Varying Soil Conditions Research Articles

Evaluating the seasonal and interannual variations in water balance in northern Wisconsin using a land surface model

We evaluated the performance of the Integrated BIosphere Simulator (IBIS) land surface model in the temperate forests of northern Wisconsin (46°N, 89°W) to determine whether model formulations, driven with daily historical precipitation, temperature, relative humidity, solar radiation, and wind speed data, were capable of simulating water flow and storage within a seasonally cold climate regime. We focused concurrently on understanding seasonal and interannual variations of both the water fluxes to the atmosphere and water partitioned into surface runoff and groundwater infiltration, with special attention to the transitions from cold‐dominated (snow, ice) to warm‐dominated (rain, liquid soil moisture) hydrology. Results showed when compared with a suite of field observations IBIS simulated water and energy cycling at daily to interannual timescales with reasonable accuracy. Because of errors associated with field observations, the accuracy with which we simulated each component of the water balance is not easily quantified. By investigating the complete land surface water balance, however, we increased the likelihood that all components were being captured. The modeled monthly energy balance, annual water balance, and drainage rates were generally within 5–15% of the observed values. Modeled and observed soil temperatures generally differed by less than 3°C and had r2 values that were greater than 0.9. Soil moisture values were within 5–20%, and freeze and thaw timing was within a few days of observations. Modeled snow dynamics captured the observed snow arrival and departure (accumulation on the surface) within a few days of observations, but overestimated the average maximum depth by 86%. Because model formulations were subjected to varying soil conditions and water phases, this evaluation exercise enhanced our understanding of northern Wisconsin's water balance and increased model credibility for applications in seasonally cold climates.

First USGS Urban Seismic Hazard Maps Predict the Effects of Soils

Urban seismic hazard maps are designed to reflect the expected ground shaking from earthquakes that affect a particular location. Thus they must incorporate the effects of local geology, including soils, which are not normally included in national or regional seismic hazard maps. The U.S. Geological Survey (USGS) has released its first set of urban seismic hazard maps for Memphis, Shelby County, Tennessee. State-of-the-art methods are used to incorporate soil effects in these maps. Both probabilistic and scenario (deterministic) maps have been produced. This article briefly summarizes the seismic hazard methodology and model used to produce the maps and the knowledge uncertainties incorporated in them. Memphis, Tennessee, is a location where damaging earthquakes are only moderately likely, but where the consequences of earthquakes, mainly in the New Madrid seismic zone, can be very high (Figure 1). This densely populated urban area is built on a 1-kilometer-thick sequence of sediments deposited in a structural trough known as the Mississippi embayment. Th is thick sequence of sediments significantly affects earthquake ground motions (Bodin et al. , 2001; Hashash and Park, 2001). These urban seismic hazard maps and their derivative products represent the collaborative efforts of the USGS and its partners. A USGS website (http://www.ceri.memphis.edu/usgs/) and Open-File Report 04-1294 (Cramer et al. , 2004) document how these seismic hazard maps were generated. The Memphis maps complement the USGS national seismic hazard maps (Frankel et al. , 2002), which currently do not include the effects of local geologic structure and variations in soil conditions. Seismic hazard maps can represent the ground-motion hazard from earthquake shaking that affects a particular location. The USGS national seismic hazard maps provide an overview of seismic ground-motion hazard across the United States and are currently for a uniform soil condition (Frankel et al. , 2002). The Memphis maps …

Cereal forage breeding for New Zealand agriculture

Cereal forages provide both arable and livestock farmers with high yields of high quality dry matter to use as either standing or conserved strategic forage supplements where deficits occur when animal feed requirements exceed pasture growth. Crop & Food Research has breeding programmes for both single and multigrazing forage oats and triticales, and both green-chop and whole-crop silage forage oats, triticales and barleys. It also has an associated cereal forage management research and tech-transfer programme to ensure cereal forages achieve their potential under New Zealand's variable soil and climatic conditions. This has led to the development of new cereal forage cultivars, an increased understanding of their dry matter and quality development, and management support packages including a cereal silage booklet and maturity predictor for whole-crop cereal silage

Effects of weather variables on sugar beet yield development ( Beta vulgaris L.)

