Showing papers in "Plant and Soil in 1987"
TL;DR: Organic matter amendments to soil can be used to manage phytoparasitic nematodes and the most effective amendments are those with narrow C:N ratios and high protein or amine-type N content.
Abstract: Organic matter amendments to soil can be used to manage phytoparasitic nematodes. The most effective amendments are those with narrow C:N ratios and high protein or amine-type N content. For soil with 1.0% (w/w) organic matter amendment there is a direct relation between extent of nematode control and the N content of amendments. A special group of amendments are those containing chitinous materials. Chitin addition to soil results in stimulation of a select microflora capable of degrading the polymer. Several microbial species are known to destroy the eggs of phytonematodes (Meloidogyne spp.). Organic matter can be modified by addition of specific compounds or by inoculation with particular microbial species to produce an amendment that will induce suppressiveness.
216 citations
TL;DR: Two species, Glomus manihotis and Entrophospora colombiana were found to be most effective for a range of crops and pastures, at low pH and at a wide range of N, P and K levels.
Abstract: Greenhouse and field experiments were conducted on the effect of VA mycorrhiza (VAM) on the growth of cassava, various tropical grass and legume species, as well as beans, coffee and tea. A large number of VAM fungal species were evaluated for effectivity in increasing cassava growth and P uptake in acid low-P soils. The effectivity of VAM species and isolates was highly variable and dependent on soil pH and fertilizer applications, as well as on soil temperature and humidity. Two species, Glomus manihotis and Entrophospora colombiana were found to be most effective for a range of crops and pastures, at low pH and at a wide range of N, P, and K levels.
189 citations
TL;DR: The capacity of the cell wall for exchanging metal ions in A. yokoscense was found to be higher than in other plants growing on metalliferous habitats as mentioned in this paper.
Abstract: Cells of the roots ofA. yokoscense growing on metalliferous habitats were fractionated into their cell wall and cytoplasmic components. About 70–90% of the total copper, zinc and cadmium was located in the cell wall. Copper had a markedly greater affinity for the cell wall than zinc and cadmium, and was prevented from entering the cytoplasm. A large proportion of these heavy metals in the cell wall were exchanged as ions. The capacity of the cell wall for exchanging metal ions inA. yokoscense was higher than in other plants growing on metalliferous habitats. However, compared with different ferns unable to grow on metalliferous habitats, this capacity was not unique toA. yokoscense. Consequetly, the root cell wall ofA. yokoscense is considered to be an important site of metal ion storage and may play the role of an excretory organ for heavy metals. On the other hand, as proportion of the heavy metls was transported to the cytoplasm, where the metal content was much higher than the average for normal ferns. This would suggest thatA. yokoscense has another metabolic mechanism related to metal tolerance.
176 citations
TL;DR: It is concluded that the annual yield of symbiotically fixed N from clover/grass mixtures can be very high, provided that the proportion of clover in the mixtures exceeds 50% of total dry mass yield.
Abstract: A field study was carried out near Zurich (Switzerland) to determine the yield of symbiotically fixed nitrogen (15N dilution) from white clover (Trifolium repens L.) grown with perennial ryegrass (Lolium perenne L) and from red clover (Trifolium pratense L.) grown with Italian ryegrass (Lolium multiflorum Lam.). A zero N fertilizer treatment was compared to a 30 kg N/ha per cut regime (90 to 150 kg ha−1 annually).
175 citations
TL;DR: In this article, a model for the rate of elongation of a root tip in terms of the balance of pressures acting on the root was developed for the pea root tip, which predicts that root cells osmoregulate against both water stress and soil mechanical resistance.
Abstract: A model is developed for the rate of elongation of a root tip in terms of the balance of pressures acting on the root. Differentials of this equation give expressions for the changes in root elongation rate with respect to soil water potential and soil mechanical resistance. The model predicts that root cells osmoregulate against both water stress and soil mechanical resistance with predicts that root cells osmoregulate against both water stress and soil mechanical resistance with similar efficiencies which are less than 100%. Analysis of published data leads to the conclusion that root tips of pea osmoregulate with 70% efficiency. A working equation is developed for the elongation rate of roots in conditions of combined water stress and mechanical resistance.
168 citations
TL;DR: Mycorrhizal infection increased growth more for subterranean clover than for ryegrass for all sources of phosphorus, and the greatest benefit was obtained with the least soluble source of iron phosphate.
