A reciprocal soil exchange experiment highlights tree root colonization effects on soil nitrification

For forest ecosystems, the relationship between root biomass, root growth and soil nitrification is still debated. Following repeated findings of significant differences in soil nitrification beneath comparable stands at the Breuil experimental site, a reciprocal soil exchange experiment combining high (H)‐ and low (L)‐nitrifying stands was conducted to highlight the effect of tree root colonization on the control of nitrification. Soil percent nitrification and fine root biomass were measured in undisturbed and in transplanted soil cores after 16 and 28 months. In undisturbed soils, the fine root biomass varied by tree species and explained only 14% of the variation in percent nitrification. In transplanted soil cores, percent nitrification converged, at different rates, towards values close to those measured in the undisturbed soil at the receptor stands. On the one hand, percent nitrification increased rapidly in soil cores from L transferred to H, while soil core colonization by roots remained low during the study period. Soil cores might have been colonized by active nitrifiers from their new environment, or/and the activity of the nitrifiers originally present was less suppressed by root activity in their new environment. On the other hand, percent nitrification decreased progressively in soil cores from H transferred to L as root colonization increased. This suggests that root colonization reduced nitrifier population and activity. Our findings suggest that the often‐reported influence of forest species on soil nitrification is probably multifactorial but the tree root colonization contributes.     

Impact of soil stockpiling and mining rehabilitation on earthworm communities

As key ‘ecosystem engineers’, earthworms improve mineralization of organic matter, plant growth, soil quality, and are an important component of many terrestrial food webs. Under appropriate conditions, they are therefore likely to accelerate the restoration of soil ecosystem function after mining.Conserving naturally occurring populations and facilitating their recolonisation appears as the most efficient way to increase earthworms’ overall effect. The impact of mining activities and restoration measures on New Zealand endemic earthworm communities was tested. Earthworm biomass and diversity were compared in four different habitat types.Mining activities, not surprisingly, are shown here to have a detrimental impact on earthworm communities. Soil stockpiling induces anaerobic conditions at and below a depth of 1 m, where earthworms do not survive. The use of stockpiled soil for vegetation replanting therefore leads to low diversity and low abundance of earthworms. An alternative restoration technique consisting in transferring vegetation and soil units (the vegetation direct transfer) was efficient in preserving earthworm populations with earthworm biomass and diversity not significantly different from those observed in undisturbed areas. Based on these results, we recommend vegetation direct transfer (VDT) to be prioritised whenever it is logistically and economically feasible. When VDT is not applicable, low stockpiles should be prioritised as they will comprise a higher proportion of good quality soil (at the surface) and a lower proportion of anaerobic and compacted soil (below 1 m depth at the studied site).     

The influence of livestock dung on the abundance of exotic and native earthworms in a grassland in south-eastern Australia

It is well known that organic matter in the form of dung is utilised as a food source by some earthworms, but little has been reported on the preferences of earthworms for different types of dung in agricultural settings. An experiment was carried out in spring in south-eastern Australia to evaluate the effect that dung from different livestock has on the abundance of earthworms in a grassland environment. We were particularly interested to compare the responses of native Australian earthworms (Megascolecidae) with those of exotic earthworms (Lumbricidae and Acanthodrilidae). The attractiveness of dung from sheep, cattle and horses was measured by determining the abundance and biomass of the resident earthworm species under each dung type at varying times after adding the dung to the soil surface (0, 10, 20 and 30 days). The earthworm population consisted of three exotic species, Apporrectodea trapezoides, Microscolex dubius and M. phosphoreus, and two native species, Spenceriella macleayi and S. bywongensis. Both the number of days that the dung was available to earthworms and the type of dung influenced the numbers and biomass of the earthworms found beneath the dung pats. Significant interactions existed between time and dung type when all adult earthworms were considered as one group and also when adults were split into individual species. The various species responded differently to the dung, but horse dung was generally the more preferred dung type. The significance of these results is discussed in terms of the management of dung in an Australian pastoral context.     

