Unlimed Soil Research Articles

Decomposition in a peaty soil improved for pastoral agriculture

Abstract. The rates of CO2 production and decomposition of 13C‐enriched Lolium perenne leaves and roots in soil from the surface five cm of two upland stagnohumic gley soils were measured in laboratory experiments. One of the soils had been limed (pH 6.8) 13 years earlier. The other was unlimed (pH 3.7). Liming increased the rate of CO2 release from soil to which no L. perenne had been added. About 30% of the 13C in L. perenne leaves remained in both limed and unlimed soil after 224 days. By contrast, less 13C‐remained in the limed soil amended with L. perenne roots (44%) than in the limed soils (55%). Although the daily rate of CO2 from the plant material‐amended soils was initially greater in the improved than in the unimproved soil, it subsequently declined more rapidly.

Stimulation of Microbial Degradation of Methyl Bromide in Soil during Oxidation of an Ammonia Fertilizer by Nitrifiers

To reduce volatilization of the fumigant methyl bromide (MeBr) from soil into the atmosphere, attempts were made to enhance microbial degradation of MeBr in soil by stimulating the activity of soil nitrifiers. Disappearance of MeBr in limed Arredondo soil (pH 7.70) treated with an ammonia-based nitrogen fertilizer, (NH4)2SO4, was initially more rapid than in unlimed Arredondo soil (pH 5.5−5.7). Disappearance of MeBr in limed soil with or without treatment of (NH4)2SO4 that received 20 μg/g MeBr was more rapid than in the corresponding soil samples that received a higher rate of MeBr (50 μg/g). Due to higher nitrification activity in limed surface soil (0−15 cm depth) than in limed subsurface soil (15−30 cm depth), disappearance of MeBr in the surface soil with or without (NH4)2SO4 treatment was also more rapid than in the corresponding subsurface soil. Both microbial and chemical degradation were involved in the MeBr degradation in soil, with chemical degradation possibly being the major factor. Contribut...

Liming and re-liming needs of acidic soils used for crop - pasture rotations

Summary. In a long-term liming experiment in north-eastern Victoria, we have re-applied lime and applied gypsum (1992 season) to assess wheat grain yield responses with on-going changes in soil pH and extractable aluminium. An acid-sensitive wheat (cv. Oxley) was grown in 2 seasons (1992–93), 12 years after initial applications of lime. Where lime (2.5 t/ha) was applied in 1992 to a previously unlimed soil, grain yield was increased by 19 and 46% respectively in the 2 seasons. However, the yield from these newly limed plots was well below the yields obtained from plots limed in 1980. Re-liming plots limed in 1980 resulted in further yield increases, with lime re-applied at 2.5 t/ha increasing yields by 12% in both seasons. Gypsum decreased grain yields on unlimed soil in the year of application but in the second year gave increases in yield. Whilst pH had changed little in the unlimed soil over the 12 years, the concentrations of extractable aluminium in the root zone increased substantially such that these concentrations far exceed levels which may affect acid-sensitive wheats. Liming at 2.5 t/ha did reduce the aluminium at 0–10 cm depth, but the concentrations at 10–20 cm depth (11.7 mg/kg) are likely to restrict grain yield. The data illustrate the progressive nature of soil acidification and the risk to wheat productivity through delaying treating this soil degradation problem.

The effect of liming on heavy metal concentrations in wheat, carrots and spinach grown on previously sludge-applied soils

SUMMARYLiming is often recommended to minimize the plant uptake of potentially toxic elements from sludgeamended soils. In outdoor experiments conducted during 1989–91 in a rural location, near Brentwood (UK), wheat, carrots and spinach were grown on soils from a wide range of sites previously amended with heavy applications of sewage sludge. The objective of these studies was to examine the effect of liming on the accumulation of sludge-borne metals in the crop plants. The results showed that liming the soils to pH 7 prior to sowing significantly reduced metal concentrations in carrots and spinach, although the reduction appeared to be greater for Cd, Ni and Zn than for Cu and Pb. The wheat crop was grown on soils which had been limed 2 years previously, and the average pH of these soils was 6·5 compared to a pH value of 5·95 in the unlimed soils. This comparatively small pH difference between limed and unlimed soils (6·50–5·95) generally had little influence on metal contents in wheat.These results suggested that maintaining the soil at pH 7 is better than pH 6·5 for minimizing the accumulation of potentially toxic elements from soils which have received relatively high levels of sludge application over many years. The data for winter wheat suggested either that metal uptake into the grain was not sensitive to differences in soil pH or that a relatively small residual effect of past liming was not high enough to reduce metal uptake.

