Variability Of Soil Characteristics Research Articles

Biomass production, nutrient cycling, and carbon fixation by Salicornia brachiata Roxb.: A promising halophyte for coastal saline soil rehabilitation

ABSTRACTIn order to increase our understanding of the interaction of soil-halophyte (Salicornia brachiata) relations and phytoremediation, we investigated the aboveground biomass, carbon fixation, and nutrient composition (N, P, K, Na, Ca, and Mg) of S. brachiata using six sampling sites with varying characteristics over one growing season in intertidal marshes. Simultaneously, soil characteristics and nutrient concentrations were also estimated. There was a significant variation in soil characteristics and nutrient contents spatially (except pH) as well as temporally. Nutrient contents in aboveground biomass of S. brachiata were also significantly differed spatially (except C and Cl) as well as temporally. Aboveground biomass of S. brachiata ranged from 2.51 to 6.07 t/ha at maturity and it was positively correlated with soil electrical conductivity and available Na, whereas negatively with soil pH. The K/Na ratio in plant was below one, showing tolerance to salinity. The aboveground C fixation values ranged from 0.77 to 1.93 C t/ha at all six sampling sites. This study provides new understandings into nutrient cycling—C fixation potential of highly salt-tolerant halophyte S. brachiata growing on intertidal soils of India. S. brachiata have a potential for amelioration of the salinity due to higher Na bioaccumulation factor.

How to Use In-situ Soils as Building Materials

Using in-situ soils for building constructions is attractive in the sustainable development because these materials have low embodied energy and present an interesting hygro-thermal behavior. Several researches have been recently carried out to study soil materials. However, the variability of soil characteristics on each construction site makes that the use of an unique construction technique (soil concrete, rammed earth, adobe, …) becomes difficult to satisfy several exigencies of the modern regulations (mechanical, thermal performances, durability and earthquake resistance), and the economic criterion.This paper introduces firstly a strategy which can facilitate the use of in-situ soils for building constructions. Relevant techniques corresponding to several in-situ soil types are proposed. Then, the application of the proposed approach is showed with a case study on a building project using a soil concrete. Several aspects are investigated: material optimization, architectural design, structural-thermal performances and life cycle analysis.

Phytotoxicity of natural soils using physiological and biochemical endpoints reveals confounding factors: can a weight of evidence tackle uncertainty?

Standard assays for phytotoxicity provide a reductionist view on the performance of plants under toxic stress. To address two of the most prominent issues in plant toxicity studies, our aims were (1) to assess how well physiological and biochemical parameters complement standard toxicological endpoints when testing natural soils and (2) to assess the suitability of three commonly used control soils as comparative references. We compared the performance of Zea mays and Helianthus annuus in three control soils (artificial Organisation for Economic Co-operation and Development (OECD) soil, standard LUFA 2.2 soil, and turf-perlite) against three natural soils representing a gradient of contamination (from a deactivated uranium mine). Standard endpoints (emergence and biomass) were estimated, along with pigment content, photosynthetic parameters, cellular injury, and proline content. The toxicological profile of natural soils was highly dependent on the control soil used as reference; also, plant physiological performance was influenced by the soils’ properties. We discuss the need to interpret and combine multiple lines of evidence as a way to increase the degree of confidence one classifies soils based on their ecotoxicity, and this is where the integration of physiological and biochemical parameters bring added value. When facing large variability in soil characteristics, it is best to collect and integrate as much information possible to strengthen conclusions about phytotoxicity of natural soils. Obviously, this refutes reductionist views and places the final conclusion in the hands of expert judgment.

Effects of soil conditions on the diversity of tropical forests across a successional gradient

Soil features are an important factor influencing plant growth and distribution in different parts of the tropics. We hypothesized that in forests recovering from a disturbance, the spatial and temporal variation of soil proprieties could determine differences in forest structure and composition. We addressed this question by comparatively assessing the soil traits and forest structure and diversity that occur in two contrasting soils in second growth tropical forests of southern Brazil: Cambisols (well-drained and nutrient-poor soil) and Gleisols (periodically flooded and with greater soil Al toxicity). Three replicates of four combinations of four forest ages (9–11, 15–20, 40–55, and >100years since abandonment) and two soil types (Cambisol and Gleisol) were compared, thus encompassing 21 plots that covered 2.1ha. A total of 3355 individuals of 151 tree species were sampled in all plots. Soil characteristics changed along the succession, with Al toxicity increasing as the forests aged. Cambisols and Gleisols differed in their nutritional and structural characteristics. Forests growing in both soil types exhibited higher species density, individual density and basal area along the successional gradient, but diversity (and evenness) was higher in forests growing in Gleisol soils. Moreover, soil characteristics (sand:clay, C:N, and Al and P concentrations) and forest age determined the differences in community assemblies among soils. Considering that soil characteristics are spatially and temporally variable in the tropics and that these variations are poorly measured in successional studies, we argue that small-scale variations in soil characteristics can potentially be a powerful factor influencing the successional trajectories of second growth tropical forests in tropical regions.

