Horticultural Soil Research Articles

Insecticide dissipation from soil and plant surfaces in tropical horticulture of southern Benin, West Africa

In Sub-Saharan Africa, horticulture provides livelihood opportunities for millions of people, especially in urban and peri-urban areas. Although the vegetable agroecosystems are often characterized by intensive pesticide use, risks resulting therefrom are largely unknown under tropical horticultural conditions. The objective of this study therefore was to study the fate of pesticides in two representative horticultural soils (Acrisol and Arenosol) and plants (Solanum macrocarpon L.) after field application and thus to gain first insight on environmental persistence and dispersion of typical insecticides used in vegetable horticulture in Benin, West Africa. On plant surfaces, dissipation was rapid with half lives ranging from 2 to 87 h (alpha-endosulfan < beta-endosulfan < deltamethrin). Soil dissipation was considerably slower than dissipation from plant surfaces with half-lives ranging from 3 (diazinon) to 74 d (total endosulfan), but persistence of pesticides in soil was still reduced compared to temperate climates. Nevertheless, for deltamethrin and endosulfan, a tendency for mid-term accumulation in soil upon repeated applications was observed. The soil and plant surface concentrations of the metabolite endosulfan sulfate increased during the entire trial period, indicating that this compound is a potential long-term pollutant even in tropical environments.

Survey of organochlorine pesticides in horticultural soils and there grown Cucurbitaceae

Organochlorine pesticides (OCP) are still found in food and feed crops although they were applied about 40 years ago. There is a considerable knowledge gap concerning the extent of soil and crop contamination by OCP. We performed two surveys in 2002 and 2005 to assess the loads of OCP in 41 Swiss horticultural fields under organic and conventional production and corresponding Cucurbitaceae fruits (cucumbers, zucchini, and pumpkin), whereas these fields stay for intensive agricultural production in Europe. In addition, soil organic carbon, texture, and pH were measured also. OCP were detected in 27 out of 41 fields (65.9%). The farming practice had no influence on the contamination or level of OCP in soil. The sum of OCP-loads per field ranged from <0.01 to 1.3 mg kg −1 dry soil and pentachloroaniline (PCA, 2.1 mg kg −1), p, p′-DDT (0.5 mg kg −1), and p, p′-DDE and dieldrin (0.4 mg kg −1) were the most detected pesticides over all investigated soils. PCA (up to 0.02 mg kg −1), dieldrin (up to 0.04 mg kg −1), α-chlordane and cis-heptachloroepoxide (<0.01 mg kg −1) were detected in five cucumber samples out of 41 Cucurbitaceae samples. Statistical analysis revealed no significant influence of the measured soil properties on the OCP-load of soils and cucumbers, although there is evidence that the bioavailability of OCP in soils to Cucurbitaceae plants was influenced by the sorption of the compounds to soil organic matter and by the polarity of the pesticide molecules. It is suggested, that OCP contamination is widespread in all European regions with intensive plant production and associated pesticide use, and deserves more attention with respect to save food production.

Uptake of SigmaDDT, arsenic, cadmium, copper, and lead by lettuce and radish grown in contaminated horticultural soils.

Horticultural soils can contain elevated concentrations of selected trace elements and organochlorine pesticides as a result of long-term use of agrichemicals and soil amendments. A glasshouse study was undertaken to assess the uptake of weathered SigmaDDT {sum of the p, p'- and o, p-isomers of DDT [1,1,1-trichloro-2,2- bis( p-chlorophenyl)ethane], DDE [1,1-dichloro-2,2- bis( p-chlorophenyl)ethylene] and DDD[1,1-dichloro-2,2- bis( p-chlorophenyl)ethane]}, arsenic (As), cadmium (Cd), copper (Cu), and lead (Pb) residues by lettuce ( Lactuca sativa) and radish ( Raphanus sativus) from field-aged New Zealand horticultural soils. Concentrations of SigmaDDT, DDT, DDE, Cd, Cu, and Pb in lettuce increased with increasing soil concentrations. In radish, similar relationships were observed for SigmaDDT, DDE, and Cu. The bioaccumulation factors were less than 1 with the exception of Cd and decreased with increasing soil concentrations. Lettuce Cd concentrations for plants grown on four out of 10 assayed soils were equivalent to or exceeded the New Zealand food standard for leafy vegetables of 0.1 mg kg (-1) fresh weight. Concentrations of As, Pb, and SigmaDDT did not exceed available food standards. Overall, these results demonstrate that aged residues of SigmaDDT, As, Cd, Cu, and Pb in horticultural soils have remained phytoavailable. To be protective of human health, site-specific risk assessments and soil guideline derivations for residential settings with vegetable gardens need to consider the produce consumption pathway.

