Silt Loam Texture Research Articles

The influence of surfactant and organic matter content on wetting pattern of different non-water repellent soils

Non-ionic surfactants have been well researched as a tool to ameliorate water repellent conditions. However, few studies have evaluated the risks and benefits of non-ionic surfactant applications in wettable soil. The objective of this study was to evaluate the effects of a surfactant in modifying the wetting pattern in soils of different textures and organic matter contents. The experimental treatments consisted of (1) four different soil textures including sandy, sandy loam, sandy clay loam and silt loam, (2) four different organic matter contents (0.2, 0.7, 1.2 and 1.7% by weight), and (3) irrigation water treatments with or without surfactant (IrrigAid Gold). The experiment was carried out in Plexiglas boxes with one drip emitter under the soil surface. The results demonstrated the superiority of surfactant application on increasing water distribution in the soil profile for all soil textural classes. Silt loam texture had the highest side wetted area and wetting depth 45min after the initiation of irrigation. Upward capillary water movement and top wetted area significantly decreased in the surfactant treatment across all soil textures except in sandy soil. As organic matter content increased, top wetted area decreased. These findings clarified the potential ability of surfactant in increasing water infiltration in non-repellent soil in an in vitro system.

Nitrogen loss from windblown agricultural soils in the Columbia Plateau

Abstract Wind erosion of agricultural soils can degrade both air quality and soil productivity in the Columbia Plateau of the Pacific Northwest United States. Soils in the region contain fine particles that, when suspended, are highly susceptible to long range transport in the atmosphere. Nitrogen (N) associated with off-site transport of windblown particulate matter depletes the parent soil of nutrients important in sustaining the biological activity of soils. The objective of this study was to quantify the loss of N from eroding agricultural fields during high wind events. Soil eroded from fields subject to conventional tillage in winter wheat–summer fallow rotations in eastern Washington was trapped in creep and Big Spring Number Eight (BSNE) samplers installed on the leeward side of fields at heights of 0–1.5 m above the surface. The location of field sites varied over the 8 years of this study, but all sites were characterized by soils with a silt loam texture and annual precipitation of ⩽305 mm. Nitrogen content of the parent soil ranged from 0.063% to 0.090% while N content of sediment trapped by the samplers during high winds ranged from 0.053% to 0.101%. Enrichment ratios (ERs) for N ranged from 0.8 to 1.3, indicating the sediment was not highly enriched in N as compared with the parent soil. Nitrogen loss was estimated to range from 0.1 to 1.9 kg ha−1 during a high wind event. Nitrogen loss may be reduced by using conservation practices that have been proven effective in controlling wind erosion.

Toposequence and Properties of Soils in the Hilly Landscape of Lier (Buskerud Region, South Norway)

The research was carried out in the hilly landscape in the Buskerud region, south Norway. The following soil toposequence was stated, beginning from the top of the slope: Epigleyic Pheozem (Siltic) – Cumullinovic Pheozem (Endosiltic) – Epigleyic Pheozem (Skeletic Endosiltic) – Cumullinovic Pheozem (Siltic) – Mollic Gleysol (Siltic). The soils had a silt loam and sandy loam texture with a substantial admixture of gravel. The material was poorly sorted with a lepto – and platykurtic texture distribution. The amounts of organic matter, organic carbon, as well as total nitrogen and phosphorus did not show catenal changes.

Use of Hppd-inhibiting Herbicides for Control of Troublesome Weeds in the Midsouthern United States

