Unlimed Soil Research Articles

The effects of soil type and chemical treatment on nickel speciation in refinery enriched soils: A multi-technique investigation

Aerial deposition of Ni from a refinery in Port Colborne, Ontario, Canada has resulted in the enrichment of 29 km 2 of land with Ni concentrations exceeding the Canadian Ministry of the Environment’s remedial action level of 200 mg kg −1. Several studies on these soils have shown that making the soils calcareous was effective at reducing chemically extractable Ni, as well as alleviating Ni phytotoxicity symptoms in vegetable crops grown in the vicinity of the refinery. Conversely, dolomitic limestone additions resulted in increased uptake of Ni in the Ni hyperaccumulator Alyssum murale ‘Kotodesh’, a plant whose use was proposed as a remediation strategy for this area. In this paper we use multiple techniques to directly assess the role soil type and lime treatments play in altering the speciation of Ni in the Welland loam and Quarry muck soils around the refinery and relate these findings to Ni mobility and bioavailability. Stirred-flow dissolution experiments using pH 4 HNO 3 showed that Ni release from the limed Quarry muck and Welland loam soils was reduced (∼0.10%) relative to the unlimed soils (∼2.0%). Electron microprobe analysis (EMPA) identified approximately spherical NiO and Ni metal particles, which are associated with no other metals, and range from 5 to 50 μm in diameter. Synchrotron micro-X-ray absorption fine structure and X-ray fluorescence spectroscopies showed that Ni and Al layered double hydroxide (Ni–Al LDH) phases were present in both the limed and unlimed mineral soils, with a tendency towards more stable (e.g., aged-LDH and phyllosilicate) Ni species in the limed soil, possibly aided by the solubilization of Si with increasing pH. In the muck soils, Ni–organic complexes (namely fulvic acid) dominated the speciation in both limed and unlimed soils. The results reported herein show that both soil type and treatment have a pronounced effect on the speciation of Ni in the soils surrounding the Port Colborne refinery. We provide the first evidence that Ni–Al LDH phases can form in anthropogenically enriched mineral field soils at circumneutral pH, and can lead to a reduction in Ni mobility. In the organic soils Ni is strongly complexed by soil organic matter; a property enhanced with liming. Interestingly, increased accumulation of Ni by A. murale grown in the limed muck and loam soils indicates that the plant may be capable of removing Ni from those fractions typically considered unavailable to most plants.

Effect of Liming on the Plant Availability and Distribution of Zinc and Copper among Soil Fractions

Information on the redistribution of applied micronutrients into different fractions as a result of lime application is important to predict plant accumulation of nutrients and to select appropriate chemical extraction procedures for evaluation of micronutrient availability. The present work was carried out to study the influence of liming on the availability and redistribution of zinc (Zn) and copper (Cu) among soil fractions. Additionally, the effect of liming was evaluated on the recovery of these micronutrients by different chemical extractants (Mehlich‐1, Mehlich‐3, and diethylenetriaminepentaacetate (DTPA), which were correlated with Zn and Cu concentrations in corn (Zea mays L.) plants and soil fractions (exchangeable, organic matter, amorphous iron oxides, and crystalline iron oxides). The results showed that Zn added to soil samples that did not receive lime was retained mainly in the exchangeable and organic matter fractions. The liming resulted in distribution of Zn into iron oxides and as a result decreased the plant accumulation of Zn. Mehlich‐3 was the most efficient extractant to predict the plant accumulation of Zn in the acid soils, whereas DTPA was the most efficient in the limed soils. The oxide crystalline fraction was the major fraction responsible for retaining Cu in the soils. However, Cu added to soil was distributed mainly into organic matter. Mehlich‐3 was the most suitable extractant for predicting the bioavailability of Cu in limed or unlimed soils.