Effect of wood fly ash and compost on nitrification and denitrification in agricultural soil

Wood ash from biofuel combustion plants and compost from source-separated household waste are commonly spread on forest, agricultural and horticultural soils as a valuable source of plant nutrients. However, due to anthropogenic activities, wood ash may contain high concentrations of heavy metals. Heavy metals are toxic to microorganisms and therefore, soil microbial response to wood ash should be considered when soil is amended with ash. Compost is known to improve soil structure and may also act as a bioremediating agent, mitigating any toxic effects of wood ash on soil microorganisms. In the present study, the aim was to investigate whether wood ash has any toxic effect on soil microbial activity and, if this is the case, whether compost could mitigate these effects. The effect of wood fly ash on potential ammonium oxidation rate (PAO) and potential denitrification rate (PDA) in arable soil was investigated in one dose–response assay and in two pot experiments with or without plants, respectively. The treatments were amendment with wood fly ash, compost or a combination of wood fly ash and compost. PAO and PDA were assessed immediately or after 7 and 90 days in the different experiments. Wood fly ash decreased PDA to 16–56% compared to the control, while PAO varied between 82% and 205%. Sole compost addition stimulated both processes. This positive effect was also observed in the combined wood fly ash–compost treatment. In conclusion, wood ash had a toxic effect on PDA, both on an immediate, short-term and long-term basis. Amendment of compost clearly mitigated this toxic effect. The observed toxicity could be an effect of the metal content of ash.

Seaweed Compost as an Amendment for Horticultural Soils in Patagonia, Argentina

Seaweed (fresh, dry) or its products (extracts, composts, soil conditioners) have been long used in agriculture to enhance plant growth and productivity. In this study, we evaluated the effects that seaweed composts at different doses and degree of maturation had on the yield of tomatoes (Licopersicon esculentum Mill. cv. platense) grown on a horticultural soil in northeastern Patagonia. We used 10 tomato plants per treatmentplot set in a randomized block design. Treatments were: 1) soil without amendment, control (S); 2) 5 kg m−2 of compost aged 9 months (C9-5); 3) 10 kg m−2 of compost aged 9 months (C9-10); 4) 5 kg m−2 of compost aged 20 months (C20-5); and 5) 10 kg m−2 of compost aged 20 months (C20-10). Total weight and number of tomatoes, and aerial plant biomass (excluding fruits) were significantly higher for the compost treatments than those of the control. Also, compost treated plants bore mature fruits, in average, 9 days earlier and presented higher resistance to diseases than controls. The weight of tomatoes per plant grown in C20 was significantly higher than that of C9, differences that could be attributed to the lower salinity of compost C20 (C20 and C9 electrical conductivities were 1.5 and 15 dS m−1, respectively). The increased yield and resistance to diseases on tomato plants by addition of seaweed compost appear to be related to a complex number of factors not yet fully understood. It seems, however, that a combination of higher nutrient availability (mainly P) due to slight increases in pH of the soil amended, together with increases in readily available K and an improvement in soil physical conditions (increase in pore size and probably amelioration of hydric conditions), may have been responsible for the higher production of seaweed amended plots as compared to the control.

