Showing papers in "Plant and Soil in 1971"

An effective water extraction method for the determination of plant-available soil phosphorus

Abstract: A new variant of the water-extraction method for the assessment of soil phosphorus availability to the plant was recently developed by Van der Paauw and Sissingh. The correlation between the water-extractable soil phosphate (Pw value) and the response of the plant, measured in most cases by the P2O5 content of dry matter, was high on Dutch soil types and was not affected by differences in such soil factors as organic matter content, particle size content, CaCO3 content, pH, phosphate-fixation capacity and other factors related to the origin of the soil. In other words, the relationship was the same for all soil types investigated.7 In order to investigate whether an equally good result would be obtained with soil types from widely diverging origin and properties, the method was evaluated in a pot experiment with potato (tops) and spring wheat grown successively on different soil types of European, American and Australian origin. A high correlation between Pw value and the P2O5 content of spring wheat was found, which explained 88% of the variance. All soil types of different origin could be represented by one regression line. The dry-matter yield of wheat was also closely correlated with Pw value, although the yield was also influenced by the pH of the soil. With potatoes a high correlation between water-extractable P and P2O5 content of the tops was found in the series of European soils, but on part of the American and Australian soils the P2O5 contents of plants were higher than those on European soils with corresponding Pw values. This difference could not be explained. In general it may be stated that the Pw value provides a reliable estimate of the availability of soil phosphorus to the plant in a wide variety of soil types.

Analytical technique of the Pw method, used for the assessment of the phosphate status of arable soils in the Netherlands

Abstract: The paper deals with the analytical technique of a new method for the assessment of the phosphate status of soils, characterized by aqueous extraction at a wide water : soil ratioviz 60 : 1 (volume/volume) the soil being moistened 22 hours preceding the extraction

The role of Alnus in improving the forest environment

Abstract: Worldwide experience indicates that alder contributes significantly to the supply of nitrogen in the ecosystem. This contribution markedly benefits soil fertility. A definite potential exists for employing alder in forest management in much the same way that legumes are utilized in agriculture. Current research indicates also thatAlnus rubra may play a significant role in controllingPoria weirii, a virulent root pathogen which causes extensive losses of commercial timber tree species in western North America and Japan.

Biological nitrogen fixation: A key to world protein

Abstract: 1. Characteristics and methodology of the C2H2-C2H4 assay forin situ measurement of N2 fixation are outlined. 2. Electron micrographic analysis of the developmental morphology of the natural soybean symbiosis and C2H2-C2H4 analysis indicate that increasing N2-fixing activity from 12–35 days of age is accompanied by an increase in bacteroid number per cell, bacteroid number per vesicle and inclusions per bacteroid. The mole ratio of leghemoglobin to nitrogenase also increases from 50 to a relatively constant plateau of 500 to 1500 during this period. The quantitative validity of the C2H2-C2H4 assay as a measure of N2 fixation during a complete growth cycle of soybeans on nitrogen-free medium is demonstrated by Σ (C2H2→C2H4)×28/3 values which are 75–95% of the values determined for N2 fixed by Kjeldahl analyses. 3. A technique for the establishment of the first callus N2-fixing symbiosis in mixed cultures ofRhizobium legume provides a defined experimental system for exploration of legume symbiosis. N2-fixing activity is about 1% of the natural system and is influenced by exogenous auxins and cytokinins. Morphology, including infection threads and vesicle enclosed bacteroids, is similar to the nodule system. 4. N2-fixing activity of field-grown soybeans, including varieties which differed in flowering characteristics and maturity dates, and of peanuts was determined biweekly with the C2H2-C2H4 assay. Activity extended from nodule initiation to senescence and correlated with the nitrogen demands of the plant and in most cases >90% of the N2 fixed during the 60–70 day period of fruit formation and maturation. A logarithmic relationship between N2-fixing activity and age, and N2 fixed and age was demonstrated as a fundamental characteristic of these annual symbionts,i.e. log N2 fixed =k(t−t 0), wheret 0 is age at activity initiation. The resultant parameters: 1) age at activity initiation, 2) calculated rate of daily increase (7–9% for soybeans and 7–10% for peanuts), 3) age at end of logarithmic phase (about 80 days for soybeans), and 4) total N2 fixed (about 250 mg per soybean plant) are useful bases for evaluation of environmental, bacterial and host effects on N2 fixation. Various N fertilizers applied at planting and flowering inhibited N2 fixation of soybeans by decreasing the rate of daily increase. 5. Physical and chemical characteristics of nitrogenase, including those of crystalline Mo-Fe protein, reactions of nitrogenase, and model studies are consistent with a proposed mechanism. 6. Potential utilities of N2 fixation research include increased food protein production via initially enhanced N2 fixation of legumes such as soybeans and eventually extension of N2-fixing symbioses to non-legumes and new chemistry of N2, including the direct incorporation of aerial N2 into important organic compounds.