Response of Acacia mangium to vesicular – arbuscular mycorrhizal inoculation, soil pH, and soil P concentration in an oxisol

The vesicular–arbuscular mycorrhizal (VAM) fungus Glomus aggregatum and the legume species Acacia mangium were grown together in a manganese-rich oxisol at pH 4.3 to 6.0 and at soil P concentrations favorable for VAM-host growth (0.02 mg ∙ L−1) and sufficient for non-VAM host growth (0.8 mg ∙ L−1). At the lower P concentration, vesicular–arbuscular mycorrhizal fungal (VAMF) colonization of roots increased as soil pH increased from 4.3 to 5.0. However, colonization of roots was not significantly influenced by further increases in pH. Growth of A. mangium at 0.02 mg P/L in the presence of G. aggregatum was inferior to that observed at 0.8 mg P/L, suggesting that there was some degree of host–endophyte incompatibility. Increasing P concentration from 0.02 to 0.8 mg P/L increased target soil pH in the unlimed soil from 4.3 to 4.8 and reduced the concentration of available soil Mn from 13.2 to 2.1 mg ∙ L−1. Thus, the better plant growth observed at the higher P concentration at pH < 5 was mainly due to the alleviation of Mn toxicity due to the precipitation of the cation directly by excess phosphate and (or) phosphate-induced elevation of soil pH. The poor VAMF inoculation effect observed at the lower soil P level in the unlimed soil was thus largely due to the toxicity of high concentrations of Mn2+ and H+ ions. Keywords: hydrogen ion, calcium, manganese-rich, manganese toxicity, pinnule P, soil acidity, VAMF colonization, VAMF effectiveness.

SHORT COMMUNICATION: Lime-amended acid soil has elevated pH 30 years later

Lime-amended acid soil (a single application in 1963 at rates of 4.5 and 6.7 t ha−1) at Scott, Saskatchewan had pH of 0.5 and 1.1 units higher, respectively, than unlimed soil, when measured more than 30 yr later in 1994. However, no differences in soil-available phosphorus levels and crop yield were detected. Key words: Soil acidity, lime, phosphorus, Brassica rapa L., Triticum aestivum L.

Soil solution chemistry and alfalfa response to CaCO3 and MgCO3 on an acidic Gleysol

Soil acidity is a limiting factor for forage production. Liming is a common agricultural practice for acid soils, yet there is limited information on the effects of soil solution chemistry in response to liming. Soil from the Ap horizon of an Orthic Humic Gleysol was amended with 0, 2.5 or 5.0 g CaCO3 kg−1 and 2.1 or 4.2 g MgCO3 kg−1 to determine the changes due to liming in soil solution composition before planting and after three cuts of alfalfa (Medicago sativa L.). The soil solution samples were extracted by immiscible displacement with C2Cl4. The low equivalent rate of CaCO3 and MgCO3 decreased the concentrations of Fe from 889 to less than 22 μM, Mn from 286 to less than 6 μM, Al from 45 μM to undetectable level before plant growth. Soil pH, dissolved organic carbon (DOC), Cu and NH4-N concentrations in the soil solutions extracted after the third cut of alfalfa were increased compared with those measured before planting. Concentrations of Ca, Mg, K, Na, Mn, Zn, Fe, Al, NO3-N, SO4 and Si were all decreased after the third cut compared with those measured before planting. Step-wise multiple regression analysis indicated that the dry matter (DM) yield of the first cut was positively correlated to NO3-N and negatively correlated to Mn concentration in the soil solutions (R2 = 0.65**); whereas the DM yield of the second and third cuts and of the roots were negatively correlated with Mn concentrations (R2 = 0.75**, 0.63**, and 0.60**, respectively). The regression analysis supported visual Mn toxicity, suggesting that Mn toxicity, not Al concentration, was the main limitation to alfalfa growth in unlimed soil. Key words: Alfalfa, liming, soil solution chemistry, immiscible displacement, plant nutrition

