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Nitrogen (N) deposition in heavily polluted southern Californian shrublands is estimated to be 20-45 kg N x [ha.sup.-1] x [yr.sup.-1], but more exposed locales can receive as much as 145 kg N x [ha.sup.-1] x [yr.sup.-1]. This large anthropogenic N input has the capacity to alter the composition of plant communities. We conducted N-fertilization experiments in chaparral and coastal sage scrub (CSS) stands over a five-year period to test the hypothesis that plant community composition would change in response to dry-season N addition because of an increase in the relative abundance of herbaceous plant species. Our results indicate that dry-season addition of N significantly altered the community composition of CSS but not chaparral. Contrary to our original hypothesis, changes in community composition were due to changes in the relative abundance of dominant shrubs and not herbaceous plant species. Given that community-level responses to changes in resource availability may take years to decades in order to fully materialize, our results suggest that continued dry-season input of N will cause even larger changes in community composition over time. These results have implications for plant species composition and diversity of mediterranean-type shrublands as N deposition increases with population growth and fossil-fuel use. Key words: Adenostoma fasciculatum; air pollution; Artemisia californica; Ceanothus greggii; disturbance; diversity; N-deposition treatments; plant community composition; Salvia mellifera; secondary succession; semiarid shrublands; southern California chaparral and coastal sage scrub.

Oxidation-reduction (redox) reactions regulate many chemical processes that occur in soils. Saturation, C availability, microorganisms, and temperature dictate the rate and type of redox reactions that will occur. The measurement of redox potential enables researchers to predict the stability of redox-sensitive species, such as Fe oxides. We determine the amount of time Mid-Atlantic Piedmont floodplain soils must be saturated at a given temperature before becoming reduced with respect to ferrihydrite. Three representative floodplains in Maryland and Delaware were selected for this study. Redox potential, pH, temperature, and depth to water table were measured in six profiles over a 2-yr period. At lower temperatures, longer periods of saturation were required to induce soil reduction with respect to ferrihydrite (p < 0.0001). The soils were reduced with respect to ferrihydrite after the soils were saturated for 2 to 20 d depending on the 14-d average soil temperature ranging from 1 to 21[degrees]C. When the soil temperature was between 1 and 3.9[degrees]C, saturation was required for 20 d before the onset of reducing conditions. At 4 to 6.9[degrees]C, 11 d of saturation were required, while at 7 to 8.9[degrees]C, 7 d of saturation were required. When the soil temperature was above 9[degrees]C, reduction occurred after approximately 2 d. This investigation reveals the importance of considering soil temperature when relating length of saturation to reduction, specifically pertaining to floodplain soils in the Mid-Atlantic Piedmont physiographic province.

Tolerance to low P soils is a desirable trait in common bean (Phaseolus vulgaris L.) cultivars grown in acid-weathered soils. Genetic variability in response to P-deficient soils exists in the Andean gene pool. G19833, a low P-tolerant indeterminate Andean landrace, has been evaluated for quantitative trait loci (QTL) and tolerance to low P in combination with Mesoamerican parents. Our goal was to expand our understanding of phenotypic traits and QTL from G19833 expressed in an Andean background. An [F.sub.5:7] recombinant inbred line (RIL) population developed from two Andean bean genotypes, G19833 and AND696, a determinate line susceptible to low P soils, was examined under low and high soil P levels in replicated field trials. Phosphorus uptake was reduced by 70% and yield by 60% in low P compared to high P treatments. A linkage map was developed with 11 linkage groups and a total length of 1105 cM. Quantitative trait loci for root growth, seed yield, seed P content, and P use efficiency colocalized near the fin gene on linkage group B1. Quantitative trait loci for root growth traits, seed yield, and P uptake colocalized on B11. Quantitative trait loci for root length density (cm [cm.sup.-3]) and root surface area ([cm.sup.2]) did not colocalize with QTL for P uptake. This study indicates that root traits did not play an important role in tolerance to low P soil in an Andean x Andean cross, contrary to previous results with the same P-efficient Andean parent (G19833) crossed to a Mesoamerican bean genotype.

