Michael J. Goss

Movement of Faecal Bacteria through the Vadose Zone

The impact of biosolid and soil type on the movement of faecal coliforms through the vadose zone was investigated following the application of animal manure to soil. Two types of biosolid, solid and liquid manure, were applied to two soil types at a wide range of initial water contents. Bacteria present in the soil solution were collected using calibrated ceramic-porous-cup samplers. Estimated bacterial migration velocities in the soil profile were consistent with the hypothesis that bacteria move mostly through soil macropores, as the rate of transport was faster than the average pore-water velocity. Macropore transport was more likely to occur in wet soils, but it was not necessarily restricted to soils with high initial soil water content. A larger soil clay content, lower total soil porosity, and lower saturated hydraulic conductivity resulted in a greater likelihood that suspended bacteria would be funnelled through pores of larger diameter and faster pore water velocity, increasing the potential vertical transport length of bacteria through the vadose zone. Total porosity was not a significant factor in enhancing deep transport of faecal bacteria. The potential of faecal bacteria to be transported to depth in soil was correlated with the water content of the manure. We conclude that application of animal manure to soil can readily lead to groundwater contamination with faecal bacteria especially under moist soil conditions, and that macropores are important in the transport.

A Review of the Use of Organic Amendments and the Risk to Human Health

Abstract Historically, organic amendments—organic wastes—have been the main source of plant nutrients, especially N. Their use allows better management of often-finite resources to counter changes in soils that result from essential practices for crop production. Organic amendments provide macro- and micronutrients, including carbon for the restoration of soil physical and chemical properties. Challenges from the use of organic amendments arise from the presence of heavy metals and the inability to control the transformations required to convert the organic forms of N and P into the minerals available to crops, and particularly to minimize the losses of these nutrients in forms that may present a threat to human health. Animal manure and sewage biosolids, the organic amendments in greatest abundance, contain components that can be hazardous to human health, other animals and plants. Pathogens pose an immediate threat. Antibiotics, other pharmaceuticals and naturally produced hormones may pose a threat if they increase the number of zoonotic disease organisms that are resistant to multiple antimicrobial drugs or interfere with reproductive processes. Some approaches aimed at limiting N losses (e.g. covered liquid or slurry storage, rapid incorporation into the soil, timing applications to minimize delay before plant uptake) also tend to favor survival of pathogens. Risks to human health, through the food chain and drinking water, from the pathogens, antibiotics and hormonal substances that may be present in organic amendments can be reduced by treatment before land application, such as in the case of sewage biosolids. Other sources, such as livestock and poultry manures, are largely managed by ensuring that they are applied at the rate, time and place most appropriate to the crops and soils. A more holistic approach to management is required as intensification of agriculture increases.

Strategies to decrease nitrate leaching in the Brimstone Farm Experiment, Oxfordshire, UK, 1988–1993: the effects of winter cover crops and unfertilised grass leys

Nitrate losses in drainflow were measured over five years on eight hydrologically isolated field plots, pairs of which had the following cropping regimes: (a) a 3-yr unfertilised, ungrazed grass ley followed by winter and spring cereals, (b) mixed cropping including winter cover crops, spring cereals, winter cereals, winter fallow and spring beans, (c) a similar sequence to (b) but with a winter fallow replacing the cover crop in the first year and a winter cover crop replacing the fallow in the third year, and (d) continuous winter cereals (control plots). Less nitrate was lost in winter drainflow from winter cover crops than from the winter fallows, but over all five years less nitrate was leached from the continuous cereal plots than from those with mixed cropping. Most of the extra nitrate lost from the mixed cropping regimes probably resulted from mineralisation of the cover crop residues, which occurred at times when subsequent crops could not take advantage of the mineral nitrogen released. Crops grown after the grass ley and cover crops did not benefit from their residues, in terms of either grain yield or of total nitrogen uptake. We conclude that on heavy clay soils in UK a cropping regime of continuous winter cereals offers the best compromise between profitable crop production and minimised nitrate loss to surface waters.

Analysis of matrix effects critical to microbial transport in organic waste‐affected soils across laboratory and field scales