Screening Methods to Develop Alfalfa Germplasms Tolerant of Acid, Aluminum Toxic Soils

Soil acidity and aluminum (Al) toxicity are major problems limiting performance of alfalfa (Medicago saliva L.) in many parts of the world, but neither an effective screening procedure nor a tolerant cultivar is available. The objective of this study was to evaluate different screening methods for selection of acid soil tolerant alfalfa germplasms in the greenhouse during 1991–1994. The general screening methods included selection in unlimed soil, selection in unlimed soil containing a limed germination layer, selection for either tolerance or sensitivity to acid soil stress with Al toxicity in tissue culture, selection in unlimed soil with tandem selection for Al tolerance in tissue culture, and selection in unlimed soil containing a limed, fertilized germination layer with tandem selection for Al tolerance in tissue culture. All selected populations and checks were evaluated during 1994 in greenhouse cups containing the following soil treatments: (i) cups filled with unlimed soil, (ii) cups filled with limed soil, and (iii) cups filled with unlimed soil containing a germimation layer of limed soil. Most of the selected populations possessed better root and shoot growth than the original base population (GA‐TE) in unlimed soil, but only the population selected in unlimed soil showed better root and shoot growth in unlimed soil with a limed germination layer. No population had poorer performance than GA‐TE in limed soil. Selection in cell culture for Al toxicity tolerance did not improve tolerance per se, but selection for Al sensitivity enhanced sensitivity. In terms of success, resources, and time, screening in unlimed soil was the most effective method to improve acid soil stress tolerance.

Liming effects on availability of Cd, Cu, Ni and Zn in a soil amended with sewage sludge 16 years previously

A field study was conducted to determine the plant uptake of metals in soils amended with 500 Mg ha−1 of municopal sewage sludge applied 16 yr previously. Results showed that metals were available for plan uptake after 16 yr, but that liming greatly reduced the plant availability of most metals. The application of sludge also resulted in high rates nitrification and subsequent lowering of the soil pH before the uptake study was started. The sludge-amended soil (a mesic Dystric Xerochrept) was adjusted with lime one month prior to planting from an unlimed pH of 4.6 to pH 5.8, 6.5 and 6.9. Food crops grown were: (i) bush bean (Phaseolus vulgaris L. cv. Seafarer), (ii) cabbage (Brassica oleracea L. v. capitata L. cv. Copenhagen market), (iii) maize (Zea mays L. cv. FR37), (iv) lettuce (Lactuca sativa L. cv. Parris Island, (v) (Solanum tuberosum L. cv. (vi) tomato (Lycopersicum esculentum L. cv. Burpee VF). With the exception of maize, yields were significantly reduced in the unlimed sludge-amended soil. However, liming increased yields above the growth level of the unlimed untreated soil for cabbage, maize, lettuce, potato tuber and tomato fruit. Soluble and exchangeable of Cd. Ni and Zn were also reduced after liming the sludge-amended soil. In both limed and unlimed soils, the majority of the soil Cu was found in insoluble and unavailable soil fractions. To evaluate trace metal uptake, the edible portion of each crop was analyzed for Cd, Cu, ni and Zn. Liming redoced uptake of Cd, Ni and Zn in most crops, but generally did not change Cu, This study shows the benefit of pH adjustment in reducing relative solubility and plant uptake of metals as well as increasing crop yield in acid soils.