Abstract: The effect of inoculation with a mycorrhizal fungus on the growth of subterranean clover and of ryegrass was measured using three sources of phosphorus with different solubilities. These were (in order of decreasing solubility): potassium dihydrogen phosphate, colloidal iron phosphate and crystalline iron phosphate. Mycorrhizal infection increased growth more for subterranean clover than for ryegrass for all sources of phosphorus. For both species the greatest benefit from mycorrhizal inoculation was obtained with the least soluble source of iron phosphate. It is suggested that the mycorrhizas were able to explore the soil more thoroughly and hence were able to locate and use the point sources of phosphorus in the insoluble iron phosphates.
154 citations
TL;DR: In this paper, the effect of a hot summer fire on soil nutrient contents in the upper 2 cm of Aleppo pine forest with a dense woody understory was studied from September 1985 to May 1986.
Abstract: The effect of a hot summer fire on soil nutrient contents in the upper 2 cm of Aleppo pine forest with a dense woody understory was studied from September 1985 to May 1986.
151 citations
TL;DR: The ability of maize and soybean to grow better than rice under water stress conditions may be due to their ability to maintain turgor as a result of the slow decline in leaf water potential brought about by low, transpiration rate and continued uptake of nutrient, especially K, which must have allowed osmotic adjustment to occur.
Abstract: A pot experiment was conducted in the greenhouse to determine and compare the responses of rice (Oryza sativa L. var, IR 36), maize (Zea mays L. var. DMR-2), and soybean (Glycine max [L.] Merr. var. Clark 63) to soil water stress. Leaf elongation, dawn leaf water potential, transpiration rate, and nutrient uptake in stressed rice declined earlier than in maize and soybean. Maize and soybean, compared with rice, maintained high dawn leaf water potential for a longer period of water stress before leaf water potential. Nutrient uptake under water stress conditions was influenced more by the capacity of the roots to absorb nutrients than by transpiration. Transport of nutrients to the shoots may occur even at reduced transpiration rate It is concluded that the ability of maize and soybean to grow better than rice under water stress conditions may be due to their ability to maintain turgor as a result of the slow decline in leaf water potential brought about by low, transpiration rate and continued uptake of nutrient, especially K, which must have allowed osmotic adjustment to occur.
150 citations
TL;DR: Yellow-poplar (Liriodendron tulipifera L.) seedlings were planted in unfertilized forest soil in boxes with a removable side panel and grown in atmospheres containing either ambient or elevated CO2, and bacterial populations differed due to CO2 only at the final harvest.
Abstract: Yellow-poplar (Liriodendron tulipifera L.) seedlings were planted in unfertilized forest soil in boxes with a removable side panel and grown in atmospheres containing either ambient (367 μl l−1) or elevated (692 μl l−1) CO2. Numbers of total bacteria, nitrifiers, and phosphate-dissolving bacteria in the rhizosphere and in nonrhizosphere soil were measured every 6 weeks for 24 weeks. Seedling growth and nutrient content were measured at a final whole-plant harvest. Root, leaf, and total dry weights were significantly greater, and specific leaf area was significantly less, in 692 ml l−1 than in ambient CO2. Uptake per gram plant dry weight of N, S, and B was lower at elevated CO2, whereas uptake of P, K, Cu, Al, and Fe was proportional to growth in both CO2 treatments. Total uptake and uptake per g plant dry weight of Ca, Mg, Sr, Ba, Zn, and Mn were not affected by CO2 treatment. Bacterial populations differed due to CO2 only at the final harvest, where there were significantly fewer nitrite-oxidizers and phosphate-dissolving bacteria in the rhizosphere of seedlings grown at 692 μl l−1 CO2.
127 citations
TL;DR: Three legume species in combination with five grass species were used to study N transfer in mixtures, using the 15N dilution technique, and the greatest advantage from a grass-legume mixture varied with early maturing tall fescue, orchardgrass, and bromegrass, to intermediate timothy, and least with late maturing red fescues.