A Comparison of Hydroponics, Soil, and Root Staining Methods for Evaluation of Aluminum Tolerance in Medicago truncatula (Barrel Medic) Germplasm

ABSTRACTAluminum toxicity and soil acidity are major constraints in alfalfa (Medicago sativa subsp. sativa) production in the world. Despite intense research efforts, neither an effective screening procedure nor an Al‐tolerant alfalfa germplasm is available. This dictates the need for identifying a new source of Al‐tolerant genes in the closely related species M. truncatula (barrel medic). Our objectives were to compare three Al tolerance screening methods: (i) a seedling‐based hydroponics method, (ii) a soil‐based plant method, and (iii) an Al‐stressed seedling‐based lumogallion root staining method in 32 M. truncatula accessions. The soil system compared the genotypes for dry root and shoot weights in unlimed soil and for relative weights. The lumogallion root staining of Al‐stressed seedlings compared the genotypes for fluorescence intensity of Al‐bound lumogallion within the root tips. In the hydroponics system, the genotypes were compared for root elongation and relative growth. The three methods were different from each other, with altered rankings for genotypes across the methods. The soil assay demonstrated a higher capacity for discriminating Al response among genotypes with a higher reproducibility. Most of the genotypes that were Al‐tolerant in soil were also Al‐tolerant using the hydroponics and root staining methods. The results suggested that a combination of soil‐based and hydroponics screening might be essential to identify Al‐tolerant genotypes possessing multiple Al tolerance mechanisms.

Carbon and nitrogen mineralization in acidic, limed and calcareous agricultural soils: Apparent and actual effects

Soil pH and calcium carbonate contents are often hypothesized to be important factors controlling organic matter turnover in agricultural soils. The aim of this study was to differentiate the effects of soil pH from those related to carbonate equilibrium on C and N dynamics. The relative contributions of organic and inorganic carbon in the CO 2 produced during laboratory incubations were assessed. Five agricultural soils were compared: calcareous (74% CaCO 3), loess (0.2% CaCO 3) and an acidic soil which had received different rates of lime 20 years ago (0, 18 or 50 t ha −1). Soil aggregates were incubated with or without rape residues under aerobic conditions for 91 days at 15 °C. The C and N mineralized, soil pH, O 2 consumption and respiratory quotient (RQ=ΔCO 2/ΔO 2) were monitored, as well as the δ 13C composition of the evolved CO 2 to determine its origin (mineral or organic). Results showed that in non-amended soils, the cumulative CO 2 produced was significantly greater in the limed soil with a pH>7 than in the same soil with less or no lime added, whereas there was no difference in N mineralization or in O 2 consumption kinetics. We found an exponential relationship between RQ values and soil pH, suggesting an excess production of CO 2 in alkaline soils. This CO 2 excess was not related to changes in substrate utilization by the microbial biomass but rather to carbonates equilibrium. The δ 13C signatures confirmed that the CO 2 produced in soils with pH>7 originated from both organic and mineral sources. The contribution of soil carbonates to CO 2 production led to an overestimation of organic C mineralization (up to 35%), the extent of which depended on the nature of soil carbonates but not on the amount. The actual C mineralization (derived from organic C) was similar in limed and unlimed soil. The amount of C mineralized in the residue-amended soils was ten times greater than in the basal soil, thus masking the soil carbonate contribution. Residue decomposition resulted in a significant increase in soil pH in all soils. This increase is attributed to the alkalinity and/or decarboxylation of organic anions in the plant residue and/or to the immobilization of nitrate by the microbial biomass and the corresponding release of hydroxyl ions. A theoretical composition (C, O, H, N) of residue and soil organic matter is proposed to explain the RQ measured. It emphasizes the need to take microbial biomass metabolism, O 2 consumption due to nitrification and carbon assimilation yield into account when interpreting RQ data.

Significance of Pelleting The Seed with Phosphate and Lime on The Cultivation of Soybean in Acid Soils in Sitiung, West Sumatera