Transgenic crops provide cotton and soybean producers additional weed control options for many of the most problematic weeds in mid southern US. production systems. The expected commercialization of 4-hydroxyphenylpyruvate dioxygenase (HPPD)-resistant soybean in 2017 and cotton in 2020 will provide producers the option to apply HPPD-inhibiting herbicides that will offer an alternative mechanism of action for previously hardto- control weeds. Experiments were conducted in 2010 and 2011 to determine the efficacy of HPPD-inhibiting herbicides applied pre emergence (PRE) or post emergence (POST) for control of problematic weeds of cotton and soybean in the mid southern US. PRE experiments were conducted to understand the length and degree of control of Palmer amaranth and barn yard grass that could be expected with HPPD-inhibiting herbicides compared with current standards on silt loam and clay soil textures. The HPPD herbicides evaluated included mesotrione, tembotrione, and isoxaflutole compared to several standards currently labeled in soybean. In the POST experiment, applications of isoxaflutole, tembotrione, glyphosate, and two rates of glufosinate applied alone and both HPPD herbicides combined with glyphosate or glufosinate were evaluated for control of Palmer amaranth, barn yard grass, hemp sesbania, and yellow nutsedge. When herbicides were applied PRE, the HPPD-inhibiting herbicides and the current standard treatments all provided greater than 90% control of Palmer amaranth 4 weeks after treatment (WAT) on both soil textures. Barn yard grass control with HPPD-inhibitors was generally weaker than the current standards with the exception of mesotrione which proved to be comparable to the standards 4 WAT. In the POST experiment, all treatments, except for glyphosate alone, provided excellent (>85%) control of Palmer amaranth less than 10 cm in height. Barn yard grass, yellow nutsedge, and hemp sesbania were effectively controlled with HPPDinhibiting herbicides with and without glufosinate or glyphosate.

Effect of Distillery Effluent (Spent Wash) Application on Aggregate Size Distribution and Stability in Sodic Soils

Sodic soils of sandy loam, silt loam and clay loam textures having exchangeable sodium percentage (ESP) classes of 20, 40, 60 and 80 were reclaimed with 0, 10, 20, 30 and 40 % solutions of distillery effluent (DE) and gypsum in columns. Soil texture, types of amendment and initial ESP had a larger impact on chemical properties, aggregate stability and size distribution. With increase in concentration of DE, a significant reduction in ESP, pH and insignificant increase in electrical conductivity (EC) of soil was observed for all three textures. Organic carbon (OC) content was also increased significantly in soils amended with DE. Size distribution of water-stable aggregates (WSA) of soils reclaimed using 40 % solution of DE and gypsum were found at par. Depending upon initial ESP and type of amendments used, mean weight diameter (MWD) of WSA varied from 0.51 to 1.14, 0.61 to 1.37 and 0.54 to 1.63 mm for sandy loam, silt loam and clay loam soils respectively. The percentage of water-stable macro-aggregates (WSMA) (>2 mm diameter) ranged from 2.2 to 18.2 in sandy loam, from 2.2 to 19.5 in silt loam and from 4.6 to 28.5 in clay loam soils. Combined as well as individual effects of initial ESP, EC, pH, and OC were found highly significant on WSMA and MWD of WSA in distillery effluent amended soils.

Mineralization of Soil Carbon and Nitrogen Following Physical Disturbance: A Laboratory Assessment

Uncertainty persists regarding the influence of physical disturbance on mineralization of soil organic matter. This study examined how disturbance affects mineralization in soils with different management histories and textures. Results from a 100-d incubation (20°C, −10 kPa) using cores (0–15 cm deep; 5-cm diameter) from a field trial at Lincoln, New Zealand with different agronomic treatments in the previous 5 yr (pasture, arable cropping, and chemical fallow) confirmed that mineralization is strongly influenced by management history (C mineralized ranged from 390 mg kg−1 in fallow soil to 1570 mg kg−1 under pasture). However, there was no difference in C or N mineralization between disturbed (sieved <4 mm) and intact cores. In another experiment, comparisons of mineralization in intact and disturbed (<4 mm) cores from 14 arable and pasture fields with either silt loam or clay loam texture also showed no effect of disturbance. In a final experiment, large, air-dry aggregates (19–40 mm) from two soil types (silt loam and clay loam) were fragmented using a compressive force and the resulting subaggregates separated into size classes (<0.25, 0.25–1, 1–2, 2–4, 4–9.5, and 9.5–13.2 mm) by dry sieving. Mineralization increased only when aggregate size was below a certain threshold value (∼3 mm diameter); mineralization was ∼25–50% greater in fine (≤1 mm) vs. large (4–40 mm) aggregates, likely due to exposure of previously-occluded organic matter. Unless a substantial quantity of fine aggregates is generated, the influence of physical disturbance may be small.