Community-wide spatial and temporal discordances of seed-seedling shadows in a tropical rainforest.

Several factors decrease plant survival throughout their lifecycles. Among them, seed dispersal limitation may play a major role by resulting in highly aggregated (contagious) seed and seedling distributions entailing increased mortality. The arrival of seeds, furthermore, may not match suitable environments for seed survival and, consequently, for seedling establishment. In this study, we investigated spatio-temporal patterns of seed and seedling distribution in contrasting microhabitats (bamboo and non-bamboo stands) from the Brazilian Atlantic Forest. Spatial distribution patterns, spatial concordance between seed rain and seedling recruitment between subsequent years in two fruiting seasons (2004–2005 and 2007–2009), and the relation between seeds and seedlings with environmental factors were examined within a spatially-explicit framework. Density and species richness of both seeds and seedlings were randomly distributed in non-bamboo stands, but showed significant clustering in bamboo stands. Seed and seedling distributions showed across-year inconsistency, suggesting a marked spatial decoupling of the seed and seedling stages. Generalized linear mixed effects models indicated that only seed density and seed species richness differed between stand types while accounting for variation in soil characteristics. Our analyses provide evidence of marked recruitment limitation as a result of the interplay between biotic and abiotic factors. Because bamboo stands promote heterogeneity in the forest, they are important components of the landscape. However, at high densities, bamboos may limit recruitment for the plant community by imposing marked discordances of seed arrival and early seedling recruitment.

Phytodiversity and Seasonal Variations in the Soil Characteristics of Shrublands of Dachigam National Park, Jammu and Kashmir, India

The panorama of Indian biological resources is much wider making it one of the mega biodiverse (hotspot) centres of the world. Biodiversity is an element of natural resource base which is the main component of sustainability in both production and utilization of the ecosystem services. The present study was carried out on the Shrublands of the Dachigam National Park of Western Himalaya, Kashmir, in the year 2010. The vegetation was analysed for floristic composition, phytosociological aspects and seasonal variations in major soil characteristics of the study area. A seasonal variation in soil parameters was observed with temperature varying from 2 to 21°C, moisture 7.28–32.34%, pH 5.1–7.44, electrical conductivity 150–520 μS/cm, organic carbon 3.27–5.98%, organic matter 5.63–10.30%, total nitrogen 2500–4600 ppm, total phosphorus 757–1226 ppm and total potassium 15, 500-18, 550 ppm. A total of 35 shrub species were recorded belonging to 13 families and 19 generas with maximum richness and density in protected site and least at village site.

Dynamic changes in soil and vegetation during varying ecological-recovery conditions of abandoned mines in Beijing

Vegetation restoration in abandoned mines is very difficult and time consuming because of the harshness of the ecosystem, i.e., the extremely high and steep slopes. To accelerate the process of vegetation recovery in abandoned mines, understanding the rules of vegetation succession and the variation in soil characteristics during this process is very important. In the Zhoukoudian vegetation restoration experiment demonstration area (a 12ha area located in Fangshan District, Beijing, China), engineering measures, such as biological greening bags, eco-stick slope protection, container seedling planting and vegetative-carpet greening technologies, were applied to accelerate the process of vegetation recovery. In this study, 149 human-restored and spontaneously recovering slopes under three substrates were sampled to investigate the dynamic changes in soil and vegetation in different stages of succession by means of space-for-time substitution. WinTWINS was used to classify the samples, which experienced different recovery periods, into 6 plant community types. According to the results, the species richness index, Simpson’s predominance index, the Shannon–Wiener index and the soil fertility of the communities dominated by young trees (V, VI) were higher than those of the communities dominated by grasses (I, II) or shrubs (III, IV); thus, plant communities V and VI are considered optimal representations of severely damaged surface-mine ecosystems. Our results suggest that native species should be planted to accelerate the succession process by implementing the best engineering measures for different substrate types during the initial restoration.

