Rhizobia in tropical legumes—X. Growth in coir-dust-soil compost

Conditions affecting the growth of two rhizobia (RRIM 968 isolated from Centrosema pubescens and CB 1809 from Glycine max) in the coir-dust-soil compost used in Malaysia were examined. Whilst differences in growth between the two isolates were observed, recommended conditions for rhizobial production are: compost—(coir-dust 8 g; Sungei Buloh series soil—25 g ; calcium carbonate—5 g; and distilled water—60 ml) incubation—at 25°C for 12d; storage—commercially for about 3 months at 20°C. Under these conditions more than 10⁹ viable rhizobial cells·g^?1 compost are obtainable, while more than 10⁸·g^?1 survive 5 months in storage.Addition of a “sticker” (methyl-ethyl cellulose) to the compost during incubation was encouraging.     

Rhizobia in tropical legumes—VIII. Serological characteristics of Psophocarpus tetragonolobus (L.) DC. isolates

Antisera were prepared against six inoculant strains of rhizobia for Psophocarpus tetragonolobus, and used to react with 62 different strains in both agglutination and immunodiffusion systems. A wide array of reactions occurred, indicating the extent of heterogeneity amongst strains capable of nodulating the same host. In agglutination reactions, the heat-stable somatic antigens could be arranged in 25 serogroups. In gel diffusion, antigens which produced strong precipitin bands usually showed agglutination relationships, but the corollary was not true. The immunodiffusion technique easily distinguished homologous and cross-reacting reactions and could be reliably used in field experiments with P. tetragonolobus.     

Rhizobia in tropical legumes—VII. Effectiveness of different isolates on Psophocarpus tetragonolobus (L.) DC

Rhizobia isolated from fourteen different genera of legumes were tested for their N-fixing effectiveness with Psophocarpus tetragonolobus in standard Leonard jar trials. Isolates from all plants except Pithecellobium jiringa were able to form nodules with P. tetragonolobus although a wide range of effectiveness amongst the different rhizobia was demonstrated. Thus P. tetragonolobus may be considered promiscuous with respect to its rhizobial requirements. Based on this experiment, a group of rhizobia comprising three elite strains (RRIM 56 from P. tetragonolobus, UMKL 36 from Lablab purpureus and CB 756 from Macrotyloma africanum, a moderately effective strain (NGR 258 from P. tetragonolobus), and two strains of low effectivity (RRIM 968 from Centrosema pubescens and UMKL 12 from Phaselus angularis) were selected for further study. When these were used to inoculate P. tetragonolubus growing in soil taken from virgin jungle (less than 1.54 rhizobia g^?1 soil); RRIM 56 and UMKL 36 again performed well, but NGR 258 outperformed CB 756.     

Rhizobia in tropical legumes—IX. pot and field trials with inoculants for Psophocarpus tetragonolobus (L.) DC.

Antigenically identifiable inoculants for Psophocarpus tetragonolobus were evaluated in three non-sterile soils contained in pots (sandy-clay, Renggam series; a loamy-sand, Sungei Buloh series; silty-clay, Munchong series). Most-probable-numbers of indigenous rhizobia ranged from 4 (Renggam series) to 13 (Munchong series) g^?1. Only two (RRIM 56 and 968) of the eight rhizobia tested formed > 50% of the nodules in all soils. Recovery of two strains (RRIM 968 and UMKL 12) was significantly poorer from the Munchong series soil which had the most indigenous rhizobia and the highest silt plus clay content. In a field trial using a Sungei Buloh series soil containing 700 rhizobia g^?1 capable of nodulating P. tetragonolobus, none of the applied strains formed > 18% of the nodules; two formed no nodules. There were no significant increases in plant yield in response to inoculation in the field trial and in two soils in the pot trials. In Sungei Buloh series soil, RRIM 56 formed 90% of the nodules when the indigenous rhizobia were 5 cells g^?, and 14% when the population was 700 g^?1. This raises the question of the need to inoculate seed sown into soils with high indigenous rhizobial populations, but there was some indication of increasing representation of inoculant strains in nodules with time.     

The colonization of host-root and soil by Rhizobia—I. Species and strain differences in the field

Growing-season populations of rhizobia associated with annual host-plant roots and nearby soil were examined in a field soil showing a nodulation problem in the second year after establishment. Rhizobium lupini reached higher populations at a faster rate than R. trifolii. A sharp drop in the population of R. trifolii associated with subterranean clover roots early in the growing season was followed by a recovery to high numbers. No such phenomenon occurred with R. lupini. The numbers of rhizobia under patches of non-nodulated plants in second-year stands were very low, usually <5/g soil, whereas the numbers under healthy plants in problem stands were similar to those under established stands. Differences in the colonization of both root and soil by R. trifolii in the first year were reflected in the second-year nodulation.     