Modelling the impact of declining soil organic carbon on soil compaction: Application to a cultivated Eutric Cambisol with massive straw exportation for energy production in Northern France

Loss of organic matter has been recognized as being a major threat to soils in Europe with important consequences for the physical functioning of soils. We present the result of a numerical analysis of the integrated effects of changes in soil porosity and soil water status, along with decreased soil organic carbon (SOC) and the subsequent changes in the risk of compaction. This study concerns the impact of straw exportation on the risk of soil compaction. We evaluated the risk of compaction of a cultivated Eutric Cambisol in Northern France having a dominant silt loam soil texture, by simulating vehicle wheeling during sugar beet cropping for contrasting soil organic carbon contents (4.7, 11.1 and 23.4gkg−1). To do this, we coupled two models: (1) a crop model (STICS) to calculate the changes in the water content of the 0–30cm depth layer; and (2) a compaction model (COMPSOIL) to calculate soil stresses as a function of vehicle characteristics. Our study suggests that a decrease in SOC reduces the risk of topsoil deformation due to a decrease in soil water content, which tends to augment soil precompression stress. The method requires improvement in the future because it is very sensitive to input parameters for soil physical properties. Nevertheless it provides the first method for evaluating the impact of SOC decline on soil compaction. Its genericity permits it further applications to various soil management practices that decrease SOC.

Characterizing Compaction Variability with an Electromagnetic Induction Sensor in a Puddled Paddy Rice Field

Paddy rice (Oryza sativa L.) fields are repeatedly puddled at water saturation to loosen the top soil and to form a uniformly compacted plow pan required to reduce losses of water and nutrients. In paddy growing conditions however, the non-invasive detection of compaction variation within the plow pan layer is challenging. This paper evaluates a proximal soil sensing based methodology to identify areas compacted by different intensities of puddling to support precise land preparation of paddy rice fields. Therefore, a 1.6-ha alluvial paddy field of silt loam texture (Aeric Haplaquepts) located in the Brahmaputra floodplain of Bangladesh was selected. Three areas within the field were variably puddled and characterized by soil properties and soil apparent electrical conductivity (ECa). The Floating Soil Sensing System (FLoSSY) employing the EM38 electromagnetic induction sensor was used to record the ECa of the soil for each of the puddling intensities. The effects of plow pan compaction on water percolation losses and paddy yield were assessed. The results show that the variably puddled areas had significant differences in soil bulk density which was linked to the soil penetration resistance. Spatial comparison of ECa data sets showed that the ECa values increased systematically under increased puddling. Sufficient soil compaction could be identified when percolation losses were significantly the lowest and paddy yield was significantly the highest. It was concluded that a non-invasive ECa survey using electromagnetic induction based soil sensing allowed the detection of soil heterogeneity linked to soil compaction caused by puddling, which offers an interesting potential for precision puddling and land preparation in paddy rice fields.

Bog Turtle (Glyptemys muhlenbergii) Wetland Habitat: an Emphasis on Soil Properties

Bog turtles (Glyptemys muhlenbergii) access saturated wetland soils and move through them to thermoregulate, find cover, and hibernate. Variability in the physical properties of the soil that affects suitability for turtle use is little understood. We identified dominant soil series and measured soil organic carbon (SOC) content and particle size in the top 18 cm of surface soils from Southwestern Virginia wetlands frequently used by bog turtles and similar wetlands not known to be used. A static cone penetrometer was used to evaluate soil strength in specific locations where bog turtles were found and adjacent random areas. Soils were poorly developed alluvium with aquic soil regimes. Levels of SOC were greater in locations with more continuous surface saturation and averaged 10% in the wettest locations. Proportions of sand, silt, and clay in wetlands were consistent with loam and silt loam textures. Levels of SOC and dominant particle sizes were not different in similarly saturated areas of wetlands that were frequently used or not known to be used by bog turtles. However, some wetlands not known to be used completely lacked areas that were always saturated. Based on penetrometer data, bog turtle use was centered on low strength soils. The physical qualities of surface soils in bog turtle wetlands result from the depositional environment and hydrology. The soil information derived from this study may assist biologists to determine whether wetlands are used by bog turtles, and also establishes reference soil conditions for use during wetland restoration projects that occur within the geographic range of the bog turtle.