Several experiments containing 2 field, 2 pot and I rhizotron were conducted to develop a low input agricultural practice(pelleting seed) for production of soybean plant (cv. Tidar) on heavily acid soils of Sitiung, West Sumatra. The field and polexperiments were conducted in Sitiung and in the greenhouse at the Agriculture Division, Center for the Application ofIsotopes and Radiation Technology, National Nuclear Energy Agency, Jakarta, respectively, in 1990 - 1992. The rhizotronexperiment was conducted in 1994 at the Laboratory of Microbiology, Department of Agrotechnology and Food Sciences.Wageningen University. Wageningen, The Netherlands. Lime-pel/eting seeds with the equivalent of 50 kg lime ha·1 increased nodulation, growth and yield both in unlimed and limed soils. Considerable increases in nodulatio, growth and yield were obtained when a small amount of P fertiliser (J 0 kg TSP ha·l ) was incorporated in the lime-pellet. The beneficial effects of both lime-pelleting and [lime+TSPj-pelleting were more pronounced on nodulation than on growth and yield. and greater in umimed soils than in limed soils. Large effects were obtained in nodulation, growth and yield of soybean in field experi1ltl!nts by pelleting seeds with lime or with lime + TSP. However, the pel/eted soybean plants grown in unlimed soils remained small and yields were negligible. To sustain growth and production of soybean in these acid soils, adequate quantities of lime and of P fertiliser would be necessary. In the present study, a combination of broadcast lime at 2.0 t ha-I with [lime+TSPj-pelleting of inoculated seeds was found superior to the application of 7.0 t ha-I of lime with inoculated seeds only. A I toxicity and P deficiency were the main problems in these acid soils. For the low-input production of soybeans considerations shOllld be directed to the correction of these factors.

Stable isotope probing analysis of the influence of liming on root exudate utilization by soil microorganisms

Rhizosphere microorganisms play an important role in soil carbon flow, through turnover of root exudates, but there is little information on which organisms are actively involved or on the influence of environmental conditions on active communities. In this study, a 13CO2 pulse labelling field experiment was performed in an upland grassland soil, followed by RNA-stable isotope probing (SIP) analysis, to determine the effect of liming on the structure of the rhizosphere microbial community metabolizing root exudates. The lower limit of detection for SIP was determined in soil samples inoculated with a range of concentrations of 13C-labelled Pseudomonas fluorescens and was found to lie between 10(5) and 10(6) cells per gram of soil. The technique was capable of detecting microbial communities actively assimilating root exudates derived from recent photo-assimilate in the field. Denaturing gradient gel electrophoresis (DGGE) profiles of bacteria, archaea and fungi derived from fractions obtained from caesium trifluoroacetate (CsTFA) density gradient ultracentrifugation indicated that active communities in limed soils were more complex than those in unlimed soils and were more active in utilization of recently exuded 13C compounds. In limed soils, the majority of the community detected by standard RNA-DGGE analysis appeared to be utilizing root exudates. In unlimed soils, DGGE profiles from 12C and 13C RNA fractions differed, suggesting that a proportion of the active community was utilizing other sources of organic carbon. These differences may reflect differences in the amount of root exudation under the different conditions.

Flux and turnover of fixed carbon in soil microbial biomass of limed and unlimed plots of an upland grassland ecosystem

The influence of liming on rhizosphere microbial biomass C and incorporation of root exudates was studied in the field by in situ pulse labelling of temperate grassland vegetation with (13)CO(2) for a 3-day period. In plots that had been limed (CaCO(3) amended) annually for 3 years, incorporation into shoots and roots was, respectively, greater and lower than in unlimed plots. Analysis of chloroform-labile C demonstrated lower levels of (13)C incorporation into microbial biomass in limed soils compared to unlimed soils. The turnover of the recently assimilated (13)C compounds was faster in microbial biomass from limed than that from unlimed soils, suggesting that liming increases incorporation by microbial communities of root exudates. An exponential decay model of (13)C in total microbial biomass in limed soils indicated that the half-life of the tracer within this carbon pool was 4.7 days. Results are presented and discussed in relation to the absolute values of (13)C fixed and allocated within the plant-soil system.

Increased risk of zinc deficiency in wheat on soils limed to correct soil acidity

