Soil Nutrient Enrichment Research Articles

Compost spreading in Mediterranean shrubland indirectly increases biogenic emissions by promoting growth of VOC-emitting plant parts

We investigated the effect of sewage sludge compost spreading on plant growth and leaf terpene emissions and content of Quercus coccifera, Rosmarinus officinalis and Cistus albidus in a Mediterranean shrubland. Measurements were performed during 3 consecutive summers on 2 different plots treated in 2002 or 2007 with 50 or 100 tons of compost per hectare, corresponding to observations carried out 2 months to 7 years after spreading. A slight nutrient enrichment of soil and leaves (R. officinalis and C. albidus) was observed, especially for phosphorous. Terpene emissions were not affected by compost spreading, although they tended to increase on treated plots after 6 and 7 years for R. officinalis and C. albidus respectively. Terpene content was not affected by any compost treatment. Leaf and stem growth were significantly enhanced by compost spreading after 2 and/or 7 years in all species with little difference between doses. Total leaf biomass on the last growth units was increased by more than 50% in C. albidus and more than 90% in Q. coccifera. The results suggest that compost spreading in Meditteranean shrublands has no or little direct effect on leaf terpene emissions, but indirectly leads to their increase through leaf biomass enhancement. Simulation of terpene emissions at stand level revealed an increase of terpene fluxes ranging between 6 and 13%, depending on the plant species. Overall, compost spreading was assessed to result in an emission rate of 1.1 kg ha−1 y−1 for a typical Q. coccifera shrubland, but can reach 2.6 kg ha−1 y−1 for a typical R. officinalis shrubland.

Managing small remnants of native forest to increase biodiversity within plantation landscapes in the south west of Western Australia

Recent expansion of industrial-scale plantations into agricultural areas in Australia has the potential to assist biodiversity conservation by rehabilitating ecosystems at the landscape scale and reducing edge effects, isolation and disturbance within remnants of native vegetation. However, the efficient management of remnants for biodiversity within a plantation estate requires knowledge of both the causes and the consequences of remnant degradation. With this in mind, we examined key ecosystem features and processes relating to soil chemistry, decomposition, native tree health and regeneration and vertebrate abundance, within small forest remnants (1–4 ha) embedded within Eucalyptus globulus plantations in south west Western Australia. Soil nutrient enrichment was significantly associated with a scale of vegetation modification in order from: (1) intact forest, (2) remnants with native understorey (UDN), (3) remnants with exotic understorey (UDE), (4) plantation and (5) pasture. We propose that, in this region, UDE remnants will often remain in a degraded state even after plantation establishment and the cessation of stock grazing. This is due, in part, to more rapid rates of nutrient turnover sustaining higher nutrient availability in the soil following the replacement of ligneous understorey plants with annual ones. Cotton strips placed in surface soils were often disintegrated in UDE remnants and largely intact in UDN remnants, indicating that decomposition was accelerated in the former. Continued tree decline and regeneration failure within UDE remnants will also reinforce the UDE condition. There was less canopy seed set and little or no seedling establishment in UDE remnants compared to UDN remnants. Therefore, management interventions to assist native tree regeneration in UDE remnants are needed. Fauna trapping highlighted the desirability of retaining, and preferably restoring, small remnants in plantations. Small native mammals were found exclusively in remnants and fewer introduced Mus musculus were present in UDN remnants. Higher numbers of native lizards were found in UDN remnants, but this result was not significant (marginally).

Analysis of persistence soil nutrient status in abandoned cattle kraals in a semi arid area in Botswana