Using Remote Sensing and Soil Physical Properties for Predicting The Spatial Distribution of Cotton Lint Yield

This field crop research study addresses the potential of image based remote sensing to provide spatially and temporally distributed information on timely basis for site-specific cotton crop management. Universal applicability of site specific crop management is hampered by lack of timely distributed and economically feasible information on soils and crop conditions in the field and their interaction. The objectives of this study were to demonstrate (1) how site-specific lint yield and associated soil physical properties in a cotton (Gossypium hirsutum L.) production field are related to changes in NDVI across the growing season, and (2) when multispectral images should be collected to optimize the cost and efficiency of remote sensing as a tool for site-specific management of the cotton crop. Temporal multispectral images data acquired comprised 10 dates (1998) and 17 dates (1999) during growing seasons, respectively with analysis focused on 24 areas of interest (AOI) (each 2 x 8 m) located in two transects on a 162-ha farm field. Along each transect, soil textural classification ranged from sandy loam to silt loam. At an early growth stage [~300-600 degree days (DDs) after emergence], low NDVI and plant density were associated with soils having low saturated hydraulic conductivity (ks) and characterized as drainage ways. Among the AOI’s, maximal NDVI was reached at approximately 1565 DD in 1998 and 1350 DD in 1999. A strong range of Pearson correlation (r2=0.65 – 0.83) between lint yield and NDVI during flowering stage (~800-1500 DDs) supports the utility of NDVI maps for site-specific application. However, values for NDVI did not correlate well with lint yields beyond 1500 DDs [fruit (boll) opening stage] and decreased sharply on sites with sandy soil texture. Visual separation of seasonal trends in the NDVI vs. DD relationship was also related to sandy soil vs. silt loam soil texture and seasonal rainfall difference between years. Based on the statistical relationship between NDVI vs. DD it was concluded that acquisition of a single imagery during peak bloom period would be sufficient for predicting the spatial distribution of lint yield and will also be economically feasible. Results of this study indicate that spatial variability in soil physical properties induced variability in crop growth and yield. Similar methodology could be adopted for site-specific management of other crops

RESPONSE OF CORN (ZEA MAYS L.) PLANT TO VARIABLE WATER SUPPLY AT DIFFERENT GROWTH STAGES

Afield experiment was conducted during two autumn seasons, on silt loam soil texture. The aim was to study the effect of different levels of irrigation during growth stages: Normal irrigation(control) (S1), reducing water amount (eliminating one irrigation) during different plant growth stages: Vegetative (S2), flowering (S3), maturity (S4) , vegetative + flowering (S5) , flowering + maturity (S6) , vegetative + maturity (S7) , and during all growth stages (S8), of three varieties which were: Yugoslavian hybrid, Ipa hybrid 2052, and synthetic Ipa5012, on water consumptive use and grain yield, and using drought susceptibility Index (S) as a criterion index to measure the ability of different Varity to drought tolerant.. Treatments were arranged as factorial experiments with three replications using Randomized Complete Block Design (RCBD).. Amount of water for

Effectiveness of the GAEC cross-compliance standard Ploughing in good soil moisture conditions in soil structure protection

Researches have been carried out within the framework on the EFFICOND Project, focused at evaluating the effectiveness of the standards of Good Agricultural and Environmental Conditions (GAECs) established for Cross Compliance implementation under EC Regulation 1782/2003. In particular the standard 3.1b deals with soil structure protection through appropriate machinery use, with particular reference to ploughing in good soil moisture conditions. The study deals with the evaluation of soil structure after tillage in tilth and no-tilth conditions at soil moisture contents other than the optimum water content for tillage. The Mean Weight Diameter (MWD) of water stable aggregates was used as an indicator of tillage effectiveness. The study was carried out in the period 2008-2009 at six experimental farms belonging to Research Centres and Units of the Italian Agricultural Research Council (CRA) with different pedo-climatic and cropping conditions. Farm management and data collection in the different sites were carried out by the local CRA researchers and technicians. The comparison of MWD values in tilth and no tilth theses showed statistically significant differences in most cases, depending on topsoil texture. On clay, clay loam, silty clay, and silty clay loam topsoils a general and significant increase of MWD values under no tilth conditions were observed. No significant differences were observed in silt loam and sandy loam textures, probably due to the weak soil structure of the topsoils. Moreover, ploughing in good soil moisture condition determined higher crop production and less weed development than ploughing in high soil moisture conditions.