Addition of lime to ameliorate soil acidity has been observed to induce zinc (Zn) deficiency for wheat in sandy soils of south-western Australia, reducing grain yields. The implications of widespread use of lime to treat acid soils for the residual value of Zn in these soils are not known. In a glasshouse experiment, using a Zn-deficient sand from south-western Australia, 3 levels of finely powdered calcium carbonate were added and incubated in moist soil for 6 weeks at 22°C to produce three different pH values (1 : 5 soil : 0.01 m CaCl2): 4.9 (original soil not treated with calcium carbonate), 5.8, and 7.4. Five amounts of Zn, as solutions of Zn sulfate, were then incubated in moist soil for 0, 30, 60, 120, and 180 days before sowing spring wheat (Triticum aestivum L.). The residual value of the applied Zn was determined using yield of dried shoots, Zn content in dried shoots, and soil test Zn (DTPA extraction). This was done by calculating the effectiveness of the incubated Zn for all 3 soils relative to the effectiveness of Zn applied just before sowing wheat (0 day incubation, freshly applied Zn) for the soil not treated with calcium carbonate. As measured using yield of dried shoots, Zn content of dried shoots, or soil test Zn, the residual value of the incubated Zn decreased with increasing soil pH and with increasing period of incubation of Zn with moist soil before sowing wheat. The critical Zn concentration, associated with 90% of the total yield of dried wheat shoots, was (mg Zn/kg) 13 in the youngest mature growth (apex and youngest emerged leaf), and 20 for rest of dried shoots. These values were similar to current critical values for unlimed soils. The relationship between yield of dried shoots and DTPA soil test Zn was similar for unlimed and limed soils, so similar critical soil test Zn was applicable on the sandy soil regardless of soil pH. Critical DTPA soil test Zn, the soil test Zn that was related to 90% of the maximum yield of dried shoots, was 0.14 mg Zn/mg soil. To combat the increased risk of Zn deficiency on soils limed to ameliorate soil acidity, fertiliser Zn needs to be re-applied to the soil when soil and plant tests indicate a high likelihood of deficiency.

Liming and choice of pasture species improve rhizobial persistence in an acidic chromosol (red-brown earth)

An experiment was conducted to determine the persistence of soil root-nodule bacteria as influenced by different rates of lime and the previous pasture species. The work was done at Condobolin, central-western New South Wales, on a chromosol (red-brown earth), acidic in the upper profile (pHCa 4.6), which was representative of soils for an extensive region of the eastern Australian wheat belt. In autumn 1997, the experimental area was treated with 4 rates (6.0 t/ha, 3.0 t/ha, 1.5 t/ha, nil) of finely-ground agricultural limestone and sown with 5 pasture species: lucerne (Medicago sativa), barrel medic (M. truncatula), subterranean clover (Trifolium subterraneum), rose clover (T. hirtum) and ryegrass (Lolium rigidum). The pastures were removed with herbicide and cultivation in September 2000. The land lay fallow for 9 months and then was sown to wheat (Triticum aestivum) in autumn 2001 and again in autumn 2002. The most probable numbers of soil (0–10 cm) populations of the root–nodule bacterium for Medicago species (Sinorhizobium meliloti) and for the Trifolium species (Rhizobium leguminosarum bv. trifolii) were counted in May 2001 and May 2002. Soil pH, which was significantly (P<0.05) elevated 12 months after liming, declined substantially during the next 4 years although there was no concomitant decline in the pH of unlimed soil. The pasture species were highly productive of both pasture dry matter and nitrogen. The majority of legume pasture nitrogen was a consequence of symbiotic nitrogen fixation. There was a small but significant (P<0.05) dry matter response to application of lime in lucerne and barrel medic, and a larger nitrogen response to liming in lucerne, barrel medic and rose clover. Nitrogen fixation by rose clover appeared suboptimal. It was assumed from the density of plants that large populations of rhizobia developed in the soil during the growth of the legumes. Nine months after removal of the pasture, rhizobia numbers had fallen to low levels but did not fall further during the following year. The initial fall was attributed to high soil temperatures and low soil moisture during the Condobolin summer. The population of rhizobia for Trifolium species was about twice that of the rhizobia for Medicago species but the difference was not statistically significant. Liming had an overriding influence on the size of rhizobial populations, except in plots that had previously grown ryegrass where numbers remained low irrespective of rate of liming. Overall, most probable numbers escalated with each increase in rate of liming, from 10/g soil in the nil lime plots to 708/g in the 6 t/ha lime plots. The rhizobial homology of the pasture species (i.e. Sinorhizobium meliloti for the Medicago species and Rhizobium leguminosarum bv. trifolii for the Trifolium species) had an underlying but major influence on most probable numbers and in determining which rhizobial species occurred more commonly. Estimated populations of rhizobia in soils from homologous legumes were about 8 times those found in soils from non-homologous legumes. The benefits of applying lime to this red-brown earth soil may not have been merely a consequence of correction of low soil pH; increased levels of calcium may also have had a role. The results are discussed in relation to re-establishment of legume leys after the cereal phase of the cropping system.