Ocorrência e atividade de fungos micorrízicos arbusculares em plantios de eucalipto (eucalyptus sp.) no litoral norte da Bahia, Brasil

Nas últimas décadas, tecnologias alternativas vêm sendo estudadas visando tornar o cultivo do eucalipto (Eucalyptus sp.) mais econômico e sustentável. Entre estas, as associações micorrízicas merecem destaque devido aos inúmeros benefícios que proporcionam às plantas hospedeiras. Este trabalho teve como objetivo avaliar a ocorrência e atividade de fungos micorrízicos arbusculares em plantios de eucalipto utilizados comercialmente pela Copener Florestal Ltda. no litoral norte da Bahia. Foi observada grande variabilidade na densidade de esporos (36,2 a 203,2 esporos em 50 g de solo), colonização micorrízica (10,6 a 57,8%) e nos teores de glomalina facilmente extraível e total (0,34 a 1,92 mg g de solo-1 e 0,48 a 3,88 mg g de solo-1) nos plantios de eucalipto. Os resultados neste estudo permitiram concluir que, embora os clones apresentem suscetibilidade à micorrização em condições de campo, variações nas características do solo afetam aspectos ecológicos dos fungos micorrízicos arbusculares nos plantios de eucalipto da Copener Florestal Ltda. no litoral norte da Bahia.

Spatial variability of some soil properties: a case study of the Lower Seyhan river basin inTurkey

The aim of this study was to evaluate the performance of a closed drainage system in one area of the Lower Seyhan river basin in Cukurova, Turkey by measuring spatial variations in soil characteristics. Seven parallel transects which had a 150 m length were selected at 5 m intervals within the study area, and 104 soil samples were collected and analysed for soil pH, electrical conductivity (EC), exchangeable sodium (Na) content and exchangeable sodium percentages (ESP). Results were subjected to inverse distance weighting (IDW) interpolation. EC, pH and ESP estimates obtained from IDW interpolation were compatible with the results of soil analysis. Cross validation was performed to determine the accuracy of the interpolation technique. Interpolation of EC values showed a high mean error in 120–150 cm depth (9.010%), which was attributed to poor drainage conditions. Minimum sample number, maximum sample number, maximum radius and power were found to have an influence on the accuracy of IDW interpolation. ESP, exchangeable Na, EC values were generally low for shallow soil horizons, with values increasing with increases in depth. Data sets were analyzed with two-way ANOVA (the factors were six pipe regions (1–6) and five soil depths (30, 60, 90, 120, 150 cm)) and means compared with Duncan’s multiple range test. It was found that the efficiency of drainage pipe, in regions 1, 2, 3 and 4 can diminish rather than the other pipe regions.

Meta‐modeling soil organic carbon sequestration potential and its application at regional scale

Upscaling the results from process-based soil-plant models to assess regional soil organic carbon (SOC) change and sequestration potential is a great challenge due to the lack of detailed spatial information, particularly soil properties. Meta-modeling can be used to simplify and summarize process-based models and significantly reduce the demand for input data and thus could be easily applied on regional scales. We used the pre-validated Agricultural Production Systems sIMulator (APSIM) to simulate the impact of climate, soil, and management on SOC at 613 reference sites across Australia's cereal-growing regions under a continuous wheat system. We then developed a simple meta-model to link the APSIM-modeled SOC change to primary drivers, i.e., the amount of recalcitrant SOC, plant available water capacity of soil, soil pH, and solar radiation, temperature, and rainfall in the growing season. Based on high-resolution soil texture data and 8165 climate data points across the study area, we used the meta-model to assess SOC sequestration potential and the uncertainty associated with the variability of soil characteristics. The meta-model explained 74% of the variation of final SOC content as simulated by APSIM. Applying the meta-model to Australia's cereal-growing regions reveals regional patterns in SOC, with higher SOC stock in cool, wet regions. Overall, the potential SOC stock ranged from 21.14 to 152.71 Mg/ha with a mean of 52.18 Mg/ha. Variation of soil properties induced uncertainty ranging from 12% to 117% with higher uncertainty in warm, wet regions. In general, soils in Australia's cereal-growing regions under continuous wheat production were simulated as a sink of atmospheric carbon dioxide with a mean sequestration potential of 8.17 Mg/ha.