There is much data on the impact of weather variables on the growth of sugar beet from studies conducted under controlled conditions or single field experiments, but these data are of only limited validity for other sites or larger areas. The aim of the present study was to quantify the influence of weather conditions on the growth of sugar beet for the further development of simulation models, based on data representative of sugar beet cultivation in Germany. For this purpose, 27 field trials were conducted in 2000–2001 in commercial fields with variable climatic and soil conditions. From the end of May until the end of the season, beets were harvested manually every 4 weeks, the dry matter yield of leaves and taproot was determined and their growth rates were calculated. Temperature, solar radiation, rainfall and humidity were recorded daily for each site and the potential evapotranspiration and climatic water balance were estimated. The soil water content to a depth of 0.9 m was determined at every harvest date. Several functions were developed to describe the growth of sugar beet as affected by the given meteorological variables. From sowing to the end of June, the dry matter accumulation of both leaves and taproot was strongly enhanced by increasing temperature and during this period leaf dry matter increased linearly with thermal time. After reaching 700 °C d, the taproot dry matter accumulated exponentially with thermal time. The optimum mean daily air temperature for taproot growth was approximately 18 °C. Higher temperature occurring in July and August decreased final taproot yield, but by the end of the season, growth was independent of temperature. High solar radiation advanced growth during the first 65 days after sowing and again in October. Neither the water input by rainfall and irrigation nor the climatic water balance adequately described the growth of the leaves or taproot, but it was shown that the increase in taproot dry matter during July and August depended on the amount of available water in the soil. The maximum sugar yield that can theoretically be achieved in Germany and comparable agroclimatic regions was calculated as 24 t ha −1. The present data reliable for a large agroclimatic region in Europe are of significant value as input for simulation models.

Accelerated Soil Dissipation of Tebuconazole following Multiple Applications to Peanut

Repeated application may increase rates of pesticide dissipation in soil and reduce persistence. The potential for this to occur was investigated for the fungicide, tebuconazole (alpha-[2-(4-chlorophenyl)ethyl]-alpha-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol), when used for peanut (Arachis hypogaea L.) production. Soil samples were collected from peanut plots after each of four tebuconazole applications at 2-wk intervals. Soil moisture was adjusted to field capacity as necessary and samples were incubated in the laboratory for 63 d at 30 degrees C. Untreated plot samples spiked with the compound served as controls. Results indicated accelerated dissipation in field-treated samples with the time to fifty percent dissipation (DT50) decreasing from 43 to 5 d after three tebuconazole applications. Corresponding increases in rates of accumulation and decay of degradates were also indicated. Best-fit equations (r2 = 0.84-0.98) to dissipation kinetic data combined with estimates of canopy interception rates were used to predict tebuconazole and degradates concentration in soil after each successive application. Predicted concentrations compared with values measured in surface soil samples were from twofold less to twofold greater. Use of kinetic data will likely enhance assessments of treatment efficacy and human and ecological risks from normal agronomic use of tebuconazole on peanut. However, the study indicated that varying soil conditions (in particular, soil temperature and water content) may have an equal or greater impact on field dissipation rate than development of accelerated dissipation. Results emphasize that extension of laboratory-derived kinetic data to field settings should be done with caution.

Effects of spatially variable ground motions on the seismic response of a skewed, multi-span, RC highway bridge

This paper presents a study of the influence of spatially variable ground motions on the longitudinal seismic response of a short, three-span, 30-degree skewed, reinforced concrete highway bridge. Linear and nonlinear finite element models are created for the bridge and linear elastic and nonlinear inelastic time history analyses conducted. Three different types of illustrative excitations are considered: The first utilizes spatially variable ground motions incorporating the effects of variable soil conditions, loss of coherency and wave passage as input motions at the structures' supports. The time history with the smallest peak displacement and the one with the largest peak displacement from the spatially variable ones are then used as uniform input motions at all bridge supports. The comparative analysis of the bridge model shows that the uniform ground motion input with the largest peak displacement cannot provide conservative seismic demands for all structural components—in a number of cases it results in lower response than that predicted by spatially variable motions. The present results indicate that there is difficulty in establishing uniform input motions that would have the same effect on the response of bridge models as spatially variable ones. Consequently, spatially variable input motions need to be applied as excitations at the bridge supports.