The aim of this study was to analyze the depletion of soil nutrients with time on abandoned kraals in a peri-urban area of Botswana. Active kraals are enriched with nutrients through the accumulation of animal droppings and this study was aimed at assessing how long the impact of this soil nutrient enrichment persists after kraal abandonment. A total of 25 disused kraals, that had been abandoned for periods ranging from 1 to 45 years were sampled. The soil parameters analyzed included particle size distribution (%), bulk density (g/cm3), pore space (%), moisture content (%), pH in water and KCl solution, EC (µS/cm), organic matter (%), CEC (meq/100g), exchangeable Ca++(cmolc/kg), Mg++(cmolc/kg), K+(cmolc/kg), Na+ (cmolc/kg), nitrogen [NH4-N (mg/kg), NO3-N (mg/kg), TKN (%), and Olsen P (mg/kg). Results showed that soil nutrient concentrations on abandoned kraals generally were significantly higher than at the control sites. Soil nutrient concentrations decreased with time as abandoned kraals retrogressed towards their pre-kraal conditions. However, the effects of soil nutrient enrichment from animal wastes persist long after kraal abandonment. For example, soil Olsen P, Ca++ and Mg++ levels in kraal sites that had been abandoned for over 45 years were still significantly higher than in the control sites. In a pastoral system such as is practiced in Botswana where kraal manure is not used as soil amendment, the whole ecosystem suffers as soil nutrients are transferred and concentrated at isolated spots (kraals). Key words: Abandoned kraal, soil nutrient status, pastoral systems, semi-arid.

Analysis of the effects of kraal manure accumulation on soil nutrient status through time

This study investigated the influence of the accumulation of animal wastes on the soils of active kraal sites through time. This investigation involved the sampling and analysis of the soils of kraals that had been in use for periods ranging from 2 to over 45 years. Soil sampling and analysis were done both in the dry and wet seasons for comparative purposes. The properties of the kraal soils were compared with those of control sites. Samples were taken from 25 kraals categorized into 5 age (length of use) groups: 40 years. The soils were sampled at two depths, 0 ‐ 15 and 15 ‐ 35 cm. Soil parameters analyzed included particle size distribution (%), bulk density (g/cm 3 ), pore space (%), moisture content (%), pH in water and in potassium chloride solution, EC (µS/cm), organic matter (%), CEC (meq/100g), exchangeable bases: Ca ++ (cmolc/kg), Mg ++ (cmolc/kg), K + (cmolc/kg), Na + (cmolc/kg); nitrogen: NH4-N (mg/kg), NO3-N (mg/kg), TKN (%), and Olsen P (mg/kg). Results showed a direct correlation between length of active kraal utilization and impact of animal waste concentration on the soil with correlation coefficients as high as r = 0.99 and r = 0.95 for pH and OM respectively. Nutrient levels in kraal soils of all ages were significantly higher (P = 0.05) than those of the control site soils. Most nutrient elements showed increases ranging from about 2 - 30 times greater than in the control site soils. Soil nutrient levels were higher in the dry season than in the wet season. The nutrient enrichment in the kraals extended deep into the soil, at least, to the 35 cm depth. The organic and nutrient enrichments of the soils also had very positive effects on soil moisture and structural characteristics. However, this highly localized nutrient enrichment of kraal soils is detrimental to the long term sustainability of arid ecosystems and soil productivity. The nutrients concentrated in kraals have been harvested from the surrounding areas by grazing animals and transferred to the kraal sites. In a situation of sedentary kraaling that exists in semi arid lands of Botswana where rotation of kraal sites or the harvesting of animal manure from kraals for use as soil manure is not commonly practiced, the concentration of soil nutrients at scattered kraal spots causes an imbalance in the spatial pattern of soil and plant productivity in the arid land ecosystem. The entire ecosystem is made poorer by this phenomenon.

Effects of soil types and enhanced nutrient levels on the productivity of earthworm (eudrilius eugeniae, kinberg)

The productivity, in terms of ability to reproduce, of the earthworm Eudrilius eugeniae (Kinberg), was studied in the laboratory under three (sandy, loamy and clayey) soil conditions with and without cow dung enrichment, in order to determine their individual suitability for the culture and breeding of the species. Ten earthworms of equal sizes were each introduced into two groups of twelve pots, each subdivided into three groups of four pots each, containing 9500g of ordinary sandy, loamy or clayey soils (served as control), and 300g cow dung enriched sandy, loamy and clayey soils (served as experimental). Experimental and control pots were moistened with 750cm3 of water every three days for ten weeks. Both sets of pots were assessed for total earthworm population, their weights and lengths. Percentage increases in earthworm population in the control soil media were 72.5%, 92.5% and 170% in clayey, sandy and loamy soils respectively. Experimental pots yielded 560%, 1700% and 3395% increments in earthworm population for clayey, sandy and loamy soils respectively. Population increments amongst the three soil media differed significantly (P<0.05). Nutrient enriched soils produced significantly higher earthworm population than ordinary soils (P<0.05). The study shows superiority of loamy and nutrient enhanced soil in enhancing earthworm productivity.

