Showing papers in "Plant and Soil in 1975"
TL;DR: In this paper, a quantitative estimate of the amount of nitrogen symbiotically fixed by a legume crop growing under normal field conditions was made by simultaneous determinations of the AN values by the legume and a non-nodulating crop.
Abstract: A quantitative estimate is made of the amount of nitrogen symbiotically fixed by a legume crop growing under normal field conditions. The method involves simultaneous determinations of the “AN” values by the legume and a non-nodulating crop, using15N-labelled nitrogen fertilizer. The fertilizer is applied at a low rate to the legume crop to avoid interference with the symbiotic N fixation process, but at a normal rate to the non-nodulating crop. The amount of symbiotically fixed nitrogen expressed in kg N/ha is calculated by multiplying the difference in A value between the legume and the non-nodulating crop with the % utilization of fertilizer N by the legume crop.
171 citations
TL;DR: A model of the way the rate of growth of a plant may be affected by the level of supply of a nutrient is presented and a method of applying this information to soil grown plants is suggested.
Abstract: A model of the way the rate of growth of a plant may be affected by the level of supply of a nutrient is presented. Growth rate is linked to the nutrient level of the photosynthetic tissues, which is assumed to control changes in the net assimilation rate, the leaf area per unit shoot weight, the shoot: root ratio, the root surface area, and the distribution of nutrient between root and shoot. The uptake of nutrient depends on the concentration of nutrient at the root surface, the root surface area and its absorbing power. All these relationships may be determined in stirred solution culture. A method of applying this information to soil grown plants is suggested.
142 citations
TL;DR: In this paper, the role of colourless sulfur bacteria in the sulfur cycle is well documented, although the quantitative data are virtually absent, such as: the rate of oxidation of (S35) sulfur compounds, rate of C14O2-fixation, the rates of acid production and numbers and growth rates of the bacteria.
Abstract: The bacteria belonging to the families of the Thiobacteriaceae, Beggiatoaceae and Achromatiaceae are commonly called the colourless sulfur bacteria. While their ability to oxidize reduced inorganic sulfur compounds has clearly been established, it is still not known whether all these organisms can derive metabolically useful energy from these oxidations. During the last decades research has mainly focussed on the genus Thiobacillus. Bacteria belonging to this genus can oxidize a variety of reduced inorganic sulfur compounds and detailed information is available on the biochemistry and physiology of these energy-yielding reactions. The thiobacilli, most of which can synthesize all cell material from CO2, possess a well-regulated metabolic machinery with high biosynthetic capacities, which is essentially similar to that of other procaryotic organisms. Although the qualitative role of colourless sulfur bacteria in the sulfur cycle is well documented, quantitative data are virtually absent. Activities of colourless sulfur bacteria in nature must be related to direct and indirect parameters, such as: the rate of oxidation of (S35) sulfur compounds, the rate of C14O2-fixation, the rate of acid production and numbers and growth rates of the bacteria. However, chemical reactions and similar activities of heterotrophic organisms mask the activities of the colourless sulfur bacteria to various extents, depending on the condition of the natural environment. This interference is minimal in regions where high temperature and/or low pH allow the development of a dominant population of colourless sulfur bacteria, such as hot acid sulfur springs, sulfide ores, sulfur deposits and some acid soils. The oxidation of inorganic sulfur compounds is carried out by a spectrum of sulfur-oxidizing organisms which includes: 1) obligately chemolithotrophic organisms 2) mixotrophs 3) chemolithotrophic heterotrophs 4) heterotrophs which do not gain energy from the oxidation of sulfur compounds but benefit in other ways from this reaction, and 5) heterotrophs which do not benefit from the oxidation of sulfur compounds. The spectrum is completed by a hypothetical group of heterotrophic organisms, which may have a symbiotic relationship with thiobacilli and related bacteria. Such heterotrophs may stimulate the growth of colourless sulfur bacteria and thereby contribute to the oxidation of sulfur compounds. Future research should focus in the first place on obtaining and studying pure cultures of many of the colourless sulfur bacteria. In the second place, studies on the physiological and ecological aspects of mixed cultures of colourless sulfur bacteria and heterotrophs may add to a better understanding of the role of the colourless sulfur bacteria in the sulfur cycle.
141 citations
TL;DR: Treating roots of tomato seedlings with these cultures accelerates plant growth and increases yield of fruit, effects probably caused by activity of the plant hormones.