Cropping history and peat amendment-induced changes in strawberry field earthworm abundance and microbial biomass

Common agricultural practices, e.g. soil tillage and organic amendment, may affect field earthworm communities considerably. However, there is little data to show how long the changes persist after a certain action. The effect of peat, commonly used in Finland to improve the horticultural soil structure, on key soil organisms is also largely unknown. Earthworm abundance and microbial biomass were studied in a strawberry field experiment (soil type silty clay) with a history of different crops (strawberry, timothy, caraway, rye, turnip rape, fiddleneck, onion and buckwheat) and peat treatments. Sampling was carried out after three years of perennial cropping of strawberry. Half of the area was peat-amended twice three years apart. The earthworm community consisted mainly of Aporrectodea caliginosa and Lumbricus terrestris. Soil peat amendment almost doubled the number of endogeic A. caliginosa, but had no effect on the anecic L. terrestris. The effect of cropping history on earthworms diminished after three years of strawberry cropping. Only the positive effect of caraway on juvenile Lumbricus spp. was detectable three years after its cropping had been finished. However, some crops had secondary effects on the earthworm distribution without significant influence on their numbers while they were grown, e.g. high numbers of A. caliginosa were recorded from soil with a history of timothy ley. The effect of strawberry cropping was contradictory: six years of continuous strawberry cropping decreased the number of the anecic L. terrestris, but during the last three years on strawberry, the proportion of L. terrestris increased from 6% to 40% in the experimental area with a concomitant great drop in the number of A. caliginosa. The role of different agricultural practices (no tillage, mulching, inter-row grass cover and pesticides) is discussed. The crop-induced changes persisted in the microbial biomass for three years (onion cropping reduced microbial biomass C), but soil amendment had no effect on microbes. The abundance of A. caliginosa was associated with soil organic C, but not with soil microbial biomass.

Evaluation of composted sewage sludge as nutritional source for horticultural soils

Water deficit and soil degradation have become some of the major problems for crop production in semi-arid regions, as it is the South East of Spain. As a matter of fact, considerable productivity loss and risk of erosion have to be taken into account in these areas, especially those with an horticultural use (Davis, 1989). Utilization of sewage sludge in agriculture. Agricultural Progress 64, 72–80]. Horticultural soils are highly vulnerable and prone to erosion, as vegetables are generally fast-growing species under intensive exploitation regimes. High-rate chemical inputs contribute to horticultural soil degradation and have a dramatic effect on soil microbial population and nutrient balance whilst, at the same time, have a counter-effect on price competitiveness of the vegetables to be commercialized. In this paper we monitored variations in physical, chemical and biological properties of a cauliflower plot where four increasing quantities of compost were applied. We carried out a three-stage sampling schedule in order to check the effect of compost applications doses. We conclude that a 2 kg compost/m 2 application had a positive effect on physical and biological properties of the soil and provides a supply of nutrients to grow cauliflowers on its surface under intensive exploitation regimes without loss in biomass yield.

Effect of organic amendments on some physical, chemical and biological properties in a horticultural soil

The aim of the present work was to assess the response of selected soil physical, chemical and biological properties, after two applications of different organic amendments to a soil with an extended horticultural use. Vermicompost from household solid waste (HSW) and from horse and rabbit manure (HRM), and chicken manure (CM) were applied at rates of 10 and 20 Mg ha −1. The proportion of water stable soil aggregates (Ws) was significantly higher ( p < 0.05) in HSW, HRM and CM at 20 Mg ha −1. The proportion of ethanol stable soil aggregates (Es) was significantly higher in HSW, HRM and CM at 20 Mg ha −1, and CM at 10 Mg ha −1. After the first amendment application, HSW and HRM at 20 Mg ha −1 resulted in higher soil organic carbon (SOC), while all the treatments showed a significant increase after the second amendment application. Linear relationships were found between Ws and Es with SOC. An increment in microbial respiration in all the amended plots was observed with the exception of HRM at the rate of 10 Mg ha −1.

Trace element and ΣDDT concentrations in horticultural soils from the Tasman, Waikato and Auckland regions of New Zealand

The long-term routine use of agrichemicals can result in elevated levels of trace elements and persistent organic pollutants in soils. Trace element concentrations and ΣDDT levels were measured in soil (0–7.5 cm) samples collected from horticultural and grazing properties in 3 regions of New Zealand (Auckland, Tasman and Waikato). Elevated levels of arsenic (<2 to 58 mg kg − 1 ), cadmium (<0.1 to 1.5 mg kg − 1 ), copper (5 to 523 mg kg − 1 ), lead (5 to 243 mg kg − 1 ) and ΣDDT (<0.03 to 34.5 mg kg − 1 ) were detected in soils from all 3 regions. With the exception of cadmium and zinc, significantly higher levels of contaminants were generally detected in horticultural soils than in grazing soils. Our results have implications for the on-going use of agrichemicals as concentrations of cadmium, copper, tin and zinc in some samples exceeded ecotoxicity based soil criteria. The p, p′-DDE : DDT ratios indicate that the degradation of DDT in NZ horticultural soils may be inhibited by the co-contamination with trace elements.