The abundance of microbial functional genes in grassy woodlands is influenced more by soil nutrient enrichment than by recent weed invasion or livestock exclusion.

A diverse soil microbial community is involved in nitrogen cycling, and these microbes can be affected by land management practices and weed invasion. We surveyed 20 woodlands with a history of livestock grazing, with livestock recently excluded from 10 sites. We investigated whether soil nutrients were lower when grazing was excluded and higher when exotic grasses dominated the understory. Second, using quantitative real-time PCR, we investigated whether microbial nitrogen functional gene (NFG) abundance was altered with soil nutrient enrichment, livestock exclusion, and exotic grass invasion. The target genes were chiA (decomposition-ammonification), nifH (nitrogen fixation), nirK and narG (denitrification), and bacterial amoA (nitrification). Woodland soils were enriched in phosphorus and nitrogen compared to reference condition sites, but soil nutrients were not lower following livestock exclusion. Total nitrogen and nifH were negatively correlated in grazed woodlands, suggesting that aboveground herbivory reduces the capacity for belowground nitrogen fixation. Woodlands dominated by exotic grasses had higher levels of nitrate, narG, and nirK than those dominated by native grasses. We hypothesize that the increase in potential for denitrification was due to increases in soil nitrate, rather than changes in plant composition. Overall, soil physicochemistry explained more variation in NFG abundance than livestock presence or plant invasion, particularly for chiA and bacterial amoA, with significant relationships between the abundance of all five NFGs and total nitrogen or nitrate. All woodlands investigated had a history of anthropogenic disturbance and nutrification, and soil nutrient levels and the abundance of NFGs are likely to be related to long-term land management practices.

Ecological stoichiometry explains larger-scale facilitation processes by shrubs on species coexistence among understory plants

Plant facilitation (positive plant–plant interactions) strongly influences biodiversity, structure, and dynamics in plant communities, and the topic has received considerable attention among ecologists. Most studies of facilitation processes by shrubs have been conducted at small spatial scales between shrubs and their neighboring species. Yet, we know little about whether facilitation processes by shrubs at a small scale (i.e., a patch scale) also work at a larger scale (i.e., a site scale) in terms of the maintenance of biodiversity. Here, we report that the facilitative effects of shrubs on plant diversity at a larger scale can be explained by changing ecological stoichiometry. The soil fertility showed unimodal shape along shrub cover gradient, suggesting that the facilitative effects of a shrub do not necessarily increase as the shrub develops. The unimodal shape of dependence of plant species richness on shrub cover probably was generated by the unimodal dependence of soil fertility on shrub cover. Soil nutrient enrichment by shrubs shifted low N:P ratios of plant communities with low levels of shrub cover to more balanced N:P ratios at intermediate levels of shrub cover. At the peak N:P ratio along the gradient in shrub cover, the maximum species richness and functional richness were observed, which was consistent with the unimodal relationship predicted by the resource balance hypothesis. Thus, our findings showed that facilitation processes by shrubs at a patch scale also work at a larger scale in terms of the maintenance of biodiversity. Because observed larger-scale facilitation processes are enhanced at some intermediate levels of shrub cover, this study offers practical insight into the need for management practices that allow some intermediate levels of grazing by livestock for optimizing the role of larger-scale facilitation processes in the maintenance of biodiversity and ecosystem functioning in arid and semi-arid rangelands.