A method of extracting earthworms from cores of soil with minimum damage to the soil

 Lumbricid earthworms have often been shown to increase the growth of plants. The earthworms and plants were generally grown together in the same soil, although sometimes earthworms were reluctant to enter the soil. It was not possible to isolate the mechanism for the increased growth, as no method was available to extract the earthworms with no damage to the soil before the plants were grown. A method is described which enabled Aporrectodea caliginosa, but not A. trapezoides, to enter all cores, and which extracted A. caliginosa from the cores probably with minimum damage to the soil. Received: 20 October 1998     

Livestock grazing activities and wild boar rooting affect alpine earthworm communities in the Central Pyrenees (Spain)

In alpine areas, shifts in traditional grazing activities are globally affecting ecosystem properties and rural livelihoods. The ongoing decrease in extensive husbandry, with a decline in sheep numbers and a relative increase in cattle stocking rates, has resulted in the abandonment of large alpine grazing areas. This pastoral change has been recently associated with increased disturbances of wild boar (Sus scrofa), mainly within cattle-stocked ranges. In turn, cattle areas favor earthworm communities, a preferred trophic resource for wild boars in mountain environments. However, it is unknown whether wild boar disturbances, together with grazing activities, can affect earthworm communities. Our aim is to analyze the abundance, richness and ecological categories of earthworms and soil parameters (soil C and N concentrations, moisture, and C:N ratio) in relation to the occurrence of wild boar disturbances and grazing activities at different stocking pressures. We sampled two different grazing scenarios differing in the distribution of cattle along a grazing gradient, which was represented by three levels of stocking pressure (high, intermediate and low). Our results showed a complex effect of grazing activities and disturbances on the abundance and richness of earthworms, along with variations in C:N ratio and soil moisture, especially with increasing cattle presence. At high-stocking pressures differences in earthworm abundance and richness between disturbed and undisturbed areas were limited, whereas at intermediate-stocking pressures earthworms were favored by wild boar disturbances. Ecological categories of earthworms responded differently; endogeic species were the most affected by grazing pressures and wild boar rooting, with highest occurrence at high-stocking pressures and within boar disturbed areas. In sum, pastoral use and soil disturbances affected earthworm community structure and composition in complex ways. These results indicate an interaction of processes that is relevant to understand current changes in alpine ecosystems.     

The extent and significance of bioturbation on 137Cs distributions in upland soils

Differences between measured ¹³⁷Cs activity–depth profiles and idealised undisturbed profiles generated from an exponential model suggest that faunal turbation has redistributed ¹³⁷Cs in mineral and organic upland soils in southern Scotland. Bioturbation is also demonstrated by the vertical displacement of other inputs to the soils of known age (non-native tree pollen and spheroidal carbonaceous particles, SCPs). The causes and mechanisms of bioturbation were further investigated by soil micromorphology. Well-drained mineral soils with active populations of earthworms are the most bioturbated, showing near-complete homogenisation to depths of about 20 cm. Enchytraeids also seem to remobilise ¹³⁷Cs by the digestion of organic matter and may be the main cause of ¹³⁷Cs redistribution in organic-rich upland soils. Relative rates of mixing are evaluated by comparing ¹³⁷Cs depth profiles.     

Role of earthworms in regenerating soil structure after compaction in reduced tillage systems