Surface micro‐topography causes hot spots of biogeochemical activity in wetland systems: A virtual modeling experiment

Wetlands provide important ecohydrological services by regulating fluxes of nutrients and pollutants to receiving waters, which can in turn mitigate adverse effects on water quality. Turnover of redox‐sensitive solutes in wetlands has been shown to take place in distinct spatial and temporal patterns, commonly referred to as hot spots and hot moments. Despite the importance of such patterns for solute fluxes the mechanistic understanding of their formation is still weak and their existence is often explained by variations in soil properties and diffusive transport only. Here we show that surface micro‐topography in wetlands can cause the formation of biogeochemical hot spots solely by the advective redistribution of infiltrating water as a result of complex subsurface flow patterns. Surface and subsurface flows are simulated for an idealized section of a riparian wetland using a fully integrated numerical code for coupled surface‐subsurface systems. Biogeochemical processes and transport along advective subsurface flow paths are simulated kinetically using the biogeochemical code PHREEQC. Distinct patterns of biogeochemical activity (expressed as reaction rates) develop in response to micro‐topography induced subsurface flow patterns. Simulated vertical pore water profiles for various redox‐sensitive species resemble profiles observed in the field. This mechanistic explanation of hot spot formation complements the more static explanations that relate hot spots solely to spatial variability in soil characteristics and can account for spatial as well as temporal variability of biogeochemical activity, which is needed to assess future changes in the biogeochemical turnover of wetland systems.

Geographical and interspecific variation and the nutrient‐enrichment hypothesis as an adaptive advantage of myrmecochory

In myrmecochory, the relocation of diaspores to ant nests may lead to the enhancement of plant fitness because ant nests and their middens are often richer in essential nutrients than surrounding areas. This idea is the basis of the nutrient‐enrichment hypothesis (NEH), which suggests that nutrient enrichment may be a major selective influence in the evolution of myrmecochory. However, there is little evidence regarding whether the greater plant performance and fitness enhancement in ant nests is due to nutrient enrichment or other benefits of directed dispersal. Here, we present the results of a large‐scale seed‐sowing experiment that tests the NEH in the ant‐dispersed perennial herb Helleborus foetidus, exploring geographical and inter‐ant taxa variation. Experiments were conducted in three well‐separated regions of the Iberian Peninsula, targeting the nests of major and minor local ant dispersers (nine ant species in total) and the soil beneath maternal plants as seed destinations. Seedling emergence, survival and early establishment rates, as well as variation in soil characteristics, were obtained for each seed destination at each region. Our results do not fully support the NEH in our study system. Instead, we found that the advantage of ant nest soil for establishment in H. foetidus was conditional. Differences in soil fertility and concomitant differences in seedling establishment between ant nests and beneath the canopy of maternal plants were observed in some regions and for some ant species, but not in others. Thus, the conditional outcomes arise from inconsistencies among regions, between stages of seedling regeneration and among ant species in the advantages of being dispersed to nests. Because variation in the guilds of ant dispersers of myrmecochore plants across their ranges is common, this study illustrates the need to consider geographic and inter‐ant taxa variation for a complete evaluation of the NEH.

Assessing spatial variability in soil characteristics with geographically weighted principal components analysis

Dimensionality reduction methods such as principal components analysis (PCA) provide a means of identifying trends in soil characteristics which may be represented by a wide range of variables. However, these characteristics may be highly spatially variable and so the results from PCA represent, in some sense, an “average” of locally distinct characteristics. One approach to account for these local differences is to introduce a geographical weighting scheme into the PCA process. In this paper, such an approach is assessed in the exploration of soil characteristics in the state of Pennsylvania, USA. Data from 878 georeferenced soil profiles which include different soil parameters (n = 12) were extracted from the National Soil Survey Center database. Where data are parts of compositions (e.g., percentages of sand, silt, and clay), analysis using raw data is not appropriate and such data were transformed using log ratios (specifically, balances). Single variables (i.e., those which are not parts of compositions) were logged. The first two principal components explain over 50% of the variance. The mapped values suggest marked spatial variation in soil characteristics, but it is not possible to assess which of these variables explain most variation in particular regions from the simple maps of raw variables. Geographically weighted PCA (GWPCA) provides additional information which is obscured by PCA, and it also provides a set of component scores and loadings at all data locations. The soil variable with the largest loading at most locations of Pennsylvania is the logged base saturation (BSln), and this supports the findings of the conventional PCA analysis. While BSln loads most highly in most of the eastern third, the middle and the south west of the state, the northwest is less spatially consistent in terms of the variables which explain most variation. For GWPC 1, the variable with the second largest loading at most locations (i.e., primarily the south and west) is CEC.B1 (the log ratio of Ca, Mg, and Na to K and EXACID), while CEC.B2 (the log ratio of Ca and Mg to Na), pHln (logged pH) and BSln dominate in other areas. The GWPCA results suggest that there is marked spatial variation in multivariate soil characteristics across Pennsylvania state and that results from standard PCA obscure this considerable variation.