Nutrient Release and Fungal Succession during Decomposition of Crop Residues in a Shifting Cultivation System

Litter decomposition and nutrient‐release patterns of three dominant crop species were studied in a jhum cultivation system in the humid tropics of northeast India. Crop residues showed an exponential weight‐loss pattern with time. The release of nitrogen (N), phosphorus (P), and potassium (K) followed a similar pattern with weight loss, and their mineralization constants were 3.46–20.47, 2.25–18.41, and 3.82–24.70, respectively. The microbial population and fungal diversity in the decomposing litter varied with incubation time and depended mainly on the litter nutrient concentrations. Overall, the foliage residues of Capsicum frutescens and Eleusine coracana with carbon (C)/N < 25 are of good quality, and they decomposed (t99 = 122 and 333 days, respectively) fastest and released 99% of their nutrients (C, N, and K) between 74 and 263 days of incubation. Thus, all the foliage residues, particularly those of Capsicum frutescens and Eleusine coracana, can play a significant role for soil nutrient enrichment in poorly managed jhum cultivation system.

Massively parallel 454‐sequencing of fungal communities in Quercus spp. ectomycorrhizas indicates seasonal dynamics in urban and rural sites

We analysed two sites within and outside an urban development in a rural background to estimate the fungal richness, diversity and community composition in Quercus spp. ectomycorrhizas using massively parallel 454-sequencing in combination with DNA-tagging. Our analyses indicated that shallow sequencing ( approximately 150 sequences) of a large number of samples (192 in total) provided data that allowed identification of seasonal trends within the fungal communities: putative root-associated antagonists and saprobes that were abundant early in the growing season were replaced by common ectomycorrhizal fungi in the course of the growing season. Ordination analyses identified a number of factors that were correlated with the observed communities including host species as well as soil organic matter, nutrient and heavy metal enrichment. Overall, our application of the high throughput 454 sequencing provided an expedient means for characterization of fungal communities.

Eucalyptus recruitment in degraded woodlands: no benefit from elevated soil fertility

Grasses and forbs compete heavily with young tree seedlings for available resources, greatly reducing tree seedling establishment success. Soil nutrient enrichment associated with agricultural intensification can increase the growth of both herbaceous and woody lifeforms growing in isolation, but may change the balance of competitive advantage when growing together. The effects of nitrogen and phosphorus enrichment on pasture biomass and competition with two Australian grassy woodland trees (Eucalyptus albens and Eucalyptus microcarpa) was investigated in a field plot trial. Soil nutrients increased pasture biomass, but had no measurable effect on tree growth in our experiment. Competition from pasture species, even at low levels, led to high tree seedling mortality and greatly reduced tree seedling growth compared with pasture-free plots. However, when pasture-free plots were excluded from the analysis, tree seedling leaf area was not strongly correlated with herbaceous biomass. Tree seedling establishment was severely restricted even at the lowest levels of pasture biomass. We conclude that increased soil fertility resulted in a competitive advantage to the pasture, and does not improve tree seedling establishment when grown either with or without exotic herbaceous pasture (grassy understorey) species.

Integration water, energy and sanitation solution for stand-alone settlements

Lake Victoria basin has a large rural and rapidly growing peri-urban population that lacks sustainable solutions to safe and adequate water supply, energy and sanitation. Access to safe water and sanitation was 60% and 53%, respectively, by 2006. An Integrated Water, Energy and Sanitation Solution (IWESS) has been muted as a sustainable way of utilising the natural resources through a concept that turns waste into a resource thereby taking advantage of what is currently considered as problem sources and converting them into useful inputs. Tests from the Pilot sites developed show that grey and black water, kitchen and solid human waste can be used as separate inputs into an integrated waste management technological chain system that incorporates a constructed wetland-biogas-sand filter system to purify water and biodegrade solid waste to provide water for non-potable uses, biomass and biogas for energy and timber supply and manure for soil nutrient enrichment.

Teaching ecological sanitation in a school environment in Zimbabwe

Teaching the importance of sanitation and hygiene may be extended to teaching how to build simple toilets. This article describes how primary school children were taught the importance of ecological sanitation for health and for nutrient-enrichment of soils. Under the supervision of teachers, five designs of toilets were constructed, as well as handwashing devices. Urine was collected and used to water maize and other plants on demonstration plots. Local acceptance increased following open days to which local dignitaries and parents were invited.