Correspondence of the fine-scale spatial variation in soil chemistry and the herb layer vegetation in beech forests

The objective of this paper is to analyse the degree to which the variation in soil conditions corresponds to the occurrence of specific plant species at micro-scale. The investigation was performed in beech forests with seven plant species growing on three sites with different geological substrates of the Triassic period (Muschelkalk, Oberer and Mittlerer Buntsandstein). At each site three to five plant species of ca. 20 individuals each were selected by stratified random sampling. The growth location of a plant individual was considered to be a potential microsite. At the gowth locations, soil solution was exctracted in situ by low tension lysimetry from the rooted topsoil exactly beneath the selected plant individuals. A soil sample was taken from the same spot and analysed for pH(H 2O) and exchangeable cations. In addition, the vegetation was recorded around each target individual and species composition was related to chemical soil properties by multivariate analyses. The three sites were found to form a gradient with respect to most analysed soil parameters. Variation coefficients of soil properties increased in the sequence pH, exchangeable Ca, K, Mg, Al, Fe, Mn. Concentrations of cations in the soil solution varied to a higher degree than those of exchangeable cations with the sole exception of Fe that showed a lower variation in the soil solution. Averaged over all sites, the microsite values for pH and exchangeable Ca exhibited a distinct sequence for the investigated species with decreasing values in the root horizon in the sequence Mercurialis perennis, Arum maculatum, Lamiastrum galeobdolon, Galium odoratum, Viola reichenbachiana, Oxalis acetosella and Luzula luzuloides. Within sites, only few significant differences were found between the potential microsites of specific species. The microsites of species on Muschelkalk differed in pH, concentrations of exchangeable Ca and K and of Ca in the soil solution. The microsites on Mittlerer Buntsandstein differed in pH and concentration of exchangeable Fe. No significant differences between species were found on Oberer Buntsandstein. Species composition in a area of 3.14 m 2 around the sample locations varied only to a minor degree as was revealed by canonical correspondence analysis (CCA). In addition, the low level of encountered variation could only be explained to a small degree by the soil variables. It is concluded that the analysed environmental factors are of minor importance for fine-scale species occurrences. At a scale of meters or less, biotic parameters might exert a greater influence than soil parameters.

Using Geophysics to locate burials and other cultural features, Isle of the Dead, Port Arthur, Tasmania

Multi-technique geophysical investigations have been conducted on the convict-period cemetery on the Isle of the Dead, Port Arthur, Tasmania. With the exception of historic photographs and some limited historical research, very little is known about the layout of burials or physical characteristics of the subsurface. Approximately 1100 burials took place on the island and less than 10% of these were formally marked. Apparent conductivity and magnetic surveys were conducted across the accessible portion of the island to locate subsurface artefact that may be associated with individual burials. The results show gradual variations in soil conditions over the site, some surface cultural features such as pathways, and numerous near-surface unidentified ferrous objects. Although some of these features showed apparent linear patterning, this did not correlate with individual areas of disturbance visible in the ground penetrating radar (GPR) profiles. 500 MHz and 250 MHz GPR surveys provided detailed subsurface information and was used to define the lateral extent of individual anomalous responses and areas containing complex multiple reflectors. The former were classified into various types, according to amplitude, shape and continuity of the reflectors. They were interpreted as possible or probable graves and located on a cultural sensitivity plan as zones of high archaeological potential. Of the techniques used so far, GPR appears to be the most effective method for detecting disturbances associated with graves on the Isle of the Dead.