New non-tillage or reduced tillage agricultural practises are being increasingly adopted but generally result in higher soil compaction. Due to their recognised physical influence mainly through burrow creation, it is often claimed that earthworm activity could alleviate soil compaction in these systems. To put this assumption to the test, an experimental compaction event was carried out on one plot of arable land. The abundance and biomass of earthworms were evaluated in compacted (under wheel tracks) and non-compacted (between wheel tracks) zones, seven times over a two-year period. In addition, the functional consequences of earthworm activity, defined by burrow abundance assessed in 2D and 3D and water infiltration, were measured three times over the same period. The short-term (less than three months) effects of the compaction were clear: soil bulk density increased from 1.46 to 1.57 g cm⁻³, the abundance and biomass of earthworms were greatly reduced (−40% and −70% respectively) and the number and continuity of macroporosity were lower under wheel tracks at least until a depth of 30 cm. After these initial detrimental effects, we observed a rapid recovery of earthworm populations with no statistical difference between compacted and control zones more than three months after the compaction. However, the recovery of soil functional properties linked to earthworm activity, macroporosity and water infiltration, was much slower and took between 12 and 24 months. Despite these modifications, there were no significant changes in soil bulk density with time during the two-year period. This study demonstrates that earthworms are important actors in the regeneration of compacted soil. Although the complete regeneration of compacted soil by earthworms is a slow process, agricultural practises that promote earthworm density and activity should be encouraged in reduced or minimum tillage systems.     

Habitat quality, conspecific density, and habitat pre-use affect the dispersal behaviour of two earthworm species, Aporrectodea icterica and Dendrobaena veneta, in a mesocosm experiment

Dispersal capacity is a life-history trait that may have profound consequences for earthworm populations: it influences population dynamics, species persistence and distribution and community structure. It also determines the level of gene flow between populations and affects processes such as local adaptation, speciation and the evolution of life-history traits. It may play a great role in soil functioning by determining the spatial distribution of ecosystem engineers such as earthworms. Dispersal is an evolutionary outcome of the behaviour in response to the ecological constraints of the species. Hence different dispersal behaviour is expected from the different ecological types of earthworms. Nevertheless the dispersal behaviour of earthworms has been little documented.In this work we test a series of basic mechanisms that are fundamental and complementary to understand earthworms dispersal behaviour. We focus on the dispersal triggered by environmental conditions, a fundamental process usually termed “conditional dependent dispersal”. We show experimentally in mesocosms that in one week: 1) earthworm dispersal can be triggered by low habitat quality, either through soil quality or the presence/absence of litter. 2) Earthworms can be subject to positive density dependent dispersal, that is the rate of dispersal increases when density increases; and 3) earthworm dispersal can be reduced by the pre-use of the soil by conspecific individuals that are no longer present.Our results suggest that earthworms may be more mobile than expected from previous estimations, and that they present high capacities of habitat selection. In the light of our findings we elaborate a behavioural scenario of earthworm foraging, and propose several priority working directions.     

Near‐surface macropore flow and saturated hydraulic conductivity in drained and restored blanket peatlands

The impacts of blanket peatland management on water tables, near‐surface macropore flow and saturated hydraulic conductivity were investigated using automated dipwells and mini‐disc tension infiltrometers. Three neighbouring hillslopes which were undisturbed, drained and restored by drain blocking were studied. Mean water table depths at the undisturbed sites were slightly shallower than at the restored site and water tables at both sites were significantly shallower relative to the drained treatment. Through time, however, the water table at the restored treatment behaved in a markedly different way to that at the undisturbed site. Water tables reached the peat surface for only 2% of the time for the drained and restored treatments compared to 18% for the undisturbed treatment. The proportion of runoff flowing through macropores in the near‐surface layers of the peat was found to be large (≥60%) across all three treatments, yet functional macroporosity was found to be significantly greater in the undisturbed peat relative to the two other treatments. Meanwhile, saturated hydraulic conductivity was found to be significantly higher at the restored treatment relative to the two other treatments, with mean conductivities ca. 1.5 times greater, suggesting a form of heightened soil–water interaction. Combined, the results indicate that although restoration by ditch blocking may result in a relatively successful water table recovery, there may not be the full reinstatement of peatland hydrological processes.     