Abstract: Three legume species (alfalfa, red clover, and birdsfoot trefoil) in combination with five grass species (timothy, bromegrass, red fescue, tall fescue, and orchardgrass) were used to study N transfer in mixtures, using the 15N dilution technique. The advantage of grass-legume mixtures was apparent. Total herbage and protein yields of grasses in mixtures were higher than those alone, especially at the later cuts. This benefit of mixed cropping is mainly due to N transfer from legumes to associated grasses. N2-fixation and N transfer by alfalfa rated highest, red clover intermediate, and birdsfoot trefoil lowest. The importance of each pathway of N transfer from legumes appeared to differ between species. Alfalfa and red clover excreted more N than trefoil, while the latter contributed more N from decomposition of dead nodule and root tissue. The greatest advantage from a grass-legume mixture, with respect to the utilization of N released from the legume, varied with early maturing tall fescue (Kentucky 31), orchardgrass (Juno), and bromegrass (Tempo), to intermediate timothy (Climax), and least with late maturing red fescue (Carlawn).
123 citations
TL;DR: In this article, a simplified model for soil compression around plant roots is developed, which assumes that the root volume is accommodated by loss of porosity in the surrounding soil, and that there is a minimum soil porosity below which soil will not be compressed; the density decreases exponentially with distance from the roots surface with an exponent which is a constant multiple of the root diameter.
Abstract: A simplified model is developed for soil compression around plant roots. The main assumptions are that the root volume is accommodated by loss of porosity in the surrounding soil; that there is a minimum soil porosity below which soil will not be compressed; and that the density decreases exponentially with distance from the roots surface with an exponent which is a constant multiple of the root diameter. These assumptions lead to simple, practical expressions for the soil porosity around roots and for the amounts of materials such as nutrients or organisms which lie within certain distances from a root surface.
TL;DR: The seasonal patterns of growth and symbiotic N2 fixation under field conditions were studied by growth analysis and use of15N-labelled fertilizer in a determinate pea cultivar grown for harvest at the dry seed stage.
Abstract: The seasonal patterns of growth and symbiotic N2 fixation under field conditions were studied by growth analysis and use of15N-labelled fertilizer in a determinate pea cultivar (Pisum sativum L.) grown for harvest at the dry seed stage.
TL;DR: In this article, Nitrogen (N) dynamics were studied in conventional and no-tillage agroecosystems on the Georgia Piedmont, where ammonium nitrate and winter legume residues were compared.
Abstract: Nitrogen (N) dynamics were studied in conventional and no-tillage agroecosystems on the Georgia Piedmont. Nitrogen inputs in the form of ammonium nitrate (95 kg-N/ha) and winter legume (crimson clover) residues were compared. The legume provided adequate N for summer crop (grain sorghum) production, but water use by the legume reduced the ability of sorghum to utilize the N. Legume N inputs became availabe to plants more gradually than fertilizer inputs. Weed growth and potential denitrification activity were higher in legume-N treatments than in fertilizer-N treatments. Tillage affected the timing of N avaialbility more than the total amount of available N. Summer crops took up more N under conventional tillage while winter crops took up more N under no-tillage. Denitrification activity was higher under no-tillage but was not a significant output from the agroecosystems. Leaching losses of N differed seasonally between treatments but were not significant in any of the agroecosystems.
TL;DR: The potential for increasing productivity in salt-affected areas can be realized if cooperation is called for among soil and water scientists, agronomists, plant physiologists and biochemists, cytologists, and plant geneticists, breeders, and biotechnologists.
Abstract: Advances in and prospects for the development of salt tolerant crops are discussed. The genetic approach to the salinity problem is fairly new, but research has become quite active in a short span of time. Difficulties and opportunities are outlined. Salinity varies spatially, temporally, qualitatively, and quantitatively. In addition, the responses of plants to salt stress vary during their life cycle. Selection and breeding, including the use of wide crosses, are considered the best short-term approaches to the development of salt tolerant crops, but the new biotechnological and molecular biological techniques will make increasingly important contributions. Cooperation is called for among soil and water scientists, agronomists, plant physiologists and biochemists, cytologists, and plant geneticists, breeders, and biotechnologists. Given such cooperation and adequate support for these endeavors, the potential for increasing productivity in salt-affected areas can be realized.
TL;DR: The Na-induced inhibition of Ca uptake and transport appears to be more limiting to shoot growth of M9 and M-201 than Na toxicity per se, and both ions were accumulated preferentially in the tillers and older leaves.