Identification of soil attributes most determinant to crop yield is still a matter of debate. The main objective of the present study was to relate the variations in corn (Zea mays L.) yield and N uptake to 16 soil attributes. Samples were collected in 2005 and 2006 from a long-term experiment. Soil organic C (SOC), total N (TN), potential mineralizable N (PMN), N[O.sub.3] extractable with KC1 (N[O.sub.3]-KC1) and Ca[Cl.sub.2] (N[O.sub.3]-Ca[Cl.sub.2]), N[O.sub.3] adsorbed on anion exchange membranes (N[O.sub.3]-AEM), N extracted with NaHC[O.sub.3] read at 205 nm (N-NaHC[O.sub.3]-205) and 220 nm (N-NaHC[O.sub.3]-220), N present in fulvic acid (FA-N), humic acid (HA-N) and non-humified fractions (NHF-N), mean weight diameter of aggregates (MWD), total, macro- and microporosity, and bulk density ([D.sub.b]) were measured. Principal component analysis (PCA) was conducted with the measured soil attributes, and the principal components (PCs) were used in a stepwise regression with corn yield and N uptake. In both years, a maximum of 88% of the total variance was explained. The stepwise regression analysis indicated that the first two PCs explained 78 to 91% of the variability in corn yield and N uptake. Based on the PCA, TN, HA-N, N[O.sub.3]-KC1, N[O.sub.3]-Ca[Cl.sub.2], N[O.sub.3]--AEM, and PMN appeared as primary indicators of corn yield and N uptake, whereas MWD, FA-N, and NHF-N appeared as secondary indicators. When the variability in corn yield and N uptake explained by each N availability index was assessed, N[O.sub.3]-KC1 and N[O.sub.3]Ca[Cl.sub.2] appeared as the best predictors of corn yield because of their ease of measurement and reliability across years. Abbreviations: CV, coefficient of variation; [D.sub.b], bulk density; FA-N, N in fulvic acids; HA-N, N in humic acids; MSA, measure of sampling adequacy; MWD, Mean weight diameter of water-stable soil aggregates; NHF-N, N in the non-humified fraction; N-NaHC[O.sub.3]--205, N extracted by 0.01 M NaHC[O.sub.3] and absorbance read at 205 nm; N-NaHC[O.sub.3]--220, the absorbance of a 0.01 M NaHC[O.sub.3]--extract at 220 nm; N[O.sub.3]--AEM, cumulative N[O.sub.3]--N adsorbed on anion exchange membranes; N[O.sub.3]Ca[Cl.sub.2], N[O.sub.3]--N extracted by Ca[Cl.sub.2]; N[O.sub.3]--KCl, N[O.sub.3]--N extracted by 2 M KC1; PCA, Principal Component Analysis; PCs, Principle Components; PMN, potentially mineralizable nitrogen; SOC, soil organic carbon; TN, total Nitrogen; ***, significant at the 0.001 probability level.

Several research groups have evaluated the Illinois soil N test (ISNT) as a tool for identifying the N responsiveness of corn (Zea mays L.). These studies have shown mixed results. Research in New York improved the ISNT accuracy by adjusting the critical ISNT value (0-20-cm depth) for organic matter estimated by loss-on-ignition (LOI), resulting in an ISNT x LOI curve above which corn tended to be nonresponsive. We conducted 34 N rate trials (2005-2007) to further evaluate the accuracy of the ISNT x LOI curve in predicting the N responsiveness of corn in rotation with grass-legume sod or soybean [Glycine max (L.) Merr.]. First-year corn did not respond to sidedress N (16 trials), yet the ISNT x LOI curve predicted that sidedress N was needed for six sites. For second-, third-, or fourth-year corn after sod and corn after soybean, the ISNT x LOI curve accurately predicted N responsiveness for 15 of 18 sites (eight responsive and 10 nonresponsive sites). The ISNT values of first- and second-year corn were closely correlated ([ISNT.sub.year2] = -12.8 + 1.1 [ISNT.sub.year1], [r.sup.2] = 0.96, P < 0.001). The results of laboratory and field trials on ISNT dynamics from spring sod plowdown through sidedress showed an ISNT peak 1 to 4 wk after plowdown, indicating that samples taken at or after sidedress do not reflect sod N credits. We conclude that the ISNT x LOI curve accurately identified nonresponsive sites as long as the sample was not collected within 5 wk of sod plowdown and that sod N credits need to be taken into account for first-year corn. Abbreviations: DM, dry matter; EONR, economically optimum nitrogen rate; ISNT, Illinois soil nitrogen test; LOI, loss-on-ignition; PSNT, presidedress nitrate test.

