increased soil moisture content. Compared with the control in soil with plants (CK), the H and P treatments decreased soil bulk density (BD) by 0.09 g·cm−3 and 0.08 g·cm−3, respectively (p < .05) after 90 days of culture. Meanwhile, the H, P, and HP treatments increased soil moisture content (MC) by 10.6%, 33.9%, and 16.5%, respectively (p < .05). For soil without plants, the P-NP treatment decreased BD by 0.18 g·cm−3 (p < .05) after 90 days of culture. Although there were differences in soil pH and conductivity (EC) between treatments, they were not significant. As the culture time was prolonged, the relative abundance of soil Latescibacteria in soil without plants significantly increased compared with that in soil with plants. Principal component analysis (PCA) showed that the effects of polymer material application on soil microbes were not significantly different at the early stage of culture. However, there was significant (in soil with plants, r = 0.540, p = .004) or extremely significant difference (in soil without plants, r = 0.333, p = .045) between treatments after 90 days of culture. Among them, the difference between P treatment and CK was the most significant. Further analysis showed that the P treatment increased relative abundances of soil Acidobacteria, Gemmatimonadetes, and Nitrospirae by 20.6%, 42.8%, and 31.1% compared with CK, respectively (p < .05); and the P-NP treatment increased relative abundances of Gemmatimonadetes, Chloroflexi, and Latescibacteria by 60.5%, 35.7%, and 29.3% (p < .05) compared with CK-NP, respectively. The redundant analysis (RDA) showed that the application of polymer materials could improve the structure diversity of soil bacterial communities by increasing soil MC and regulating C/N ratio, regardless of soil with/without plants.

Ecoenzymatic stoichiometry reveals microbial phosphorus limitation decreases the nitrogen cycling potential of soils in semi-arid agricultural ecosystems

Variations in soil microbial metabolism currently represent one of the greatest areas of uncertainty with regard to soil nutrient cycles and the control of terrestrial carbon (C) and nitrogen (N) loss and are poorly understood in agricultural ecosystems with intensive farming practices. In this study, extracellular enzymatic stoichiometry models and quantitative PCR techniques were used to examine microbial metabolic limitation and its relationship with N-cycling gene expression in semi-arid agricultural ecosystems considering four N fertilization levels (N 0, N 100, N 250, and N 400 kg N ha−1) and two agronomic strategies (film mulching and no mulching). Film mulching increased microbial C limitation (reflecting microbial C metabolism size; 0.189 of the total effects), while very small effects on microbial phosphorus (P) limitation were observed (-0.007 of the total effects). N fertilization increased the microbial demand for P (microbial P limitation; 0.504 of the total effects). Increased microbial C metabolism was mainly attributed to increased soil moisture content after film mulching, which enhanced microbial decomposition of organic C (high C-acquiring enzyme activities). Changes in nutrient stoichiometry and the increase in N availability due to N fertilization were largely responsible for increased microbial P limitation. Furthermore, microbial P limitation negatively affected the abundance of AOA amoA, AOB amoA (involved in nitrification), nirK, nirS, nosZ (involved in denitrification) genes, strongly inhibiting nitrification and denitrification potential (-0.743 and -0.761 of the total effects, respectively). The present results suggest that agricultural ecosystems with film mulching are conducive to organic residue decomposition, while appropriate P limitation under N fertilization could reduce the loss of N due to nitrification and denitrification in soil. This study highlights the importance of elemental stoichiometry-driven microbial metabolic variation in understanding soil nutrient cycles and optimizing agricultural practices.