Abstract: Culture supernatants ofAzotobacter vinelandii andAzotobacter beijerinckii contain auxins, at least three gibberellin-like substances and three cytokinin-like substances. Treating roots of tomato seedlings with these cultures accelerates plant growth and increases yield of fruit, effects probably caused by activity of the plant hormones. Amounts of hormones produced in these cultures are similar to those produced byAzotobacter chroococcum andAzotobacter paspali.
122 citations
TL;DR: Endogone spores usually occurred in barley and potato plots given intermediate amounts of phosphate, and there was most VA infection in barely and potato roots from plots given least phosphate, although the effects of phosphate were much less marked than those reported for nitrogen under field conditions.
Abstract: The numbers of Endogone spores (mainly of the laminate type) and the amount of vesicular-arbuscular (VA) mycorrhiza were examined in field soil given different phosphate treatments and planted with a rotation of potatoes, barley and swedes. Most spores usually occurred in barley and potato plots given intermediate amounts of phosphate, and there was most VA infection in barely and potato roots from plots given least phosphate. The effects of phosphate were much less marked than those reported for nitrogen under field conditions. Swede roots were not infected. In pot experiments swede seedlings inoculated with Endogone did not become mycorrhizal and they inhibited mycorrhizal development in seedlings of onion, which is normally a strongly mycorrhizal plant.
120 citations
TL;DR: It appears that these contrasting features of rape and onions broadly compensated for each other so that the P concentration range over which the two species responded was much the same.
94 citations
TL;DR: In this paper, the authors measured the influx of P per meter of corn (Zea mays L.) root for corn grown in nutrient culture by following the rate of loss of P from solution over a 4 to 6 hour period.
Abstract: The influx of P per meter of corn (Zea mays L.) root for corn grown in nutrient culture was measured by following the rate of loss of P from solution over a 4 to 6 hour period. Experiments were conducted on corn grown for 12, 14, 28, 35, 43, 52, and 80 days. The maximum P influx, Km(the Michaelis constant), P efflux, and the minimum concentration to which the plants reduced the solution P level were measured on plants with untrimmed and trimmed roots. Reducing root length by trimming did not alter P uptake characteristics of corn roots. Trimming was done one or two days prior to the measurement of P flux.
90 citations
TL;DR: It was not possible to find in any of the strains' symbiotic properties a consistent explanation of their competitiveness in nodule formation, however it is perhaps significant that TA1 (the more successful strain) formed its first nodule slightly ahead of its competitors.
Abstract: The relative success of a commercial strain (TA1) competing with ineffective Uruguayan strains of Rhizobium trifolii for the colonisation of the root surface and in forming nodules has been tested with Trifolium subterraneum and T. vepens, and with a species indigenous to Uruguay (T. polymorphum). Competing pairs of strains were tested on hosts, raised from surface-sterilized seed and maintained on seedling agar in tube culture, so as to permit representation on the root surface and in each nodule to be determined. Relative nodulation success was estimated as a competitive index (C): the ratio of nodules formed by one strain to those formed by the other when equally represented on the root surface. On T. repens and T. subterraneum the effective strain (TA1) dominated the ineffective Uruguayan competitor (U73) so that CTA1:U73 ranged from 18 to greater than 94, and its success was very little dependent on relative representation on the root surface. On T. polymorphum, with which TA1 and U73 were both ineffective, the former was still superior (CTA1:U73=2–4), but was not as dominant as it was on the other two hosts; its success was more dependent on its root-surface representation. A mixture of several, all ineffective, Uruguayan strains narrowed the competitive advantage of strain TA1 and caused its relative nodulating success to become more dependent on representation on the root. The greater intrinsic nodulating competitiveness of strain TA1 was to some extent offset by its relatively poor colonisation of the root surface, where it could be outgrown by the Uruguayan strains, particularly when a medium or low level of inoculation permitted considerable growth. Delay in the addition of TA1 to an established population of U73 resulted in additional representation of the latter in nodules of T. subterraneum. However strain U73 was largely restricted to the earlier-formed nodules and the total, as distinct from the proportion, of TA1 nodules was largely unaffected by the start given its competitor. Nodules due to mixed infections were regularly encountered (up to 18%), particularly in the case of T. subterraneum. It was not possible to find in any of the strains' symbiotic properties a consistent explanation of their competitiveness in nodule formation. However it is perhaps significant that TA1 (the more successful strain) formed its first nodule slightly ahead of its competitors.