The effect of mixing organic biological waste materials and high-N crop residues on the short-time N2O emission from horticultural soil in model experiments

Manipulating the N release from high-N crop residues by simultaneous mixing of these residues with organic biological waste (OBW) materials seems to be a possible method to reduce NO3− leaching. The aim of this study was to examine whether the incorporation of OBW materials together with a high-N crop residue (celery) had also an effect on N2O emission from horticultural soil under short-term and optimised laboratory conditions. A sandy loam soil and celery residues were mixed with different OBW materials and brought into PVC tubes at 80% water-filled pore space and 15°C. Every 2.5 h, a gas sample was taken and analysed by gas chromatography for its N2O concentration. The soil amended with only celery residues had a cumulative N2O emission of 9.6 mg N kg−1 soil in 50 h. When the celery residues were mixed with an OBW material, the N2O emission was each time lower than the emission from the celery-only treatment (between 3.8 and 5.9 mg N kg−1 soil during maximum 77 h), except with paper sludge (17.2 mg N kg−1 soil in 100 h). The higher N2O emission from the paper sludge treatment was probably due to its unusually low C:N ratio. Straw, green waste compost 1 (GWC1) and 2 (GWC2), saw dust, and tannic acid reduced the N2O emission of the celery treatment by 40 to 60%. Although the N2O reduction potential can be expected to be lower and with differing dynamics under field conditions, this study indicates that apart from reducing NO3− leaching, OBW application may at the same time reduce N2O emissions after incorporation of high-N crop residues.

Screening plant species native to Taiwan for remediation of 137Cs-contaminated soil and the effects of K addition and soil amendment on the transfer of 137Cs from soil to plants

This study aims to screen plant species native to Taiwan that could be used to eliminate 137Cs radionuclides from contaminated soil. Four kinds of vegetables and two kinds of plants known as green manures were used for the screening. The test plants were cultivated in 137Cs-contaminated soil and amended soil which is a mixture of the contaminated one with a horticultural soil. The plant with the highest 137Cs transfer factor was used for further examination on the effects of K addition on the transfer of 137Cs from the soils to the plant. Experimental results revealed that plants cultivated in the amended soil produced more biomass than those in the contaminated soil. Rape exhibited the highest production of aboveground parts, and had the highest 137Cs transfer factor among all the tested plants. The transfer of 137Cs to the rape grown in the soil to which 100 ppm KCl commonly used in local fertilizers had been added, were restrained. Results of this study indicated that rape, a popular green manure in Taiwan, could remedy 137Cs-contaminated soil.

Localisation of nickel and mineral nutrients Ca, K, Fe, Mg by Scanning Electron Microscopy microanalysis in tissues of the nickel-hyperaccumulator Alyssum bertolonii Desv. and the non-accumulator Alyssum montanum L.

Plants of the nickel-hyperaccumulator Alyssum bertolonii Desv. and of the non-accumulator A. montanum L. growing on a serpentine site in Tuscany, Italy, and plants of A. montanum from a nearby non-serpentine site were analysed for metal concentration and localisation. The leaves of A. bertolonii contained 160 times more nickel than those of A. montanum from the same site, thus demonstrating its hyperaccumulation capacity towards this metal. On the other hand, both species showed an inversion of the Ca/Mg ratio in their organs relative to the soil. Nickel localisation in plant tissues was examined by Scanning Electron Microanalysis (SEM/EDX). In A. bertolonii, a specific pattern of nickel distribution was detected, with the highest concentrations present in parenchyma and sclerenchyma cells for the roots; in the shoots, the highest amounts of nickel were found in the stem epidermis, the leaf epidermal surface, and the leaf trichome base. This particular nickel tissue distribution pattern was not found in the non-accumulator A. montanum growing on serpentine soil. Other mineral nutrients, namely Mg, Ca, K, Fe, instead, had a similar distribution in the two species. The A. montanum plants from the non-serpentine site had very low nickel levels in their tissues, and these were of the same magnitude as those found in A. bertolonii plants grown in a greenhouse on commercial horticultural soil with low nickel concentration. In A. bertolonii plants, the tissue-specific allocation patterns appeared to depend on the degree of nickel hyperaccumulation, which is, in turn, directly linked to the soil characteristics.

