Nodulation and growth ofLablab purpureus (Dolichos lablab) in relation to rhizobium strain,liming and phosphorus

Summary Greenhouse experiments were done with two purposes: (1) to identify strains of rhizobia effective and acid-tolerant in symbiosis withLablab purpureus, and (2) to determine whether soil acidity or the symbiotic condition increased the phosphate requirement for growth.Five rhizobial strains were tested in one neutral soil, two acid soils, and the two acid soils limed to pH 6.6. In the neutral and limed soils, three of the strains were effective (CB1024, CB756, TAL169), but only two strains (CB756, TAL169) remained effective in acid soil.Strain CB756 and plus-N treatments were further compared in a factorial trial involving combinations of five levels of P with lime, no lime and CaCl₂ treatments, applied to an acid soil. Some of the treatments were also applied to plants inoculated with CB1024. Between the N-fertilized and CB756 treatments there was no clear difference in growth response to applied P, and the critical internal concentration of P for 95% of maximal growth was the same (0.22% shoot dry weight). Increasing P beyond levels needed for maximal growth increased nodulation and N concentration in plants inoculated with CB756. It lowered N concentration in N-fertilized plants. There was evidence suggesting that the P requirement of symbiotic plants increased if the soil was acid, or if CB756 were replaced by CB1024 as microsymbiont; but the critical statistical interactions were not significant.     

New polygalacturonases from Trichoderma reesei: characterization and their specificities to partially methylated and acetylated pectins

Two extracellular isoenzymes of polygalacturonases PG1 and PG2 were isolated from 3-day-old culture filtrates of Trichoderma reesei. The two enzymes were purified to homogeneity by ion-exchange, gel filtration and hydrophobic interaction chromatographies. PG1 and PG2 exhibit similar molecular weights from gel filtration and SDS-PAGE. Their properties, including optimal pH and temperature, thermal stability and Km were compared. Characterization of substrate specificity showed that the two enzymes had higher affinity toward PGA (B0100) derived from sugar beet pectin (SBP) than PGA from lime pectin. A series of SBPs with different distribution patterns of methyl and acetyl groups, produced by treatment with either plant pectin methylesterase (P-series) or fungal pectin methylesterase (F-series) or base catalysis (B-series), was used as substrates for PG1 and PG2. Substrates with a low degree of esterification were preferred substrates. The activities of PG1 and PG2 were strongly correlated to the degree of methylation and very little effect from acetylation. The products generated by digestion of selected lime and SBPs were analysed using matrix assisted laser desorption ionisation time of flight (MALDI TOF) MS. A mode of action revealed a random cleavage pattern for PG1 and PG2, confirming that these enzymes are endopolygalacturonases.     

The Demand for and Supply of Field Biologists

The first-year zoology course at University College Cardiff is based on a self-instructional system using printed texts, audiovisual programmes, and integrated practical work. Each course ‘Unit’ has in addition a ‘General Session’ in the lecture theatre and structured tutorial work; some Units have associated fieldwork. The students work in a specially designed teaching laboratory and proceed at their own preferred time and pace. Each aspect of the course and its organization is described, with emphasis on the modifications to the original scheme which have been introduced during its first three years of existence in the light of experience.     

Pathogenesis ofSynchytrium endobioticum

Summary Field plots infested withSynchytrium endobioticum pathotype 2 were amended with agricultural lime, NH₄NO₃ and/or urea and planted with cv. Arran Victory. A weekly survey of changes in pH from planting to harvest revealed constant pH in absence of the chemicals, fluctuating pH with lime, very large increase then falling off with urea, and depressed below normal pH with NH₄NO₃. Best disease control occurred in urea-treated plotsvs NH₄NO₃-treated plots. Addition of lime, although it elevated pH, did not suppress the disease with urea or NH₄NO₃ added. Mechanisms for suppression by urea are related to its role as an ammonia producer and microbial stimulator, and their implication for infection byS. endobioticum.Contribution No. 81, Research Station, Agriculture Canada, P.O. Box 7098 St. John's, Newfoundland, A1E 3Y3     