Design and construction of MRT project Contract 825 of CCL1 in Singapore

Contract 825 of CCL1 consists of 4 underground MRT stations and tunnels going under and adjacent to existing MRT lines and old buildings within difficult and changeable ground conditions. A summary of the scope and challenges that exist within the project is presented together with some of the key aspects of the design and construction of stations, which were used to overcome these challenges. Methods such as using top-down construction method with diaphragm walls as main soil retaining structure, extensive geotechnical instruments to monitor the deflection and settlement of diaphragm wall, adjacent ground and existing building and MRT structures. The instruments provide very useful information to control the site activity and reducing disturbance to existing structures. Underpinning work carried out at DBG station is also described in this paper. All the four stations are built using the top-down construction method. A key consideration for choosing this construction method was to reduce soil movements and ground water lowering induced by the 28 to 35 m deep excavation, within close proximity to existing buildings and MRT structures. This together with requirements to reduce the disruption on the heavy traffic flow and disturbance to the environment led to the choice of top-down construction with diaphragm walls acting both as temporary and permanent soil retaining structure. The selected method required a close integration between design and construction teams as the diaphragm walls were designed both for temporary and permanent conditions. The planning of the different traffic diversions to enable necessary access and openings for construction activities had also to be considered in the D-wall design. The design philosophy and principles using Plaxis analysis is described in Section 3. The varying soil conditions called for different types of equipment for D-wall excavation. The experiences during D-wall installation are reflected in Section 4. The extension of the Dhoby Ghaut station is carried out very close to the existing station and MRT tunnels imposing restrictions on the construction activities. Of special interest is the underpinning works for the B2-link between two existing stations on each side of the new one. This is described in Section 5. As the project involves deep excavations and tunnels close to and under existing sensitive structures and MRT lines, instrumentation systems to provide feedback and assurance on design assumptions and predictions are important. The full range of geotechnical instruments has been employed on the contract with specific instrumentation schemes designed for specific structures. For the in-tunnel instrumentation, real time prism monitoring and real time track electrolevels have been utilized following the approach taken on earlier MRT projects, (Shirlaw et al 2000). For the historical surface structures individual schemes have been designed taking into account the predicted movement, the nature of the foundations, and settlement history, as far as feasible. These schemes involve limited but targeted real time electrolevels backed up by precise leveling and structure monitoring, together with recording of ground and diaphragm wall movements and piezometric changes within the various different strata. The monitoring is linked to sophisticated data collection allowing rapid processing into graphical format for ease of interpretation and dissemination to involved parties. This allows maximum benefit to be gained from the data in the form of controlling the construction works and feedback into the design process. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Multivariate control of plant species richness and community biomass in blackland prairie

Recent studies have shown that patterns of plant species richness and community biomass are best understood in a multivariate context. The objective of this study was to develop and evaluate a multivariate hypothesis about how herbaceous biomass and richness relate to gradients in soil conditions and woody plant cover in blackland prairies. Structural equation modeling was used to investigate how soil characteristics and shade by scattered Juniperus virginiana trees relate to standing biomass and species richness in 99 0.25 m2 quadrats collected in eastern Mississippi, USA. Analysis proceeded in two stages. In the first stage, we evaluated the hypothesis that correlations among soil parameters could be represented by two underlying (latent) soil factors, mineral content and organic content. In the second stage, we evaluated the hypothesis that richness and biomass were related to (1) soil properties, (2) tree canopy extent, and (3) each other (i.e. reciprocal effects between richness and biomass). With some modification to the details of the original model, it was found that soil properties could be represented as two latent variables. In the overall model, 51% and 53% of the observed variation in richness and biomass were explained. The order of importance for variables explaining variations in richness was (1) soil organic content, (2) soil mineral content, (3) community biomass, and (4) tree canopy extent. The order of importance for variables explaining biomass was (1) tree canopy and (2) soil organic content, with neither soil mineral content nor species richness explaining significant variation in biomass. Based on these findings, we conclude that variations in richness are uniquely related to both variations in soil conditions and variations in herbaceous biomass. We further conclude that there is no evidence in these data for effects of species richness on biomass.

Modeling Nitrogen Management Effects on Winter Wheat Production Using RZWQM and CERES‐Wheat

Agricultural system models can provide an alternative, less time‐consuming and inexpensive means of determining the optimum crop N requirement under varied soil and climatic conditions. In this context, we parameterized the Root Zone Water Quality Model (RZWQM) for winter wheat (Triticum aestivum L.) production and then evaluated it along with the CERES‐Wheat model to assess their potential as N management tools at Akron, Co. Both models were evaluated with data from five N treatments (0, 28, 56, 84, and 112 kg N ha−1) and three crop seasons (1987–1988, 1988–1989, and 1989–1990). Data from 1987–1988 zero‐N treatment were used for model calibration, and the rest of the data were used for model validation. Genetic coefficients for winter wheat (cv. TAM 107) were developed for the CERES‐Wheat model. The crop parameters required for the generic crop model of RZWQM were parameterized using information from the literature or by calibration. Both models were calibrated first for soil moisture and then for biomass and grain yield. Grain yield predictions had a root mean square error (RMSE) of 500 and 363 kg ha−1, respectively, for CERES‐Wheat and RZWQM. Aboveground biomass was predicted with RMSEs of 1247 and 1441 kg ha−1, respectively. Long‐term simulations of both RZWQM and CERES for winter wheat growth using historical weather data (1912–2001) showed that 56 kg ha−1 N applied as broadcast incorporated is a viable N management option in eastern Colorado, taking into account the grain yield, crop N uptake, N leaching into groundwater, and residual soil N at harvest. Model simulations also showed that the wheat–fallow cropping system is less water use efficient than a continuous wheat system under rainfed agriculture in eastern Colorado.