76 citations
TL;DR: The significance and catalytic role of the sulfur cycle for the degradation of organic material under anaerobic conditions is demonstrated and the phototrophic bacteria are shown to be beneficial for the higher forms of life in lakes.
Abstract: The unique characteristic of the phototrophic purple and green sulfur bacteria as well as of members of the purple nonsulfur bacteria is their ability to oxidize H2S to sulfate under anaerobic conditions in the course of their anoxigenic photosynthesis. Carbon dioxide — assimilated into cell material — is the electron acceptor of this oxidation process. Thus, a reoxidation of the H2S formed under anaerobic conditions by sulfate reducing bacteria is achieved without the consumption of molecular oxygen.
76 citations
TL;DR: In this paper, it was suggested that homoserine, released from the main root of pea seedlings during the formation of lateral roots, might selectively stimulate the growth of R. leguminosarum when a mixture of Rhizobium strains, belonging to different cross-inoculation groups, is present in the surroundings of the young pea root.
Abstract: Rhizobium leguminosarum, grew equally well with homoserine and glutamic acid as the nitrogen source or as the sole source of nitrogen, carbon and energy. Strains of R. trifolii, R. phaseoli and R. meliloti behaved entirely differently. With glutamic acid as the only C and N source, growth was similar to that of R. leguminosarum, but with homoserine growth was practically absent or in case of R. meliloti considerably reduced. It was suggested that homoserine, released from the main root of pea seedlings during the formation of lateral roots, might selectively stimulate the growth of R. leguminosarum when a mixture of Rhizobium strains, belonging to different cross-inoculation groups, is present in the surroundings of the young pea root. re]19740122
75 citations
TL;DR: Results of the present study indicate that transient peaks in the concentration of bicarbonate and possibly of organic acids in the soil solution following soil submergence may induce temporary zinc deficiencies.
Abstract: Solution culture studies revealed no marked difference in the ability of the resistant variety IR8 or the susceptible variety IR184-67 to absorb zinc from low external concentrations comparable with those occurring in the soil solutions of deficient soils. However IR8 appeared to have a slightly lower tissue requirement for zinc than IR184-67 (critical values 0.23 and 0.27 μg atoms/g respectively) and IR8 was significantly less susceptible to bicarbonate concentrations (<1 mM). Despite these differences, the two varieties appeared equally susceptible to zinc deficiency during the first four weeks of growth under field conditions.
TL;DR: The K content of fruit was closely correlated with the dry matter content, and for a given K treatment, the same equation described the uptake of K into the fruit of boty varieties.
Abstract: The effect of K nutrition on the growth in sand culture of young tomato plants, cv. Amberley Cross, was examined and the concentrations of K in the nutrient feed and in the leaves associated with maximum flower number, fruit set and yield were determined. The distribution of K between and with-in fruit trusses of normal and K-deficient plants, cv. Amberley Cross and Moneymaker grown in peat/loam was also studied. Total dry weights of 6-wk-old plants grown in sand were maximal when the nutrient feed contained 0.53–5.03 me K+/l, although plants receiving 10.23 me K+/l retained more water in the foliage and therefore had the greatest foliage fresh weight. Both peduncle length and height of the basal truss were increased by K in the feed up to 10.23 me/l, the highest concentration used. Flower development was retarded below 0.53 me K+/l, and fruit setting efficiency was reduced below 2.03 me K+/l. Fruit ripened faster on plants receiving low concentrations of K. Maximum fruit yields were produced on plants grown in sand receiving 5.03 or 10.23 me K+/l. The K content of fruit was closely correlated with the dry matter content, and for a given K treatment, the same equation described the uptake of K into the fruit of boty varieties. However, fruit trusses of cv. Moneymaker contained the most K, and this is attributed to their high dry matter content. The element was evenly distributed between and within trusses from normal and K-deficient plants of both varieties. More than ten times more K and five times more N and P was taken up into fruit of plants receiving 5.03 or 10.23 me K+/l. The K status of young fully expanded leaves associated with maximum dry weight production in 6-wk-old plants was 1.4±0.2 g K+/100 g dry weight in the whole leaf (1.1±0.1 in the laminae, 2.1±0.3 in the petioles). Maximum fruit yield without the production of excessive foliage was associated with 5.2±0.8 g K+/100 g dry weight in the whole leaf (3.8±0.6 and 8.1±1.1 in the laminae and petioles, respectively). re]19740619
TL;DR: Rushes and sedges have evolved extensive and finely branched root systems rather than the mycorrhizal habit for extracting P from infertile soils, and in pot experiments, they differ from mycotrophic angiosperms in rejecting mycorRHizal infection, even if suffering P deficiency.