Abstract: The response of the rice cultivars ‘M9’ and ‘M-201’ to nutrient cultures salinated at −0.4 MPa with varying ratios of Na and Ca was studied. Although the dry matter production of both cultivars was sensitive to the Na/Ca ratio, this correlation was significant only for M-201. Calcium nutrition was severely affected by the composition of the external solution, and the laminae exhibited Ca-deficiency symptoms at Na/Ca molar ratios of 78 and 198. Sodium concentration in the shoot decreased as the Na/Ca ratio in the external solution decreased. Patterns of Na and Cl distribution in the shoot tissues were similar; both ions were accumulated preferentially in the tillers and older leaves. The Na-induced inhibition of Ca uptake and transport appears to be more limiting to shoot growth of M9 and M-201 than Na toxicity per se.
TL;DR: Research with several cassava clones at CIAT has shown that high root yield under mid—term stress is not incompatible with high yield under nonstress conditions, and plant types with highield potential under both conditions are characterized.
Abstract: Cassava (Manihot esculenta Crantz) is a staple food for a large sector of human population in the tropics. It is widely produced for its starchy roots by small farmers over a range of environments on poor infertile soils with virtually no inputs. It is highly productive under favorable conditions and produces reasonably well under adverse conditions where other crops fail. The crop, once established, can survive for several months without rain. There is a wide variation within the cassava germplasm for tolerance to prolonged drought and the possibility to breed and select for stable and relative high yields under favorable and adverse conditions does indeed exist. Research with several cassava clones at CIAT has shown that high root yield under mid—term stress is not incompatible with high yield under nonstress conditions. Plant types with high yield potential under both conditions (e.g. the hybrid CM 507–37) are characterized by having slightly higher than optimum leaf area index under nonstress conditions, higher leaf area ratio and more intensive and extensive fine root system.
TL;DR: In experiments with perennial ryegrass and wheat, silicon concentration in flowing solution culture was maintained constant at 0, 10 and 20 mgl−1 (ryegrasses) or 0, 20 and 40 mgl −1 (wheat) as mentioned in this paper.
Abstract: In experiments with perennial ryegrass and wheat, silicon (Si) concentration in flowing solution culture was maintained constant at 0, 10 and 20 mgl−1 (ryegrass) or 0, 20 and 40 mgl−1 (wheat). Uptake and transport were measured in both species at frequent harvests over periods of up to 80 days. By the final harvests the initial differences in concentration between plants grown at high or low Si were largely eliminated. Much more Si was taken up by both species from the culture solution than was present in the transpiration stream. With ryegrass, the calculated cumulative amounts taken up through mass flow by plants grown at 10 or 20mgl−1 Si, represented less than 40 and 70 per cent, respectively, of the total Si uptake. Up to 94 per cent of the Si taken up by wheat was transported rapidly to the shoots; older leaves contained up to 11.8 per cent Si.
TL;DR: The efficacy of the alumina system for differentiating between bean (Phaseolus vulgaris L.) genotypes for growth at different levels of phosphorus availability was determinated and comparisons were made between plants receiving N either from fertilizer or nitrogen fixation.
Abstract: The efficacy of the alumina system for differentiating between bean (Phaseolus vulgaris L.) genotypes for growth at different levels of phosphorus availability was determinated. In addition to response to P levels, comparisons were made between plants receiving N either from fertilizer or nitrogen fixation. When the cv. Carioca was provided with either 100 ppm of N or inoculated withRhizobium leguminosarum biovarphaseoli, differences in shoot dry weight and nodule number were related to P level. There was a greater proportion of green, ineffectivevs. red, active nodules at the low P concentration than at the higher P concentration. In a second experiment, two cvs., Puebla 152 and Carioca and the breeding line UW 24-21, either were inoculated with rhizobia or provided with 150ppm of N. Each genotype-nitrogen combination was grown at 8 levels of P. There was a positive effect of P level on shoot dry weight, nodule number and nodule mass. Root mass was affected less than nodule or shoot mass by the P level of the growth medium. Nodule mass, but not P concentration in the nodules, was affected by P level, whereas in the other plant tissues, P concentrations were lower at lower P levels in the media.
TL;DR: In this article, the efficiency and balance of nitrogen from one year's application was studied in a long-term fertigation experiment, where enriched nitrogen fertilizer, K15NO3, was applied to a 22-year-old Shamouti orange tree with a history of high N applications (N3) and to an N-starved tree (N1).
