Showing papers in "Plant and Soil in 1976"
TL;DR: In this article, the uptake of cadmium by the roots of plants and its transport to shoots was examined using solution culture, and it was concluded that although the root can take up large quantities of Cadmium from solution, there are mechanisms which may restrict the movement of cadmetric through plants, and thus to animals.
Abstract: The uptake of cadmium by the roots of plants, and its transport to shoots was examined using solution culture. Uptake by the roots of perennial ryegrass over a period of 4 hours from an aqueous solution containing 0.25 ppm cadmium as CdCl2 was (i) enhanced by killing the roots and (ii) depressed when Ca2+, Mn2+ or Zn2+ were added to the solution. The distribution of cadmium between the roots and shoots of 23 species was examined at 4 days after a single, 3-day exposure to a nutrient solution containing 0.01 ppm added Cd. In all except 3 species, i.e. kale, lettuce and watercress, more than 50 per cent of that taken up was retained in the roots. The concentration in the roots was always greater than in the shoots, and in fibrous roots of fodder beet, parsnip, carrot and radish it was greater than in the swollen storage roots. When perennial ryegrass was similarly exposed to solutions containing 0.01, 0.05, and 0.25 ppm added cadmium, uptake, as measured at 3 days after adding cadmium, increased with increasing rates of addition, but the proportion retained in the roots was constant (approximately 88 per cent). There was no further transport from roots to shoots during the next 21 days, with the result that the concentration in the shoots decreased progressively with increasing growth. It is concluded that although the roots of several species can take up large quantities of cadmium from solution there are mechanisms which may restrict the movement of cadmium through plants, and thus to animals.
334 citations
TL;DR: The P concentration profile around the primary root of a rape seedling with root hairs, growing in a low-P soil, showed considerably greater depletions than predicted by this method, suggesting an enhanced release of soil P into solution in the rhizosphere.
Abstract: Autoradiographs of rape (Brassica napus L.) seedlings growing in a Begbroke Sandy Loam treated to different P levels showed P accumulations near root apices of primary and lateral roots, without corresponding depletion from the adjacent soil, indicating marked translocation.
159 citations
TL;DR: In this paper, the root systems of Scots pine in a plantation were studied by three methods; soil coring, soil monoliths, and a root trench with observation windows were used to estimate root length, root diameters and the initiatio of new root tips.
Abstract: The root systems of Scots pine in a plantation were studied by three methods; soil coring, soil monoliths, and a root trench with observation windows were used to estimate root length, root diameters and the initiatio of new root tips. The vertical and horizontal distribution of roots is described and root distribution has been related to distance from the tree and soil heterogeneity. It was found that the initiation of new root tips was not readily relatable to the soil environment and the usefulness of the root window technique for observing new root tips is questioned.
93 citations
TL;DR: In this paper, the effects of buffer capacity on the plant-availability of labile soil phosphate, when measured as intensity (I) or quantity (Q), were described and tested using results from a greenhouse experiment on 24 Sherborne soils.
Abstract: The effects of phosphate buffer capacity on the plant-availability of labile soil phosphate, when measured as intensity (I) or quantity (Q), are described and tested using results from a greenhouse experiment on 24 Sherborne soils. In multiple regression studies, phosphate buffer capacity with I or Q measurements as independent variables accounted for up to 94% of the variance in P uptake by ryegrass, the maximum buffer capacity being generally more useful than the equilibrium buffer capacity.
88 citations
TL;DR: Chromium toxicity decreased cation levels in plants as discussed by the authors and the highest level of Cr in leaves was about 30 ppm and in general there was a decreasing gradient in Cr from roots to stems to leaves.