Health of remnant woodlands in fragments under distinct grazing regimes

Fragmented remnant woodlands in agricultural landscapes are of high conservation value world-wide. Many eucalypts in agricultural landscapes of Australia are in decline. We aimed to investigate nutrient enrichment as a process that may contribute to eucalypt decline. We studied remnant woodlands that had been exposed to distinct recent and current livestock grazing treatments: Currently Intense Grazed; Recently Intense Grazed (until 3 years ago); Recent Intermediate Grazed; and Recent Lightly Grazed by livestock. We assessed soil nutrient status and penetrability, eucalypt foliar nutrition and stable isotope ratios for N and C, attributes of understorey vegetation, and tree health. Soils of the Currently Intense Grazed treatment had high levels of ammonium and Colwell-P. Total N, P, C:N ratio and soil penetrability were generally high in Currently Intense Grazed and Recently Intense Grazed treatments relative to Recent Intermediate Grazed and Recent Lightly Grazed treatments. Foliar N, N stable isotope ratios, P and carbon stable isotope ratios ( δ 13C) were generally higher (less negative δ 13C) in trees on Currently Intense Grazed and Recently Intense Grazed treatments than in trees on Recent Intermediate Grazed and Recent Lightly Grazed treatments. Soil surface litter, tall and low shrubs and rock were positively correlated with tree health. Grasses and eucalypt foliar N, P and δ 13C were negatively correlated with tree health. Soil nutrient enrichment increased with increasing grazing intensity and was associated with increased weed invasion and with poor tree health that was in turn correlated to increased foliar N and P and less negative δ 13C in woodland trees in this study. We argue that minimising soil nutrient enrichment of fragmented remnant woodlands is important, given the association of elevated soil nutrition with poor tree health, to ensure the persistence of eucalypts in agricultural landscapes.

Vegetation Change and Soil Nutrient Distribution along an Oasis‐Desert Transitional Zone in Northwestern China

Abstract Many studies have focused on soil nutrient heterogeneity and islands of fertility in arid ecosystems. However, few have been conducted on an oasis‐desert transitional zone where there is a vegetation pattern changing from shrubs to annual herbs. The goal of the present study was to understand vegetation and soil nutrient heterogenity along an oasis‐desert transitional zone in northwestern China. Three replicated sampling belts were selected at 200 m intervals along the transitional zone. Twenty‐one quadrats (10 × 10 m) at 50 m intervals were located along each sampling belt. The vegetation cover was estimated through the quadrats, where both the soil under the canopy and the open soil were sampled simultaneously. The dominated shrub was Haloxylon ammodendron in the areas close to the oasis and Nitraria tangutorum dominated the areas close to the desert. In general, along the transitional zone the vegetation cover decreased within 660 m, increased above 660 m and decreased again above 1 020 m (close to the desert). The soil nutrients (organic matter, total N, NO3− and NH4+) showed significant differences along the zone. The soil nutrients except the soil NH4+ under the canopy were higher than those in open soil, confirming “islands of fertility” or nutrient enrichment. Only a slight downward trend of the level of “islands of fertility” for soil organic matter appeared in the area within 900 m. Soil organic matter both under canopy and in interspace showed a positive correlation with the total vegetation cover, however, there was no significant correlation between the other soil nutrients and the total vegetation cover. We also analyzed the relationship between the shrubs and annuals and the soil nutrients along the zone. Similarly, there was no significant correlation between them, except soil organic matter with the annuals. The results implied that annual plants played an important role in soil nutrient enrichment in arid ecosystem.

Litterfall and nutrient return in a semi-arid southern African savanna woodland dominated by Colophospermum mopane

The objective of this study was to investigate litter production, litter standing crop and nutrient return to soil in a semi-arid southern African savanna in Bulawayo, Zimbabwe. We used a randomized block design with five blocks of 100 × 100 m demarcated in a 10-ha pocket of Colophospermum mopane-dominated open woodland protected from grazing and fire. Litter traps were installed beneath large (8.3 m crown diameter) and small mopane trees (2.7 m crown diameter) and in the intercanopy area, representing 27, 3 and 62% of the woodland area, respectively. Mean annual total litterfall over 2 years of observations was 197, 83 and 35 g m−2 yr−1 beneath large and small trees as well as in the intercanopy area, respectively. Leaf proportions of total litterfall beneath large and small trees and in the intercanopy area were 68.6, 73.0 and 75.3%, respectively. Litterfall followed a uni-modal distribution pattern and was much higher during the period of May–September (dry period) compared to other months. The total potential annual element inputs via litterfall beneath large trees were 2 and 5 times greater than beneath small trees and in the intercanopy area, respectively. Total litter standing crop was 405, 177 and 67 g m−2 beneath large and small trees and in the intercanopy area, respectively. Concentrations of N, P and K in litterfall and surface soil were closely correlated with each other. At all sampling sites, element accession to soil through litterfall followed the decreasing sequence C > Ca > N > Mg > K > P. These results suggest that litterfall is a major process responsible for soil organic matter and nutrient enrichment beneath isolated trees in semi-arid savannas.