Tunnelling through varying soil conditions in north-west Greece

Tunnel S2 of the Egnatia Motorway is excavated through heavily fractured limestone and sheared sediments. Originally a fold and thrust belt was formed in the Alpine orogenic phase. Post-orogenic tectonics resulted in heavy fragmentation. The underlying material consists of clays and clayey sandy gravels. The basement of the clastic formation consists of evaporites. This variety of geological conditions resulted in considerable variability of tunnelling conditions and the need for extensive primary support measures. Owing to the mixed and rapidly changing geological conditions the type and intensity of primary support measures were selected according to geomechanical conditions at the crown. Slope stability problems were encountered during the excavation of the entrance portal, and because of the associated risk an additional study has been carried out to determine appropriate soil parameters for the excavation works through such a medium. Oedometer tests and direct shear tests were carried out to investigate the susceptibility of the material to structural breakdown and to define peak and post-rupture strength characteristics.

Tunnelling through varying soil conditions in north-west Greece

Tunnel S2 of the Egnatia Motorway is excavated through heavily fractured limestone and sheared sediments. Originally a fold and thrust belt was formed in the Alpine orogenic phase. Post-orogenic tectonics resulted in heavy fragmentation. The underlying material consists of clays and clayey sandy gravels. The basement of the clastic formation consists of evaporites. This variety of geological conditions resulted in considerable variability of tunnelling conditions and the need for extensive primary support measures. Owing to the mixed and rapidly changing geological conditions the type and intensity of primary support measures were selected according to geomechanical conditions at the crown. Slope stability problems were encountered during the excavation of the entrance portal, and because of the associated risk an additional study has been carried out to determine appropriate soil parameters for the excavation works through such a medium. Oedometer tests and direct shear tests were carried out to investigate the susceptibility of the material to structural breakdown and to define peak and post-rupture strength characteristics.

Effects of Temperature on Germination of 10 Native Legume Species

Seeds of 10 species of legumes native to Missouri germinated poorly when the temperature was lower than 15 °C (59 °F). The fastest time to first germinated seed occurred at 20 °C (68 °F) for all species except purple and white prairie clover, which germinated first at 25 °C (77 °F). The fastest germination rate was first reached at 20 °C (68 °F) for hoary tick clover, sessile tick clover, and slender lespedeza, at 25 °C (77 °F) for white prairie clover, purple prairie clover, panicled tick clover, hairy lespedeza, and tall lespedeza, and at 30 °C (86 °F) for Illinois bundleflower and roundhead lespedeza. Maximum total germination percentage also varied among species. For both the prairie clovers and roundhead lespedeza, hairy lespedeza, and slender lespedeza, the lowest temperature at which maximum total germination percentage occurred was 15 °C (59 °F). For Illinois bundleflower and the 3 tick clovers, the lowest temperature at which maximum total germination percentage occurred was 20 °C (68 °F). For most species, the fastest germination rate occurred at a higher temperature than the maximum germination percentage. Many species attained maximum germination percentage and fastest germination rate across a range of temperatures rather than at a single optimal temperature. Species that rapidly and completely germinate across a wide range of temperatures should germinate more reliably under variable soil conditions than species that exhibit a narrow range.

Sustaining water resource use in the degraded environment of the Irangi Hills, central Tanzania

The Irangi Hills in the semiarid central Tanzania are known for their severe land degradation, particularly through soil erosion. This study aims at investigating the dynamics in the local resource management and adaptive farming strategies. A combination of conventional survey methods, participatory analysis, soil description and aerial photo interpretations were used in the analysis of spatial and temporal land-use patterns. Results from the study showed that farmers utilised all possible niches in the landscape with the agricultural practices varying considerably, depending on spatial variations in soil conditions, water availability and retention capacity of the soil. The hard clayey soils were often ploughed at the end of the rainy season, before the soil dried out, to facilitate timeliness of planting in the following growing season, and to enhance water infiltration at the onset of the rainy season. Seasonally waterlogged soils were intensively cultivated and planted late during the growing season, with crops maturing only from groundwater resource. To make effective use of available groundwater resources during the dry season, the droughty and often infertile sands in ephemeral watercourses are used for growing vegetables or sugarcane in sunken holes without additional fertilisers/manure. This suggests that the crops grown obtain sufficient nutrients only from groundwater resources. However, the sustainability of cultivation in these ephemeral waterways is still questionable.