Abstract: Chromium applied to a noncalcareous soil at 50 ppm did not decrease yields of bush beans (Phaseolus vulgaris L. var Improved Tendergreen), but when EDTA (ethylenediamine tetraacetic acid) was added with it, it did. Very little Cr was present in leaves. In solution culture 10-5
M Cr and higher were toxic. With solution culture the highest level of Cr in leaves was about 30 ppm and in general there was a decreasing gradient in Cr from roots to stems to leaves. EDTA had less effect in solution cultures on Cr toxicity because the Cr was already in solution. Chromium toxicity decreased cation levels in plants.
84 citations
TL;DR: The nitrogen and phosphorus contents of organic materials as a factor in determining the trend of mineralization of these elements when plant materials are added to the soil, were studied in an incubation experiment over a period of 12 weeks as mentioned in this paper.
Abstract: The nitrogen and phosphorus contents of organic materials as a factor in determining the trend of mineralization of these elements when plant materials are added to the soil, were studied in an incubation experiment over a period of 12 weeks. Nitrogen mineralization increased with decreasing C:N ratio. No nitrogen mineralization was recorded above C:N ratio of 16.1 and the critical ratio lay between this and 23.0, with the plant materials used. Initial phosphorus immobilization occurred when plant materials ranging in C:P ratio from 501 to 112 were decomposed in the soil. The release of the immobilized phosphorus as incubation progressed suggests that green manuring should be considered of long-term benefit as far as phosphorus is concerned.
75 citations
TL;DR: In this paper, the maximum buffer capacity of a group of 24 soils was derived from the Lamgmuir high-energy adsorption parameters, and the results showed that changes in the intensities and quantities of labile P and equilibrium buffer capacities resulting from fertilization were related to the high energy adaption parameters.
Abstract: The Langmuir two-surface adsorption equation is used to derive a phosphate adsorption characteristic, the maximum buffer capacity, which integrates the intensive and extensive components of adsorption and is independent of P saturation. Changes in the intensities and quantities of labile P and equilibrium buffer capacities resulting from fertilization of a group of 24 soils are shown to be related to the Lamgmuir high-energy adsorption parameters and in particular the maximum buffer capacity.
73 citations
TL;DR: In this article, a study of tomato and cucumber plants was conducted for one to two weeks in nutrient solutions with heavy metals added, and the results showed great differences in cadmium and nickel uptake.
Abstract: Rape, cucumber, wheat, oats and tomato were grown for one to two weeks in nutrient solutions with heavy metals added. Of the metal ions tested (Cr3+, Cu2+, Co2+, CrO4
2-, Ni2+, Cd2+, Pb2+, Mn2+, Zn2+ and Ag+), manganese, nickel and lead exhibited the greatest mobility in cucumber plants, which resulted in the highest shoot/root concentration ratio. Silver was not translocated to the shoots of cucumber plants in measurable amounts. When the plants were grown with 1.0, 10 and 100 μM cadmium or nickel in the solution, the shoot and root concentration increased 5–10 times if the metal ion concentration of the solution was increased 10 times. The plants showed great differences in cadmium and nickel uptake. In the shoot, the cadmium concentration increased in the order: oats = wheat < cucumber = rape < tomato, and in the root in the order: oats = wheat < cucumber = rape < tomato. The great uptake of cadmium and nickel by tomato is notable and agrees with other reports. The nickel, and especially the cadmium, concentration in roots and shoots increases with the age of the plant. The results are discussed and related to other investigations. The need for research on the uptake mechanisms of non-essential heavy metals is emphasized. re]19750415
72 citations
TL;DR: The greater ability of rape to extract P from poor soil appears to be related to its long and abundant root hairs, but uptake cannot wholly be explained by the roots and their hairs acting as simple sinks for P.
71 citations
TL;DR: It was not possible to relate competitive nodulating success to any single feature of the host: rhizobium symbiosis, and this result argues against use of mixed inocula including any strain ineffective on any of the hosts for which the inoculum is recommended.