Telling a different story: The promote role of vegetation in the initiation of shallow landslides during rainfall on the Chinese Loess Plateau

Vegetation is widely used for controlling landslides around the world; however, rainfall-induced shallow landslides occur frequently on vegetation-covered slopes on the Chinese Loess Plateau during the rainy season. To probe this phenomenon, we conducted on-site investigations and measurements in the Nanxiaohegou catchment on the Loess Plateau to explore the effects of soil properties and vegetation on shallow loess landslides. Most of the loess landslides on vegetation-covered slopes were small scale with depths ranging from 0.3m to 1.0m, corresponding to the topsoil being saturated due to rainfall. Majority of shallow landslides occurred on herbage-covered area, which made up 69% of total landslides. There are significant differences in soil properties between the upper layer (root-soil composite) and the lower layer (loess) of the sliding surface. Our study demonstrated that root plays a leading role in landslide erosion and that the most adverse effect of vegetation on landslides is mainly the increase in soil moisture content in the shallow soil through the root zone creating preferential infiltration flow paths. There are remarkable differences in landslide erosion depths and landslide erosion intensities among different vegetation types. The landslide erosion depth and landslide erosion intensity increased linearly with increasing main root depth, indicating that the vegetation root depth determines the landslide erosion intensity during rainfall. Therefore, the potential implications of vegetation especially the herbage to promote landslide occurrences during rainfall should be given more attention in the future.

The Utility of SMAP Soil Moisture and Freeze-Thaw Datasets as Precursors to Spring-Melt Flood Conditions: A Case Study in the Red River of the North Basin

We evaluated NASA soil moisture active–passive (SMAP) soil moisture (SM) and freeze-thaw (FT) datasets for the utility to identify FT and SM conditions as precursors to a 2017 spring-melt flood event in the Red River of the North Basin. SMAP FT and SM datasets were analyzed at basin-scale and at specific North Dakota Agricultural Weather Network (NDAWN), National Oceanic and Atmospheric Administration (NOAA), and Red River of the North U.S. Geological Survey (USGS) stations prior to and during the observed flood. Results indicate that SMAP FT dataset had better agreement with NDAWN and NOAA air temperature measurements than with soil temperature. SMAP FT and SM were able to observe FT states and saturated soil conditions at basin-level and significant increases in SM content up to five days before USGS gauge height increase and the manifestation of the flood event. A Spearman's rank ( $R_{s}$ ) cross-correlation coefficient lag function was applied to SMAP SM and USGS river gauge heights and the strength of the relationship varied by location and lead time. Downstream locations near and in the flood area (North Grand Forks, Oslo, North Drayton) displayed moderate to strong relationships at 1-, 3-, and 4-day lead times ( R s = 0.67, 0.84, 0.71; p $R_{s}= 0.88; p ), well during the flood event recorded. This study suggests that SMAP SM and FT datasets can potentially provide useful information on surface state conditions to spring-melt floods in the Red River of the North Basin.

Effect of tillage and nutrient management on sorghum (Sorghum bicolor) productivity in Alfisols of semi-arid tropical India

The combined effects of tillage intensity (conventional-CT, reduced-RT or no tillage-NT) and nutrient management (inorganic and/or organic) on sorghum [Sorghum bicolor (L.) Moench] production, soil properties, weed dynamics, energy use, and economics were studied on an Alfisols in Hyderabad, India for 3 years (2011-2013). Results revealed that conventional tillage significantly increased growth parameters, viz. leaf area index, SPAD, and plant height as compared to NT, and produced 14% higher grain yield (2.94 Mg/ha) when compared to RT (2.57 Mg/ha) and 58% to NT (1.86 Mg/ha) system. No tillage significantly increased the density of grassy weed Brachiaria reptans (34.50/ m2) as compared to RT (21.83/m2) and CT (26.33/m2). However, the density of Cyperus iria (78.67/m2) and Digera arvensis (17.0/m2) increased significantly in CT. Conventional tillage significantly increased soil moisture content and Azotobacter population at 0-15 cm soil depth compared to NT conditions. Conventional tillage and application of RDF (80:40:40 kg NPK/ha) recorded maximum yield, net returns, B:C ratio and energy productivity.