Effects of incubation temperature and oxygen tension on nitrogenase activity of legume root nodules

Abstract: Acetylene reduction and H2 evolution by legume root nodules from several plant species depended on incubation temperature; some nodules were active from 2 to 40°C. Acetylene reduction rates differed between plant species, with maximum activity at temperatures between 20 and 30°C forVicia faba, V. sativa, Trifolium pratense, T. subterraneum, Medicago truncatula and soybean, at 35°C forM. sativa and at 40°C for cowpea. OnlyM. sativa and cowpea reduced substantial amounts at 37.5°C. Temperatures from 2 to 10°C only slightly lessened activity ofT. subterraneum andV. sativa nodules. Nitrogenase functioned at temperatures which prevent establishment of other aspects of the symbiosis. The rate of acetylene reduction was constant for several hours at temperatures below 15°C, and activity continued for several days at 2°C for some species, but declined with time at warmer temperatures. Some nitrogenase was denatured at warmer temperatures, but the O2 tension in the assay vial also affected activity. In closed assay vessels nodule respiration decreased the pO2 and reduced nitrogenase activity. Activity was restored by adding O2 or regassing assay vials with air or Ar/O2. When the pO2 was maintained, acetylene reduction and H2 evolution by detached soybean nodules continued unchanged for 6 h.

Soil analysis by means of a 1:2 volume extract

Abstract: The use of the 1:5 weight extract in soil analysis presents some difficulties. Conductivity determinations as a means of assessing the salt status are unreliable for those soils containing appreciable amounts of gypsum, and it is also desirable that the soil organic matter content be known when interpreting the analytical data.

Factors in the physical and biological environment affecting nodulation and nitrogen fixation by legumes

Abstract: The effects of root temperature on the four main stages of nodule formation and function are reviewed. Compared with results obtained under optimal conditions, lower root temperatures retard root hair infection more than they affect nodule initiation, nodule development (including bacteroid tissue development and degeneration), or nitrogen assimilation. Higher root temperatures upset the formation of bacteroid tissue and hasten its degeneration. Tropical and subtropical legumes have higher minimum temperatures for nodule formation than temperate species. Low and high shoot temperatures affect nodulation and nitrogen fixation, but the effect is less severe than that of similar root temperatures. Various approaches to minimise adverse environmental effects are considered. These include the selection of appropriate biological material (both host plants and bacterial strains) for the prevailing conditions, and the adoption of management practices designed to utilise the environment or to minimise its adverse effects. The importance of increase in bacteroid volume in relation to increase in rate of nitrogen fixation is considered, and the concept of compensation in nodule production and activity is examined. The limited information on defoliation effects on the nodulation of both temperate and tropical legumes is reviewed and aspects requiring examination are discussed.

Continuous cultivation of West African soils: Organic matter diminution and effects of applied lime and phosphorus

Abstract: Five years of sustained cropping of cleared ferallitic and alluvial soils in Sierra Leone reduced the organic matter originally under bush of both soils by 50 per cent and the cation exchange capacities by 30 per cent. The rate of organic matter loss was sharply reduced after the 3rd year and organic matter cycling was stabilized by the 5th year. It was predicted that this equilibrium could be sustained after the 5th year provided that other factors of soil fertility have not become degraded.