Chemical Modifications Caused by Liming Below the Limed Layer in a Predominantly Variable Charge Acid Soil

Despite the low mobility in soil, surface liming has increased plant growth and yield. Since only the topsoil is affected by this technique, the benefits may be caused by improvements in soil solution. This experiment aimed to assess chemical changes in the solid phase and leached solutions after addition of calcitic limes to a Humic Hapludox. Calcium carbonate or calcium hydroxide was throughly mixed with soil samples at rates of 0, 0.25, 0.50, 1.0, and 1.50-times that required to raise soil pH to 6.0 (equivalent to 0, 3.5, 7.0, 14, and 21 t ha−1). After 60 days, treated samples were transferred to the top (30 cm) of leaching columns, filled with unlimed soil in the bottom (23 cm). Water was percolated weekly through the columns during 12 weeks. Chemical determinations were performed on all leached solutions, and at different soil depths below the limed layer at the end of the experiment. Calcium (Ca), magnesium (Mg), and aluminum (Al) increased linearly in the percolated solution with increases on lime sources; the opposite occurred for leachate pH, probably due to hydrolysis of Al that was replaced from the negative charges on unlimed soil by added calcium. Calcitic limes increased pH and Ca, and decreased Al and Mg in the solid phase below the limed layer up to a maximum of 3 cm. Lime, thus, positively affected only the top of the unlimed solid phase; its effect on leached solution, however, was similar to that caused by neutral salts on acid soils, with increases in cations and decreases in pH.

Combined N, P, K fertilization and liming maximises crop productivity of acid loams in Lithuania

Crop response to fertilization and liming was investigated in field and pot trials on sandy loam Dystric Albeluvisols (pH 4.2–4.3). Treatments in the field trial were: 1, no fertilizer; 2, PK; 3, NK; 4, NP; 5, NPK; 6, lime; 7, lime+PK; 8, lime+NK; 9, lime+NP; 10, lime+NPK. In the pot trial, they were: 1, no fertilizer; 2, N; 3, P; 4, K; 5, NP; 6, NK; 7, PK; and 8, NPK applied to unlimed and limed soils. All treatments were in four replicates. Crops sensitive to soil acidity (winter wheat, fodder beet, spring barley and clover-timothy ley) and the less acid-sensitive winter rye, potatoes, oats and lupins and oats mixture were sown in the field trial. In the pot trial, the acid-sensitive spring barley and red clover, and the less acid-sensitive oats and lupin-oats served as the test crops. Combined application of fertilizers (NPK) increased yields of crops sensitive to soil acidity in plots receiving lime by 23%, and those of crops less sensitive to soil acidity by 18% in comparison to crops grown on unlimed soils. The results of pot experiments corroborated the field results. When N was applied alone, crop yields were always higher than those recorded for P or K treatments on both the unlimed and limed treatments. N application proved to be a prerequisite for high crop yields in the soils investigated. Thus, the efficiency of P and K fertilizers increased in the order NK<NP<NPK, with the effects being accentuated more in the limed than in the unlimed treatments. The results demonstrated the importance of multi-nutrient (NPK) fertilization in combination with liming for enhancement of high crop productivity in the unlimed soil investigated. N applied alone in combination with liming produced relatively good yields; hence, where resources are limited for the purchase of P and K fertilizers, applying N and lime can be a viable option in the short term.