Potentially bioavailable metals in sediment from a tropical polymictic environment—Rio Grande Reservoir,Brazil

Background, aim and scope  Although many recent studies have focused on sediment potential toxicity, few of them were performed in tropical shallow aquatic environments. Those places can suffer short-time variations, especially due to water column circulations generated by changes in temperature and wind. Rio Grande reservoir is such an example; aside from that, it suffers various anthropogenic impacts, despite its multiple uses. Materials and methods  This work presents the first screening step for understanding sediment quality from Rio Grande reservoir by comparing metal content using three different sediment quality guidelines. We also aimed at verifying any possible spatial heterogeneity. Results and discussion  We found spatial heterogeneity varying according to the specific metal. Results showed a tendency for metals to remain as insoluble as metal sulfide (potentially not bioavailable), since sulfide was in excess and sediment physical–chemical characteristics contribute to sulfide maintenance (low redox potential, neutral pH, low dissolved oxygen, and high organic matter content). On the other hand, metal concentrations were much higher than suggested by Canadian guidelines and regional background values, especially Cu, which raises the risk of metal remobilization in cases of water circulation. Further study steps include the temporal evaluation of AVS/SEM, a battery of bioassays and the characterization of organic compounds.     

Studies on the survival of algae added to chemically treated soils—1. methodology

A modification of the method of Tchan (1952) for the direct enumeration of soil algae was evaluated with a view to determining effects of pesticides and herbicides upon soil algae. Modifications to Tchan's technique were the use of a Hg vapour u.v., light source for microscopy and a specially designed haemocytmeter slide. These modifications increased the intensity of fluorescence of algal cells, facilitated accurate estimation of numbers in soil as shown by high percentage recoveries of known numbers of algal cells added to sterile soil, and enabled transmitted or incident light systems to be used equally successfully.Using direct microscopy, various algal cells in culture were examined for fluorescence. Fluorescence during different stages of growth of two species of unicellular green algae was determined. Viable cells at all stages of growth were found to fluoresce. Newly killed cells, inactivated by heat, acid and herbicide treatment were found not to fluoresce. Twenty seven species of algae, selected for their wide range of structure and for their common occurrence in British soils were all found to fluoresce either in culture or when incubated in sterile soil.Four different (agronomic) soil types were examined for indigenous algae. To overcome seasonal variations that occur in numbers of algae, the effect of seeding soils with a mixed inoculum of algal cells was determined.The effects of shaking and ultra-sonicating soil suspensions before examination were compared in order to recover efficiently a known number of cells added to different soils. Survival of added algae in four soils of pH 5.8–7.8, and in one soil maintained at moisture contents ranging from 20–100% of the moisture holding capacity was determined. Growth of algae in soil at two different light intensities was also examined.     

Relationship of seed pericarp color with seed quality in sugar beet (Beta vulgaris L. var. altissima Döll)

Genetic Resources and Crop Evolution - Quantitative traits of seed pericarp color were used to evaluate the sugar beet (Beta vulgaris L.) seed quality. These traits were measured on 10 single cross...     

Long-term fertilization effects on carbon pools and carbon management index of loamy soil under grass–forage legumes mixture in semi-arid environment

ABSTRACT

Soil organic carbon (SOC) is a key component for sustaining crop production. A field experiment was conducted during 2004–2018 to assess the changes in soil carbon fractions under different fertilization practices in grass-legumes mixture. The result indicates that application of farmyard manure (FYM) at 80 Mg ha^–1 has increased SOC concentration leading to carbon sequestration rate of 4.2 Mg ha^–1 year^–1. Further, it has increased the proportion of labile carbon in the total SOC and have accumulated 126, 60, 83 and 95% higher very labile, labile, less labile and non-labile C stock than that of control plot, respectively, in top 30 cm soil layer. Inorganic fertilization and FYM 20 Mg ha^–1 influenced SOC concentration, SOC stock and C sequestration rate similarly. The highest carbon management index (264) was found in the treatment receiving FYM 80 Mg ha^–1 and it was positively correlated with SOC (r = 0.84**). The sensitivity index of the SOC varied from 26 to 152% and the differences were greatest in FYM treatments. The result indicates that grass-legumes mixture build-up the SOC in long term and the addition of FYM further increases it.     