Response of conifer seedlings to nitrate and ammonium sources of nitrogen

Abstract: Differences in growth responses of Douglas fir, western hemlock, Sitka spruce, and white spruce to nitrate and ammonium N sources were examined in sand culture and artificial soil culture. Effects of the two forms of N on growth, needle area, and N uptake of three Douglas fir halb-sib progenies were examined in a second sand culture. Response of Douglas fir to the two forms of N was followed over two years in nursery soil of different pH levels. In sand culture 1 mean seedling dry weight of all species, except hemlock, was greatest when ammonium N and nitrate N were provided in equal amounts. In all species, except Sitka spruce, ammonium alone resulted in greater growth than nitrate alone. Use of ammonium N resulted in greater growth of all species, than was obtained with nitrate N, at pH values in the region 5.4 and 7.5 in artificial soil culture. Only Douglas fir showed substantial differences due to N source below pH 5. Growth of all species was greater at pH 5.4 than at 7.5 in each N source treatment. Growth of Douglas fir seedlings was greatest with ammonium N and least with nitrate N in sand culture 2. Supply of nitrate and ammonium in equal proportions resulted in intermediate growth. Leaf area/plant weight ratio was unaffected by N source. Analysis of nutrient solutions showed appreciable nitrification of ammonium N during the 7 days between solution changes. In the three greenhouse experiments, with little exception, increase in proportion of ammonium in N supply resulted in increase of seedling tissue N concentration. This effect was more pronounced in roots than shoots. Total N uptake by ammonium fed seedlings was about double the N uptake of nitrate fed seedlings in sand culture 2. Nursery grown Douglas fir seedlings showed greater growth response to ammonium sulphate than to calcium nitrate, and this appeared due entirely to form of N supply in the first year. A similar response in the second year was partly due to greater soil acidification by ammonium sulphate. Compared with calcium nitrate, ammonium sulphate increased N concentration of one-year old shoots, but this difference was not detected by foliar analysis of two-year old seedlings.

The influence of phosphorus and nitrogen on millet and clover growing in soils affected by salinity

Abstract: The growth of foxtail millet and clover in soils of varying degrees of salinity (0.5 to 13 mmhos/cm), treated with nitrogen and phosphorus, was studied. Salinity levels were achieved by addition of sodium chloride. Nitrogen (10 to 60 ppm N) and phosphorus (6.4 to 44.8 ppm P) were added as NH4NO3 and H3PO4, respectively.

Uptake of solutes by multiple root systems from soil: I. An electrical analog of diffusion to root systems

Abstract: SummaryThe theoretical treatment of diffusion of solutes to a number of parallel, competing roots is difficult, but an electrical analog has been constructed which allows solute uptake by such a system to be simulated easily and rapidly. The construction, theory and operation of the analog are described. Differences in diffusion coefficients, dimensions, root size and uptake properties can all be dealt with. Approximate methods are available for simulating mass flow with diffusion, slow release of nutrients in the soil, the presence of root hairs, and incomplete root-soil contact.

Symbiotic nitrogen fixation under stress conditions

Abstract: An outline is given of the possibility selecting Rhizobium strains capable of performing a relatively good symbiosis with leguminous plants, growing under stress conditions. A Rhizobium strain capable of nodulating pea plants in acid soils is described. A pea cultivar, resistant to the majority of Rhizobium strains when growing at 20°C, is found to require a short period of a higher temperature for successful nodulation. The effect of non-photosynthetic light and its possible significance under natural conditions is discussed.

The nodulation and nitrogen fixation of isolated roots ofPhaseolus vulgaris L.

Abstract: At a concentration of 3%, carbon dioxide completely inhibits nodulation. Ethylene at concentrations of 0.4 ppm and above is extremely inhibitory towards nodulation. The gaseous emanations from isolated root cultures, when permitted to accumulate, completely prevent nodulation and also inhibit the nitrogen fixation of existing nodules. Evidence is presented which suggests that ethylene is the active principle of the gaseous emanations.

The nitrate stress syndrome of the nodulated field pea ( Pisum arvense L.) Techniques for measurement and evaluation in physiological terms

Abstract: Nodulated plants of field pea (Pisum arvense L.) were grown for 4 weeks in a range of constantly maintained levels of nitrate labelled with N15. The total and labelled nitrogen in soluble and insoluble fractions of different parts of the treated plants were determined, and from such measurements the distribution of the nitrogen assimilated from nitrate and from the atmosphere was assessed.