Multi-elemental EDXRF mapping of polluted soil from former horticultural land

The distribution of major and trace elements was systematically investigated by use of energy dispersive X-ray fluorescence spectrometry (EDXRF) on a former horticultural soil. The purpose of the study was to combine mapping of soil element concentration levels with multivariate statistics for characterisation of soil metal pollution in relation to previous and present land use. A 1-ha study site was chosen from a former horticulture where a previous preliminary survey indicated increased concentration levels of toxic elements. The soil was sampled from the top 20 cm of the soil surface in a 10×10-m grid-like pattern covering the 1-ha study area. In addition, three soil profiles were studied. The elemental composition of the soil samples was investigated by EDXRF while the composition of aqueous soil extracts was determined by total reflection X-ray fluorescence spectrometry (TXRF). Based on mapping and multivariate statistically analysis of the data obtained by EDXRF, most elements were found in almost constant concentration levels in the top soil throughout the investigated site. However, the contents of the toxic elements Zn, Cu, As, and Pb were found to vary significantly within the area. Hence, the samples with high accumulations of As also contained relatively high amounts of Zn, Cu, and Pb, which indicates that toxic-element-containing pesticides have been applied to the soil surface in the area of the former green houses at the study site. The Pb/As mass ratio in the soil indicates that PbHAsO 3 was the preferential lead arsenate used for pest management at the investigated site, while Cu as Bordeaux liquid (CuSO 4) and Zn were applied to minimize the leaf damaging effect from the former compounds. Calculations indicated that As annually was applied to the soil in the former greenhouses in doses up to 4 kg As/ha while Pb had been annually applied in doses up to 12 kg Pb/ha. The enrichment of Zn, Cu, As and Pb was greatest in the top 20 cm of the soil and no anthropogenic enrichment of these elements occurred below a depth of 50 cm, indicating that the toxic elements are rather immobile in this soil. The results of this investigation suggest that EDXRF used in combination with multivariate statistics is a strong tool for multi-element mapping of elemental contents, sources and mobility in the terrestrial environment.

Chemical Changes in Agricultural Soils of Korea: Data Review and Suggested Countermeasures

The monitoring of chemical properties, including heavy metals, in soils is necessary if better management and remediation practices are to be established for polluted soils. The National Institute of Agricultural Science and Technology initiated a monitoring study that investigated fertility and heavy metal contents of the benchmarked soils. The study covered paddy soils, upland soils, and horticultural soils in the plastic film houses, and orchard soils throughout the Korea from 1990 to 1998. Likewise, 4047 samples of paddy and 2534 samples of plastic house in 1999 and 2000 were analyzed through the Soil Environment Conservation Act. Soil chemical properties such as pH, organic matter, available phosphate and extractable calcium, magnesium and potassium contents, and heavy metal contents such as cadmium, copper, lead, zinc, arsenic, mercury, and cobalt contents were analyzed. The study showed that the average contents of organic matter, available phosphate, and extractable potassium rapidly increased in plastic house soils than in upland or paddy soils. Two kinds of fertilizer recommendation systems were established for the study: the standard levels by national soil average data for 77 crops and the recommendation by soil test for 70 crops. Standard nitrogen fertilizer application levels for cereal crops changed from 94 kg/ha in 1960s, 99 kg/ha in 1970s, 110 kg/ha in 1980s to 90 kg/ha in 1990s. The K2O-fertilizer also changed from 67 kg/ha in 1960s, 76 kg/ha in 1970s, 92 kg/ha in 1980s, and only 44 kg/ha in 1990s. In rice paddy fields, the average contents of Cd, Cu, Pb, and Zn in surface soils (0-15 cm depth) were 0.11 mg kg(-1) (ranged from 0 to 1.01), 4.70 mg kg(-1) (0-41.59), 4.84 mg kg(-1) (0-66.44), and 4.47 mg kg(-1) (0-96.70), respectively. In the uplands, the average contents of Cd, Cu, Pb, Zn, and As in surface soils (0-15 cm depth) were 0.135 mg kg(-1) (ranged from 0 to 0.660), 2.77 mg kg(-1) (0.07-78.24), 3.47 mg kg(-1) (0-43.00), 10.70 mg kg(-1) (0.30-65.10), and 0.57 mg kg(-1) (0.21-2.90), respectively. In plastic film houses, the average contents of Cd, Cu, Pb, Zn, and As in surface soil were 0.12 mg kg(-1) (ranging from 0 to 1.28), 4.82 mg kg(-1) (0-46.50), 2.68 mg kg(-1) (0-46.50), 31.19 mg kg(-1) (0.19-252.0), and 0.36 mg kg(-1) (0-4.98), respectively. In orchard fields, the average contents of Cd, Cu, Pb, Zn, As, and Hg in surface soils (0-20 cm depth) were 0.11 mg kg(-1) (ranged from 0-0.49), 3.62 mg kg(-1) (0.03-45.30), 2.30 mg kg(-1) (0-27.80), 16.60 mg kg(-1) (0.33-105.50), 0.44 mg kg(-1) (0-4.14), and 0.05 mg kg(-1) (0.01-0.54), respectively. For polluted soils with over the warning content levels of heavy metals, fine red earth application, land reconsolidation and soil amelioration such as lime, phosphate, organic manure, and submerging were recommended. For the countermeasure areas, cultivation of non-edible crops such as garden trees, flowers, and fiber crops; land reformation; and heavy application of fine red earth (up to 30 cm) were strongly recommended. Land use techniques should be changed to be harmonious with the environment to increase yield and income. Soil function characteristics should be taken into account.