Abstract: The efficiency and balance of nitrogen from one year's application was studied in a long-term fertigation experiment. Enriched nitrogen fertilizer, K15NO3, was applied to a 22-year-old Shamouti orange tree with a history of high N applications (N3) and to an N-starved tree (N1). The distribution of N in the different parts of the trees and in the soil was determined after the experimental trees were excavated. Similar total recovery of the labeled fertilizer N was found in the trees and soil in both treatments (N1−61.7% N3−56%). However, the distribution between tree and soil was different. The amount of recovered residual fertilizer in the soil was much larger in the N3 treatment than in N1. The highest percentage of fertilizer N was found in the new organs,i.e. fruits, twigs and leaves. The roots and branches took up only 6–14% from the labeled fertilizer. Only 20.9% of the leaf N and 23.4% of the fruit N in the N3 tree originated in the labeled fertilizer, indicating translocation of N from older parts of the tree to new growth. Evidence was found of storage of N in the wooded branches, while the roots contained a surprisingly small part of labeled fertilizer.
TL;DR: It is thought that the binding capacity of the roots for NH4 is an important factor in preventing NH4/NH3 toxicity at supraoptimal pH, and at this pH, the roots of the growth inhibited plants were characterized by increased levels of total N and free NH4.
Abstract: Seedlings of 14 species were grown for 14–28 days on nutrient solution with 6 mmol.l−1 NH4 as the sole nitrogen source. Solutions acidity was were kept constant at pH 4.0, 5.0, 6.0 and 7.0 by continuous titration with diluted KOH. The following species were used: barley, maize, oats sorghum, yellow and white lupin, pea, soybean, carrot, flax, castor-oil, spinach, sugarbeet and sunflower. Most plant species grew optimally at pH 6.0 with slight reductions at pH 5.0. Growth of many species was severely inhibited at pH 4.0, but this inhibition was not observed with the legume and cereal species. Yield depressions at pH 4.0 relative to pH 6.0 were well correlated with the respective relative decreases of the K concentration in their roots (P<0.002). In the roots of two species (sunflower and flax) total N concentrations were also strongly reduced at pH 4.0. apparently, the interactions between uptake of K, NH4 and H ions become the prevalent problem at suboptimal pH. At pH 7.0, yields were also considerably decreased, with the exception of the lupines. At this pH, the roots of the growth inhibited plants were characterized by increased levels of total N and free NH4. It is thought that the binding capacity of the roots for NH4 is an important factor in preventing NH4/NH3 toxicity at supraoptimal pH.
TL;DR: A number of examples is given demonstrating the co-existence of pea genotypes and their specific Rhizobium strains isolated within the same region.
Abstract: A number of examples is given demonstrating the co-existence of pea genotypes and their specific Rhizobium strains isolated within the same region. R. leguminosarum strains compatible with the cultivated pea have a narrow symbiotic range and they are widely distributed in European soils. This is presumably due to the narrow genetic base of the cultivated pea and its wide-spread cultivation in European soils. Rhizobium strains capable of nodulating a primitive pea line from Afghanistan were only found in soils of the Middle East and Central Asia. A more restricted distribution of specific Rhizobium strains was found for fulvum peas from Israel. Rhizobium strains effective with the fulvum pea were found in Israeli soils. A good example of co-evolution due to geographical isolation was found in south Turkey. Here a pea line was found which can form an effective symbiosis with local Rhizobium strains but not with strains from other parts of Turkey.
TL;DR: In this paper, two experiments were conducted in saline culture solution to find out the causes of rolling and bleaching of young leaves of rice, observed previously in experiments on coastal saline-sodic soil.
Abstract: Two experiments were conducted in saline culture solution to find out the causes of rolling and bleaching of young leaves of rice, observed previously in experiments on coastal saline-sodic soil. Symptoms similar to those methioned above were observed on young leaves of cv. KS282 in saline culture solution with Na/Ca ratios of 100 or greater. These symptoms were due to Ca deficiency but not of Cu, since Cu concentration was higher in saline shoots than in the control. The decreasing Na/K or Na/Ca ratio in the saline solution decreased Na and Cl concentration in the shoot. In addition to salinity, Na/Ca and Na/K ratios of the growth medium significantly influenced the shoot and root growth of rice.
TL;DR: Level of P fertilization had no effect on water relations or soluble carbohydrate content of nonmycorrhizal roses and the water status of droughted rose was impoved more by G. intraradices than byG.