Microbiological differences between limed and unlimed soils and their relationship with cavity spot disease of carrots (Daucus carota L.) caused by Pythium coloratum in Western Australia

Application of lime (4000 kg ha-1) to a soil used for commercial carrot production (pH 6.9) significantly (p<0.05) reduced the incidence of cavity spot disease of carrots compared to unlimed soil (pH 5.1). It significantly (p<0.01) increased soil microbial activity as measured by the hydrolysis of fluorescein diacetate and arginine ammonification. The application of lime resulted in a significant (p<0.01) increase in the total numbers of colony forming units (efu) of aerobic bacteria, fluorescent pseudomonads, Gram negative bacteria, actinomycetes and a significant (p<0.01) decrease in the cfu of filamentous fungi and yeasts compared to unlimed soil. Liming also increased the cfu of non-streptomycete actinomycetes rarely reported in similar studies. These non-streptomycete actinomycetes were estimated and isolated using polyvalent Streptomyces phages and the dry heat technique to reduce the dominance of streptomycetes on isolation plates. The non-streptomycete actinomycetes isolated included species of Actinoplanes, Micromonospora, Streptoverticillium, Nocardia, Rhodococcus, Microbispora, Actinomadura, Dactylosporangium and Streptosporangium. The numbers of actinomycetes antagonistic to Pythium coloratum, a causal agent of cavity spot disease of carrots increased in soil amended with lime. Application of lime also reduced the isolation frequency of P. coloratum from asymptomatic carrot roots grown in soil artificially infested with the pathogen, 3, 4 and 5 weeks after sowing.

The effect of ionic strength on soil P reactions is negligible

The electrolyte concentration of the soil solution affects the availability of some nutrients in the soil, especially of P, but it is not know at what salt concentration the reactions start to be significantly affected and their magnitude. This study was carried out to evaluate the effect of rates of potassium chloride (KCl) on some soil parameters that determine supplying of P, K, Ca, Mg, and Al in an unlimed acid soil. Increasing rates of KCl (from zero up to 2000 mg K kg−1) were applied to soil samples fertilized with 360 mg P kg−1. Solution (Cli) and exchangeable (Csi) forms of P, Ca, Mg, K, and Al were determined in the treated soil samples after 30-days of incubation; cation activity in solution and their selectivity coefficients were then calculated. Addition of KCl at rates equal to or above 500 mg K kg−1 caused a large relative increase on P in the soil solution (Pli) but a small and insignificant increase on the absolute value of Pli. All forms of soil K increased with increases on K applied, and buffer power for K varied according to the range of soil K. At all KCl rates, K displaced Ca, Mg, and Al from the solid phase to the soil solution, but had no effect on the extractable values. The relative preference of cations for the adsorption sites increased with increase on cation valency, and only those selectivity coefficients involving K were affected by K applied.

Evaluation of agronomic effectiveness of phosphate rocks for aluminum‐tolerant soybean cultivar

Abstract The effect of liming on the agronomic effectiveness of three phosphate rocks (PRs) Pesca and Huila from Colombia and Sechura from Peru as compared with TSP was evaluated in a greenhouse experiment for an Al‐tolerant soybean cultivar grown on an acid Ultisol. On both unlimed (pH 4.4) and limed (pH 5.0) soils, the agronomic effectiveness of P sources in terms of increasing seed yield followed the order of TSP > Sechura PR > Huila PR > Pesca PR > check, an order similar to that of solubility of P sources. Liming slightly decreased the effectiveness of Pesca PR, whereas liming had no effect on Huila PR. A significant increase in agronomic effectiveness was observed upon liming for Sechura PR and TSP. Soil‐available P as extracted by the Pi method was closely related to the amount of N fixed by soybean crop that, in turn, was related to the soybean seed yield. Values of relative agronomic effectiveness (RAE) of PRs with respect to TSP were calculated by assuming the check = 0% and TSP = 100%. On unlimed soil, the RAE values of PRs were: Pesca PR = 31%, Huila PR = 42%, Sechura PR = 84%. On the limed soil, the RAE values were: Pesca PR = 8%, Huila PR = 24%, Sechura PR = 66%. It can be concluded that the use of PR with respect to that of TSP for soybean crop is more favorable in the unlimed soil than in the limed soil, provided that the soybean plant is relatively Al‐tolerant.