Abstract: Paired rhizobial strains supplied in several proportions were used to study inter-strain competition in association with Macroptilium atropurpureum (DC) URB (siratro) and Stylosanthes guianensis (Aubl.) Swartz (Stylo, line I R I 1022). Plants raised from surface sterilized seed, were grown on agar in large cotton-wool plugged tubes, and populations and inter-strain ratios determined in the inoculum and on the root at several times after inoculation. The nodules were mapped in order of appearance and the strains they contained identified at harvest.
68 citations
TL;DR: C14-labelled humic acid enhanced the growth of both roots and shoots showing that by-products of microbial degradation of humic Acid are unnecessary for this enhanced plant growth.
Abstract: A technique is described for growing wheat plants in nutrient solutions containing C14-labelled humic acid under axenic conditions. The general appearance of axenic plants was indistinguishable from plants grown in association with microbes. C14-labelled humic acid enhanced the growth of both roots and shoots showing that by-products of microbial degradation of humic acid are unnecessary for this enhanced plant growth. Thus humic acid had a direct effect on the growth processes. The C14-labelled humic acid was taken up by the roots and virtually none was transported to the shoot. Only some 30 to 40 per cent of the incorporated radioactivity was associated with the root cell walls and thus more than 60 per cent was in the cytoplasm and may have influenced the biochemical processes involved in the regulation of plant growth.
TL;DR: It is concluded that K + and NH4 + do not compete for common binding sites of the uptake mechanism in rice roots and this lacking competition suggests the speculation that NH4+-N is absorbed mainly in form of NH8 by plant cells.
Abstract: Abstract1. Rice was grown for 5 months in a sand solution culture at two different
(1)K levels. The higher K supply resulted in a reduced uptake of Na +, Mg ++, and Ca++ by shoots. The uptake of NH4+-N of the shoots, however, was increased by the higher K supply.(2)In short term experiments, ill which the NH4+-N of the uptake solution was labelled by N 15, increasing K concentrations in the uptake solution did not depress the NH4 + uptake of young rice plants. Higher K concentrations in the uptake solution favoured the translocation of labelled N from the roots to the shoots. In some cases the higher K levels resulted also in an enhanced transfer rate of labelled N from the soluble to the insoluble N fraction.(3)Increasing levels of Mg++ in the uptake solution did not affect the uptake of labelled NH4-N.(4)I t is concluded that K + and NH4 + do not compete for common binding sites of the uptake mechanism in rice roots. This lacking competition suggests the speculation that NH4+-N is absorbed mainly in form of NH8 by plant cells.
TL;DR: In this paper, the authors measured the absorption of Zn65 by plant roots from a layer of dry top soil (suction > 15 bar) using a technique that obviated water stress in the plant.
Abstract: Absorption of Zn65 by plant roots from a layer of dry top soil (suction > 15 bar) was measured using a technique that obviated water stress in the plant.
TL;DR: In this article, a procedure is described that allows assay of soil urease activity using a phosphate buffer (pH 8.8) and a urea substrate concentration of 0.007 M. The method is precise, and compares favourably with other procedures.
Abstract: A procedure is described that allows assay of soil urease activity. The method uses a phosphate buffer (pH 8.8) and a urea substrate concentration of 0.007 M. Incubation for 4 h at 37°C is recommended and urease activity is estimated by determining the amount of ammonium produced by urea hydrolysis in soil. The method is precise, and compares favourably with other procedures. re]19750710
TL;DR: Both the formation of enlarged ‘lenticles’ and increased nodule cortication are regarded as adaptive anatomical responses which facilitate continued symbiotic nitrogen fixation and vegetative growth of this legume under waterlogged conditions.
Abstract: Various periods of waterlogging (up to 32 days duration) were imposed upon cowpea plants grown in pots under controlled glasshouse conditions. Particular attention was paid to treatment effects on nodule cortication, nitrogenase activity and fixation efficiency, and the consequent differences in plant dry weight and nitrogen content.
TL;DR: On several alkaline calcareous soils, Zn and Cu deficiency occurred mainly in lowland rice (Oryza sativa L.) and was rarely found in wheat (Triticum aestivum L.).