Evaluating Local Crop Residue Biomass Supply: Economic and Environmental Impacts

The increasing interest in energy production from biomass requires a better understanding of potential local production and environmental impacts. This information is needed by local producers, biomass industry, and other stakeholders, and for larger scale analyses. This study models biomass production decisions at the field level using a case example of a biomass gasification facility constructed at the University of Minnesota—Morris (UMM). This institutional-scale application has an anticipated feedstock demand of about 8,000 Mg year−1. The model includes spatial impacts due to sub-field variation in soil characteristics and transportation costs. Results show that the amount of biomass producers could profitably supply within a 32.2-km radius of UMM increases as plant-gate biomass price increases from $59 to $84 Mg−1, with 588,000 Mg annual biomass supply at $84 Mg−1. Results also show that the most profitable tillage and crop rotation practices shift in response to increasing biomass price with producers shifting from a corn-soybean rotation toward continuous corn. While biomass harvest is conducive to increased soil erosion rates and reduced soil organic carbon levels, changes in crop production practices are shown to at least partially offset these impacts. Transportation costs tend to concentrate and intensify biomass production near the biomass facility, which also tends to concentrate environmental impacts near the facility.

Soil water regimes of reclaimed upland slopes in the oil sands region of Alberta

Leatherdale, J., Chanasyk, D. S. and Quideau, S. 2012. Soil water regimes of reclaimed upland slopes in the oil sands region of Alberta. Can. J. Soil Sci. 92: 117–129. Large oil sands deposits in the Athabasca oil sands region of Alberta, Canada, are recovered through surface mining, creating a large-scale disturbance. Reclamation requires reconstruction of soil profiles to return the land to equivalent land capability and support the required end land use. Soil water regimes must be understood to allow for planting of appropriate vegetation species. This study quantified soil water regimes on reclaimed upland slopes of various reclamation prescriptions and determined whether soil water was affected by slope position. Slope position did not have a consistent effect on soil water. Spatial variability in soil characteristics and vegetation distribution likely had a greater influence on soil water than did slope position. The upper slope soil profiles had highly dynamic water regimes and a greater response to precipitation events than the lower soil profiles. Differences in water-holding capacity among sites were attributed to differences in clay, sand and organic matter content. Overwinter soil water recharge varied dramatically by site. Capillary barriers resulting from the textural discontinuities created by the reclamation prescriptions enhanced soil water retention within the profiles in at least two sites, and hence are desirable in reclamation scenarios, especially where reclamation material is coarse textured.

Forest soils adjacent to urban interstates: Soil physical and chemical properties, heavy metals, disturbance legacies, and relationships with woody vegetation

While urban ecology is an expanding field of study, some natural areas within the urban environment remain under-examined. These include naturally regenerating forest communities adjacent to urban interstates. In addition, the status of interstate soils and their relationships with the community composition of forested interstate verges has received little ecological study. The purpose of this study was to examine variation in soil conditions along forested interstate corridors in Louisville, KY and to explore the extent to which soil characteristics (e.g., bulk density, pH) and heavy metals (e.g., Pb, Zn) vary with respect to three factors: interstate (e.g., traffic density), surrounding urban environment (e.g., industrial land use), and interstate construction legacies. Additionally, we explored the relationships between several edaphic factors and woody vegetation structure in these forested verges. We found that the degree and direction of the slope of land towards the interstate and the distance to the interstate pavement were strong determinants of soil characteristics and heavy metal concentrations, suggesting that the movement of de-icing salts, heavy metals, and other pollutants from the interstate was important in determining forest soil conditions along urban interstates. Since within our study area these highways did not extend into rural lands, variation in urban land uses and cover within 26 km of the city center was not large enough to explain variation in soil characteristics or heavy metals, except for a positive correlation between chromium and surrounding industrial land use. We did find that past physical soil disturbance caused by interstate construction (e.g., imported fill) left an important legacy on soil characteristics, heavy metal retention, and woody plant growth patterns in forests adjacent to urban interstates. The legacy of interstate construction on the current forest community structure (e.g., lower species richness) and the future forest (e.g., reduced tree regeneration) may further alter ecosystem productivity and ecosystem services provided by these forests and their soils.