Soybean Response to Fluid Fertilizers Placed Near the Seed at Planting

As soybean [Glycine max (L.) Merr.] producers strive to improve profitability, placement of fertilizer either in contact with or near the seed should be given serious consideration. This study was conducted for the purpose of evaluating the impact of three fluid fertilizers applied at two rates near the seed at planting on soybean emergence, early growth, P uptake, and yield. All combinations of three factors (fertilizer grade, rate of application, and placement) were combined in a complete factorial in fields of cooperating soybean producers. The use of 10–15–0 (N–P–K) at 56 L ha−1 produced substantial reductions in emergence at sites where the soil had a silt loam texture. High rates of 4–4.4–8.3 and 3–8–15 fertilizer applied in contact with the seed also reduced emergence. When compared with the control, fertilizer placed near the seed increased whole plant weight, P concentration in the plant, and P uptake. Even though some treatments produced a substantial reduction in emergence, there was no significant negative effect on yield. The soybean crop growing on soils with very high levels of soil test P and K was apparently able to compensate for the reduced emergence. The data from this study lead to the conclusion that placement of fertilizer near the seed at planting should not be a suggested management practice.

Watershed scale temporal stability of soil water content

The recognition of temporally stable locations with respect to soil water content is of importance for soil water management decisions, especially in sloping land of watersheds. Neutron probe soil water content (0 to 0.8 m), evaluated at 20 dates during a year in the Loess Plateau of China, in a 20 ha watershed dominated by Ust-Sandiic Entisols and Aeolian sandy soils, were used to define their temporal stability through two indices: the standard deviation of relative difference ( SDRD) and the mean absolute bias error ( MABE). Specific concerns were (a) the relationship of temporal stability with soil depth, (b) the effects of soil texture and land use on temporal stability, and (c) the spatial pattern of the temporal stability. Results showed that temporal stability of soil water content at 0.2 m was significantly weaker than those at the soil depths of 0.6 and 0.8 m. Soil texture can significantly ( P < 0.05) affect the stability of soil water content except for the existence of an insignificant difference between sandy loam and silt loam textures, while temporal stability of areas covered by bunge needlegrass land was not significantly different from those covered by korshinsk peashrub. Geostatistical analysis showed that the temporal stability was spatially variable in an organized way as inferred by the degree of spatial dependence index. With increasing soil depth, the range of both temporal stability indices showed an increasing trend, being 65.8–120.5 m for SDRD and 148.8–214.1 m for MABE, respectively. This study provides a valuable support for soil water content measurements for soil water management and hydrological applications on sloping land areas.

EVALUATION OF THE POTENTIAL FOR PROTEACEAE PRODUCTION IN NEW CALEDONIA

In 2003, while initiating an investigation into the potential of New Caledonia's native Proteaceae flora for ornamental purposes, we introduced 17 commercial taxa of South African and Australian Proteaceae as cut flowers and foliage in order to diversify the local floriculture industry. These taxa included Leucadendron 'Brook's Red', 'Inca Gold', 'Safari Sunset', 'Wilson's Wonder' and 'Long Tom'; Leucospermum 'Caroline', 'High Gold', 'Purple Gem', 'Scarlet Ribbon' and 'Sunrise'; Protea cynaroides and P. cynaroides 'Australis', Protea laurifolia 'Rose Mink', Protea neriifolia 'Silvertips' and Protea 'Pink Ice'; Serruria florida and Telopea 'Dawn Fire'. An experimental site with supposed adequate pedoclimatic conditions was identified in Northern New Caledonia. Soil analysis showed a silt loam texture with pH 5.6 and a very low level of 7 ppm for plant-available phosphorus. Average temperatures recorded throughout the trial were found to be the coolest (17-18°C) during the months of July and August, with the hottest (25-27°C) months being January and February. Preliminary results indicated that Telopea 'Dawn Fire', Serruria florida, Leucospermum 'Purple Gem' and L. 'Sunrise' were clearly not adapted to the growing conditions of the experimental site. In terms of yield, the Leucospermum cultivars, i.e. 'Scarlet Ribbon', 'Caroline' and 'High Gold' yielded the best results, whilst the two top performing Leucadendron cultivars were 'Inca Gold' and 'Safari Sunset'. Amongst the Protea species, P. neriifolia 'Silvertips' and P. cynaroides showed exceptional production potential.