Soil Respiration and Carbon Storage of an Acrisol Under Forest and different Cultivations in rio de Janeiro State, Brazil

Soil respiration rates of a clay-loam textured Acrisol under different uses (Atlantic forest, manioc, horticulture and pasture) from Rio de Janeiro State were measured. The relationship between carbon dioxide (CO2) emissions and soil physico-chemical properties were investigated. Rates of CO2 emission of two sites (Atlantic forest and horticulture) were also evaluated in different seasons in 1997 and 1998. In the forest site, monthly means of measured respiration rates showed good correlation with soil temperature in the range 19.6–24.1°C (r2 = 0.89). In the horticulture site, no change was observed with soil moisture alone, in the range 3.0–13.2 wt%. In the horticulture soil, even when the surface soil was very dry, respiration rates increased in the hot, wetter summer but remained higher than the mean flux from forest soil. The CO2 emission flux of the Acrisol under different use showed good correlation with soil temperature (r2 = 0.72) and moisture (r2 = 0.61).

Integration of water treatment, environmental and information technologies: Amagasaki project

The Hanshin Water Supply Authority (HWSA) supplies drinking water to approximately 2.4 million consumers in the Hanshin area, including the city of Kobe. The HWSA has completed a project integrating two aging plants into a new water treatment plant (Amagasaki WTP) with a capacity of 373,000 m3 per day. The Amagasaki WTP has three significant special merits: water treatment, environmental, and information technology. The water treatment system is based on a multiple-barrier concept that estimates the value of water treatment technology not by individual processes, but by the overall performance of the system. The treatment train consists of coagulation/sedimentation, ozonation/activated carbon fluidized-bed adsorption, and coagulation/high-rate filtration, most of which fully utilize upward-flow. The key environmental technology characteristic of the new WTP is its achievement of zero-emissions. This design reduces CO2 discharge from the plant, as well as making it possible to completely recycle the sludge as an alternate material of agricultural and horticultural soils. Improvement of customer relations is a feature of the information technology. The authority provides information on the safety of the finished drinking water, watershed management, and the maintenance of source water quality. A visitors' area and emergency water supply facility for use in disasters have also been set up at the WTP. The Amagasaki WTP started commercial operation in April 2001. The completion of this renovated plant will significantly raise the quality of service to the customers.