Effects of the properties of the bacterial community on pH adaptation during recolonisation of a humus soil

A humus soil with a pH of 4.9 was fumigated with chloroform for 5 h, after which only 1% of the initial bacterial activity remained. Half of the fumigated soil was limed to a pH of 7.5. Both the unlimed soil (UL) and the experimentally limed soil (EL) were inoculated with unfumigated (UL) soil or a field-limed (FL) soil with a pH of 6.1. The pH tolerance and activity of each developing bacterial community were monitored over time in the different treatments (UL UL, UL FL, EL UL and EL FL, subscripts indicate inoculum). The activity and pH tolerance of the resulting bacterial communities were measured using thymidine (TdR) incorporation. To study pH tolerance the pH of the bacterial suspensions (bacteria directly extracted from soil) was altered to pH 8.3 and 3.6 using different pH buffers before TdR incorporation. The logarithmic ratio of TdR incorporation at pH 8.3 and 3.6 was used as a measure of pH tolerance. The source of inoculum had a clear effect in the experimentally limed soil. The tolerance of the bacterial community to high pH increased very rapidly and was always higher in the EL FL soil than in the EL UL soil for up to 78 days of incubation. The bacterial activity was also highest in the EL FL soil for the major duration of the experiment. The source of inoculum had little effect on the unlimed soils, since both the UL UL and UL FL soils had the same low pH tolerance and bacterial activity. The tolerance to high pH was initially higher in the EL UL soil than that observed in a comparable non-fumigated, limed soil by Pettersson and Bååth (2003), indicating that the non-colonised environment following fumigation facilitated a more rapid development of bacterial community tolerance to pH changes.

The rate of change of a soil bacterial community after liming as a function of temperature.

The response of a bacterial community to liming of a forest humus soil (pH 4.9 increased to pH 7.5) was studied in the laboratory at three temperatures (5, 20, and 30 degrees C). As a comparison an unlimed soil (pH 4.9) and a soil limed in the field 15 years ago (pH around 6) were also included. The bacterial community tolerance of pH was measured using TdR incorporation. The pH of the bacterial suspensions (bacteria directly extracted from soil) was altered to 3.6 and 8.3 using different buffers before measuring TdR incorporation. The logarithmic ratio between TdR incorporation at 8.3 and 3.6 was then used as an indicator of the community pH tolerance. The rate of changes in the community tolerance to pH after liming was fastest for the soil incubated at 30 degrees C, but only minor differences in rate of change could be seen between samples incubated at 5 and 20 degrees C. Changes in phospholipid fatty acid (PLFA) pattern after increasing the pH were most rapid for the bacterial community in the soil incubated at 30 degrees C followed by the soil incubated at 20 degrees C, whereas no changes could be seen in the PLFA pattern of the soil incubated at 5 degrees C, even after 82 days' incubation. Thus, the changes in the PLFA pattern were considerably slower than the changes in bacterial community tolerance to pH measured using TdR incorporation.

A glasshouse evaluation of the comparative effects of organic amendments, lime and phosphate on alleviation of Al toxicity and P deficiency in an Oxisol

The effects of additions of four organic amendments to an Oxisol on soil pH, exchangeable and soil solution Al, extractable P and maize growth were compared with those of lime and P in a glasshouse experiment. The organic amendments were: grass residues, household compost, filter cake (a waste product of sugar mills) and layer poultry manure and they were added at a rate equivalent to 20 t/ha with or without the addition of either lime (equivalent to 0, 5 or 10 t/ha) or P (equivalent to 0, 10 or 50 kg/ha). Lime applications to the control (unamended) treatment resulted in a marked reduction in exchangeable Al, and concentrations of total (AlT) and monomeric (Almono) Al in soil solution and the proportion of AlT present as Almono. In unlimed soils, amendment additions increased pH and decreased exchangeable Al in the order: poultry manure&gt;filter cake&gt;household compost&gt;grass residues&gt;control. The addition of all the organic amendments increased soil pH and reduced AlT and Almono to low concentrations regardless of whether lime was applied or not. As a result, there was no yield response to applied lime in any of the amended treatments. Olsen-extractable P concentrations in soils followed the order: poultry manure&gt;filter cake&gt;household compost&gt;grass residues&gt;control and there was no yield response to applied P for the poultry manure and filter cake treatments. The decrease in adsorption of subsequently added P induced by additions of organic amendments followed the order: poultry manure&gt;household compost&gt;filter cake&gt;grass residues. It was concluded that the addition of organic amendments to acid soils is a practicable way of liming them and reducing the potential for Al toxicity and it can also reduce fertilizer P requirements.