Algal and bacterial non-symbiotic nitrogen fixation in paddy soils

Abstract: The nitrogen fixing activity of three Ivory Coast soils was tested in the laboratory by the acetylene reduction assay and the Kjeldahl method. Nitrogen fixation due to algae was estimated to be of the order of 4 to 8 (acetylene method) and 7 μg N per g soil per day (Kjeldahl method). Nitrogen fixation due to bacterial activity in the rice rhizosphere was estimated to be of the order of 2 to 5 (acetylene method) and 1 to 3 μg N per g soil per day (Kjeldahl method). These results emphasize the importance of the bacterial nitrogen fixation in the rhizosphere which had been hitherto overlooked. Comparison of acetylene method and Kjeldahl method results shows discrepancies the origin of which has been discussed. Time course of acetylene reduction by rhizosphere soils exhibits a lag phase which may be attributed to Postgate's switch off — switch on process.

Effects of water stress on nitrogen fixation in root nodules

Abstract: Water stress is known to affect the formation and longevity of leguminous root nodules. Work in Dundee has shown that it also affects rates of nitrogen fixation in nodules, lichens and blue-green algae.

Contribution to nitrogen fixation and soil fertility by photosynthetic bacteria

Abstract: The nitrogen fixation ability ofRhodopseudomonas capsulatus (a member of the photosynthetic bacteria) has been investigated. This organism can fix N2 most effectively under illuminated anaerobic conditions. However, in mixed culture in symbiotic association with heterotrophic bacteria, this microorganism using pyruvic acid excreted by the heterotrophs is capable of fixing nitrogen even under an apparent aerobic environment.

Effect of oxygen partial pressure on nitrogen fixation and acetylene reduction in a sandy loam soil amended with glucose

Abstract: Small samples of soil amended with 2% (w/w) of glucose were preincubated either aerobically or anaerobically and then assayed (N2 15 and C2H2-C2H4) either aerobically or anaerobically for different time periods. One-hour C2H2-C2H4 assays showed greatest activity when anaerobic assay followed anaerobic preincubation. During the anaerobic preincubation a lag of 12–24 h occurred before rapid increase in one-hour assay activity was observed. When aerobic assay followed aerobic preincubation a longer lag was observed and lower activities were obtained. When anaerobic assay followed aerobic preincubation (orvice versa) negligible activities were observed in short assays, and longer assays showed increasing activity related to changes in atmosphere and/or microbial population in the closed system. Preincubation of soil on a diffusion gradient at a series of different partial pressures of oxygen confirmed the above pattern and showed that as preincubation pO2 increased, the anaerobic assay activity rapidly decreased. As preincubation pO2 decreased from 0.2 atm the aerobic assay activity decreased but less rapidly. The activities observed were related to the sizes of the Azotobacter and Clostridium populations. There was no evidence of aerobic or anaerobic C2H2 reduction in any cultures of ‘oligonitrophiles’ isolated. Incorporation of N2 15 was related to C2H2 reduction activity in the soil system studied. However, observed C2H4/N2 molar ratios ranged from 10 to 22 and appeared to be highest in samples which were preincubated anaerobically.

Salinity tolerance within the grass speciesAgrostis stolonifera L

Abstract: Eight populations ofAgrostis stolonifera, collected from maritime and inland habitats, were grown in solution culture and in sand culture at various concentrations of sodium chloride from 0 ppm to 5,000 ppm Na. NaCl had less effect upon the dry weight yield of populations from maritime habitats, with soils of high Na content, than upon populations from inland or maritime habitats with soils of low Na content. The correlation between per cent reduction in dry weight yield and the Na content of the native soil of each population was r=−0.73. Populations from inland or maritime habitats, with soils of low Na content, contained more Na in their shoot materials, and higher Na/K ratios, than did populations from high Na soils, at all Na concentrations. The effect of NaCl upon the root elongation of each population was not correlated with the effect upon dry weight yield, nor with the Na content of their native soil. The effect of Na Cl upon root elongation was highly dependent upon the composition of the culture solution used. It is concluded that the effect of NaCl on root elongation is not an adequate measure of salinity tolerance in this species.