Abstract: SUMMARY On several alkaline calcareous soils, Zn and Cu deficiency occurred mainly ill lowland rice (Oryza sativa L.) and was rarely found in wheat (Trilicum aestivum L.). Zinc and Cu requirement of plants was not responsible as the critical Zn and Cu contents ill tops of the two plant species were almost similar i.e. 17.4, 6.5 and 14.5, 5.6 ppm respectively. Neither did rice absorb Zn and Cu less efficiently. On the contrary, their rates of absorption in rice were double than in wheat. They were 22.2, 6.3 and 10.2, 3.3 ng atoms/g fresh root/h respectively in the two plant species. Flooded soil conditions appeared to be responsible for Zn and Cu deficiency in rice as their deficiency was found maillIy in plant samples collected from continuously flooded fields. The mechanism is not known. Both Zn and Cu inhibited uptake of each other in wheat on most of the soils. In rice, only applied Zn depressed Cu uptake but Cu had generally little effect on Zn uptake. Little Cu inhibition of Zn uptake in lowland rice seems to be related to flooded soil conditions. The mechanism is yet to be known. The antagonising element accentuated the deficiency of the other element both in wheat and rice and severely reduced their yields on soils marginal to deficient in Zn or Cu supplies. It is recommended that their soil availability status should be thoroughly considered before their fertilizers are applied.
TL;DR: The effect of the salinity, alkalinity and Fe application on the dry matter yield and availability of Fe, Mn, P and Na were studied in the greenhouse on pea crop.
Abstract: The effect of the salinity, alkalinity and Fe application on the dry matter yield and availability of Fe, Mn, P and Na were studied in the greenhouse on pea (Pisum sativum L.) crop. The highest dry matter yield was recorded in normal soil which decreased with the increase in the salinity and alkalinity, minimum being at 40 ESP. Alkalinity was more harmful to pea crop than salinity. Fe at 10 ppm increased the dry matter yield significantly. Highest Fe concentration (408.12 ppm) was recorded in 40 ESP soil followed by 20 ESP (395.2 ppm). Salinity alongwith marginal or higher alkalinity reduced harmful effect of alkalinity. The uptake of Fe was the highest in normal soil due to the high dry matter yield. All the three sources increased the concentration of Fe and its uptake than the control in all the soils but did not show much distinction among themselves. The concentration of Mn decreased more with the increase in alkalinity than salinity but salinity with alkalinity improved Mn concentration. Similarly uptake of Mn also decreased sharply with the increase in salinity and alkalinity. The application of Fe sources decreased Mn concentration but increased the uptake. The highest decrease was caused with FeSO4 and lowest with Fe rayplex. Like Mn the concentration and uptake of P decreased with the increased levels of salinity and alkalinity. The addition of Fe decreased the concentration of P, highest depression being with Fe KE-MIN. Increase in ESP increased the concentration and the uptake of Na greatly. Addition of Fe through all the sources increased Na concentration and uptake significantly but sources did not differ much in their effect on Na.
TL;DR: Yearly rates of nitrogen fixation associated with seven species of grass were measured on two artificially-established prairies using the C2H2 reduction method to measure the activity of soil cores taken within the stands of grass, and the choices made did not appear to have a substantial effect on the accuracy of the measurements.
Abstract: Yearly rates of nitrogen fixation associated with seven species of grass were measured on two artificially-established prairies. The C2H2 reduction method was used to measure the activity of soil cores taken within the stands of grass. Nitrogenase activity was specifically associated with Panicum virgatum and Sporobolus heterolepis, which had activities estimated at 3.6 and 2.9 kg N ha-1 yr-1. Fixation in stands of the other grasses ranged between 0.2 and 1.8 kg N ha-1 yr-1; free-living organisms might have fixed the N2 without specific association with the grasses, which were Andropogon gerardi, Andropogon scoparius, Spartina pectinata, Stipa spartea, and Poa pratensis. Three relic prairies were also examined, but the rates of fixation were no higher, except for S. heterolepis, which at one relic prairie had rates that extrapolated to 9 kg N ha-1 yr-1. The choices made for core location, size, depth, length of C2H2 incubation, and the time of day of sampling did not appear to have a substantial effect on the accuracy of the measurements. The organisms associated with S. heterolepis required O2 for N2 fixation, and they were located in the soil or on the smaller roots which remained when the major roots were removed from the soil. re]19750217
TL;DR: The capacity to cause branching was absent from all non-invasive mutants, but was increased in ineffective invasive forms, compared with the effective parent strain, and Avirulent mutants were incapable of causing marked curling.