Effects of Liming on Soils and Streamwaters in a Deciduous Forest: Comparison of Field Results and Simulations

AbstractSoil and stream chemical responses to liming in a deciduous forest watershed at Coweeta, NC, are compared with simulation results using the Nutrient Cycling Model (NuCM). Field comparisons of limed and unlimed soils after 23 yr indicated substantial net retention of applied Ca2+ and Mg2+ in upper soil horizons, even in black locust (Robinia pseudoacacia L.) sites where NO−3 leaching was elevated. We hypothesized that NuCM simulations would also show that (i) retention of most applied Ca2+ and Mg2+ in the upper horizons and (ii) increased Ca2+ and Mg2+ retention with increased cation exchange capacity (CEC) and exchangeable H+ (simulating pH‐dependent CEC). Both hypotheses were supported by simulation results for Ca2+, but not for Mg2+. Most applied Mg2+ in the simulations was retained in the BC horizon, where the largest pool of exchangeable Mg2+ was initially located. Increasing CEC and exchangeable H+ did result in increased retention of applied Ca2+ and Mg2+ in surface horizons. However, increasing CEC caused lower Mg2+ retention in the BC horizon, which offset the surface horizon increases and resulted in lower total retention of applied Mg2+. Simulated BC horizon soil solution concentrations mimicked the general patterns in streamwater NO−3, Mg2+, Na+, Cl−, SO2−4, and K+ between 1971 (12 yr after liming) and 1979. NuCM simulations did not, nor was it possible to simulate the observed effects of an insect outbreak on streamwater NO−3.

Boron retention in limed forest mor

Boron (B) retention was studied in the mor humus of podzolic soil from boreal Norway spruce (Picea abies (L.) Karst.) forests. In a long-term liming experiment, ground limestone had been applied 30 years earlier and again 12 years before sampling. Additionally a short-term field experiment was done to separate the effect of increased pH from calcium (Ca) addition. In the short-term experiment the treatments were control and two doses of CaCO 3, CaSO 4 and sodium + potassium (Na + K) carbonate mixture. These treatments were applied in the year before sampling. The B retention data conformed to a Freundlich model better than to a Langmuir model. Considerable B adsorption occurred, probably mostly due to the large organic matter content of mor. Liming significantly increased the quantity of adsorbed B in both experiments. Incubation with added B for 8 weeks considerably increased B retention and reduced the difference between limed and unlimed soil. CaSO 4 had no effect on B retention characteristics, whereas Na + K treatment caused changes similar to those of lime. Therefore Ca probably has little influence on B adsorption in this pH range (3.0–5.9).

Mycorrhizal and nonmycorrhizal host growth in response to changes in pH and P concentration in a manganiferous oxisol

Glomus aggregatum and Leucaena leucocephala were allowed to interact in a manganese-rich oxisol at pH 4.3–6.0 and at soil P concentrations considered optimal for mycorrhizal host growth and sufficient for nonmycorrhizal host growth. At 0.02 mg P l-1, vesicular-arbuscular mycorrhizal fungal (VAMF) colonization of roots increased as soil pH increased from 4.3 to 5.0. However, VAMF colonization of roots did not respond to further increases in pH. At pH 6.0, growth of mycorrhizal Leucaena observed at 0.02 mg P was comparable with that observed at 0.8 mg P l-1. Increasing P concentration from 0.02 to 0.8 mg P 1-1 increased target soil pH from 4.3 to 4.7 and reduced the concentration of available soil Mn from 15.1 to 1.9 mg 1-1. Thus, the normal plant growth observed at the higher P concentration at pH<5 was mainly due to the alleviation of Mn toxicity as a result of its precipitation by excess P. VAMF colonization levels observed at pH 5.0–6.0 were similar, but maximal plant growth occurred at pH 6.0, suggesting that the optimal pH for mycorrhizal formation was substantially lower than for VAMF effectiveness. The poor growth of Leucaena at the lower P concentration in the unlimed soil was largely due to high concentrations of Mn2+ and H+ ions.