Study on Spatial Variability of Soil Characteristics on Different Land Use Types Based on Land Parcel Scale - A Case Study in Kenli County

Soil characteristics spatial variability is one of the important attributes of soil, while land use is the most universal, the most direct and the most profound factor which affect soil quality. In this study, by the land statistics analysis of the soil characteristic in Kenli County, we study the spatial variability of soil characteristics on different land use types and the reasons for these variations produced. Research found that land use type has profound effect on soil characteristics in Kenli County. Different land parcel, different soil or terrain and different management measures can make it cause different variation structure.

Spatial Variations in Soil Chemistry and Organic Matter Content across aVochysia divergensInvasion Front in the Brazilian Pantanal

The Pantanal is a large and diverse wetland that spans three South American countries including parts of Brazil, Paraguay, and Bolivia. An invasive tree,Vochysia divergensPohl (commonly known as Cambara), has been expanding throughout the Pantanal for more than four decades forming monospecific stands. Given the rapid and extensive spread of Cambara, and the potential for woody plant invasion to alter soil organic matter and nutrient stocks, we hypothesized that Cambara invasion would significantly increase soil organic matter and nutrient content. To test this hypothesis we sampled the soil, litter, and vegetation of a monospecific Cambara stand, a grassland (campo) stand in the process of Cambara invasion (transitional), and a campo stand free of Cambara during the dry season in July and August of 2009 and 2010 when stands were free from seasonal flooding. Surface (0–10 cm) soil in sites dominated by Cambara had significantly higher soil organic matter (SOM), P, and cation content, and higher cation exchange capacity (CEC), but soil pH and K+concentration were less coincident with Cambara presence. The variation of soil characteristics was also significantly higher in the transitional site, indicating that the transition from a grassland‐ to a Cambara‐dominated system significantly increased the spatial variability of soil chemistry. These results indicate that Cambara invasion fundamentally alters the C and nutrient storage of Panatanal soils. Future research will investigate if these results are general for Cambara invasion and address mechanisms of how Cambara invasion affects the nutrient cycling and storage of Pantanal soils.

Variations in soil characteristics affecting the occurrence of Aphanomyces root rot of sugar beet – Risk evaluation and disease control

Damping off and chronic root rot of sugar beet caused by Aphanomyces cochlioides is a major constraint in cultivation of sugar beet, with occurrence of the disease in Sweden being concentrated to specific areas. This study examined soil factors that can be used for risk assessment of Aphanomyces root rot. Soils from 134 field plots were assessed over three years for Aphanomyces root rot potential in bioassays and analysed for easily measured soil factors such as soluble nutrients, pH and soil electrical conductivity (EC). Classification of the field plots into four groups with increasing disease severity index (DSI) according to the bioassay revealed that the group with the lowest DSI (<39) had an average soil calcium (Ca) content of 430 mg/100 g and a soil EC of 1.12 mS/cm, which were significantly higher than in the groups with DSI >40. From these results, we concluded that soil Ca concentration is an easily measured factor that can be used to identify soils with an increased risk of Aphanomyces root rot. We suggest that the Ca content should be above 250 mg Ca/100 g soil to avoid problems with Aphanomyces root rot in sugar beet. To gain a more thorough understanding of the geographical variation in Aphanomyces root rot and its connection to the geological origin of the soils, a number of other soil factors were analysed in the field plots, including clay mineralogy, CEC, and particle size distribution. Aphanomyces root rot was very rare in soils with a high proportion of smectite and vermiculite relative to illite and kaolin minerals, here predominantly calcareous soils developed on clay till in south-western Scania.

AN ECONOMIC ANALYSIS OF VARIABLE RATE TECHNOLOGY

Variable Rate Technology (VRT) offers an opportunity to improve production efficiency by allowing input applications to fluctuate in response to spatial variations in soil characteristics and nutrient levels. Society may also benefit from reduced negative externalities, such as surface and groundwater contamination, from input applications. Using a dynamic spatial model, this study examines how the interaction among variability, spatial autocorrelation, and mean level of soil fertility affects optimal sampling density and the economic gains from VRT. VRT was found to be profitable under selected conditions, and the optimal grid size will vary with these conditions. In the case where variability and mean fertility levels are significantly high associated with low spatial autocorrelation, VRT produces greater net returns than Uniform Rate Technology (URT), even with the smallest grid size to base the input application decisions. Results also demonstrate that optimal grid size increases with increased spatial autocorrelation.