Abstract: The branching of clover root hairs was due to a factor (or factors) readily extracted from cells of Rhizobium trifolii and found in seedling solution supporting clover roots inoculated with this organism. Part of the active material was retained within a dialysis sac but a smaller, escaping fraction evoked the same response. The branching fraction was stable at 100°C and, partly, to nuclease and periodate, but was unstable when left in contact with the cells and when treated with trypsin. The dried residue of active filtrate contained 2% nucleic acid, 20% protein and about 34% carbohydrate which included antigenic lipopolysaccharide (approximately 1.6%). The branching response could not be attributed to either of these polysaccharides or to indole acetic acid. The capacity to cause branching was absent from all non-invasive mutants, but was increased in ineffective invasive forms, compared with the effective parent strain.
TL;DR: The results indicated that Al tolerance is a heritable trait in these alfalfa populations and that recurrent selection can be used effectively to develop strains having differential tolerance to Al-toxic soils.
Abstract: Aluminum toxicity limits root growth in acid subsoils that are difficult to lime. An alternative to subsoil liming is the development of plants having greater tolerance to Al. Alfalfa (Medicago sativa L.) is considered an Al-susceptible species. Preliminary studies indicated that alfalfa cultivars differ in Al tolerance, but the extreme plant-to-plant variation within cultivars prevented the establishment of clearcut cultivar differences. Tolerant and susceptible plants were selected from each of six cultivars (‘DuPuits’, ‘Atlantic’, ‘Team’, ‘Buffalo’, ‘Grimm’, and ‘Sirsa 9’) grown on an Al-toxic Bladen soil at pH 4.1 to 4.3. The tolerant selections were repotted and interpollinated to form one population of polycross seed. Susceptible selections were treated similarly to form a second population. These two populations, tolerant and susceptible, were subjected to an additional cycle of recurrent phenotypic selection for tolerance and susceptibility, respectively, to Al-toxic Bladen soil at pH 4.6. Plants from the population selected for tolerance to the acid Bladen soil were significantly higher in both root and top vigor on Al-toxic Tatum soil than plants from the population selected for susceptibility. The results indicated that Al tolerance is a heritable trait in these alfalfa populations and that recurrent selection can be used effectively to develop strains having differential tolerance to Al-toxic soils. The observation that only 2% of the plants from the tolerant population were in the most tolerant class suggests a good opportunity for more progress in selecting toward Al tolerance.
TL;DR: In this paper, the capacity, intensity, and kinetic factors, as measured by E-value, solution P concentration, and soil P release rate to a distilled water sink respectively, were unpronouced and infrequent upon water-saturation of ten rice soils.
Abstract: Phosphorus supply factors (capacity, kinetic, intensity, and diffusivity) and plant growth were the approaches used to assess P supply of flooded rice soils. Increases in the capacity, intensity, and kinetic factors, as measured by E-value, solution P concentration, and soil P release rate to a distilled water ‘sink’ respectively, were unpronouced and infrequent upon water-saturation of ten soils. However, increases in the diffusitivity factor, as measured by 32P diffusion coefficients, were at least ten-fold as soil moisture increased. The greatest increases in P diffusion occurred as soil moisture increased beyond one-third bar.