This technical note defines an 'effective soil density' that controls the velocity of small strain shear waves in saturated soil. Biot theory indicates that the ratio of effective density to saturated density will generally range from 0.75 to 1.0 and is a function of specific gravity of solids, porosity, hydraulic conductivity, and shear wave frequency. For many geotechnical applications, effective density will be equal to saturated density for low hydraulic conductivity soils (clays and silts) and may be less than saturated density for high hydraulic conductivity soils (clean sands and gravels). The findings are relevant to applications involving the propagation of small strain shear waves through saturated soil, and in particular for laboratory and field tests in which shear modulus is back-calculated from measured shear-wave velocity. CE Database subject headings: Soil properties; Density; Saturated soils; Shear modulus; Wave velocity; Hydraulic conductivity; Wave propagation.

Nitrate (N[O.sub.3.sup.-]) leached from golf greens has the potential to impair water quality. Dissolved organic N (DON) is also increasingly recognized as a form leached from fertilized soils. A controlled experiment was conducted to determine (i) the significance of DON in total N leaching losses under simulated golf-green profiles and (ii) the short-term contribution of fertilizer to leaching of inorganic and organic N forms. Various turfgrasses were grown in lysimeter columns designed to simulate a golf-green profile. Fertilizer was applied at 25 kg N [ha.sup.-1] every 14 d for 55 d, and the last application was labeled with [.sup.15]N. Leachates were analyzed for N[O.sub.3.sup.-]-N, N[H.sub.4.sup.+]-N, and DON. The [.sup.15]N recovery was assessed in plant, soil, and leachates. In the presence of plants, 10 to 70% (average 40%) of total N leached was accounted for by DON. Application of [.sup.15]N revealed that one-half to two-thirds of N[O.sub.3]-N leached in the following 14 d was derived from the fertilizer, whereas the majority of leached DON was derived from soil residual N. Nevertheless, D[O.sup.15]N was present in most leachate samples collected for 14 d after fertilizer application, indicating that only a few days were required to convert mineral fertilizer to leachable organic forms. We conclude that DON may be a significant component of total N leaching losses from putting greens and would account for part of the N losses traditionally attributed to volatilization and denitrification.

Soil C decomposition is sensitive to changes in temperature, and even small increases in temperature may prompt large releases of C from soils. But much of what we know about soil C responses to global change is based on short-term incubation data and model output that implicitly assumes soil C pools are composed of organic matter fractions with uniform temperature sensitivities. In contrast, kinetic theory based on chemical reactions suggests that older, more-resistant C fractions may be more temperature sensitive. Recent research on the subject is inconclusive, indicating that the temperature sensitivity of labile soil organic matter (OM) decomposition could either be greater than, less than, or equivalent to that of resistant soil OM. We incubated soils at constant temperature to deplete them of labile soil OM and then successively assessed the C[O.sub.2]-C efflux in response to warming. We found that the decomposition response to experimental warming early during soil incubation (when more labile C remained) was less than that later when labile C was depleted. These results suggest that the temperature sensitivity of resistant soil OM pools is greater than that for labile soil OM and that global change-driven soil C losses may be greater than previously estimated. Key words: decomposition; soil organic matter; temperature sensitivity.