Earthworms as colonizers of natural and cultivated soil environments

For cultivated soils, the important function of earthworms as ecosystem engineers and their major contribution to the composition and functioning of soil ecosystems with a varying species diversity has been extensively addressed. However, the role of earthworms as colonizers of virgin, uncultivated soil in the process of soil formation has been little researched and long underrated. To better understand this role, the following questions need to be considered: (1) what makes an early colonizer successful, what are its characteristics, and which species are the most successful and under what circumstances are they successful?; (2) what are the limiting factors in these colonization processes with respect to environmental conditions and also to interspecific interactions?; (3) what do earthworms contribute to the further colonization by other soil animals?; and (4) how do they impact the soil itself and what could therefore be the consequences for soil management and restoration?These questions have recently been addressed from the perspective of new (or ‘alien’) earthworm species invading ecosystems, suggesting a massive influx of species, competitive to the originally present fauna. This idea is, however, contrary to colonization, which suggests a gradual exploration of a previously uninhabited area. Unlike recent research, this review approaches colonization primarily as a spatial dispersal process and part of natural succession processes, and is mainly illustrated with examples of Palearctic species, either in Europe or introduced elsewhere. To begin, the various stages of colonization: dispersal, establishment, population growth and interspecies relations are analysed. Next, the colonization processes, the possible limiting environmental factors and the sequence of the appearance and establishment of species are described. Dispersal rates and sequences of colonization by different earthworm species are given for different soil ecosystems. For colonization, limiting environmental factors such as pH, soil type and heavy metal contents as well as the presence of organic matter seem to play a more important role than inherent ecological characteristics like r/K selection. Finally, the role of earthworms in the early colonization of soils that are earthworm-free because of non-cosmopolitan distribution, drained former sea bottom, permanently water-logged soils or anaerobic, acid peaty soils are reviewed. If we understand the role of earthworms in succession, we will be able to improve their role in soil restoration and soil management.     

Earthworm casts form stable aggregates in physically degraded soils

Topsoils affected by surface mining suffer severe physical degradation and lose most of their earthworm populations. After mining, replaced soils are planted to grassland and managed to improve soil structure. Earthworm inoculation into selected restored areas produced populations similar to those of undisturbed soils within 3 years. Soil properties in inoculated areas were compared with those of controls to evaluate the contribution of casts to bulk soil aggregation, and soil organic matter and root content responses to earthworm activity. Crumb porosity and coarse particle content were measured in water-stable macro-aggregates and earthworm casts to establish whether aggregates were formed by earthworms. Over a 5- to 6-year period, inoculation increased stable aggregation (>2 μm, >60 μm and >3 mm), even at 0- to 5-cm depth where it reduced soil organic matter content. Productivity and root content were also increased by inoculation; roots and organic matter were re-distributed to greater depth. Crumb porosity decreased with casts > aggregates (inoculated plots) > aggregates (control plots). Coarse particle content increased with casts < aggregates (inoculated plots) < aggregates (control plots). Coarse particle and porosity data were consistent with much of the newly aggregated soil being processed and formed by earthworms as casts. Whilst levels of soil organic matter were often closely associated with percentage stable aggregation, root content showed weaker associations. Aggregation percentage was most closely associated with abundance of Aporrectodea longa, although at particular depths significant correlations were also obtained for Aporrectodea caliginosa and Lumbricus terrestris. Results suggest that earthworms, rather than plant roots, initiate aggregation in severely degraded grassland soils.     