TL;DR: In this article, the concentrations of several N fractions, soluble sugars and N/S ratios were determined in Golden Bantam sweet corn and hybrid field corn grown in nutrient solutions and/or soil with various SO4-S levels provided.
Abstract: The concentrations of several N fractions, soluble sugars and N/S ratios were determined in Golden Bantam sweet corn and hybrid field corn grown in nutrient solutions and/or soil with various SO4-S levels provided. When the level of SO4-S supplied was less than that needed for maximum growth, higher-than-normal concentrations of amide (asparagine) N and lower-than-normal soluble sugar concentrations were found in the plants. An inadequate S supply appears to limit the plants capacity to synthesize protein to a much greater extent than it inhibits the nitrogen uptake mechanism.
TL;DR: In this article, the concentration of total calcium, ionic calcium, citric and malic acids have been measured in xylem sap extracted from apple shoots, and the implication of these findings on the mobility of calcium in the xylm is discussed.
Abstract: Concentrations of total calcium, ionic calcium, citric and malic acids have been measured in xylem sap extracted from apple shoots. Ionic calcium, as measured by an ion selective electrode, was about 50 per cent of the total calcium. The remainder of the soluble calcium was present as complexes with citric and malic acids. The implication of these findings on the mobility of calcium in the xylem is discussed.
TL;DR: The use of methyl-cellosolve plus mono-ethanolamine as a CO2 absorber allows measurements of weakly labelled materials and this method is suitable for fast routine analysis.
Abstract: A rapid procedure is proposed for simultaneous measurement of total and radioactive carbon in soils, soil extracts and plant materials. The procedure involves dry or wet combustion of the sample, total carbon determination with an automatic analyser and C14O2 absorbtion in a liquid for scintillation measurement. The use of methyl-cellosolve plus mono-ethanolamine as a CO2 absorber allows measurements of weakly labelled materials. This method is suitable for fast routine analysis. re]19750929
TL;DR: Natural vegetation common to the forested areas of Nova Scotia was sampled and analyzed for the nutrient elements calcium, phosphorus, cobalt, molybdenum, manganese, zinc and copper, showing considerable variation within and between species.
Abstract: Natural vegetation common to the forested areas of Nova Scotia was sampled and analyzed for the nutrient elements calcium, phosphorus, cobalt, molybdenum, manganese, zinc and copper. Results showed considerable variation within and between species. Variations due to plant part, season and location of sampling also occurred but to a lesser degree. With the possible exception of molybdenum and copper, the elements are present in adequate quantities for normal nutrition. The average range of nutrient content for cobalt was found to be 0.09 to 0.44; molybdenum 0.01 to 0.32; zinc 13.0 to 91.0; manganese 44 to 594; copper 4.9 to 31.7 in terms of parts per million while calcium ranged from 0.36 to 1.11 per cent and phosphorus from 0.06 to 0.21 per cent. re]19750210
TL;DR: Repeated wilting prior to flowering markedly reduced seed yields compared with the unstressed controls, and nodule weight and nitrogenase activity per plant were also much reduced.
Abstract: Separate experiments examined nodulation and seed yield of cowpea cv. Prima after (a) changes in the level of combined nitrogen from 25 to 0 or 60 ppm N, (b) cycles of wilting and rehydration, and (c) shading to ca 50% full daylight. Plants were grown in the simulated tropical environment of a plastics ‘bubble’ house and experienced these changes over the growth stages: emergence to first flower, first flower to mid pod-fill or mid pod-fill to maturity. Seed yields of nodulated plants were unaffected by combined nitrogen supply and almost double those of non-nodulated plants (100 g cf 56 g per plant)-due mainly to increases in pod number per plant and mean seed weight. Reducing the nitrogen level from 25 to 0 ppm N, especially between mid pod-fill and maturity, reduced seed yields of non-nodulated plants to 36 g per plant. At the first flowering stage, plants grown without combined nitrogen had nitrogenase activities less than 10% of those supplied with 25 ppm N; 60 ppm N at any stage of development more than halved nitrogenase activity when compared with plants supplied with 25 ppm. Repeated wilting prior to flowering markedly reduced seed yields compared with the unstressed controls (41 g cf 76 g per plant)-mainly by decreasing subsequent pod production. Nodule weight and nitrogenase activity per plant were also much reduced. Wilting after flowering did not reduce yield, and nitrogenase activity was less affected. Shading throughout, or from first flower onwards, reduced seed yield by about 25% because fewer pods were produced. All shading treatments significantly increased mean seed weight compared with unshaded controls (116–121 mg cf 105 mg).