Abstract: Few rushes and sedges were infected by endomycorrhizal fungi in the field, and many of the infections which were formed were mainly of mycelium in the rhizosphere with only occasional lodgements in epidermal cells. In a pot experiment using a soil of very low P availability, rushes and sedges remained non-mycorrhizal and yet produced more shoot dry matter than mycorrhizal Poa colensoi (Graminae). Rushes and sedges had much longer root systems than non-mycorrhizal Poa colensoi, but comparable shoot P concentrations. I suggest that they have evolved extensive and finely branched root systems rather than the mycorrhizal habit for extracting P from infertile soils. In pot experiments, they differ from mycotrophic angiosperms in rejecting mycorrhizal infection, even if suffering P deficiency. re]19740401
TL;DR: The tips of the mainRoot as well as those of the lateral roots were found to be important sites of exudation and a release of ninhydrin-positive compounds occurred during the formation of lateral roots, a process whereby the main root is severely damaged.
Abstract: The sites of exudation of young pea roots were localized. The tips of the main root as well as those of the lateral roots were found to be important sites of exudation. Furthermore, a release of ninhydrin-positive compounds occurred during the formation of lateral roots, a process whereby the main root is severely damaged.
TL;DR: Ethylene is microbially decomposed in aerobic soil conditions faster than it is produced in anaerobic soils, and the organisms responsible form only a small part of the soil population.
Abstract: Ethylene is microbially decomposed in aerobic soil conditions faster than it is produced in anaerobic soils. The organisms responsible form only a small part of the soil population and their activity is slowed by concentrations of carbon dioxide greater than five per cent.
TL;DR: In this article, the effect of silicon on lodging of rice induced by added N was studied in the field with three varieties of rice and the resistance to lodging was measured by applying a pulling force to the rice stalk until it broke or bent to about 30° angle with the surface of the soil.
Abstract: Effect of silicon on lodging of rice induced by added N was studied in the field with three varieties of rice The resistance to lodging was measured with a special equipment by applying a pulling force to the rice stalk until it broke or bent to about 30° angle with the surface of the soil
TL;DR: It is suggested that in a heterogeneous environment development of a particular member depends not only upon the conditions in its immediate surroundings but also upon the growth of the remainder of the root system.
Abstract: The highly co-ordinated development of root systems in uniform environments implies the existence of complex mechanisms for the regulation of growth. It suggests that in a heterogeneous environment development of a particular member depends not only upon the conditions in its immediate surroundings but also upon the growth of the remainder of the root system. Experiments have been carried out in which normal patterns of development were disturbed by the removal or desiccation of parts of the root system or its partition between environments of different temperature. The results demonstrated a clear dependence of the development of any part of the root system upon that of the remainder and indicated that there were a range of possible interactions between members. re]19740410
TL;DR: Seedlings of Eucalyptus gummifera (Gaertn), a species common on the highly weathered acid Hawkesbury Sandstone soils of the Sydney region, were grown in sterile quartz culture as discussed by the authors.
Abstract: Seedlings of Eucalyptus gummifera (Gaertn.), Hochr. a species common on the highly weathered acid Hawkesbury Sandstone soils of the Sydney region, were grown in sterile quartz culture. The plants were provided with four aluminium treatments (0, 0.5, 1.0, 10.0 ppm Al) at each of two phosphorus concentrations (1.0 and 100.0 ppm P).
TL;DR: In this paper, the root and shoot dry weights were reduced slightly by the ethylene treatment; seminal root extension was inhibited greatly while lateral root growth was stimulated; absorption of ions and their transport from root to shoot within the plant was not affected.