Temporal Soil Moisture Variations in Different Vegetation Cover Types in Karst Areas of Southwest China: A Plot Scale Case Study

For different vegetation types, soil moisture content shows varying characteristics in different seasons and under different precipitation conditions. However, these characteristics have not been extensively analyzed in karst regions of southwest China. In this study, the soil moisture content of four plots of bare land, grassland, shrubland, and forestland was monitored, and the soil moisture content and corresponding meteorological data for each plot were analyzed. The results indicate that the average soil moisture content in grassland was the highest with weak temporal variation and that in bare, shrub, and forest lands soil moisture content was low with moderate temporal variation. The average soil moisture content in bare, grass, and forest lands was higher in the rainy season than in the dry season, whereas in shrubland, the soil moisture content was higher in the dry season than in the rainy season. Increase in soil moisture content during each precipitation event correlated with the rainfall amount. With increasing rainfall amount, soil moisture content in forest and shrub lands increased more than in bare and grass lands. The peak soil moisture time in each vegetation type plot varied and the peak soil moisture time was related to soil moisture content before a rainfall event. Temperature showed a strong negative correlation with soil moisture content for all vegetation cover types in both the dry and rainy season. Wind speed also showed a strong negative correlation with soil moisture content for all vegetation types during the dry season. Relative humidity had a strong positive correlation with soil moisture content in bare, shrub, and forest lands during the dry season as well as in the four vegetation types during the rainy season. These results demonstrate the variations in soil water characteristics across different vegetation types in karst regions of southwest China.

Biochar incorporation increased nitrogen and carbon retention in a waste-derived soil.

The synthesis of manufactured soils converts waste materials to value-added products, alleviating pressures on both waste disposal infrastructure and topsoils. For manufactured soils to be effective media for plant growth, they must retain and store plant-available nutrients, including nitrogen. In this study, biochar applications were tested for their ability to retain nitrogen in a soil manufactured from waste materials. A biochar, produced from horticultural green waste, was added to a manufactured soil at 2, 5 and 10 % (by weight), then maintained at 15 °C and irrigated with water (0.84 mL m-2 d-1) over 6 weeks. Total dissolved nitrogen concentrations in soil leachate decreased by 25.2, 30.6 and 44.0 % at biochar concentrations of 2, 5 and 10 %, respectively. Biochar also changed the proportions of each nitrogen-fraction in collected samples. Three mechanisms for biochar-induced nitrogen retention were possible: i) increased cation and anion exchange capacity of the substrate; ii) retention of molecules within the biochar pore spaces; iii) immobilisation of nitrogen through microbial utilisation of labile carbon further supported by increased soil moisture content, surface area, and pH. Dissolved organic carbon concentrations in leachate were reduced (-34.7 %, -28.9 %, and -16.7 %) in the substrate with 2, 5 and 10 % biochar additions, respectively. Fluorescein diacetate hydrolysis data showed increased microbial metabolic activity with biochar application (14.7 ± 0.5, 25.4 ± 5.3, 27.0 ± 0.1, 46.1 ± 6.1 µg FL g-1 h-1 for applications at 0, 2, 5, and 10 %, respectively), linking biochar addition to enhanced microbial activity. These data highlight the potential for biochar to suppress the long-term turnover of SOM and promote carbon sequestration, and a long-term sustainable growth substrate provided by the reuse of waste materials diverted from landfill.

Modelling PAH Degradation in Contaminated Soils in Canada using a Modified Process‐Based Model (DNDC)