TL;DR: Kikuyu (Pennisetum clandestinium Hochst) grew relatively poorly on the Wollongbar krasnozem at soil pH values below 4.36 as mentioned in this paper.
Abstract: Kikuyu (Pennisetum clandestinium Hochst) grew relatively poorly on the Wollongbar krasnozem at soil pH values below 4.36. At these low pH values dry matter yields were increased by raising the pH or by application of high rates of phosphate. Both treatments decreased the concentration of soluble soil-Al on which the concentration of Al in tops was linearly dependent (r=0.95).
TL;DR: Flooding induced increased contents of various ions in soil solutions appear to be a major cause of accentuating Zn and Cu deficiency in rice and of obscuring the predictability of soil tests for Znand Cu availability to lowland rice.
Abstract: SummaryThe effect of flooding on chemical composition of solutions of two alkaline calcareous soils were studied for incubation periods of 0, 2, 3, 4, 5 and 8 weeks. Flooding slightly reduced pH of both the soils. The concentration of Ca, Mg, HCO3, Mn, Fe, P, and total soluble salts markedly increased. This occurred rapidly in the beginning but at a much slower rate later on during incubation. Drying the soils from 7th to 8th week of submergence greatly depressed their concentration. Flooding had no effect on Cu but increased Zn concentration. The contents of various ions in submerged soils generally had little relationship to those in dry soils. Manganese and Fe strongly depressed 65 Zn absorption by rice (Oryza sativa L.) from solution cultures.Flooding induced increased contents of various ions in soil solutions appear to be a major cause of accentuating Zn and Cu deficiency in rice and of obscuring the predictability of soil tests for Zn and Cu availability to lowland rice. re]19750515
TL;DR: It was found that the competitive interactions could be explained in terms of phosphate uptake, and that the ratio of root weight: length was proportional to root density, in competition experiments with Lolium perenne and Agrostis tenuis.
Abstract: In competition experiments with Lolium perenne and Agrostis tenuis on sandy soil with nitrogen supplied and therefore not limiting, it was found that the competitive interactions could be explained in terms of phosphate uptake, and that the ratio of root weight: length was proportional to root density. The effects of competition were then investigated in an experimental system that enabled them to be distinguished from those of nutrient supply. High levels of nutrients specifically stimulated the production of fine laterals whereas competition affected length and weight of the root system of Lolium equally. The ecological implications are discussed in the light of recent physiological work on root responses to nutrient supply. re]19750324
TL;DR: An incubation study on mineralization and gaseous losses of nitrogen was conducted on three soils with increasing levels (1.1 to 50 mmhos/cm) of salinity and two levels of urea and ammonium sulphate upto 6 weeks.
Abstract: An incubation study on mineralization and gaseous losses of nitrogen was conducted on three soils with increasing levels (1.1 to 50 mmhos/cm) of salinity and two levels of urea and ammonium sulphate upto 6 weeks. Mineralization of nitrogen increased with time and decreased with the increase of salinity. It was more from ammonium sulphate than urea, and relatively more from the lower dose. The gaseous losses of NH4-N increased with salinity. About 35±5 per cent of added N was lost in the gaseous form at maximum (ECe=45 to 50 mmhos/cm) salinity and losses were more from light than heavier soils. Salinity and pH, both were correlated negatively with the N mineralisation and positively with the gaseous losses of ammonia in these salt-affected soils. re]19751105