Abstract: !Summary Shoot water relations and carbohydrate levels were compared for droughted nonmycorrhizal and vesicular-arbuscular (V A) mycorrhizal Rosa hybrida L. cv 'Samantha' plants grown with high and low phosphorus fertilization. Leaf diffusive conductance (g,) of plants colonized by Glomus intraradices Schenk and Smith and Glomus deserticola Trappe, Bloss and Menge were 2 x and 1.5 x greater, respectively, than in nonmycorrhizal plants. Regardless of P fertilization, leaf osmotic and bulk water potentials were 0.5 to 1.1 MPa higher in mycorrhizal than in nonmycorrhizal plants. Leaf starch, chlorophyll and water contents were higher InG. intraradices-colonized plants than .in the high-P nonmycorrhizal plants, while fructose, glucose and total soluble carbohydrates were lower. Level.of P fertilization had no effect on water relations or soluble cart .bohydrate content of nonmycorrhizal roses. The water status of droughted rose was improved more ,i by G. intraradices than by G. deserticola.
TL;DR: Comparison between dark, deep horizons (sombric horizons), which are certainly of illuvial origine, would confirm thatδ13C of grassland and a forest sombric horizon were almost equal at around −22‰, which might mean that, in natural ecosystems, the isotopic carbon composition of the soil underlying humus would be independent of the vegetation type.
Abstract: The natural relationship 13C/12C- determined in three soil profiles under grass vegetation indicated a depletion in organic I3C at depth: the 613C was between - 18%0 and - 15%0 in the A horizons and ranged from - 18 to - 22%0 at depth. Previous work showed that in forest soils, where 613C was near - 28%0 in the upper horizon, there was, on the contrary, a relative enrichment of the lower strata. This meant that 6I3C, initially different in the various topsoils, became more equal at depth. Comparison between dark, deep horizons (sombric horizons), which are certainly of illuvial origine, would confirm this: 613C of grassland and a forest sombric horizon were almost equal at around - 22%0. These results might mean that, in natural ecosystems, the isotopic carbon composition of the soil underlying humus would be independent of the vegetation type. This would have practical implications for the use of I3C as a tracer for soil organic matter studies.
TL;DR: In this article, the effect of barley roots on denitrification was examined, and a pot experiment was designed to compare N2O production and denitification in soils with and without barley plants.
Abstract: To examine the effect of barley roots on denitrification, a pot experiment was designed to compare N2O production and denitrification in soils with and without barley plants. Denitrification, N2O resulting from denitrification and nitrification, and respiration were estimated by incubating pots with soil with and without intact plants in plastic bags at high moisture levels. C2H2-inhibition of nitrous oxide reductase (partial pressure of 10 kPa C2H2) was used to determine total denitrification rates while incubations with ambient air and with C2H2 at partial pressures of 2.5–5 Pa were used to estimate the amounts of N2O released from autotrophic nitrification and from denitrification processes. Other sources of N2O were presumed to be negligible. Potential denitrification, nitrification and root biomass were measured in subsamples collected from four soil depths. A positive correlation was found between denitrification rates and root biomass. N2 was the predominant denitrification product found close to roots; N2O formed by non autotrophic nitrifiers, assumed to be denitrifiers originated in soil not affected by growing roots. Apparently, roots promote denitrification because they consumed oxygen, thereby increasing the anaerobic volume of the soil. The ratio of actual to potential denitrification rates increased over time, especially in the presence of roots.
TL;DR: Exposure of germinating seeds of lettuce, barnyard grass and wheat to volatile substances released from pulverised leaves of some Cruciferae species resulted in delay of germination and reduction of overall growth.
Abstract: Exposure of germinating seeds of lettuce, barnyard grass and wheat to volatile substances released from pulverised leaves of some Cruciferae species resulted in delay of germination and reduction of overall growth.B. juncea andB. nigra volatiles were the most damaging to all of the tested species. It is suggested that degradation products of glucosinolates occuring in cruciferous plants caused this allelopathic action.
TL;DR: The cortex of the main root was found to be alive for the whole life- span of the plant, whereas the life-span of the root hairs was only 2 to 3 days as evidenced by electronmicroscopical examination of cell integrity.