Historical influences on the vegetation and soils of the Martha’s Vineyard, Massachusetts coastal sandplain: Implications for conservation and restoration

Both disturbance history and previous land use influence present-day vegetation and soils. These influences can have important implications for conservation of plant communities if former disturbance and land use change species abundances, increase colonization of nonnative plant species or if they alter soil characteristics in ways that make them less suitable for species of conservation interest. We compared the plant species composition, the proportion of native and nonnative plant species, and soil biogeochemical characteristics across seven dominant land use and vegetation cover types on the outwash sandplain of Martha’s Vineyard that differed in previous soil tillage, dominant overstory vegetation and history of recent prescribed fire. The outwash sandplain supports many native plant species adapted to dry, low nutrient conditions and maintenance of native species is a management concern. There was broad overlap in the plant species composition among pine ( Pinus resinosa, P. strobus) plantations on untilled soils, pine plantations on formerly tilled soils, scrub oak ( Quercus ilicifolia) shrublands, tree oak ( Q. velutina, Q. alba) woodlands, burned tree oak woodlands, and sandplain grasslands. All of these land cover categories contained few nonnative species. In contrast, agricultural grasslands had high richness and cover of nonnative plants. Soil characteristics were also similar among all of the woodland, shrubland and grassland land cover categories, but soils in agricultural grasslands had higher pH, extractable Ca 2+ and Mg 2+ in mineral soils and higher rates of net nitrification. The similarity of soils and significant overlap in vegetation across pine plantations, scrub oak shrublands, oak woodlands and sandplain grasslands suggests that the history of land use, current vegetation and soil characteristics do not pose a major barrier to management strategies that would involve conversion among any of these vegetation types. The current presence of high cover of nonnative species and nutrient-enriched soils in agricultural grasslands, however, may pose a barrier to expansion of sandplain grasslands or shrublands on these former agricultural lands if native species are not able to outcompete nonnative species in these anthropogenically-enriched sites.

Mercury release from deforested soils triggered by base cation enrichment

The Brazilian Amazon has experienced considerable colonization in the last few decades. Family agriculture based on slash-and-burn enables millions of people to live in that region. However, the poor nutrient content of most Amazonian soils requires cation-rich ashes from the burning of the vegetation biomass for cultivation to be successful, which leads to forest ecosystem degradation, soil erosion and mercury contamination. While recent studies have suggested that mercury present in soils was transferred towards rivers upon deforestation, little is known about the dynamics between agricultural land-use and mercury leaching. In this context, the present study proposes an explanation that illustrates how agricultural land-use triggers mercury loss from soils. This explanation lies in the competition between base cations and mercury in soils which are characterized by a low adsorption capacity. Since these soils are naturally very poor in base cations, the burning of the forest biomass suddenly brings high quantities of base cations to soils, destabilizing the previous equilibrium amongst cations. Base cation enrichment triggers mobility in soil cations, rapidly dislocating mercury atoms. This conclusion comes from principal component analyses illustrating that agricultural land-use was associated with base cation enrichment and mercury depletion. The overall conclusions highlight a pernicious cycle: while soil nutrient enrichment actually occurs through biomass burning, although on a temporary basis, there is a loss in Hg content, which is leached to rivers, entering the aquatic chain, and posing a potential health threat to local populations. Data presented here reflects three decades of deforestation activities, but little is known about the long-term impact of such a disequilibrium. These findings may have repercussions on our understanding of the complex dynamics of deforestation and agriculture worldwide.