Algal carbon has been increasingly recognized as the primary carbon source supporting large-river food webs; however, many of the studies that support this contention have focused on lotic main channels during low-flow periods. The flow variability and habitat-heterogeneity characteristic of these systems has the potential to significantly influence food web structure and must be integrated into models of large-river webs. We used stable-isotope analysis and IsoSource software to model terrestrial and algal sources of organic carbon supporting consumer taxa in the main channel and oxbow lakes of the Brazos River, Texas, USA, during a period of frequent hydrologic connectivity between these habitat types. Standardized sampling was conducted monthly to collect production sources and consumer species used in isotopic analysis. Predictability of hydrologic connections between habitat types was based on the previous 30 years of flow data. IsoSource mixing models identified terrestrial [C.sub.3] macrophytes (riparian origin) as the primary carbon source supporting virtually all consumers in the main channel and most consumers in oxbow lakes. Small-bodied consumers (< 100 mm) in oxbow lakes assimilated large fractions of algal carbon whereas this pattern was not apparent in the main channel. Estimates of detritivore trophic positions based on [delta][sup.15]N values indicated that terrestrial material was likely assimilated via invertebrates rather than directly from detritus. High flows in the river channel influenced algal standing stock, and differences in the importance of terrestrial and algal production sources among consumers in channel vs. oxbow habitats were associated with patterns of flooding. The importance of terrestrial material contradicts the findings of recent studies of large-river food webs that have emphasized the importance of algal carbon and indicates that there can be significant spatial, temporal, and taxonomic variation in carbon sources supporting consumers in large rivers. Key words: Brazos River, Texas, USA; floodplain; food web; IsoSource; isotopes; oxbow lakes.

This study investigates the impact of the Flux-Adjusting Surface Data Assimilation System (FASDAS) and the four-dimensional data assimilation (FDDA) using analysis nudging on the simulation of a monsoon depression that formed over India during the 1999 Bay of Bengal Monsoon Experiment (BOBMEX) field campaign. FASDAS allows for the indirect assimilation/adjustment of soil moisture and soil temperature together with continuous direct surface data assimilation of surface temperature and surface humidity. Two additional numerical experiments [control (CTRL) and FDDA] were conducted to assess the relative improvements to the simulation by FASDAS. To improve the initial analysis for the FDDA and the surface data assimilation (SDA) runs, the fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5) simulation utilized the humidity and temperature profiles from the NOAA Television Infrared Observation Satellite (TIROS) Operational Vertical Sounder (TOVS), surface winds from the Quick Scatterometer (QuikSCAT), and the conventional meteorological upper-air (radiosonde/rawinsonde, pilot balloon) and surface data. The results from the three simulations are compared with each other as well as with NCEP-NCAR reanalysis, the Tropical Rainfall Measuring Mission (TRMM), and the special buoy, ship, and radiosonde observations available during BOBMEX. As compared with the CTRL, the FASDAS and the FDDA runs resulted in (i) a relatively better-developed cyclonic circulation and (ii) a larger spatial area as well as increased rainfall amounts over the coastal regions after landfall. The FASDAS run showed a consistently improved model simulation performance in terms of reduced rms errors of surface humidity and surface temperature as compared with the CTRL and the FDDA runs.

Byline: Annett Wolf (1,2,5), Eleanor Blyth (3), Richard Harding (3), Daniela Jacob (4), Elke Keup-Thiel (4), Holger Goettel (4), Terry Callaghan (5,6) Abstract: We tested the sensitivity of a dynamic ecosystem model (LPJ-GUESS) to the representation of soil moisture and soil temperature and to uncertainties in the prediction of precipitation and air temperature. We linked the ecosystem model with an advanced hydrological model (JULES) and used its soil moisture and soil temperature as input into the ecosystem model. We analysed these sensitivities along a latitudinal gradient in northern Russia. Differences in soil temperature and soil moisture had only little influence on the vegetation carbon fluxes, whereas the soil carbon fluxes were very sensitive to the JULES soil estimations. The sensitivity changed with latitude, showing stronger influence in the more northern grid cell. The sensitivity of modelled responses of both soil carbon fluxes and vegetation carbon fluxes to uncertainties in soil temperature were high, as both soil and vegetation carbon fluxes were strongly impacted. In contrast, uncertainties in the estimation of the amount of precipitation had little influence on the soil or vegetation carbon fluxes. The high sensitivity of soil respiration to soil temperature and moisture suggests that we should strive for a better understanding and representation of soil processes in ecosystem models to improve the reliability of predictions of future ecosystem changes. Author Affiliation: (1) Department of Physical Geography and Ecosystem Analyses, Lund University, Lund, Sweden (2) Department of Environmental Science, Universitatsstr. 22, CH-8092, Zurich, Switzerland (3) Centre for Ecology and Hydrology, Wallingford, UK (4) Max-Planck-Institut fur Meteorologie (MPI-M), Hamburg, Germany (5) Abisko Scientific Research Station, Abisko, Sweden (6) Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK Article History: Registration Date: 04/10/2007 Received Date: 06/07/2006 Accepted Date: 03/10/2007 Online Date: 27/11/2007