Abstract: Following observations that ethylene can occur in anaerobic or partially anaerobic soils at concentrations which can affect plant growth, shoot and root growth of barley plants, maintained in solution culture, were examined after long-term exposure of the roots to ethylene in air; the subsequent growth on transfer to a similar but ethylene-free environment was also studied. Both root and shoot dry weights were reduced slightly by the ethylene treatment; seminal root extension was inhibited greatly while lateral root growth was stimulated; absorption of ions and their transport from root to shoot within the plant was not affected. On transfer to an ethylene free environment the extension rate of the seminal axes increased markedly and was the greater the shorter the period of the preceding ethylene treatment; the extension of laterals initiated during the ethylene treatment was stimulated greatly but the growth of those formed subsequently was inhibited.
TL;DR: In this article, a direct method of estimation of silica in rice plant tissues is reported, which involves the digestion of finely ground plant samples with concentrated nitric acid in corning-glass conical flasks followed by dissolution in Na2CO3 in stainless-steel beakers; the plant silica is thereby converted into molybdenum reactive form which is estimated colorimetrically.
Abstract: A direct method of estimation of silica in rice plant tissues is reported. This involves the digestion of finely ground plant samples with concentrated nitric acid in corning-glass conical flasks followed by dissolution in Na2CO3 in stainless-steel beakers; the plant silica is thereby converted into molybdenum reactive form which is estimated colorimetrically. This method represents an improvement over the time consuming fusion procedure followed ordinarily and also dispenses with use of platinumware. re]19740501
TL;DR: In this article, field investigations were conducted to study the effect of a weathered fly ash sample on yield and nutrient concentration of corn and on composition of displaced soil solutions, and to determine rates of fly ash that could be applied to soils without adversely affecting plant growth.
Abstract: Field investigations were initiated in 1971 to study the effect of a weathered fly ash sample on yield and nutrient concentration of corn (Zea mays L.) and on composition of displaced soil solutions, and to determine rates of fly ash that could be applied to soils without adversely affecting plant growth. Application of weathered ash at rates ranging from 18 to 288 metric tons/ha did not decrease corn grain yields on either Groseclose silt loam or Woods-town loamy fine sand. Corn grain yields were increased on the Woodstown soil in 1972 where cumulative rates of 216 and 288 metric tons/ha of fly ash were applied, which was attributed in part to increased soil moisture. Plant analysis data indicated that B and Mn concentrations were not increased to toxic levels as had been reported in other investigations with unweathered fly ash. Soil solution data verified that toxic amounts of these elements were not released from the weathered ash sample.
TL;DR: It was confirmed that the available fertilizer N was largely depleted, because uptake of labeled N was minimal during the second growing season and labeled N tended to become increasingly diluted by internal cycling as it moved from the roots into the crown.
Abstract: The movement of N in an 11-year-old slash pine forest ecosystem was followed over two growing seasons by using N15-labeled ammonium sulphate, applied in the spring at 0, 56, and 224 kg N/ha. The initial uptake of P32, applied as concentrated superphosphate at 90 kg P/ha, and of labeled N from the highest application rate was followed in two trees for 71 days.
TL;DR: In this paper, Douglas fir seedlings were grown in a series of 7 sub-irrigated sand culture experiments in which N was supplied from either a nitrate or an ammonium source.
Abstract: Douglas-fir (Pseudotsuga menziesii Mirb. Franco) seedlings were grown in a series of 7 sub-irrigated sand culture experiments in which N was supplied from either a nitrate or an ammonium source. The first five experiments were designed to identify factors that influence seedling growth response to N source; the last two were concerned with N uptake from the two different sources under sterile conditions. In the five non-sterile cultures, seedling growth was generally greater on ammonium than on nitrate-N. In nonsterile cultures, the level of N supply affected response to N source, but greater growth occurred on the ammonium source at all levels despite this interaction. P accumulated in roots and was relatively low in shoots of nitrate seedlings. Different levels of P supply did not affect response to N source. Ca concentration of nitrate-fed seedlings was high compared with ammonium-fed seedlings, and increase in Ca supply caused a small increase in seedling growth on nitrate-N, but not on ammonium-N. Seedling growth response to N source was unaffected by light intensity, but frequency of sub-irrigation had a marked effect. Irrigation once in two days or once a day resulted in greater growth occurring on nitrate-N, whereas irrigation eight times a day or four times a day resulted in greater growth of ammonium-fed seedlings. In sterile cultures, which were sub-irrigated once a day, seedling growth was greater on nitrate-N than on ammonium-N. Aseptically grown seedlings of three different Douglas-fir provenances accumulated up to seven times the initial seed N content during 12 weeks of growth on nitrate-N. The conclusion was that Douglas-fir seedlings can grow satisfactorily on nitrate-N sources without the intervention of any other organism, and thus must be capable of nitrate reduction. re]19740805
TL;DR: Rhizobia were found to possess greater tolerance for alkalinity than their host legumes, however, delayed nodulation in lentil and berseem resulting in decreased yield of the plants at pH values higher than 9.0 was observed.