蚯蚓菌根互作对土壤酶活、 甘薯根系生长及养分吸收的影响

【目的】蚯蚓和丛枝菌根真菌处于不同的营养级,但在促进植物生长和提高土壤肥力等方面却都发挥着积极作用。单独对土壤微生物或土壤动物的研究较多,但对土壤微生物与土壤动物之间相互作用的研究很少。因此研究它们对土壤和植物生长的作用可为挖掘土壤生物的潜力和提高土壤生物肥力提供依据。【方法】采用盆栽试验,研究了蚯蚓(Eisenia fetida)与丛枝菌根真菌(Rhizophagus irregularis)互作对甘薯生长和养分吸收的影响。试验采用两因素完全随机试验设计,分为接种和不接种菌根真菌及添加和不添加蚯蚓。试验共4个处理: 不加菌根和蚯蚓(CK); 接种菌根真菌(AM); 添加蚯蚓(E); 添加蚯蚓和菌根真菌(E+AM),每个处理4次重复。调查了甘薯养分吸收、 根系形态及土壤养分变化,采用Canoco4.5软件对土壤生物与植物对应关系进行RDA (redundancy analysis)分析。【结果】接种菌根真菌显著提高了甘薯地上和地下部生物量(P0.05),而添加蚯蚓的处理仅提高了甘薯地上部生物量。同时添加蚯蚓和菌根的处理显著提高了甘薯地上地下部生物量,并且高于其他三个处理(P0.05)。与对照相比,接种菌根真菌显著提高了土壤磷酸酶活性(P0.01),增幅近一倍; 同时提高了土壤磷的植物有效性,土壤有效磷含量下降了30%左右。添加蚯蚓后土壤脲酶活性从5.45 mg NH+4-N/g显著增加到8.71 mg NH+4-N/g,土壤碱解氮的含量从5.82 mg/kg显著增加到6.89 mg/kg (P0.05)。RDA分析表明蚯蚓菌根互作对甘薯地上和地下部氮磷含量、 根表面积、 根体积、 根平均直径和根尖数均存在显著的正交互效应。蚯蚓菌根互作通过调控土壤酶和改变土壤养分有效性促进甘薯对土壤氮磷养分的吸收。【结论】蚯蚓(Eisenia fetida)通过调控土壤脲酶和碱性磷酸酶增加了土壤中氮磷的有效性从而促进甘薯地上部生长。丛枝菌根真菌(Rhizophagus irregularis)通过调控土壤磷酸酶和增加植株地上地下部吸磷量从而促进甘薯生长。添加蚯蚓或接种菌根真菌均能增加根系吸收面积和根体积从而促进甘薯对养分的吸收。蚯蚓和菌根真菌相互作用通过调控土壤酶和改变土壤养分有效性以及促进根系发育从而互补的促进甘薯养分吸收和生长。     

Lumbricid macrofauna alter atrazine mineralization and sorption in a silt loam soil

Atrazine is a widely used herbicide and is often a contaminant in terrestrial and freshwater ecosystems. It is uncertain, however, how the activity of soil macrofauna affects atrazine fate and transport. Therefore, we investigated whether earthworms enhance atrazine biodegradation by stimulating herbicide degrading soil microflora, or if they increase atrazine persistence by facilitating herbicide sorption. Short (43 d) and medium term (86 d) effects of the earthworms Lumbricus terrestris and Aporrectodea caliginosa on mineralization, distribution, and sorption of U-ring-¹⁴C atrazine and on soil C mineralization was quantified in packed-soil microcosms using silt loam soil. A priming effect (stimulation of soil C mineralization) caused by atrazine supply was shown that likely lowered the earthworm net effect on soil C mineralization in atrazine-treated soil microcosms. Although earthworms significantly increased soil microbial activity, they reduced atrazine mineralization to ¹⁴CO₂-C from15.2 to 11.7% at 86 d. Earthworms facilitated formation of non-extractable atrazine residues within C-rich soil microsites that they created by burrowing and ingesting soil and organic matter. Atrazine sorption was highest in their gut contents and higher in casts than in burrow linings. Also, gut contents exhibited the highest formation of bound atrazine residues (non-extractable atrazine). Earthworms also promoted a deeper and patchier distribution of atrazine in the soil. This contributed to greater leaching losses of atrazine in microcosms amended with earthworms (3%) than in earthworm-free microcosms (0.003%), although these differences were not significant due to high variability in transport from earthworm-amended microcosms. Our results indicated that earthworms, mainly by casting activity, facilitated atrazine sorption, which increased atrazine persistence. As a consequence, this effect overrode any increase in atrazine biodegradation due to stimulation of microbial activity by earthworms. It is concluded that the affect of earthworms of atrazine mineralization is time-dependent, mineralization being slightly enhanced in the short term and subsequently reduced in the medium term.     