Eucalypt plantations have been increasingly fertilized with N applied postplanting in Uruguay, but information on the benefits of the practice is scarce. The objective of this study was to identify the N availability indices (NAI) able to differentiate responsive from unresponsive sites when N was applied to eucalypts 6 or 12 mo after planting (MAP). The NAI were based on soil and plant analyses. Volume yield response to N was evaluated in 20 experiments conducted in plantations of Eucalyptus globulus Labille and E. grandis Hill ex Maiden. The NAI were related to volume response expressions by using linear and quadratic-plateau models, and the model with the highest [R.sup.2] was selected. Leaf N concentration (LNC) was the NAI most strongly related to N response in both E. grandis fertilized at 6 MAP (seven sites) and E. glabulus fertilized at 12 MAP (six sites) and the estimated critical levels were 34.6 and 20.9 g [kg.sup.-1], respectively. None of the NAI could be selected in the E. globulus sites fertilized at 6 MAP, but soil mineralizable N (NMIN) was clearly related to N response when all E. glabulus sites were pooled (12 sites), resulting in a critical level of 109 mg N [kg.sup.-l]. Although the [R.sup.2] of the models describing relationships between the selected NAI and N response varied from 0.52 to 0.94, most NAI separated responsive from unresponsive sites. The results suggest that LNC and NMIN can be used as tools to improve prediction of the early eucalypt volume response to N in Uruguay. Abbreviations: AVI, absolute volume increase; CONTV, control volume; LNC, leaf nitrogen concentration; MAP, months after planting; MAXV, maximum volume; NM, nitrogen availability indices; NMIN, soil mineralizable nitrogen; RV, relative volume; SOM, soil organic matter.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.07.018 Byline: Hanna G. Sizemore, Michael T. Mellon Keywords: Mars; Mars; surface; Ices; Regoliths Abstract: Data from the Mars Odyssey Gamma-Ray Spectrometer (GRS) instrument suite and results from numerical simulations of subsurface ground-ice stability have been used to estimate the depth of martian ground-ice. Geographic correlation between these estimates is remarkable; the relative ice table depth distributions also agree well. However, GRS-based estimates of ice table depth are generally deeper than predictions based on ground-ice stability simulations. This discrepancy may be related to heterogeneities in the martian surface such as rocks, dust, and albedo variations. We develop a multi-dimensional numerical model of ground-ice stability in a heterogeneous martian subsurface and use it to place the first quantitative constraints on the response of the ice table to meter-scale heterogeneities. We find that heterogeneities produce significant undulations/topography in the ice table at horizontal length scales of a few meters. Decimeter scale rocks create localized areas of deep ice, producing a vertical depression of 10-60 cm in the ice table over a horizontal range of 1-2 rock radii. Decimeter scale dust lenses produce locally shallow ice; however the magnitude of the vertical deflection of the ice table is small (1-4 cm). The effects of decimeter scale albedo variations on the ice table are nearly negligible, although albedo very weakly enhances the effects of dark rocks and bright dust on the ice table. Additionally, we investigate the role played by rocks in estimates of ice table depth based on orbital data. Surface rocks can account for more than half of the discrepancy between ice table depths inferred from GRS data and those predicted by theoretical ice-stability simulations that utilize thermophysical observations. Our results have considerable relevance to the up-coming Mars Scout Mission, Phoenix, because they indicate that the uncertainty in the ice table depth of a given region is greater than differences between current depth estimates. Likewise, small-scale depth variability due to heterogeneities at the eventual landing site is potentially greater than differences between current depth estimates. Author Affiliation: Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, UCB 392, Boulder, CO 80309, USA Article History: Received 3 April 2006; Revised 24 July 2006

Abstract: The timing of white spruce regeneration in aspen (Populus tremuloides Michx.)--white spruce (Picea glauca (Moench) Voss) boreal mixedwood stands is an important factor in stand development. We examined boreal [...]