Limitation of vesicular-arbuscular mycorrhizal activity in Leucaena leucocephala by Ca insufficiency in an acid Mn-rich oxisol

Glomus aggregatum and Leucaena leucocephala were interacted in an acid Mn-rich oxisol unamended or amended with lime [Ca(OH)₂] or gypsum (CaSO₄) at soil P concentrations considered optimal for mycorrhizal host growth and sufficient for mycorrhiza-free growth. At 0.02 mg P 1^-1, both vesicular-arbuscular mycorrhizal fungal (VAMF) colonization and function were significantly curtailed if soil was not amended with gypsum or lime. The highest mycorrhizal effect was observed in the limed soil, followed by the soil treated with gypsum at the rate of 32 g Ca kg^-1 soil. Higher concentrations of gypsum deleteriously affected VAMF infectivity and effectivity. The first increment of gypsum compensated completely for the VAMF colonization and for part of the mycorrhizal effect that was lost due to low pH. The superiority of the limed soil to that amended with gypsum apparently lies in the fact that Ca supply was assured in the former and also that the adverse effects of toxic constituents such as H⁺ and Mn²⁺ were eliminated. We were unable to separate the effect of Ca on VAMF from its effect on the host because a P concentration sufficient for mycorrhiza-free growth was not attained due to interaction of some of the P with Ca to form insoluble phosphate.Contribution from the Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No. 4045     

Effect of lime and phosphorus applications on concentrations of available nutrients and on P,Al and Mn uptake by two pasture legumes in an acid soil

Summary Effects of increasing rates of lime and phosphorus addition on concentrations of available nutrients in soil and on P, Al and Mn uptake by two pasture legumes, lotus (Lotus pedunculatus Cav.) and white clover (Trifolium repens L.), were studied in a pot experiment using a highly leached acid (pH 4.2) soil.Liming resulted in an increase in exchangeable Ca and thus in percentage base saturation, with concomitant decreases in levels of exchangeable Al, Fe and Mn. The relationship between exchangeable Ca and Al was linear and negative with a gradient of almost unity. Liming had no consistent effect on measured CEC values. Increasing lime rates significantly reduced concentrations of Mg, K and Na in saturation paste extracts but had no effect on exchangeable Mg, K and Na levels.With increasing lime additions, available phosphate indicesviz water soluble, resin-, Morgan-and Williams-extractable all decreased significantly, Truog-extractable was unaffected, while Brayextractable generally increased. Fractionation revealed that lime additions caused a decrease in easily soluble, Fe-bound and to a lesser extent Ca-bound phosphate fractions, had no effect on reductant soluble phosphate, but resulted in an increase in the Al-bound fraction. P uptake and yield of both legumes increased with lime and P additions.Correlations between available phosphate indices and yield of both legumes were weak or nonsignificant. However, high, significant positive correlation coefficients were found between available phosphate and plant uptake of P. Indices of available Al and Mn were not generally significantly correlated with plant uptake of Al or Mn but significant negative correlations were found between available Al and Mn and yield of both species.     

Integrated Control of Clubroot

Clubroot caused by Plasmodiophora brassicae affects the Brassicaceae family of plants, including many important vegetable and broadacre crops. In the last 20 years increasing intensity of vegetable production and the rapid growth in popularity of oilseed rape as a broadacre or arable break crop have increased the severity of clubroot and the area of land affected in both the vegetable and broadacre industries. Resting spores of P. brassicae are long-lived in soil, but the number of spores can be reduced through crop rotation, fallowing, chemical application, and management of brassica weeds. The host-pathogen system is responsive to a range of control measures, including calcium and boron amendments, manipulation of soil pH, and fungicide application. Molecular tests have been developed to predict disease and resistant cultivars are available for some crops. Increasingly, a multifaceted or integrated approach is being used to manage clubroot. This approach has been particularly successful in vegetable production systems.     