Factors affecting N immobilisation/mineralisation kinetics for cellulose-, glucose- and straw-amended sandy soils

The kinetics of N immobilisation/mineralisation for cellulose-, glucose- and straw-amended sandy soils were investigated in a series of laboratory incubations. Three Scottish soils expected to exhibit a range of biological activity were used: a loamy sand, intensively cropped horticultural soil subject to large inputs of inorganic fertilisers and pesticides (Balmalcolm – pH 7.2, organic matter 3.3%); a sandy loam soil highly enriched with organic manures and used for organic vegetable production (Strathmiglo – pH 7.1, organic matter 7.3%); and a loamy sand soil of low fertility in a zero-grazing, low intensity organic ley-arable rotation (Aldrochty pH 6.0, organic matter 5.0%). Incubations of soils with 1,000 mg cellulose-C kg–1 soil at 8°C, showed peak N immobilisation of 71±6, 92±6 and 65±15 mg N g–1 added C for the Balmalcolm (after 34 days), Strathmiglo (after 34 days) and Aldrochty soils (after 63 days). The N remineralisation by the end of the incubation (>300 days) was 0, 50 and 22 mg N g–1 cellulose-C in the Balmalcolm, Strathmiglo soil and Aldrochty soils, respectively. Only about 30% of the N immobilisation could be explained by soil microbial biomass N accumulation (much less than expected from model simulations). The C/N ratio of the extra microbial biomass was quite wide (19). Bacterial, protozoan and nematode biomass accounted for only 18%, 0.1% and 0.5% of the extra C immobilisation, respectively. These data suggest that fungal biomass growth and deposition of recalcitrant fungal metabolites are the main sinks for the N immobilised. With 1,000 mg glucose-C kg –1 added to the Balmalcolm soil, about 75 mg N g–1 added C were immobilised after 6 days. Under less well aerated conditions at 15°C, immobilisation of only 10–20 mg N g–1 added cellulose C took place in 2–4 weeks, but soluble organic C increased greatly. The N remineralised after 4–6 weeks.

Organic matter components and aggregate stability after the application of different amendments to a horticultural soil

Organic matter components and aggregate stability after the application of different amendments to a horticultural soil

Cadmium accumulation in agricultural soils in Western Australia

Phosphatic fertilizers contain appreciable concentrations of cadmium (Cd) which may elevate the Cd concentrations of soils and crops, yet the impact of Cd on poorly buffered Western Australian soils is not known. We measured soil Cd, P and Zn concentrations at different depths and with total (mixed acid) and partial extractants (CaCl2, EDTA and HCl) at sites with a known phosphate fertilizer history. Accumulation of Cd in soils where P fertilizers had been applied varied greatly, with the Cd content of fertilized soils generally having significantly higher Cd contents than for unfertilized soils. In a ferruginous sandy loam, the highest concentrations of Cd were in the top 2 cm and these concentrations increased with increasing amounts of fertilizer application. A gravelly lateritic soil in an orchard contained 3.6 mg Cd kg-1, which was 20-fold higher than the equivalent unfertilized soil. Very sandy horticultural soils which are characteristic of Western Australia did not have higher exchangeable Cd, and showed small increases in total Cd, despite the high amounts of phosphatic fertilizers applied. The largest proportional increases in soil Cd were generally for analyses using partial extractants rather than for total Cd.

Earthworm communities in grasslands and horticultural soils

In a survey of 42 farm sites, comprising grassland and two types of horticultural farms (growing vegetables or flower bulbs), earthworm communities were sampled by hand-sorting and a number of soil physico-chemical characteristics recorded. For heavy metals the availability in the soil solution was estimated based on the measured absolute content. Abundance, biomass and species richness were significantly higher in grassland soils than in horticultural soils, and within the horticultural farms significantly higher in vegetable than in flower-bulb farms. No epigeic species were found in horticultural soils. The differences between the various farm types were probably related to the intensity of management practices, such as soil tillage, harvesting and crop protection measures, that result in less soil organic matter of lower quality. The data from the grassland farms were analyzed in conjunction with the physico-chemical soil characteristics, applying canonical correspondence analysis. Community parameters such as species richness and diversity apparently were not related to soil characteristics, but an appreciable part of the variation in abundance and biomass of several individual species could be explained by factors such as lutum content (particles <16 7m), pH, bio-availability of metal ions and geographical position of the sample site. It is concluded that repeated surveys of this type may become a valuable tool for monitoring soil quality.