Earthworms and pH affect communities of nematodes and enchytraeids in forest soil

In northern boreal forests the occurrence of endogeic and anecic earthworms is determined by soil pH. Increasing evidence suggests that large detritivorous soil animals such as earthworms can influence the other components of the decomposer community. To study the effects of earthworms and pH on soil nematode and enchytraeid communities, a factorially designed experiment was conducted with Lumbricus rubellus and/or Aporrectodea caliginosa. Earthworms were added to "mesocosms" containing unlimed (pH 4.8) or limed (pH 6.1) coniferous mor humus with their natural biota of micro-organisms. In the absence of earthworms, nematodes were significantly more abundant in limed than in unlimed humus. Earthworms markedly decreased the numbers of nematodes both in unlimed and limed soils. Earthworm activities eliminated enchytraeids in unlimed soil, but liming improved the survival of some species. It was concluded that liming of soil, either alone or mediated by the earthworm populations, is likely to affect soil nematode and enchytraeid community and mineralisation.

Temperature-dependent changes in the soil bacterial community in limed and unlimed soil

A humus soil with a pH(H 2O) of 4.9 was limed to a pH of 7.5 and was incubated together with samples from unlimed and field limed (pH 6.1) soils at 5, 20 and 30°C for up to 80 days. The changes in the phospholipid fatty acid (PLFA) pattern were most rapid for the bacterial community of the soil incubated at 30°C, while no changes were found in the soil incubated at 5°C. The response of the community activity to temperature was measured using the thymidine incorporation method on bacteria extracted from the soil. The bacterial community in soil incubated at 30°C became more adapted to high temperature than that in soil samples incubated at 5°C. When soil samples incubated at 30°C and 20°C were returned to 5°C for 35 days, only small changes in the PLFA pattern were found. No significant shift in community temperature adaptation was found. Thus, higher temperatures (with higher turnover) led to higher rates of change in both the PLFA pattern and the activity response to temperature, compared with lower temperatures. No effect of liming as a way of increasing substrate availability and turnover on the rate of change was observed. Changes in the PLFA pattern appeared sooner than changes in the activity response to temperature, indicating that changes in the PLFA pattern were mainly due to phenotypic acclimation and not to species replacement.

Effects of Lime and Calcium on Root Development and Nodulation of Clovers

Acidic soils can reduce the nodulation of forage legumes. Studies with a Gilpin series silt loam (fine loamy, mixed mesic, Typic Hapludult) from New, WV, were conducted to determine the effects of lime on root development, and to assess effects of soil Ca and pH on nodulation. Liming increased soil pH from 4.8 to 5.3, nodulation, and root growth of white clover (Trifolium repens L., cultivar Huia) 28 d after planting. Seedlings from unlimed soil formed fewer indeterminate and determinate roots. Next, soils were amended with either CaCO3 or a mixture of CaCO3 and CaSO4 to achieve a soil pH of 4.7 to 6.1 and soil Ca of 170 to 680 mg kg−1 soil. There was a strong quadratic relationship between number of nodules per white clover seedling 28 d after planting and soil pH. Another experiment was conducted to determine if these trends were expressed under field conditions. In 1993, field plots were amended with lime or a coal combustion by-product that supplied Ca as CaSO4 and seeded in 1994 to cool-season grasses. In spring of 1998, plots were drilled with either red (Trifolium pratense, L.) or white clover. The nodules per primary root were determined in May (1998, 1999) and August (1998). Number of nodules per primary root was more closely associated with soil pH than soil Ca. These results indicate that changes in nodulation were more closely associated with changes in soil pH than soil Ca.

The diversity of Phaseolus-nodulating rhizobial populations is altered by liming of acid soils planted with Phaseolus vulgaris L. in Brazil.