Phosphate-dissolving bacteria in the rhizosphere of some cultivated legumes

Abstract: Twelve phosphate-solubilising organisms were isolated from the rhizosphere of four cultivated legumes growing in four soil regions of India. These organisms were identified asBacillus megaterium, B. subtilis, B. brevis, B. pulvifaciens, B. pumilus andB. polymyxa. All the organisms exceptB. megaterium and one strain ofB. pulvifaciens solubilised significantly greater amounts of tricalcium phosphate over uninoculated control in liquid medium. Rhizospheres ofTrifolium alexandrinum andPhaseolus aureus appear to provide more suitable environment for phosphate-dissolving organisms than those ofCrotalaria juncea andSesbania aculeata.

Free-living nitrogen-fixing bacteria in egyptian soils and their possible contribution to soil fertility

Abstract: Azotobacter and nitrogen-fixing clostridia are ubiquitous soil inhabitants in Egypt, Iraq and probably in all of the Near East. They occur in high numbers except where barrenness, NaCl accumulation or other depressing factors exist. The soil environment has proved favourable for their development since their response to supplementation with energy materials is quite marked. The organisms are resistant to drought, but optimal activity of Azotobacter is around 60% W.H.C. while that of clostridia is at 100%. Azotobacter as well as clostridia show optimal activity around 30°C, higher temperatures favour clostridia while lower ones favour Azotobacter. Gains of soil nitrogen are linked to the growth of Azotobacter rather than to that of Clostridium. The amounts of nitrogen gained and fixation efficiency are affected by the nature of the substrate, being greatest in clay, then in sand and calcareous soils and least in liquid media. Phosphate is essential, favouring nitrogen fixation firstly by satisfying the high phosphate requirement of Azotobacter and secondly by increasing the rate of decomposition of otherwise unavailable material. Gains of combined nitrogen and fixation efficiency are also affected by the type of organic matter added. A wide C/N ratio and susceptibility to decomposition are specially beneficial properties. Plant residues enrich the soil with nitrogen, partly by enhancing nitrogen fixation and partly by causing immobilization of mineral nitrogen which would otherwise be leached out of the soil by irrigation.

Nitrogen fixation in grassland and associated cultivated ecosystems

Abstract: Nitrogen fixation in the natural, Agropyron-Koeleria grassland ecosystem was studied using the C2H2-C2H4 and N15 assays. Small soil samples and also undisturbed soil cores were used for analyses. Both techniques indicated that grassland and associated cultivated soils had low fixation rates (0.6–1.8 kg/ha per 28 days in the laboratory and, 1 kg/ha per season under actual field conditions). Algal colonies (Nostoc spp.) on the soil surface were active fixers when the surface of the grassland was moist. However, their small biomass limits the extent of fixation in most areas.

The nutritional role of Lupinus arboreus in coastal sand dune forestry

Abstract: In the artificial plant succession used to stabilise coastal sand dunes in New Zealand,Lupinus arboreus is sown into plantedAmmophila arenaria stands primarily to provide shelter for youngPinus radiata trees. Recent observations have suggested that the lupin may play a nutritional, as well as a physical part in the stabilisation technique. Work elsewhere with otherLupinus spp. and forest crops supports this theory. An attempt is being made to evaluate the significance ofL. arboreus at Woodhill State Forest with a view to possible manipulation of nitrogen supply to the tree crop. Work described in this preliminary paper has established that the presence of undamaged lupin plants can increase nitrogen uptake inP. radiata through the influence of litter and seedling exudate. Their effect could be due to direct nitrogen transfer or to stimulation of non-symbiotic nitrogen fixation. Lupin leaf washings were shown to contain ninhydrin-positive substances but did not influence nitrogen uptake byP. radiata seedlings in this experiment.

Algal nitrogen fixation in temperate regions

Abstract: A review of the few earlier investigations of nitrogen fixation by blue-green algae in temperate soils is presented. The extent of fixation by free-living algae in soil at three locations near Uppsala is discussed and compared with fixation by symbiotic algae living as phycobionts or cephalodia in lichens.