Effects of liming on phosphate availability in acid soils

Summary The critical factors involved in the plant-soil-phosphorus-lime interaction are outlined and discussed. Conflicting reports suggest that the prior liming of highly weathered acid soils can result in an increase, a decrease, or no change in the availability of applied phosphate. Adsorption of phosphate by amphoteric soil surfaces generally decreases slowly as the pH is raised from 4.0 to 7.0. However, in soils initially high in exchangeable Al³⁺, liming results in the formation of new, highly active, phosphate adsorbing surfaces as the Al³⁺ ions precipitate as insoluble polymeric hydroxy-Al cation species. Thus, if an acid soil is reacted with lime and then phosphate, without intervening air drying, liming can increase phosphate adsorption. If the same limed soil is air dried before reaction with phosphate (e.g. adsorption isotherm studies), liming decreases phosphate adsorption. Apparently, air drying alters the surface characteristics of recently limed soils, probably by promoting the crystallization of the hydroxy-Al cation polymers as gibbsite.An important phenomenon, which is often overlooked, is that liming can increase phosphate availability by stimulating mineralization of soil organic phosphorus. However, at high soil pH values, the precipitation of insoluble calcium phosphates can decrease phosphate availability. Since Al toxicity is characterised by the inhibition of the uptake, translocation and utilization of phosphate by plants, liming often increases the utilization of soil phosphate by plants through amelioration of Al toxicity.When making lime recommendations or interpreting the data collected from lime-phosphate experiments, it is important to consider all the complex interacting soil and plant factors involved.     

长期施用化肥及秸秆还田对砂姜黑土细菌群落的影响

【目的】在施用化肥的基础上进行秸秆还田是提高砂姜黑土肥力的有效措施,以往的研究只注重秸秆还田对土壤结构、肥力等物理化学性状方面的研究,缺少施肥对砂姜黑土微生物群落影响的研究。本研究以安徽蒙城典型的砂姜黑土为研究对象,以期揭示长期施用化肥和秸秆还田对砂姜黑土细菌群落的影响。【方法】采用454高通量测序对砂姜黑土不同农业施肥措施下的细菌群落进行分析研究,并通过生物信息学的分析方法揭示影响砂姜黑土细菌群落的主要因素。【结果】通过对454高通量测序数据的分析,发现砂姜黑土主要的细菌门类为放线菌、变形菌、酸杆菌、绿弯菌和拟杆菌。长期施用化肥显著提高了砂姜黑土肥力和作物产量,但导致了细菌群落结构的显著变化和多样性的显著降低。秸秆还田有利于土壤肥力的进一步提高,但是并没有缓解长期施用化肥对土壤细菌群落产生的不利影响。分析发现土壤pH的变化是导致土壤细菌群落变异的主要因素。【结论】在施用化肥的基础上进行秸秆还田有利于砂姜黑土肥力的提升,然而并没有缓解由施肥导致的土壤酸化对土壤细菌群落组成和多样性产生的不利影响。这暗示秸秆还田可能并未对砂姜黑土微生物生态产生根本性的有益影响,对于秸秆农田的利用方式还需要进一步研究,以达到农业生产效益和生态效益的并重。     

Restoration of cut‐over bogs by floating raft formation: An experimental feasibility study

Abstract. Stimulation of floating peat by the introduction of poorly humified peat from four cut‐over bogs in The Netherlands was studied in a one‐year outdoor experiment. The pH of the various peat substrates was increased by adding different amounts of lime: 0–2 to 4–8 g‐CaCO₃.kg^‐1 fresh peat. Both peat type and lime addition were found to affect the buoyancy of the peat substrates. Low nutrient concentrations in the peat, together with a high bulk density, proved to be unfavourable for creating floating peat. Three of the peat types proved to be too acidic (pH < 4.5) to produce sufficient methane (ca. 400–600 μmol.L^‐1), and buoyancy was only achieved if lime was mixed in with the peat. The smallest amount of lime added (2 g.kg^‐1 fresh peat) was sufficient to maintain buoyancy for at least one year. Lime addition did not stimulate nutrient mobilization by mineralization, although P, N and K concentrations in the peat water were relatively high. It is concluded that floating peat can be initiated by the introduction of poorly humified peat. If the peat substrates are too acidic, lime can be added to stimulate buoyancy of the peat. Results are discussed in relation to restoration prospects.