PCR-mediated restriction fragment length polymorphism (RFLP) analysis of the 16S-23S rRNA internally transcribed spacer (ITS) region and the 16S rRNA gene indicated that the rhizobial populations isolated from common bean (Phaseolus vulgaris L.) nodules in the unlimed soil from a series of five lime rates applied 6 years previously to plots of an acidic oxisol had less diversity than those from plots with higher rates of liming. Isolates affiliated with Rhizobium tropici IIB and Rhizobium leguminosarum bv. phaseoli were predominant independent of lime application. An index of richness based on the number of ITS groups increased from 2.2 to 5.7 along the soil liming gradient, and the richness index based on "species" types determined by RFLP analysis of the 16S rRNA gene varied from 0.5 to 1.4. The Shannon index of diversity, based on the number of ITS groups, increased from 1.8 in unlimed soil to 2.8 in limed soil, and, based on RFLP analysis of the 16S rRNA gene, ranged from 0.9 to 1.4. In the limed soil, the subpopulation of R. tropici IIB pattern types contained the largest number of ITS groups. In contrast, there were more R. leguminosarum bv. phaseoli types in the unlimed soil with the lowest pH than in soils with the highest pH. The number of ITS ("strain") groups within R. leguminosarum bv. phaseoli did not change with increased abundance of rhizobia in the soil, while with R. tropici IIB, the number of strain groups increased significantly. Some cultural and biochemical characteristics of Phaseolus-nodulating isolates were significantly related to changes in soil properties caused by liming, largely due to changes in the predominance of the rhizobial species groups.

Cattle manure and lime amendments to improve crop production of acidic soils in Northern Alberta

Crop production on acid soils can be improved greatly by adjusting the pH to near neutrality. Although soil acidity is commonly corrected by liming, there is evidence that animal manure amendments can increase the pH of acid soils. Fresh cattle manure and agricultural lime were compared for their effects on soil acidity and the production of canola (Brassica napus L.) and wheat (Triticum aestivum L.) in a greenhouse study. Canola and wheat yield, the nutrient content of grain and straw, and selected soil properties were determined on a Gray Luvisol (pH 4.8) from the Peace Region of Alberta. Soil pH increased with lime and manure applications, and canola and wheat yields were higher in limed and manure-amended soils than unfertilized, unlimed soils. Macronutrient uptake by canola and wheat was generally improved by liming and manure applications, and micronutrient uptake was related to the effects of lime and manure on soil pH. An economic analysis compared the costs of using cattle manure and lime to increase soil pH to 6.0. The costs of applying lime and fresh cattle manure to increase soil pH were compared, based on the fees for purchasing and applying lime or loading, hauling and applying manure. The nutrient value of manure was calculated based on the quantities of plant-available N, P and K in fresh manure. At distances less than 40 km, it is economical to substitute fresh cattle manure for agricultural lime to increase soil pH of acidic soils. However, good manure management practices should be followed to minimize the risk of nutrient transport and environmental pollution from agricultural land amended with cattle manure. Key words: Agricultural economics, canola production, cattle manure, lime, soil pH, wheat prodution

Selection for persistence under grazing in winter-active populations of the perennial grass, Phalaris aquatica L. (phalaris)

Winter-active cultivars of phalaris (Phalaris aquatica L.) have the potential to be more productive than semi-winter-dormant cultivars but may be less persistent under the stress of heavy grazing. The feasibility of improving persistence of winter-active phalaris was examined by subjecting plots of half-sib families from several winter-active populations to 2 cycles of heavy grazing pressure by sheep. Because variation among families in initial density influenced final density score in both cycles, persistence was assessed by 2 methods, final density with initial density as a covariate and the ratio of final over initial density.In Cycle 1, significant family variance was observed in a broadly based population after 3 years of continuous grazing. Changes in persistence were smaller but still significant among the families comprising cv. Holdfast after 2 years of rotational grazing on limed but not on unlimed acid soil. In Cycle 2, 4 populations selected in Cycle 1 and elsewhere were screened under continuous grazing at 2 sites, one lower in soil pH and phosphorus than the other. Family by site interaction for final density was significant (P &lt; 0.05) for one population only and this arose before grazing commenced. The selected populations displayed higher density and persistence than control winter-active cultivars. Estimates of predicted heritability were generally high but not always significant at P &lt; 0.05. Overall they were considered to indicate that differences in persistence between families were present and heritable. This was supported by the observation that generations of 2 populations selected in Cycle 1 were higher in final density and persistence than the base generations, although differences in persistence as distinct from final density were not always at the P = 0.05 significance level. The ratio of final over initial density scores was considered less appropriate than the covariate method of estimating persistence in this cycle because plots that established at very low density and increased slightly thereafter resulted in high error variance and biased selection towards families that established at low density.