Litterfall and litter accumulation in red alder stands in western Oregon

Abstract: Litter production in red alder communities 2 to 33 years old was higher than that reported for any plant community of the temperate regions. Litter production is also atypically high in communities of other nitrogen fixers, which suggests that nitrogen fixation may be an important contribution to the high litter production. Litter accumulates rapidly on the ground during the first 5 years after red alder establishment, but equilibrium is reached at the age of 6 years and maintained for several decades. During this time, the decomposition of litter equals the annual litterfall. In 50 years, cumulative litterfall reaches over 300 metric tons per ha, most of which is decomposed and incorporated into mineral soil. Favorable physical, chemical, and nutritional conditions of soil are created by alder for development of the climax vegetation.

The nutritional role ofLupinus arboreus in coastal sand dune forestry: 3. Nitrogen distribution in the ecosystem before tree planting

Abstract: SummaryIn the artificial vegetation succession used to stabilise coastal sand dunes at Woodhill State Forest, New Zealand, the biomass and litter accumulated an estimated total of 440 kg/hectare of nitrogen after the first 4 1/2 years. The lupin component was responsible for at least half of this total and is considered to be an important factor in the nitrogen economy of the forest ecosystem. The best estimate for nitrogen fixation rate by the lupin-Rhizobium symbiosis in the lupin-marram stands is 160 kg/hectare per year. Lupin seed and plant litter both made a significant contribution to nitrogen accumulation and in stands investigated at least 20 kg/hectare per year was added to the soil in litter. It is suggested that nitrogen losses to the ecosystem may result from annual attacks by the kowhai moth (Mycena maorialis) and also through leaching. Because net losses of nitrogen were recorded after the fourth year of the succession it is suggested that the optimum time for plantingPinus radiata would be during the fourth year,i.e. when the lupin stand is three years old and a maximum amount of nitrogen can be expected to be present in the biomass.

The comparative uptake and translocation by plants of calcium, strontium, barium and radium

Abstract: Calcium, strontium, barium, Ra228 and Ra226 were measured in tissues of the Brazil nut tree from different areas; ammonium acetate extracts of the underlying soil were also examined. The concentrations of radium found in the leaves and fruit were higher than had been previously reported, the highest values (up to 6600 Pc Ra226/kg) occurring in the endosperm; the soils, however, did not contain abnormally high levels of radioactivity. Strontium and barium also accumulated in the endosperm, and the ratios of all the heavy alkaline earth ions to calcium in this tissue were 20 times higher than in some stem tissues.

Non-symbiotic nitrogen fixing bacteria in tropical soils

Abstract: Several aspects of heterotrophic, free-living nitrogen-fixing bacteria specific to tropical environments are presented. WhileAzotobacter chroococcum andA. vinelandii seem to occur throughout the world,A. paspali, Derxia gummosa andBeijerinckia spp. have been found mainly in the tropics. Derxia occurred more frequently than previously supposed and was stimulated by moist soil conditions, particularly after flooding.A. paspali growth in soil even under experimental conditions, was strictly limited to the rhizosphere of a few varieties ofPaspalum notatum and the association took almost a year to become established.

Methods of measuring available nutrients in West Indian soils

Abstract: Methods of measuring available N have been compared using response and uptake data from maize grown on 155 West Indian soils in greenhouse experiments. Total soil N and Cornfield's alkaline hydrolysable N gave best estimates of available N when all soils were considered together. Correlations between test data and N uptake were best for acid soils, for soils with large cation exchange capacities and for soils with between 80 and 99 per cent base saturation. Differences between correlations for soils from different islands could usually be related to these soil properties.

Adaptation of rhizobium to subarctic environment in Scandinavia

Abstract: Strains of clover rhizobia were isolated from northern Scandinavia (68–70° N.lat.) and, for comparison, also from some places in southern Scandinavia (S. of 63° N.lat.). Pure cultures were used for studies of 1) bacterial growth in liquid culture, 2) nodulation of host plants, and 3) nitrogenase activity, as measured by the acetylene reduction technique, of the host-bacterium association. The tests were performed both at 10°C and 20°C. In all these respects, the isolates from the subarctic region showed on an average better adaptation to low temperature than the isolates from more southern areas. At 10°C, the former grew faster, nodulated their host plants somewhat earlier and showed a more vigorous acetylene reduction than the latter. At 20°C no significant differences were observed between isolates of different geographical origin. An adaptation of Rhizobium to a cold climate and a short growing season might be useful for practical purposes, because soil temperatures are usually low at sowing-time in large areas of the temperate zones.