Difference in phosphorus response among tropical green manure legumes grown under limed and unlimed soil conditions

Abstract Two pot experiments were conducted to investigate the effect of phosphorus fertilization on the growth of some tropical green manure legumes cultivated under limed and unlimed soil conditions. The species used were Cassia occidentalis, Cassia tora, Crotalaria juncea, Glycine max, Sesbania cannabina, and Seshania rostrata. The species differed in their response to lime application. Liming increased the dry matter yield of Cro. juncea, G. max, S. cannabina, and S. rostrata while it decreased the dry matter yield of Cas. occidentalis and Cas. tora. Liming decreased the concentrations of P, Fe, Mn, and Zn while it increased the concentration of Ca in all species. The Mg concentration decreased in Cas. occidentalis and Cas. tora by liming while it increased in other species. The cause of the growth depression resulting from liming depended on the species. The growth reduction in Cas. occidentalis, Cas. tora, and Cro. juncea was due to the low concentration of P in the plant tissues. The deiciency in Zn was also a factor in the growth depression of Cas. tora. Cro. juncea was found to be the most sensitive species to soil acidity. The application of P fertilizer resulted in the improvement of the dry matter yield, nodulation, nitrogen fixing activities, and nitrogen uptake. Plant responses to phosphorus fertilizer differed among species. S. cannabina and S. rostrata were noted to be more efficient species in utilizing phosphorus in soil, and less responsive species to the application of a higher level of phosphorus fertilizer. On the other hand, Cro. juncea was found to be the least efficient species in the utilization of P, and the most responsive species to phosphorus application. It was confirmed from this experiment that Sesbania sp. were useful manure legumes due to their ability to improve P availability in soils with low available P content through their decomposition, and that G. max and Cro. juncea were effective legumes showing a high biomass production under moderate soil P fertilization.

Predicting lime-induced changes in soil-pH From exchangeable aluminum, soil-Ph, total exchangeable cations and organic-carbon values measured on unlimed soils

The 'Lime-it' model is a decision support system for graziers wanting to lime acid soils. In this study we used field experimental data to test, improve and validate the model's ability to predict changes in soil pH due to variable rates of lime. Data from 13 field experiments, in which soil parameters were measured 1 year after liming acid soils, were used to derive an index of pH responsiveness to lime (LRI) at each site. Multivariate analysis was used to derive a predictive model: LRI was found to be significantly correlated (P &lt; 0.0001) with hydrogen ion concentration ([H+]x 105 ), exchangeable aluminium (Al), exchangeable cations (TEC) and percent organic carbon (C) data of the unlimed soils. The multivariate equation was then tested against an independent data set by comparing the predicted pH change with the measured pH change for eight soils. This evaluation, though generally acceptable, showed a small but significant deviation from the desired 1:1 ratio between observed and predicted pH change. We re-calibrated the model for the combined data to derive the model: LRI = 0.764 + 0.042 [H+] - 0.016 TEC - 0.097 Al - 0.016 C. When this model was tested over the whole data set for predicted v. measured pH changes, the following result was found: measured pH change = 1.01 (predicted pH change) - 0.05 (R2 = 0.85, n = 308). The implications of the predictive equation are considered with regard to the mechanisms that are thought to be associated with pH buffering.

Differential acidity tolerance of tropical legumes grown for green manure in acid sulfate soils