Growth of perennial forage legumes in acidic soils of the Appalachian Hill‐Lands after liming

A major constraint to the renovation of forage legume‐based pastures on acidic soils of the Appalachian hill‐lands is thought to be the absence of effective rhizobia. A growth chamber experiment was done with aluminum (Al) toxic, low pH (≥ 4.2) soils from four series (Berks, Lily, Tate, and Westmoreland) that were planted with alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), white clover (Trifolium repens L.), or birdsfoot trefoil (Lotus corniculatus L.). These soils, without lime addition, were previously shown not to contain effective, naturalized populations of rhizobia for these plant species. However, a non‐toxic, pH 6.8, Watauga soil was shown to have such rhizobia but only for alfalfa. In the present study, these five soils were reexamined after liming to pH ≥ 5.5 for effective, naturalized populations of rhizobia and the efficacy of soil inoculation with commercially available rhizobia. In addition to effective, naturalized R. meliloti for alfalfa in the Watauga soil, similar populations of R. trifolii for red clover, and R. lotus for birdsfoot trefoil, were now found. Such rhizobia were also found for alfalfa in the Lily soil and for red clover in the Lily and Tate soil. Thus, liming allowed the expression of effectiveness of natural rhizobia that otherwise would not have been detected in soil pot experiments without lime. Inoculation of the toxic soils after lime addition with commercial rhizobia was effective in about half of the soil‐plant combinations that did not contain populations of effective, naturalized rhizobia. Asymbiotic shoot growth of all the plant species was significantly (P ≤ 0.05) correlated with soil pH over a range of 5.5–6.6. These results indicate that, in the absence of effective, naturalized populations of rhizobia, improvement of rhizobial inocula could increase forage production by ～34% for some species on some of the toxic soils, even after the pH of the soils is increased to ≥ 5.5.     

Effects of river infrastructures on the floodplain sedimentary environment in the Rhône River

Journal of Soils and Sediments - River infrastructures such as dikes, groynes, and dams are ubiquitous on most large rivers, and although their consequences on the riverbed morphology have often...     

Grasses and legumes facilitate phytoremediation of metalliferous soils in the vicinity of an abandoned chromite–asbestos mine

Purpose

The present study was carried out in Roro region, Chaibasa, Jharkhand, India, to assess the impact of chromite–asbestos mine waste (CMW) on a nearby agroecosystem. The role of metal-accumulating grass–legume association in facilitating phytoremediation was investigated.

Materials and methods

Soil and plant samples were collected from (i) chromite–asbestos mine waste (CMW) with Cynodon dactylon, Sorghastrum nutans, and Acacia concinna; (ii) contaminated agricultural soil-1 (CAS1) from a foothill with Cajanus cajan; (iii) contaminated agricultural soil-2 (CAS2) distantly located from the hill, cultivated with Oryza sativa and Zea mays; and (iv) unpolluted control soil (CS). Total metal concentrations were quantified in both soils and plants by digesting the samples using HNO₃, HF, HClO₄ (5:1:1; v/v/v), and HNO₃ and HClO₄ (5:1; v/v), respectively, and analyzed under flame atomic absorption spectrophotometry. Metal grouping and site grouping cluster analysis was executed to group the metals and sampling sites. Translocation factor (TF) and bioconcentration factor (BCF) were calculated to determine the phytoremediation efficiency of grasses and legumes.

Results and discussion

Results indicate that total metal concentrations in the CMW were in the order of Cr?>?Ni?>?Mn?>?Cu?>?Pb?>?Co?>?Zn?>?Cd. High concentrations of Cr (1983 mg kg^?1) and Ni (1293 mg kg^?1) with a very strong contamination factor were found in the CAS, which exceeds the soil threshold limits. Further, metal and site grouping cluster analysis also revealed that Cr and Ni were closely linked with each other and the CMW was the main source of contamination. Among all the metals, Cr and Ni were mainly accumulated in grasses (C. dactylon and S. nutans) and legumes (A. concinna and C. cajan) as compared to cereals (Z. mays and O. sativa). The TF of Cr was >1 for grasses. Except for Zn, the BCF for all the metals were <1 in roots and shoots of all the plants and cereals.

Conclusions

The present study revealed that abandoned CMW is the source of contamination for agriculture lands. Phytoremediation relies on suitable plants with metal-scavenging properties. Grass–legume cover (C. dactylon, S. nutans, A. concinna, and C. cajan) has the ability to accumulate metals and act as a potential barrier for metal transport, which facilitate the phytoremediation of the CMW. Possibilities for enhancing the barrier function of the grass–legume cover need to be explored with other low-cost agronomic amendments and the role of rhizospheric organisms.