Core Ideas A novel process‐based model for degradation of soil PAHs is proposed. Model is based on dynamic interactions between water, soil, vegetation and climate. Model effectively simulates biogeochemical processes of PAH degradation in soils. Simulated results agree well with data from remediation sites in Alberta. Polycyclic aromatic hydrocarbons (PAHs) are persistent pollutants of concern. A process‐based model of the PAH degradation can improve our understanding of ecological drivers and processes. In this paper, a process‐based biogeochemistry model, DeNitrification‐DeComposition (DNDC) is modified to simulate the dynamics of PAHs degradation in soils at abandoned oil and gas well sites. This new version of DNDC‐Organic Pollutants, called DNDC‐OP, coupled the rates of PAH degradation with dynamics of soil, vegetation and climate, such as soil moisture and temperature. The model was parameterized and validated against datasets of four soil PAHs: pyrene, fluorene, chrysene and anthracene, at three different abandoned oil and gas well site locations in Alberta, Canada. The sensitivity of the parameters was analyzed and tested. The simulated results were in good agreement with the measured data with a coefficient of determination (R2) of 70 to 97%, and the root mean square error (RMSE) of 4.5 to 9.1 at all three sites. We also evaluated the influence of environmental factors, such as soil temperature and moisture, on the degradation of PAHs. An increased degradation of all four PAHs occurred with increasing soil moisture content. An increase of soil temperature from 10 to 20°C and subsequently to 25°C resulted in a decreased appearance of all four PAHs from the three well sites. The result shows that this model can be used as a tool for evaluating PAH degradation for effective reclamation strategies.

Effects of Moisture Content on the Dynamic Response and Failure Mode of Unsaturated Soil Slope Subjected to Seismic Load

Understanding the relationship between the moisture content of unsaturated soil and the instability and dynamic response of slope under the action of seismic load can bring convenience to the field of slope safety assessment. The effect of moisture content of the unsaturated soil on the failure mode and dynamic response of slope under seismic loading was investigated using shaking table tests. In this regard, three different moisture contents of 5%, 8.1%, and 12.5% were considered. The experimental results show that the amplification factor of acceleration (AFA) on the slope surface increases with the increase in both relative elevation and excitation amplitude of acceleration (EAA). As the moisture content of unsaturated soil increases, AFA tends to decrease. An empirical correlation describing the relationship among AFA, relative elevation, dimensionless EAA, and moisture content of unsaturated soil was proposed. The excitation frequency of acceleration (EFA) has a significant impact on the AFA at the middle and upper parts of the slope. The deformation of slope surface is able to reflect the failure mode of slope, which can be used in slope monitoring work. The slope with different moisture contents of unsaturated soil has different instability modes. With the increase in soil moisture content, the slope needs more energy to reach the unstable state under seismic loading. There are three typical regions of principal stress field in the slope exposed to seismic loading, which control the evolution of initial slip plane inside the slope.

Microtopographical modification by a herbivore facilitates the growth of a coastal saltmarsh plant

Increasing evidence shows that herbivores can facilitate plant growth and maintain the resistance of plant communities to trophic consumption in a variety of ecosystems. However, the positive effects of herbivores on annual saltmarsh plants in coastal ecosystems are relatively understudied. In this study, field investigations and manipulative experiments were conducted to explore whether and how microtopographical modification by the herbivorous crab Helice tientsinensis stimulates the growth of the saltmarsh plant Suaeda salsa. Results showed that, despite grazing on S. salsa, H. tientsinensis can promote density, total biomass, average plant height, average root length, and average biomass through burrowing-generated concave-convex microtopography, which can improve the edaphic environment (decreased soil hardness and salinity, and increased soil moisture content, oxidation-reduction potential, and carbon and nitrogen content), and provide plants more clustered growth opportunities that could facilitate positive intraspecific plant interactions. This study can provide scientific guidance for ecosystem restoration in coastal intertidal saltmarshes.

Conservation and production impacts of soil and water conservation practices under different socio-economic and biophysical setting: a review