Abstract: Survival, growth and symbiotic performance of rhizobia isolated from normal, saline-sodic and mildly acidic soils were studied in original and amended saline-alkali soils. Rhizobia of 4 out of 9 legumes studied for nodulation were found to be present in a highly saline-sodic soil. Majority of the strains of these bacteria did not survive in the original saline-sodic soil of pH 10.5 but as the pH was amended to lower than 10.0, all the strains survived in the soil. Virtually no differences were noticed in the survival and symbiotic characteristics of native and exotic strains ofRhizobium leguminosarum andRhizobium trifolii in the saline-sodic soil, though wide variations were observed among individual strains irrespective of their ecological origin. Rhizobia were found to possess greater tolerance for alkalinity than their host legumes. However, delayed nodulation in lentil (Lens esculenta) and berseem (Trifolium alexandrinum) resulting in decreased yield of the plants at pH values higher than 9.0 was observed.
TL;DR: Interactions between legume lectins and Rhizobium cells may not always account for the specificity expressed by the nodule bacteria for their respective legume hosts.
Abstract: Concanavalin A, a lectin from jackbean (Canavalia ensiformis), combined strongly with various nodulating and non-nodulating strains of Rhizobium regardless of their respective hosts. Thus, interactions between legume lectins and Rhizobium cells may not always account for the specificity expressed by the nodule bacteria for their respective legume hosts.
TL;DR: Several Bacillus strains from the rhizosphere of Ammophila arenaria appeared on ‘nitrogen-free’ agar plates and characterisation suggests that these strains are new nitrogen-fixing Bacillus species.
Abstract: Several Bacillus strains, from the rhizosphere of Ammophila arenaria, appeared on ‘nitrogen-free’ agar plates. They were able to grow in nitrogen-poor medium to which 0.1% yeast extract was added. Three of these bacilli were tested for their ability to fix nitrogen using the acetylene reduction assay. The C2H2-reducing activity was determined at 8-hour intervals during their growth cycle. C2H2 reduction (and accordingly N2 fixation) was greater under anaerobic than aerobic conditions. Additions of 0.1% CaCO3 significantly increased the C2H2-reducing activity under both conditions. Characterisation suggests that these strains are new nitrogen-fixing Bacillus species. re]19740121
TL;DR: In this paper, a rapid procedure for simultaneous determination of NH4-, NO2-, and NO3-N in field moist samples is proposed for small laboratories and 50 to 75 samples can be analyzed in a day.
Abstract: A rapid procedure is proposed for simultaneous determination of NH4-, NO2-, and NO3-N in field moist samples. The procedure involves extraction, with Morgan's solution followed by determination of NH4-N by Nessler's reagent, NO2-N by α-naphthylamine and sulphanilic acid and NO3-N by phenol-disulphoric acid. The method will suit small laboratories and 50 to 75 samples can be analysed in a day.
TL;DR: Fungal numbers were generally decreased, while the response of the actinomycete population depended on the concentration of fungicide applied, in field and laboratory incubated soils.
Abstract: Fungicides were applied to both field and laboratory incubated soils, in order to determine their effects on fungal and bacterial numbers, and on the frequency of celluloytic fungi. In field soils, fungal numbers were initially reduced following the application of Captan, Dicloran, Milcol, and Triarimol, but then returned to the level of the untreated soil after 157 days. The major cellulolytic fungal species were generally unaffected, or increased in frequency in treated soils. Certain species includingTrichoderma koningii andPenicillium nigricans became dominant in treated soils, while species ofChaetomium andVerticillium decreased in frequency. Bacterial numbers increased in laboratory incubated soils which were treated with Captan. Fungal numbers however, were generally decreased, while the response of the actinomycete population depended on the concentration of fungicide applied.
TL;DR: It was concluded that in low P soil the roots may be acting as rather more than simple sinks for P, but in intermediate and high P soils the simple sink remains a reasonable model for root behaviour, but methods of determining desorption isotherms in undisturbed soil are required to make precise simulations of uptake from such soils.