     

Studies on the ecology of actinomycetes in soil— VII. Actinomycetes in a coastal sand belt

Distribution of actinomyeetes in beach and dune sand at two sites was studied. At one site. dunes were eroding while at the other accretion of sand and dune development occurred. Actinomycetes occurred in low numbers in beach sand hul increased sharply when dunes were colonized by Ammophila arenaria (L) Link or Agropyron junceiforme (A & D Löve) A & D Löve. Micromonospora strains predominated in beach sand but Streptomyces was the predominant genus in dunes.Salinity tolerance of isolates was not clearly related to their source but tolerance of dune isolates was generally greater than those from the beach. Tolerance of Streptomyces strains varied but all Micromonospora isolates were intolerant of salinities above that of sea water.Evidence for increased growth of actinomycetes in the root region of A. arenaria and A. junceiforme was obtained but there was little qualitative difference between those in the root region and root-free sand. In laboratory experiments actinomycetes colonized old. dead Ammophila roots more readily than young ones and arose carly in succession on the former. Young, living roots stimulated bacteria and fungi but not actinomyeetcs. It was concluded that most activity of actinomycetes in the Ammophila root region occurred on old root tissue and it was suggested that this might be true of other plants.     

Does the enhanced P acquisition by maize following legumes in a rotation result from improved soil P availability?

Field data have suggested that under P-deficient conditions, legumes supplied with phosphate rock (PR) increase P acquisition by a subsequent maize crop compared to direct application of PR to maize. This study assessed the mechanism of this positive rotational effect in terms of soil P availability using a greenhouse trial with large volume (74 l) containers. The rotation effect was analysed in relation to PR application, previous legume growth and incorporation of the legume residues. Velvet bean (Mucuna pruriens) and maize were grown in a representative Acrisol from the Nigerian Northern Guinea savannah (NGS). All soils were applied with sufficient urea to exclude N-effects in the rotations. In a first season, velvet bean and maize responded similarly to PR application, and P uptake by both crops increased by 45%. The soil total labile P quantity (E-value) and P concentration in soil solution after plant growth were increased by PR-application only in soils previously grown by velvet bean, suggesting enhanced PR solubilisation in the legume-grown soils. In the subsequent season, grain yields and P uptake of a maize crop following velvet bean were twice as large compared to maize following a first maize crop. This residual effect of velvet bean was even significant in treatments without PR-application, although both maize and velvet bean withdrew similar amounts of P during the first season and no differences in soil P availability were observed. Furthermore, legume residue incorporation in soils previously grown by maize did not affect yields or P uptake of the subsequent maize crop, while it significantly increased the E-value and during the first 7 weeks in the second season. As such, the positive rotational effects of velvet bean were larger than predicted by soil P availability measures. Maize yield significantly increased with increasing plant P concentration among all treatments. However, the rotational effect was unrelated to internal P concentration: significantly larger yields were obtained for maize following velvet bean than for maize following maize at identical internal P. This suggested the presence of another growth-limiting which is counteracted by the previous velvet bean growth. In conclusion, our results confirmed that the introduction of a legume supplied with PR into a maize-based cropping system increases yield and P-uptake by a subsequent maize crop, compared to maize following a first maize crop supplied with PR. These stimulations, however, went beyond improved P nutrition. Results strongly suggested that the legume in the rotation system has other positive, possibly soil-microbiological effects which enhance maize growth and production.     

Chrysanthemum cultivation in expanded clay. I. Effect of the nitrogen‐phosphorus‐potassium ratio in the nutrient solution

The hydroponic technique using expanded clay for the production of chrysanthemum was studied for possible use by Brazilian flower producers. Eight varying nutrient solution nitrogen (N):phosphorus (P):potassium (K) ratio treatments in a randomized block configuration with four replications were used. Six of the treatments supplied the same solution over the entire experimental period. The N:P:K ratios in the nutrient solution compared were: 1.0:0.3:1.0, 1.0:0.3:1.5, 1.0:0.3:2.0, 1.0:0.3:2.5, 1.5:0.3:1.0, and 2.0:0.3:1.0. The other two treatments consisted of N:P:K ratios of 2.0:0.3:1.0 during the juvenile stage and 1.0:0.3:1.5 or 1.0:0.3:2.0 ratios during the reproductive stage. There were two or three daily irrigations depending on plant need. The electrical conductivity (EC) and pH of the nutrient solution were checked once each day and the nutrient solution was chanced when 50% depleted. The plants were crown to the two‐stem stage under 50 long and 4.0 short days. Harvest was made 115 days after plant establishment. There were not expressive differences in plant characteristics among the treatments. The 1.0:0.3:2.5 N:P:K ratio gave the highest flower numbers per stem, stem length, and fresh and dry weights per plant.     