Abstract: The longevity of the main root cylinder and the laterals of the primary root of maize plants was determined under controlled greenhouse conditions by means of nuclear staining with acridine orange. The cortex of the main root was found to be alive for the whole life-span of the plant, whereas the life-span of the root hairs was only 2 to 3 days as evidenced by electronmicroscopical examination of cell integrity. The onset of senescence of laterals was observed at the older part of the main root at the 6-leaf stage of the plant. Senescence of 1st and 2nd order laterals commenced near the root tip a few days after their protrusion and advanced towards the basal region of the root. In any root segment death of the cortex cells preceeded that of the stele. At the late grain filling stage all laterals along the main root exhibited advanced senescence, but stainable nuclei were seen in the root tissues of the basal part of 1st order laterals (both cortex and stele) as well as of the 2nd order laterals which emerged from that root segment. The pattern of the dying of the root tissue is discussed with regard to the P-nutrition of the shoot system by the primary root.
TL;DR: In this paper, the capacity to sorb P varied among some Ethiopian soils, and the role of Al was more important than that of Fe even though more dithionite and oxalate extractable Fe than Al was found in all soils.
Abstract: The capacity to sorb P varied among some Ethiopian soils. Volcanic ash soils sorbed the maximum P while Fluvisols and Regosols sorbed the least. Sorption of P was significantly correlated with exchangeable and extractable forms of Fe and Al as well as pH and organic matter. But is was not related to the clay content of the soils. The role of Al was more important than that of Fe even though more dithionite and oxalate extractable Fe than Al was found in all soils.
TL;DR: Good agreement was obtained between estimates of N2 fixation of sole or intercrop cowpea (1984/85 season) based on the15N natural abundance and15N fertilizer dilution techniques, both in the field and in a glasshouse pot study.
Abstract: Yields of above ground biomass and total N were determined in summer-grown maize and cowpea as sole crops or intercrops, with or without supplementary N fertilizer (25 kg N ha−1, urea) at an irrigated site in Waroona, Western Australia over the period 1982–1985. Good agreement was obtained between estimates of N2 fixation of sole or intercrop cowpea (1984/85 season) based on the15N natural abundance and15N fertilizer dilution techniques, both in the field and in a glasshouse pot study. Field-grown cowpea was estimated to have received 53–69% of its N supply from N2-fixation, with N2-fixation onlyslightly affected by intercropping or N fertilizer application. Proportional reliance on N2-fixation of cowpea in glasshouse culture was lower (36–66%) than in the field study and more affected by applied N. Budgets for N were drawn up for the field intercrops, based on above-ground seed yields, return of crop residues, inputs of fixed N and fertilizer N. No account was taken of possible losses of N through volatilization, denitrification and leaching or gains of N in the soil from root biomass. N2-fixation was estimated tobe 59 kg N ha−1 in the plots receiving no fertilizer N, and 73 kg N ha−1 in plots receiving 25 kg N ha−1 as urea. Comparable fixation by sole cowpea was higher (87 and 82 kg N ha−1 respectively) but this advantage was outweighed by greater land use efficiency by the intercrop than sole crops.
TL;DR: Tropical forage legumes and grasses compared under glasshouse conditions in a sterile low P oxisol showed a great variation in dependence on mycorrhiza, and utilization of soil P by non-mycorrhizal plants was correlated inversely with mycorRhizal dependency.
Abstract: Growth and mineral uptake of twenty-four tropical forage legumes and grasses were compared under glasshouse conditions in a sterile low P oxisol, one part inoculated and the other not inoculated with mycorrhizal fungi. Shoot and root dry weights and total uptake of P, N, K, Ca, and Mg of all the test plants were significantly increased by mycorrhizal inoculation. Mycorrhizal inoculation, with few exceptions, decreased the root/shoot ratio. Non-mycorrhizal plants contained always lower quantities of mineral elements than mycorrhizal plants. Plant species showed differences in percentage mycorrhizal root length and there was no correlation between percentage mycorrhizal infection and plant growth parameters. A great variation in dependence on mycorrhiza was observed among forage species. Total uptake of all elements by non-mycorrhizal legumes and uptake of P, N and K by non-mycorrhizal grasses correlated inversely with mycorrhizal dependency. Mycorrhizal plants of all species used significantly greater quantities of soil P than the nonmycorrhizal plants. Utilization of soil P by non-mycorrhizal plants was correlated inversely with mycorrhizal dependency.