In Ethiopia, the increase in land degradation mainly in the form of soil erosion necessitates implementation of soil and water conservation (SWC) practices. So far impact evaluation studies are scattered and not comprehensive. In this paper detailed quantitative review of impact of SWC practices under different climate and socio-economic setting were done on runoff, soil loss, siltation, soil fertility and crop yield. Up to 1980s, expert and government considered reduction of soil loss and runoff as big achievement. This was not in line with the interest of subsistence farmers who need short term benefit. The reduction of soil loss, runoff and siltation of reservoirs are positively acknowledged by majority researchers and have several beneficial effects: increase soil moisture content, groundwater recharge, increased in situ sediment deposition, making the hill slope suitable for agriculture and reduce siltation. Regarding production objective, SWC practices have mixed impact (positive and negative) on crop yield and soil fertility. In this review it was found that 62.5% of the reviewed materials revealed that SWC measures have positive impact on soil fertility either in increasing or maintaining. In contrast, 25% showed SWC treated areas had lower soil fertility than untreated and 12.5% showed no significant change in soil fertility. In summary, the impact of SWC practices especially on soil fertility and crop yield varies depending on soil erosion degree before SWC implemented, design of SWC measures, crops, plows, socio-economic, soils types and climate mainly rainfall. The review in detail discussed why SWC practices have variation in impact on soil fertility and crop yield. Finally SWC practices are an action of no option for sustainable development and food security under current soil erosion and climate change.

Effects of Biochar and Synthetic Polymer on the Hydro-Physical Properties of Sandy Soils

Synthetic polymers, such as polyacrylamide (PAM), and biochar are generally used as soil amendments to improve soil properties. This paper explores a laboratory column experiment conducted to investigate the effects of biochar (pyrolysis at 400–450 °C) and polymers, with different application rates, on the hydro-physical properties of sandy soil. The experiment evaluated four rates each of biochar (0.0% (C), 2% (B1), 4% (B2), 6% (B3) and 8% (B4)) and polymers (0.0% (C), 0.2% (P1), 0.4% (P2), 0.6% (P3), and 0.8%(P4)), as well as a mixture of them. The infiltration rate decreased significantly when a mixture of biochar and polymers was adopted. B1 showed a decrease of 32.73% while a mixture of 8% (B4) and (0.8%) P4 exhibited a decrease of 57.31%. The polymers increased the infiltration rate at low concentrations (P1 and P2) and reduced it at high concentrations (P3 and P4). The cumulative evaporation decreased significantly for most treatments. B1 recorded the highest decrease in cumulative evaporation with a percentage decrease of 31.9%. The highest decrease in hydraulic conductivity (Ks) was for B1. However, the mixture of B4 and P4 resulted in the highest increase in soil moisture content at field capacity compared to the control and other treatments. P4 and the mixture of B2 and P2 showed significant (p &lt; 0.05) increases in the percentage of stable aggregate (SA) in fraction size (0.25–0.125 mm). Although the mixture of B4 and P4 had the highest increase in soil moisture content, this study recommends using the B1 treatment on sandy soil in arid environments due to its strong hydro-physical properties and affordability.

Effects of wind velocity and soil characteristics on dust storm generation in Hawr-al-Azim Wetland, Southwest Iran

Nowadays, dust storms are an important environmental problem in Iran (especially in Khuzestan Province). The Hawr-al-Azim Wetland is a source for generation of dust storms. One-third area of this wetland is located in Iran. In this study, dust discharge is calculated using wind velocity, mean soil grain size (D50) and soil dry density. Soil characteristics were determined by data collected from 16 boreholes drilled in this wetland. Distributions of D50 and soil dry density in the wetland were determined using ordinary kriging method. Then critical wind speed was calculated in different regions of the wetland. The wetland soil is composed of medium and coarse silty soil. The dust mass discharge has reduced from 2003. The maximum monthly dust discharge mass occurs in June and July (along with a mean monthly wind velocity of 4.42 m s-1 and 4.27 m s-1, respectively). Because of the little amount of clay particles and the high wind velocity, increased soil moisture content cannot help in neither raise inthe critical shear velocity nor decreased dust mass discharge. Also, the produced dust is transported towards Northwest Iran because the dominant direction of wind is 270° to 300° relative to the north.