Precipitation as the most affecting factor on soil–plant environment conditions affects the mycorrhizal spore numbers in three different ecological zones in Turkey

Mycorrhizal symbiosis is the one of the most important relationship between microbiota and plants to sustain plant nutrition in relatively unfavourable conditions. Somehow this relation is threatened by time, therefore, definition of the factors effecting mycorrhizal symbiosis has become essential. The aim of this study was to determine the differences in specific mycorrhizal parameters such as sporulation and soil–plant environment conditions in three different regions of Turkey. During 1996?2002, 53 soil series were selected from natural and agricultural plant communities in three different agro-ecological zones of Turkey: Central Anatolia (CA), the Southeastern Anatolian (SA) project area and the Coast of Mediterranean (CM). The arbuscular mycorrhizal fungus (AMF), spore numbers and mycorrhizal root colonization were related to the annual average precipitation, soil characteristics and host plant identity.

In the CM zone (average annual precipitation of 650?mm), soils found under natural vegetation contained a maximum value of 108?spores?g^?1, with bare soils containing a minimum number of 0.1?spores?g^?1. In the CA zone (330?mm annual average precipitation), the maximum number of spores in the soil samples was 46.5?spores?g^?1 with a minimum of 6.8?spores?g^?1 and in the SA soil samples (380?mm annual average precipitation), a maximum of 48.4?spores?g^?1 and a minimum of 14.2?spores?g^?1 were recorded. The overall mean number of mycorrhizal spores g^?1 soil was 15.5?±?14.4, 22.2?±?8.6 and 27.9?±?25.4 for the CA, SA and CM zones, respectively. Mean spore numbers differed in only two of the three zones, with the third zone being intermediate. Precipitation was the most affecting factor on the sporulation of AMF. Also host plant species and certain soil parameters, such as positive correlations with CaCO₃ and N-min and a negative correlation with organic matter, have an influence on sporulation.

The key finding is that the cropping system has a large impact on spore numbers/abundance. Seventeen standing crops as well as bare soil, fallow and natural areas were compared. There are a large number of factors which can affect mycorrhizal development; in the present work, it seems that soil and crop management, and environmental factors (such as precipitation) affect sporulation and root colonization. Covering land surface with mycorrhiza-dependent cover crop, irrigation and less soil till may increase indigenous mycorrhizal spores.     

Can differences in 15N natural abundance be used to quantify the transfer of nitrogen from legumes to neighbouring non-legume plant species?

Natural variations in the stable isotope ¹⁵N are often exploited in studies of N cycling in ecosystems. Lower ¹⁵N natural abundance in non-legume plants growing in association with legumes, compared with the non-legume grown alone in pure stands have been observed in cropping, forage, and agroforestry systems. Such observations have frequently been attributed to the transfer of biologically-fixed nitrogen (N) from the legume to the companion non-legume, and various methodologies have been employed to calculate the extent of the N transfer. While some of these ¹⁵N natural abundance-based estimates of N transfer were within the range previously reported using equivalent ¹⁵N-enriched techniques (<20% of non-legume plant N and <10 kg N ha⁻¹ derived from fixed N contributed by neighbouring legumes), many of the values obtained using natural abundance were much higher (30%–83% of the non-legume N derived from fixed N representing up to 30–40 kg N ha⁻¹) than generally measured by ¹⁵N-enriched methods; with even greater estimates being determined where data were available to allow N transfer to be re-calculated on the basis of total legume N rather than fixed N (42% to >100%, and up to 110 kg N ha⁻¹ per year). This review raises concerns about the assumptions behind the natural abundance approach, and provides some alternative interpretations for the observed differences in natural ¹⁵N abundance between plants grown in the presence and absence of legumes. It was concluded that simple comparative measures of non-legume δ¹⁵N alone cannot provide a quantitative estimate of N transfer between plant species if the dominant source and the isotopic identity of the transferred N cannot be validated, and if the extent of any isotopic fractionation associated with relevant N transformations occurring during transfer cannot be defined. To date this information is not forthcoming. There is a need to greatly improve our understanding of the transfer processes before the real value of the δ¹⁵N technology can be realized. In the first instance this will primarily be achieved by carefully executed experiments under controlled conditions, and in the field, employing both ¹⁵N natural abundance and enrichment approaches so estimates of transfer can be compared, and the data interrogated using modelling approaches to explore isotopic fractionation.