Ecological and physiological variability of Sr/Ca and Ba/Ca in mammals of West European mid-Würmian food webs

The Middle to Upper Paleolithic transition in Western Europe is characterized, from an ecological point of view, by large-ungulate communities adapted to cold climatic conditions. The aim of this study is to reconstruct the trophic relationships prevailing in these paleoecosystems which have no equivalent in the modern world. Bone and dentine remains representing five mammalian assemblages dated around 35 ka BP, one of which included a Neandertal specimen, are investigated for Sr/Ca and Ba/Ca of bioapatites. Examination of the N content and U+REE luminescence of bulk material, Ca/P ratios, and Mn and Ca contents of purified samples demonstrates that the Sr/Ca and the Ba/Ca ratios of bone and dentine samples are not significantly altered by diagenesis. As a consequence of the biological discrimination of Sr and Ba in relation to Ca, Sr/Ca and Ba/Ca values are impoverished with increasing trophic position and are strongly correlated within a trophic web. The slopes of the linear regressions between Sr/Ca and Ba/Ca are consistent with modern variability. Furthermore, a statistical difference was found between Ba/Ca of foregut and hindgut herbivores. When coexisting collagen is preserved, the Sr+Ba/Ca and δ15N are strongly correlated. The distribution of values suggests that the δ15N range is mainly controlled by the variability of soil conditions whereas the δ13C range may be related to resource availability.

Time-based two dimensional modelling of NATM tunnelling

A two dimensional model is commonly employed in practice for the analysis of tunnelling. Such analyses are computationally cheap and are useful for assessing the sensitivity of the problem to the construction method, studying the influence of varying soil conditions, and (or) finding appropriate locations for placing measuring instruments. However, simulating the three dimensional nature of tunnelling in two dimensions requires certain simplifications, including the use of empirical parameters to represent the construction sequence. In many cases the choice of parameter values are arbitrary and often not fully explained. In addition, the modelling methods are often only applicable for undrained or fully drained soil conditions where no time-dependent behaviour is involved during tunnel construction. In this paper an alternative two dimensional approach termed the "time-based modelling method" is proposed that can simulate both the three dimensional effects at the tunnel heading and the time-dependent behaviour during construction. It is proposed that the new approach is appropriate for the analysis of tunnelling in a relatively permeable soil and, as an example, the method is applied to the analysis of a new Austrian tunnelling method (NATM) tunnelling problem in decomposed granite soil. The results are compared with field data and excellent agreement is obtained.Key words: numerical modelling, time-dependent behaviour, NATM tunnelling, decomposed granite soil.

Insufficient geographic characterization and analysis in the planning, execution and dissemination of agronomic research?

Understanding spatial variation in crop response to environment and management is an essential component of agronomic research. Given the increasing availability of geographic information systems (GISs) and spatial data, one might anticipate widespread use of maps, reference to geographic variation, and analyses that capitalize on the power of GIS. Such use would be reflected in improved selection of research sites or treatments, better understanding of the influence of climatic or edaphic factors on crop responses, and more easily interpretable, quantitative results presented through maps. With the notable exception of research on individual fields or local landscapes, however, published research indicated insufficient use of spatial information and analyses or even explicit consideration of the geographical context of research. To assess use of geographic information in agronomic research, we examined papers in five prominent agricultural journals for evidence of analyses at a spatial scale smaller than field plots or local landscapes but larger than national or continental levels, which we term “mesoscale”. Use of simulation models was also examined since models can quantify response to environmental factors and thus, their use might provide instructive comparisons with use of spatial analyses. Of 250 papers considered, less than half (119 papers) described the geographic context of the research, and only 90 gave geographic coordinates with sufficient precision to locate sites within a 10 km radius. Only six papers included maps of the study area. Over 150 papers used single locations, and just 26 papers, more than four sites. In experiments creating variation in soil conditions, such as through irrigation, tillage, or nutrient treatments, the limited number of treatment combinations appeared to constrain quantitative interpretation of results. Most papers involving simulation models focused on model development or validation; models were seldom used to analyze effects of climatic or edaphic conditions as a complement to other lines of research. We conclude that there is need to increase the geographic relevance of agronomic research. Suggested steps include selecting sites using an explicit sampling strategy, using larger numbers of sites, and analyzing and presenting results using tools such as GIS and crop or ecosystem simulation models.