Predicting future plant and ecosystem responses to elevated C[O.sub.2] also requires an understanding of the role of other factors, especially soil nitrogen. This is particularly challenging for global aridlands where total N and the relative amounts of nitrate and ammonia vary both spatially and seasonally. We measured gas exchange and primary and secondary C metabolites in seedlings of two dominant aridland shrub species (Prosopis flexuosa [S America] and P. glandulosa [N America]) grown at ambient (350 ppm) or elevated (650 ppm) C[O.sub.2] and nitrogen at two levels (low [0.8 mM] and high [8.0 mM]) and at either 1 : 1 or 3 : 1 nitrate to ammonia. Whereas elevated C[O.sub.2] increased assimilation rate, water use efficiency, and primary carbon metabolites in both species, these increases were strongly contingent upon nitrogen availability. Elevated C[O.sub.2] did not increase secondary metabolites (i.e., phenolics). For these important aridland species, the effects of elevated C[O.sub.2] are strongly influenced by nitrogen availability and to a lesser extent by the relative amounts of nitrate and ammonia supplied, which underscores the importance of both the amount and chemical composition of soil nitrogen in mediating the potential responses of seedling growth and establishment of aridland plants under future C[O.sub.2]-enriched atmospheres. Key words: ammonia-N; global change; nitrate-N; phenolic compounds; Prosopis flevuosa; Prosopis glandulosa; rangeland.

Soil organic carbon (SOC) is sensitive to management of tillage, residue (stover) harvest, and N fertilization in corn (Zea mays L.), but little is known about associated root biomass including rhizodeposition. Natural C isotope abundance ([[delta].sup.13]C) and total C content, measured in paired plots of stover harvest and return were used to estimate corn-derived SOC (cdSOC) and the contribution of nonharvestable biomass (crown, roots, and rhizodeposits) to the SOC pool. Rhizodeposition was estimated for each treatment in a factorial of three tillage treatments (moldboard, MB; chisel, CH; and no-fill, NT), two N fertilizer rates (200 and 0 kg N [ha.sup.-l]), and two corn residue managements. Treatments influenced cdSOC across a wide range (6.8-17.8 Mg C [ha.sup.-1]). Nitrogen fertilization increased stover C by 20%, cdSOC by only 1.9 Mg C [ha.sup.-1], and increased rhizodeposition by at least 110% compared with that with no N fertilizer. Stover harvest vs. stover return reduced total source carbon (SC) by 20%, cdSOC by 35%, and total SOC. The amount of stover source carbon ([sup.s]SC) responded to tillage (MB > CH > NT), but tillage affected the amount of cdSOC differently (NT > CH > MB). Total SOC was maintained only by both N fertilization and stover return during the 13-yr period. The ratio of SC in the nonharvestable biomass to [sup.s]SC ranged from 1.01 to 3.49; a ratio of 0.6 conforms to a root-to-shoot ratio of 0.4 when the root biomass includes 50% rhizodeposits. Tillage controlled the fraction of SC retained as cdSOC (i.e., humified; 0.26 for NT and 0.11 for MB and CH), even though N fertilization, stover harvest, and tillage all significantly influenced SC. Decomposition of labile rhizodeposits was a major component of the nonhumified fraction. Rhizodeposition was as much as three times greater than suggested by laboratory and other controlled studies. To understand and manage the entire C cycle, roots and rhizodeposition must be included in the analysis at the field level.