Comparison of Disturbed and Undisturbed Soil Core Methods to Estimate Nitrogen-Mineralization Rates in Manured Agricultural Soils

Ion exchange resin?/?soil cores are a common in situ approach to estimating soil nitrogen (N) mineralization rates. However, no studies compare the two common methods of core preparation (disturbed and undisturbed). The objective of our study was to compare N mineralized and soil temperature in disturbed versus undisturbed cores of manured agricultural soils. Undisturbed cores were prepared by driving aluminum tubes (25 cm long with 10 cm inner diameter) into soil, removing the tubes, and then inserting an ion-exchange resin bag beneath the soil at the bottom of the tube. Disturbed cores were prepared with the same materials, but soil was excavated, mixed, and then filled into tubes fitted with ion-exchange resin bags at the bottom. Soil from six agricultural fields (five of which had more than 10 years of regular dairy manure application) was incubated over four time periods during summer and winter. A total of 13 soil?/?incubation-period combinations were tested. Disturbed cores tended to have more N mineralized than undisturbed cores (P < 0.10), especially in cores prepared with the lowest clay content soil. However, variability of N mineralized was lower in disturbed cores than undisturbed cores for 11 of the 13 soil?/?incubation periods. This lower variability was significant in two of the four incubation periods (P < 0.10). There was little difference in mean soil temperatures in disturbed versus undisturbed cores or within cores versus outside but adjacent to cores. However, in summer, the daily temperature range inside cores was significantly greater than the temperature range in soil outside cores (P < 0.01).     

Chemical manipulation of soil biota in a fescue meadow

Formalin, phorate, and sodium chlorate were used in field enclosures to create artificial habitats in a fescue meadow containing (1) reduced number of earthworms, (2) reduced numbers of earthworms and soil arthropods, and (3) reduction of total soil fauna and rate of microbial decomposition. Under these conditions, confined fescue litter initially decomposed more rapidly where arthropods or earthworms were suppressed than in controls with full complements of soil animals. After one year, reduction in numbers of soil animals had no net effect on litter decomposition, with faunal activity apparently having been compensated for by increased microbial activity. Where animals and microbial activity were reduced, rate of litter loss was depressed initially but recovered after 10 months as the effects of chemical suppression of microbial populations subsided. Contrary to the effects on annual loss of litter, elimination of all or portions of the soil fauna depressed rates of loss of confined and buried roots, reflecting the role of animals in fragmenting roots before their decomposition by microorganisms.Habitat manipulations had pronounced effects on the mobility of ¹³⁴Cs, and loss of the radionuclide from labelled litter was retarded despite an accelerated rate of decomposition. This effect apparently was associated with proliferation of microorganisms on litter and microbial immobilization of the radionuclide. Immobilization of ¹³⁴Cs occurred following chemical perturbations, but only after an initial period of rapid loss resulting from increased microbial activity. Distribution of ¹³⁴Cs in soil beneath tagged litter bags reflected the role of animals in element redistribution within soil. Restricted vertical mobility of the nuclide occurred except where chemical application killed vegetation within the experimental enclosures.     

Can the invasive earthworm,Amynthas agrestis,be controlled with prescribed fire?

Biological invasions are one of the most significant global-scale problems caused by human activities. Earthworms function as ecosystem engineers in soil ecosystems because their feeding and burrowing activities fundamentally change the physical and biological characteristics of the soils they inhabit. As a result of this “engineering,” earthworm invasions can have significant effects on soil physical, chemical and biological properties. The species Amynthas agrestis (family Megascolecidae) was introduced to the United States from Asia, and has expanded its distribution range to include relatively undisturbed forests. Here, to clarify life history traits, we reared individuals under seven different conditions of food provision using litter, fragmented litter and soil, and also analyzed the stable isotope ratios of field-collected specimens to investigate their food resources in the field. Second, we examined whether prescribed fire can be used to manage invasive earthworms. We constructed eight experimental plots, each with 100 individuals of A. agrestis each, and burned half of the plots. The feeding experiment showed that the earthworms in units containing soil and some form of organic matter (litter and/or fragmented litter) produced many cocoons, indicating that litter and fragmented litter are important food resources for them. Stable isotope analyses also supported this result. During the experimental fires, average soil temperature at 5 cm depth increased by only 7.7 °C (average maximum of 32.2 °C). Litter mass was significantly reduced by the fires. Although numbers of A. agrestis and cocoons recovered from burned and unburned plots were not different, the viability of cocoons was significantly lower in burned plots. Fire may also reduce the survival rate of juveniles in the next year by depriving them of their preferred food resource. Most native earthworms in the United States live in the soil, while many invasive ones live in the litter layer and soil surface. Therefore, prescribed fire could be a viable tool for control of invasive earthworms without negatively impacting native earthworm populations.     