Evaluation of distillery effluent application effect on physico-chemical properties and exchangeable sodium content of sodic soils

Effect of distillery effluent (DE) application on electrical conductivity (EC), pH, organic carbon (OC), exchangeable Na, Ca, Mg, K content and exchangeable sodium percentage (ESP) of sodic soils of sandy loam (Hyperthermic family of Typic Haplaquept), silt loam (Hyperthermic family of Typic Haplaquept) and clay loam (Hyperthermic family of Typic Udic Ustochrept) textures was evaluated in a laboratory experiment. Six amendments, encompassing distilled water, DE solutions of four concentrations viz. 10%, 20%, 30% and 40%, and gypsum equivalent to 100% gypsum requirement (GR) were used to reclaim soils of 20, 40, 60 and 80 ESP class. Application of DE reduced pH and exchangeable Na content and increased OC, exchangeable Ca, Mg and K content of the soils appreciably but EC marginally. Magnitude of reduction in ESP was dependent on concentration of DE solution and the highest reduction in ESP of soil was observed with the application of 40% solution of DE. Extent of reduction in ESP with application of same concentration of DE was also found to be dependent on clay content of soil. It was relatively less in clay loam soil as compared to sandy loam soil. Results of this study thus indicated that distillery effluent could effectively be used in amending sodic soils of varying textures and ESP for improving their physico-chemical properties and reducing exchangeable sodium content.

Crescimento e desenvolvimento do amaranto (amaranthus spp.) sob estresse salino e cobertura morta

Investigar cultivares tolerantes à salinidade da água de irrigação e do solo é uma necessidade nas áreas agrícolas abastecidas por água de qualidade insatisfatória. O objetivo do presente trabalho foi avaliar a influência da salinidade da água de irrigação e da cobertura morta do solo no desenvolvimento vegetativo do amaranto (Amaranthus spp.) cultivado em casa de vegetação. O experimento foi realizado entre março e maio de 2006, utilizando-se colunas de PVC com 30 kg de um solo de textura franco-siltosa. Adotou-se o delineamento inteiramente casualizado, com quatro repetições e oito tratamentos, sendo testado o uso ou não de cobertura morta e quatro níveis de salinidade na água de irrigação (0,147; 1,5; 3,0; e 4,5 dS m-1, a 25 °C). A cobertura morta antecipou o início da floração e aumentou a área foliar, a altura de planta, o diâmetro de caule e a produção de biomassa. O aumento na concentração salina não ocasionou redução nos teores de Ca e Mg, no tecido foliar. O aumento na concentração de sais na água de irrigação retardou a floração do amaranto, porém a espécie apresentou tolerância até o limite de 4,5 dS m-1, pois a produção de biomassa seca não foi afetada por esse aumento de salinidade.

Management of Lignite Fly Ash for Improving Soil Fertility and Crop Productivity

Lignite fly ash (LFA), being alkaline and endowed with excellent pozzolanic properties, a silt loam texture, and plant nutrients, has the potential to improve soil quality and productivity. Long-term field trials with groundnut, maize, and sun hemp were carried out to study the effect of LFA on growth and yield. Before crop I was sown, LFA was applied at various doses with and without press mud (an organic waste from the sugar industry, used as an amendment and source of nutrients). LFA with and without press mud was also applied before crops III and V were cultivated. Chemical fertilizer, along with gypsum, humic acid, and biofertilizer, was applied in all treatments, including the control. With one-time and repeat applications of LFA (with and without press mud), yield increased significantly (7.0-89.0%) in relation to the control crop. The press mud enhanced the yield (3.0-15.0%) with different LFA applications. The highest yield LFA dose was 200 t/ha for one-time and repeat applications, the maximum yield being with crop III (combination treatment). One-time and repeat application of LFA (alone and in combination with press mud) improved soil quality and the nutrient content of the produce. The highest dose of LFA (200 t/ha) with and without press mud showed the best residual effects (eco-friendly increases in the yield of succeeding crops). Some increase in trace- and heavy-metal contents and in the level of gamma-emitters in soil and crop produce, but well within permissible limits, was observed. Thus, LFA can be used on a large scale to boost soil fertility and productivity with no adverse effects on the soil or crops, which may solve the problem of bulk disposal of fly ash in an eco-friendly manner.