Several recent studies demonstrate that yield of individual plants, and their allocation of biomass between roots and shoots, can be profoundly affected by the pattern of supply of soil-based resources. Patchy provision of soil-based resources can affect the location of root biomass, as roots often proliferate in nutrient-rich patches. Root system size is important in determining whether plants access nutrient-rich patches, and the proportion of root systems located within such patches. This proportion will alter as growth proceeds. Species with small root systems have a limited ability to place roots in nutrientrich patches even when they are very close. Of four species with different root system sizes, the growth of the species with the smallest root system was significantly limited by being located in nutrient-poor substrate even when nutrient-rich substrate was only 3.5 cm away, whereas three species with larger root systems were not disadvantaged. Both in the laboratory and in the field, root density is higher in nutrient-rich patches, and such patches can contain roots of many plants. Recent work showing that plants can respond to nonself roots sharing the same nutrient supply suggests that competition will be more severe in nutritionally patchy substrates than in homogeneous environments with the same overall nutrient supply. Taken together, these facts lead to the prediction that inter- and intraspecific plant interactions will be influenced by patterns of nutrient supply. We present evidence supporting this prediction, and indicating that population and community structure are also affected by patterns of nutrient supply. Significant differences in population yield, plant size distribution, and mortality have been recorded between populations growing under patchy and uniform conditions. Plant communities grown from identical seed inocula, with the same overall nutrient supply, provided in different spatial and temporalpatterns, differed by up to 44% in total biomass, up to 70% in root biomass, and differed in species composition. These significant effects of heterogeneous resource supply on plants merit further detailed study. We present a framework of predictions of the impacts of different types of spatial heterogeneity in nutrient supply on the performance of single plants, and on plant interactions plant populations, and plant communities. Key words: belowground competition; nutrient heterogeneity; patch scale; plant competition; plant growth; root proliferation; soil heterogeneity.

The amount of organic N mineralized as plant available nitrogen (PAN) from soil organic matter (SOM) during a crop growing season has proved difficult to assess using traditional soil testing. It was the objective of this study to evaluate the potential for computer simulation in the estimation PAN from SOM during the growing season. A secondary objective was to evaluate this approach as a way to identify soils where crops would be non-responsive to fertilizer N. Plant available N from SOM was estimated using a simple, first-order kinetic equation. Plant available N from manure was estimated using the computer model, DECOMPOSITION. Plant available N from the previous crop and from preplant fertilizer N were taken from published data. No additional fertilizer N was applied. Corn (Zea rnays L.) yield was significantly related to total PAN (sum of SOM N, manure N, crop residue N, and preplant N) and the response of corn to total PAN was typical of previously published values. Total PAN was not a good predictor of soils where corn was nonresponsive to fertilizer N, while a history of manure applications was a good predictor of nonresponsiveness. Abbreviations: ISNT, Illinois soil nitrogen test; PAN, plant available nitrogen; SOM, soil organic matter.

Byline: Dinesh Kumar, B.J. Alappat Most of the landfills in developing countries do not have any liner at the base, or a drainage layer or a proper top cover, which results in the potential problem of groundwater/surface water contamination due to the leachate. Hence, to decide whether the leachate is to be collected and treated, or may be allowed to discharge into the adjoining soil or public sewer or surface waterbody, it is essential to have an estimate of the amount of leachate and, more importantly, the composition and strength of the leachate and variation of leachate contaminants with time as the landfill site develops. In this paper, the experimental work carried out at one of the landfills in New Delhi, India, to ascertain the composition of leachate, and its effect on the groundwater in the existing situation is presented. The variation in the leachate composition with the age of deposition of solid waste has been studied. The study indicates that the leachate composition varies considerably with the age of deposition of the waste. It may be worthwhile to use different methods for the treatment of leachate from different parts of the landfill, if collected separately. It has also been concluded that since leachate contains high concentrations of organic and inorganic constituents, including heavy metals, liners must be used at the landfills. The presence of bore wells at landfill sites to draw groundwater threatens to contaminate the groundwater, and immediate remediation steps should be taken at all landfill sites that have groundwater bore wells.

A study is conducted to investigate the influence of soil storage related stress on the resistance and resilience of different microbiological soil characteristics (MSCs) by assessing the impact of single severe drying-rewetting cycle. It is concluded that various structural and functional MSCs are not resistant to drying-rewetting stress and that resilience depended strongly on the parameter investigated.

Soil formation and nutrient load in Hawaii chiefdoms is primarily driven by temperature and rain. Complex agricultural systems developed by the ancient Hawaiians create 'sweet pots' that could flourish crops such as Kohala on the big island.