蚯蚓体表液的组成及其减粘脱土机理分析

蚯蚓的体表液利于减粘脱土。本文利用现代测试仪器,结合生物化学分析技术,研究了蚯蚓体表液和泥鳅分泌液的组成;并应用土壤力学和生物化学等方面的理论,初步探讨了蚯蚓体表液减粘脱土的机理。     

Contrasting response to cropping of populations of earthworms and predacious nematodes in four soils

The activities of many soil animals make a positive contribution to soil processes and they should be considered for inclusion in indices of ‘soil quality'. To assess the potential use of nematodes and earthworms as indicators, the relationships between populations of earthworms (Lumbricidae), total number of nematodes and predacious nematodes (Mononchoidea) and six soil physical factors, soil carbon and pH were investigated in four New Zealand soils. In each, soil treatments ranged from 5–90 year pastures to cropping with maize or barley for 11–29 years. With increasing cultivation, trends in bulk density, total porosity, aggregate stability and concentration of total carbon were similar in all four soils. In Manawatu (Dystric Fluventic Eutrochrept) and Kairanga (Typic Endoaquept) soils earthworm populations were negligible under continuous cropping while Mononchoidea were abundant (11 600 and 34 100 m⁻²). In contrast, in Moutoa (Fluvaquentic Endoaquoll) and Wakanui (Aquic Ustochrept) soils earthworms persisted under cultivation, while Mononchoidea were less abundant (300 and 2500 m⁻²). At these two latter sites, aggregate stability was higher (1.14 and 0.92 mm mean weight diameter (MWD)) than in Manawatu and Kairanga soils (0.38 and 0.35 mm MWD). These relationships between aggregate stability, earthworm abundance and predacious nematodes show not only that some potential indicators may have a local rather than national application, but also that there are important interactions between soil physical properties and soil fauna which require further investigation.     

The effects of earthworms, botanical diversity and fertiliser type on the vertical distribution of soil nutrients and plant nutrient acquisition

The application of phosphorus (P)-based fertiliser to agricultural soils can result in a skewed vertical distribution of P down the soil profile, since the element tends to accumulate at the soil surface. Such accumulation can have detrimental effects on the environment, as the erosion of surface soil can facilitate the transfer of large quantities of P out of the field into water bodies. Earthworm and plant communities are intricately linked to vertical nutrient distributions in soil, with both communities either facilitating or negating the incorporation of nutrients into the soil matrix. This study aimed to investigate the effect of earthworm presence, plant community structure and fertiliser type to affect the distribution of nutrients in experimental mesocosms; with particular emphasis on the vertical distribution of P. Mesocosms were designed to simulate a soil which has a high P concentration at the surface compared to further down the soil profile. It was hypothesised that the presence of earthworms would facilitate the incorporation of P into the soil matrix and the presence of a more botanically diversity community would assimilate a greater quantity of soil nutrients. After 1 year, mesocosms were deconstructed into five depth ranges, and the distribution of nutrients were modelled and analysed. Results indicated that the presence of earthworms did redistribute soil nutrients from the surface into the matrix beneath. This redistribution was apparent from a reduction in nutrient concentrations in the 0–1 cm depth range. The presence of a more botanically diverse community not only assimilated greater soil nutrient concentrations, but also promoted a less even vertical distribution of soil nutrients, demonstrating the importance of soil biota and plant diversity in the redistribution of soil nutrients.