Coexistence mechanisms of evergreen, deciduous and coniferous trees in a mid-montane mixed forest on Mt. Emei, Sichuan, China

Structure and regeneration of a mid-montane (2200 m a.s.l.)mixed forest codominated by evergreen (Lithocarpuscleistocarpus), deciduous (Acer flabellatum)andconiferous (Tsuga chinensis, Abies fabri, andTaxus chinensis) trees were analyzed in a 40m× 60 m plot on Mt. Emei, Sichuan, China. Plant communitystructure and composition varied depending on topographic micro-habitat withinthe plot. Four topographic communities (topo-communities) were distinguishedwith dominant species corresponding to topography: (1)Abies – valley bank, (2) Acer– lower steep slope, (3) Lithocarpus – uppergentle slope, and (4) Tsuga – ridge. The coexistencemechanisms of the evergreen, deciduous, and coniferous trees were determined byidentifying the regeneration process characteristic of each dominant species,asrepresented by their seedling dispersion patterns and seedling establishmentalong the topographic gradients. The saplings and seedlings of the dominantswere distributed differently according to the topography:Lithocarpus under the canopy of parent trees and in gapsofthe upper gentle slope and ridge, Acer mainly in bothwell-lit and shady sites on the lower steep slope and on fallen logs,Abies on the valley bank but only in well-lit sites,Tsuga on the ridge, Taxus mostly onrock and well-lit sites on the slopes. Distribution of surviving saplings andseedlings was also related to the species of nearby canopy trees. We suggestthat Lithocarpus, Tsuga and Acer tendto be self-replacing in their own topographic habitats, andAbies survives as a fugitive by occupying occasionalsuitable gaps. The variation in soil conditions, particularly nutrients, withtopography affected seedling establishment and the growth of trees. Thesuccessional change of quantitative species composition, as predicted by theMarkovian model, shows the mixed forest to be in a sustained climax stage.

Spectral response of gram varieties under variable soil conditions

The spectral response of gram ( Cicer arietinum ) varieties was studied in a crop sequence experiment conducted on three soils in Gondkhairi watershed, Nagpur district of Maharashtra state. A poor relationship between leaf area and Normalized Difference Vegetation Index (NDVI) ( r =0.17) and IR/R ( r =0.11) was observed in ICCV-88202 and ICCC-37 varieties 66 days after sowing (DAS). The hypothesis that short-duration varieties should show a significant positive correlation (due to these crops attaining high biomass at an early growth stage) did not hold good. Contrary to this, in ICCV-10 (a medium maturing variety) the leaf area showed a poor relation with NDVI ( r =0.39) and IR/R ( r =0.45) at 84 DAS. As varieties ICCV-88202 (V 2 ) and ICCC-37 (V 3 ) in soil types S 1 and S 2 are high in biomass at 66 DAS (as is evident from the high values of leaf area) the possible reason for such a poor relationship is masking the effect due to profuse violet and pink flowers at the top of the plant canopy. Analysis of variance (ANOVA) results indicate that the influences due to soils and varieties yield a significant difference in IR/R ratio but a non-significant difference in NDVI both at 66 and 84 DAS. In gram with indeterminate growth habit, the biophysical parameters showed a more consistent relationship with IR/R ratio than with NDVI. The yield prediction is expected to be more valid for ICCV-10 at 66 DAS ( R 2 =0.90**), whereas ICCV-88202 and ICCC-37 are similar for such a prediction both at 66 DAS (V 2, R 2 =0.66*; V 3, R 2 =0.81**) and 84 DAS (V 2, R 2 =0.66*; V 3, R 2 =0.78**). Regression models encompassing varietal and soil influences at different growth stages were simulated to predict yields.