[1] Organic waste applications to soil (manure, various wastewaters, and biosolids) are among the most significant sources of bacterial contamination in surface and groundwater. Transport of bacteria through the vadose zone depends on flow path geometry and stability and is mitigated by interaction between soil, soil solution, air-water interfaces, and characteristics of microbial surfaces. After initial entry, the transport through soil depends on continued entrainment of bacteria and resuspension of those retained in the porous structure. We evaluated the retention of bacteria-sized artificial microspheres, varying in diameter and surface charge and applied in different suspending solutions, by a range of sieved soils contained in minicolumns, the transport of hydrophobic bacteria-sized microspheres through undisturbed soil columns as affected by waste type under simulated rainfall, and the field-scale transport of Enterococcus spp. to an unconfined sandy aquifer after the application of liquid manure. Microsphere retention reflected microsphere properties. The soil type and suspending solution affected retention of hydrophilic but not hydrophobic particles. Retention was not necessarily facilitated by manure-microsphere-soil interactions but by manure-soil interactions. Undisturbed column studies confirmed the governing role of waste type on vadose-zone microsphere transport. Filtration theory applied as an integrated analysis of transport across length scales showed that effective collision efficiency depended on the distance of travel. It followed a power law behavior with the power coefficient varying from � 0.4 over short distances to >0.9 over 1 m (i.e., very little filtration for a finite fraction of biocolloids), consistent with reduced influence of soil solution and biocolloid properties at longer travel distances.

Remediation of a Sandy Soil Contaminated with Cadmium, Nickel, and Zinc using an Insoluble Polyacrylate Polymer

Abstract This study was carried out to investigate whether an insoluble polyacrylate polymer could be used to remediate a sandy soil contaminated with cadmium (Cd) (30 and 60 mg Cd kg−1 of soil), nickel (Ni) (50 and 100 mg Ni kg−1 of soil), zinc (Zn) (250 and 400 mg Zn kg−1 of soil), or the three elements together (30 mg Cd, 50 mg Ni, and 250 mg Zn kg−1 of soil). Growth of perennial ryegrass was stimulated in the polymer‐amended soil contaminated with the greatest amounts of Ni or Zn, and when the three metals were present, compared with the unamended soil with the same levels of contamination. Shoots of plants cultivated in the amended soil had concentrations of the metals that were 24–67% of those in plants from the unamended contaminated soil. After ryegrass had been growing for 87 days, the amounts of water‐extractable metals present in the amended soil varied from 8 to 53% of those in the unamended soil. The results are consistent with soil remediation being achieved through removal of the metals from soil solution.

Comparison of Chemical Methods of Assessing Potentially Available Organic Nitrogen from Organic Residues Applied to a Sandy Soil

Abstract More than 90% of the nitrogen (N) in soils is bond as organic N compounds. The available N can be estimated on the mineral N released during time‐consuming incubations of soil. Several chemical methods have been developed as substitutes for incubations. On the other hand, there has been an increase in waste production. Residues could potentially offset the need for mineral fertilizers, being both an economic and environmental benefit. Thus, the development of a routine method for prediction of N supply both from soil organic matter (SOM) and the application of organic residues is of great interest. An incubation experiment was performed in a Cambic Arenosol to evaluate different chemical methods. Air‐dried soil was mixed with increasing amounts of composted solid municipal waste, secondary pulp‐mill sludge, hornmeal, poultry manure, the solid phase from pig slurry, and composted pig manure. Samples were incubated for 244 days under a controlled environment. Among the chemical extractants studied, hot 2 M potassium chloride (KCl) and hot 0.01 M calcium chloride (CaCl2) showed promise in indicating values of N0 (potentially available nitrogen), and these simple methods are suitable for use in routine laboratory conditions.

A review on biomass production from C4 grasses: yield and quality for end-use.

With a dry biomass production exceeding 40Mgha(-1) in many environments, Miscanthus spp. is the most productive perennial C4 grass species thanks to five advantages over North American prairie tallgrasses. However, miscanthus has a slower nutrient remobilization system, resulting in higher nutrient concentrations at harvest. Perennial C4 grasses benefit from soil microbial associations, reducing their nutrient needs. For combustion purposes, grasses with low moisture content, high lignin and low nutrients are desired. For ethanol, preferred feedstock will have lower lignin, higher sugars, starch, or cellulose/hemicellulose depending on the conversion method. Species with high stem-to-leaf ratio provide better biofuel conversion efficiency and quality. Recently-developed transgenic switchgrass lines have much higher ethanol yields and lower transformation costs. Further selection and breeding are needed to optimize biomass quality and nutrient cycling.

Techniques for Arbuscular Mycorrhiza Inoculum Reduction

Given the ubiquous presence of AM fungi, a major constraint to the evaluation of the activity of AM colonization has been the need to account for the indigenous soil native inoculum. This has to be controlled (i.e., reduced or eliminated) if we are to obtain a true control treatment for analysis of arbuscular mycorrhizas in natural substrates. There are various procedures possible for achieving such an objective, and the purpose of this chapter is to provide details of a number of techniques and present some evaluation of their advantages and disadvantages.