Combined effects of biochar and fertilizer application on maize production in dependence on the cultivation method in a sub-humid climate

ABSTRACT Low, erratic rainfall amounts and restricted accessibility of chemical fertilizer for rural farmers in developing countries may have negative effects on crop production. Agricultural methods like biochar applications, fertilizer microdosing and tied ridging can help to mitigate these constraints, but have rarely been studied in combination and under varying water availability. A field trial was conducted in split-plot design over two contrasting cropping seasons in 2016 and 2017 in Tanzania to study the effect of these agricultural methods on maize grain yield, biomass, leaf area index, plant height and soil moisture content. In both seasons each with contrasting irrigation frequencies, fertilizer microdosing increased the grain yield of maize. Biochar alone affected the yield only at high application rates (10 t/ha) and low irrigation frequency. However, when combined with fertilizer microdosing the yield effect of biochar was more pronounced. For example, combining 5 t/ha biochar with fertilizer microdosing under flat tillage increased yield by 170% compared to the control without biochar and fertilizers. Tied ridges increased soil moisture content and tended to increase maize yield compared to flat tillage, whereas biochar application resulted in significantly higher soil moisture contents. Fertilizer microdosing with biochar application can be recommended to improve maize yields mainly under flat tillage.

ANALYSIS OF THE EFFECT OF INCIDENCE ANGLE AND MOISTURE CONTENT ON THE PENETRATION DEPTH OF L- AND S-BAND SAR SIGNALS INTO THE GROUND SURFACE

Abstract. We study the functional relationship between the dielectric constant of soil-water mixture and penetration depth of microwave signals into the ground at different frequency (L&amp;amp;S) band and incidence angles. Penetration depth of microwave signals into the ground depends on the incidence angle and wavelength of radar pulses and also on the soil properties such as moisture content and textural composition. It has been observed that the longer wavelengths have higher penetration in the soil but the penetration capability decreases with increasing dielectric behaviour of the soil. Moisture content in the soil can significantly increase its dielectric constant. Various empirical models have been proposed that evaluate the dielectric behaviour of soil-water mixture as a function of moisture content and texture of the soil. In this analysis we have used two such empirical models, the Dobson model and the Hallikainen model, to calculate the penetration depth at L- and C-band in soil and compared their results. We found that both of these models give different penetration depth and show different sensitivity towards the soil composition. Hallikainen model is more sensitive to soil composition as compared to Dobson model. Finally, we explore the penetration depth at different incidence angle for the proposed L- and S-band sensor of upcoming NASA-ISRO Synthetic Aperture Radar (NISAR) mission by using Hallikainen empirical model. We found that the soil penetration depth of SAR signals into the ground decreases with the increase in soil moisture content, incident angle and frequency.

Pengaruh Jenis Biochar dan Takaran Pupuk Kandang Sapi terhadap Pertumbuhan dan Hasil Kacang Hijau (Vigna radiata L.)

Penelitian bertujuan mendapatkan jenis biochar dan takaran pupuk kandang sapi yang berpengaruh terhadap pertumbuhan dan hasil kacang hijau. Penelitian ini menggunakan rancangan acak kelompok faktorial 3 x 3 yang diulang 3 kali. Faktor pertama adalah jenis biochar yang terdiri dari 3 aras yaitu tanpa biochar, biochar sekam padi, biochar serbuk gergaji, yang diberikan sebanyak 1,5%. Faktor kedua adalah takaran pupuk kandang sapi yang terdiri dari 3 aras yaitu tanpa pupuk kandang sapi, pupuk kandang sapi 1 t/ha, pupuk kandang sapi 3 t/ha. Penelitian ini dilaksanakan pada bulan Mei sampai November 2017 di lahan petani di Desa Lorotolus, Kecamatan Wewiku, Kabupaten Malaka, Nusa Tenggara Timur. Hasil menunjukkan tidak terjadi interaksi antara perlakuan jenis biochar dan takaran pupuk kandang sapi terhadap pertumbuhan dan hasil kacang hijau. Biochar serbuk gergaji meningkatkan bobot biji per tanaman dan bobot biji per hektar, takaran pupuk kandang sapi 1 t/ha meningkatkan bobot biji per hektar dan pupuk kandang sapi meningkatkan kadar lengas tanah, meningkatkan bobot biji bernas per tanaman maupun bobot biji per hektar.