Assessment of the Spatial Distribution of Soil Properties in a Northern Everglades Marsh

Florida Everglades restoration plans are aimed at maintaining and restoring characteristic landscape features such as soil, vegetation, and hydrologic patterns. This study presents the results from an exhaustive spatial sampling of key soil properties in Water Conservation Area 1 (WCA 1), which is part of the northern Everglades. Three soil strata were sampled: floc, upper 0- to 10-cm soil layer, and 10- to 20-cm soil layer. A variety of properties were measured including bulk density (BD), loss on ignition (LOI), total phosphorus (TP), total inorganic phosphorus (TIP), total nitrogen (TN), total carbon (TC), total iron (TFe), total magnesium (TMg), total aluminum (TAl), and total calcium (TCa). Interpolated maps and model prediction uncertainties of properties were generated using geostatistical methods. We found that the uncertainty associated with spatial predictions of floc, particularly floc BD, was highest, whereas spatial predictions of soil chemical properties such as soil Ca were more accurate. The resultant spatial patterns for these soil properties identified three predominant features in WCA 1: (i) a north to south gradient in soil properties associated with the predominant hydrological gradient, (ii) areas of considerable soil nutrient enrichment along the western canal of WCA 1, and (iii) areas of considerable Fe enrichment along the eastern canal. By using geostatistical techniques we were able to describe the spatial dynamics of soil variables and express these predictions with an acceptable level of uncertainty.

Effects of Environmental Factors on Organochlorine Pesticide Residues in Soils of the Guanting Reservoir Area, China

Topsoil samples from 56 sites around the Guanting Reservoir, China, were measured for HCH and DDT concentrations. The total soil HCH content (including α -, β -, γ -, and δ - isomers) in these soil samples ranged from 0 to 7.33 ng.g− 1, with a mean of 0.69 ng.g− 1. These levels were considerably lower than those of the total DDT soil contents (including pp′-DDE, pp′-DDD, op′-DDT, and pp′-DDT), which ranged from 0 to 76.01 ng.g− 1, with a mean of 9.46 ng.g− 1. DDT was also found to be the major pollutant in the soil samples, accounting for ∼ 93% of the total organochlorine pesticide (OCP) contents. Several environmental factors including land use, soil texture, soil taxonomy, and microbial biomass were considered to be responsible for the OCP levels observed. The data provide some insight into the effects of environmental conditions such as soil formation, agricultural cultivation, nutrient enrichment, and other anthropogenic activities on the degradation of OCPs in soils. Although the OCP residues currently are below the maximum limits set for use on agricultural land in China, and only rarely would such levels pose significant ecological concern, OCPs are highly persistent in soil and bioaccumulative. The data provided in this study are considered crucial for reservoir remediation, especially since the Guanting Reservoir will serve as one of the main drinking water sources for Beijing in the foreseeable future.

PATTERNS IN SOIL FERTILITY AND ROOT HERBIVORY INTERACT TO INFLUENCE FINE-ROOT DYNAMICS

Fine-scale soil nutrient enrichment typically stimulates root growth, but it may also increase root herbivory, resulting in trade-offs for plant species and potentially influencing carbon cycling patterns. We used root ingrowth cores to investigate the effects of microsite fertility and root herbivory on root biomass in an aggrading upland forest in the coastal plain of South Carolina, USA. Treatments were randomly assigned to cores from a factorial combination of fertilizer and insecticide. Soil, soil fauna, and roots were removed from the cores at the end of the experiment (8-9 mo), and roots were separated at harvest into three diameter classes. Each diameter class responded differently to fertilizer and insecticide treatments. The finest roots (< 1.0 mm diameter), which comprised well over half of all root biomass, were the only ones to respond significantly to both treatments, increasing when fertilizer and when insecticide were added (each P < 0.0001), with maximum biomass found where the treatments were combined (interaction term significant, P < 0.001). These results suggest that root-feeding insects have a strong influence on root standing crop with stronger herbivore impacts on finer roots and within more fertile microsites. Thus, increased vulnerability to root herbivory is a potentially significant cost of root foraging in nutrient-rich patches.