Early growth of hybrid aspen ( Populus × wettsteinii Hämet-Ahti) plantations on former agricultural lands in Estonia

Since 1999 hybrid aspen plantations have been established on former agricultural lands for production of pulpwood as a practice of short rotation plantation forestry in boreal Estonia. During the early growth period the dimensions of the trees have been highly variable. The main objective of the study was to explain the high variability in early growth speed of hybrid aspens by differences in physicochemical soil properties. A network of 51 experimental plots was created to study growth–soil interactions in 5-year-old plantations at various sites. The mean height of the trees was 2.7 ± 0.02 m, mean diameter at breast height was 1.9 ± 0.02 cm and mean current year height increment was 0.7 ± 0.01 m. Mean foliar concentrations of main mineral nutrients were estimated as follows: N 2.15%, P 0.20%, K 0.76%. Trees have grown faster on Arenosols, Albeluvisols and Planosols. Growth intensity has been poor on Luvisols, Cambisols and Gleysols. While evaluating site quality based on soil texture and drainage condition, we found, that in general, hydromorphic soils have been less favourable. At a young age, hybrid aspen grew faster on automorphic soils with loamy sand and on semihydromorphic soils with loam, silt loam and sandy loam texture. The study of height increment in 5-year-old hybrid aspen plantations allows us to predict that the modest growth rate during the first years after planting could improve at an older age. Preliminary impact hierarchy of site properties, especially soil moisture condition, may change during later growth stages, when light competition in the canopy layer of the stand and nutrient competition between the tree roots in the soil will become more decisive for the growth performance of the trees.

Mapping the spatial variation of soil water content at the field scale with different ground penetrating radar techniques

Summary Two ground penetrating radar (GPR) techniques were used to estimate the shallow soil water content at the field scale. The first technique is based on the ground wave velocity measured with a bistatic impulse radar connected to 450 MHz ground-coupled antennas. The second technique is based on inverse modeling of an off-ground monostatic TEM horn antenna in the 0.8–1.6 GHz frequency range. Data were collected on a 8 by 9 m partially irrigated intensive research plot and along four 148.5 m transects. Time domain reflectometry, capacitance sensors, and volumetric soil samples were used as reference measurements. The aim of the study was to test the applicability of the ground wave method and the off-ground inverse modeling approach at the field scale for a soil with a silt loam texture. The results for the ground wave technique were difficult to interpret due to the strong attenuation of the GPR signal, which is related to the silt loam texture at the test site. The root mean square error of the ground wave technique was 0.076 m 3 m −3 when compared to the TDR measurements and 0.102 m 3 m −3 when compared with the volumetric soil samples. The off-ground monostatic GPR measured less within-field soil water content variability than the reference measurements, resulting in a root mean square error of 0.053 m 3 m −3 when compared with the TDR measurements and an error of 0.051 m 3 m −3 when compared with the volumetric soil samples. The variability between the two GPR measurements was even larger with a RSME of 0.115 m 3 m −3 . In summary, both GPR methods did not provide adequate spatial information on soil water content variation at the field scale. The main reason for the deviating results of the ground wave method was the poor data quality due to high silt and clay content at the test site. Additional reasons were shallow reflections and the dry upper soil layer that cannot be detected by the ground wave method. In the case of off-ground GPR, the high sensitivity to the dry surface layer is the most likely reason for the observed deviations. The off-ground GPR results might be improved by using a different antenna that allows data acquisition in a lower frequency range.