ESTIMATING SHORT- AND MEDIUM-TERM AVAILABILITY TO CEREALS OF NITROGEN FROM ORGANIC RESIDUES

Overused soil resources and the build-up of organic residues from industrial processes have resulted in increased risk of environmental contamination. Recycling of organic residues from industry by incorporation into agricultural soil, can provide valuable organic amendment as well as supply nutrients to crops. The effect of applying organic amendments to an agricultural sandy soil on the nitrogen nutrition of wheat (Triticum aestivum L.) and residual effects on the growth of a following maize crop (Zea mays, L.), were assessed under semi-controlled environmental conditions and were compared to nitrogen mineralization prediction obtained from an aerobic incubation. Six different organic residues (composted municipal solid waste, secondary pulp-mill sludge, hornmeal, poultry manure, the solid phase from pig slurry and composted pig manure) were added to a Cambic arenosol, incubated or used in pot experiments, to evaluate and try to predict the availability to crop plants of nitrogen released from these materials. Poultry manure was the most effective amendment in making nitrogen available and enhancing nitrogen uptake by wheat plants resulting in greater dry matter yield. The dried solid phase from pig slurry and hornmeal were also beneficial to wheat growth. There was a greater recovery of nitrogen (N), from organic materials studied, by a maize crop. Poultry manure was the residue that provided a greater residual effect on N supply to maize.

New Tools to Investigate Biological Diversity and Functional Consequences

To exploit the opportunities offered by our increased understanding of arbuscular mycorrhiza (AM) diversity and the potential to manage it requires greater knowledge of the indigenous AM fungi (AMF) involved in the symbiosis with target plants. Our ability to fully describe AMF diversity is still at early stage in terms of the taxonomic units present, despite recent developments in DNA sequencing capacity. The information required is the number of species or taxonomic groups present, the number of individuals that can be identified as belonging to the same group, and the level of variability there is within such a group in terms of their capability to enhance growth. With the techniques available it is possible to be precise over the molecular makeup of individuals but it is more difficult to be certain as to which species they may belong, particularly if that species has been mainly been identified through its morphological characteristics, especially those of its spores, rather than from DNA sequencing. Consequently it is operational taxonomic units (OTUs) or virtual taxa that are used to describe taxonomic groups, which are identified solely through molecular techniques. Nevertheless variability exists in both species and OTUs. Effectiveness of a mycorrhizal symbiosis depends on environmental conditions, but is also influenced by the community of higher plants as well as the local soil biota. Establishing linkages between genetic and the functional diversity under field conditions with biotic and abiotic stresses is more challenging. Successful assemblages of AMF combine the ability to acquire P and to protect host plants against pathogens or abiotic stresses, consistent with greater diversity being associated with greater ecosystem functioning through enhanced trait richness. To capitalize on the potential benefits from managing AMF diversity, appropriate solutions are needed for different agroecosystems and applicable on a site-by-site basis. Identifying genetic and molecular markers that allows quantitative assessment of the potential to exploit indigenous AMF is crucial. Within AMF hyphae two markers have been identified in the ribosomal DNA that can be used to identify OTUs. Similarly mitochondrial large ribosomal subunit sequences have also been used. Short-term considerations suggest that more effort is needed to identify key markers in major crops for AMF assemblages that function effectively to offset major biotic and abiotic stresses.To exploit the opportunities offered by our increased understanding of arbuscular mycorrhiza (AM) diversity and the potential to manage it requires greater knowledge of the indigenous AM fungi (AMF) involved in the symbiosis with target plants. Our ability to fully describe AMF diversity is still at early stage in terms of the taxonomic units present, despite recent developments in DNA sequencing capacity. The information required is the number of species or taxonomic groups present, the number of individuals that can be identified as belonging to the same group, and the level of variability there is within such a group in terms of their capability to enhance growth. With the techniques available it is possible to be precise over the molecular makeup of individuals but it is more difficult to be certain as to which species they may belong, particularly if that species has been mainly been identified through its morphological characteristics, especially those of its spores, rather than from DNA sequencing. Consequently it is operational taxonomic units (OTUs) or virtual taxa that are used to describe taxonomic groups, which are identified solely through molecular techniques. Nevertheless variability exists in both species and OTUs. Effectiveness of a mycorrhizal symbiosis depends on environmental conditions, but is also influenced by the community of higher plants as well as the local soil biota. Establishing linkages between genetic and the functional diversity under field conditions with biotic and abiotic stresses is more challenging. Successful assemblages of AMF combine the ability to acquire P and to protect host plants against pathogens or abiotic stresses, consistent with greater diversity being associated with greater ecosystem functioning through enhanced trait richness. To capitalize on the potential benefits from managing AMF diversity, appropriate solutions are needed for different agroecosystems and applicable on a site-by-site basis. Identifying genetic and molecular markers that allows quantitative assessment of the potential to exploit indigenous AMF is crucial. Within AMF hyphae two markers have been identified in the ribosomal DNA that can be used to identify OTUs. Similarly mitochondrial large ribosomal subunit sequences have also been used. Short-term considerations suggest that more effort is needed to identify key markers in major crops for AMF assemblages that function effectively to offset major biotic and abiotic stresses.