The growth of four tropical legumes (Cajanus cajan, Sesbania aculeata, S. rostrata, and S. speciosa) used as green manures in the tropics was studied in a glasshouse experiment. Two acid sulfate soils (Typic Sulfaquept, Bang Pakong Series; and Sulfic Tropaquept, Rangsit Series) were adjusted to four pH levels: 3.8 or 4.0 (original soil pH), 4.5, 5.5, and 6.5 (amended with lime). Dry weight was determined 49 days after sowing. Concentrations of N, P, K, Ca, Mg, Fe, Mn, and Al were also determined in aerial plant parts at harvest. The legumes responded differently to soil acidity and liming, but not to soil type. Cajanus cajan had the highest biomass production, followed by S. aculeata, S. rostrata and S. speciosa, in this order. The N concentration closely paralleled biomass production, suggesting that the growth of symbiotic rhizobia and nodulation were perhaps more susceptible to soil acidity than were the host plants. Liming to pH 5.5–6.0 was recommended for the legumes' growth based on the quadratic relationships between dry-matter yield and soil pH. In the unlimed soils, the Ca concentration in C. cajan and S. aculeata (0.32%) was twice as high as that in the two low-yielding legumes (0.15%). Furthermore, plant Ca increased exponentially (or quadratically in case of S. speciosa) as lime additions increased. It was estimated that for adequate growth, the Ca requirement in the shoot dry matter was approximately: C. cajan 1.2% Ca, S. aculeata 0.8%, S. rostrata 0.6%, and S. speciosa 0.4%. In contrast with Ca, the concentration of Fe, and to a lesser extent Mn, was significantly lower in C. cajan and S. aculeata than in S. rostrata and S. speciosa. The ratio of Ca to Al in plant tops was used to characterize plant tolerance to soil acidity, and to quantify the critical Al concentration in the plants. It appears that ≥ 90% maximum growth was attained only when Ca/Al was ≥ 150 for C. cajan and S. speciosa, ≥ 200 for S. rostrata, and ≥ 300 for S. aculeata. Cajanus cajan tolerated up to 80 mg Al kg-1 in the shoot dry matter, whereas significant growth reduction occurred in the Sesbania species at levels > 30 mg Al kg-1.

Effect of pH on competition for nodule occupancy by type I and type II strains ofRhizobium leguminosarum bv.phaseoli

The effect of soil pH on the competitive abilities of twoRhizobium leuminosarum bv.phaseoli type I and one type II strains was examined in a nonsterile soil system.Phaseolus vulgaris seedlings, grown in unlimed (pH 5.2) or limed (pH 7.6) soil, were inoculated with a single-strain inoculum containing 1 × 106 cells mL−1 of one of the three test strains or with a mixed inoculum (1:1, type I vs. type II) containing the type II strain CIAT 899 plus one type I strain (TAL 182 or CIAT 895). At harvest, nodule occupants were determined. In a separate experiment, a mixed suspension (1:1, type I vs. type II) of CIAT 899 paired with either TAL 182 or CIAT 895 was used to inoculateP. vulgaris seedlings grown in sterile, limed or unlimed soil. The numbers of each strain in the rhizosphere were monitored for 10 days following inoculation. The majority of nodules (> 60%) formed on plants grown in acidic soil were occupied by CIAT 899, the type II strain. This pattern of nodule occupancy changed in limed soil. When CIAT 899 was paired with TAL 182, the type I strain formed 78% of the nodules. The number of nodules formed by CIAT 899 and CIAT 895 (56% and 44%, respectively) were not significantly different. The observed patterns of nodule occupancy were not related to the relative numbers or specific growth rates of competing strains in the host rhizosphere prior to nodulation. The results indicate that soil pH can influence which symbiotype ofR. leguminosarum bv.phaseoli will competitively nodulateP. vulgaris.

Lime effect on soil N availability indexes as measured by plant uptake

Abstract Lime application to acid soils usually increases N mineralization but little is known about how it affects the N determined by methods that assess organic N availability. One incubation and three chemical methods were compared in twenty samples of unlimed or limed soils in a pot experiment with maize (Zea mays, L). The N availability methods included the NH4 +‐N released from soils by: a) anaerobic incubation for 7 days at 40°C; b) 2 mol/L KC1 at 100°C for 4 hours and distilled with MgO (hot KCl); c) this same procedure but distilled with 5 mol/L NaOH (hot KCl‐NaOH); and d) 30% v/v H2O2 and MnO2. In addition, inorganic N, total N and organic C were also determined in the soil samples. Readily available inorganic N presented the highest correlation coefficient with N uptake by maize but anaerobic incubation, hot KCl, hot KCl‐NaOH, and total N were also good predictors of soil N availability. The H2O2/MnO2 procedure and organic C produced inconsistent results. The amounts of N extracted by the meth...