Effects of Municipal Sewage Sludge Doses on the Chlorophyll Contents and Heavy Metal Concentration of Sugar Beet (Beta vulgaris var. saccharifera)

The present study was conducted to assess the suitability of sewage sludge amendment (SSA) in soil for Beta vulgaris var. saccharifera (sugar beet) by evaluating the heavy metal accumulation and physiological responses of plants grown at a 10%, 25%, and 50% sewage sludge amendment rate. The sewage sludge amendment was modified by the physicochemical properties of soil, thus increasing the availability of heavy metals in the soil and consequently increasing accumulation in plant parts. Cd, Pb, Ni, and Cu concentrations in roots were significantly higher in plants grown at 25% as compared to 50% SSA; however, Cr and Zn concentration was higher at 50% than 25% SSA. The concentrations of heavy metal showed a trend of Zn > Ni > Cu > Cr > Pb > Cd in roots and Zn > Cu > Ni > Cr > Pb > Cd in leaves. The only instance in which the chlorophyll content did not increase after the sewage sludge treatments was 50%. There were approximately 1.12-fold differences between the control and 50% sewage sludge application for chlorophyll content. The sewage sludge amendment led to a significant increase in Pb, Cr, Cd, Cu, Zn, and Ni concentrations of the soil. The heavy metal accumulation in the soil after the treatments did not exceed the limits for the land application of sewage sludge recommended by the US Environmental Protection Agency (US EPA). The increased concentration of heavy metals in the soil due to the sewage sludge amendment led to increases in heavy metal uptake and the leaf and root concentrations of Ni, Zn, Cd, Cu, Cr, Pb, and Zn in plants as compared to those grown on unamended soil. More accumulation occurred in roots and leaves than in shoots for most of the heavy metals. The concentrations of Cd, Cr, and Pb were more than the permissible limits of national standards in the edible portion of sugar beet grown on different sewage sludge amendment ratios. The study concludes that the sewage sludge amendment in the soil for growing sugar beet may not be a good option due to risk of contamination of Cr, Pb, and Cd.     

Effect of organic amendment on phenolic content of soil and plant and response ofMeloidogyne javanica and its host to related compounds

Summary Amendment of soil with margosa cake or sawdust supplemented with NPK fertilizers increased its phenolic content. The concentration of total phenols was related to the amount of amendment used and varied with the length of decomposition period. Total phenols estimated in ether extract were more in margosa cake amended soil than in sawdust amended soil. Roots of tomato plants grown in amended soil showed presence of higher quantity of total phenols than those grown in non-amended soil. Exposure of females ofMeloidogyne javanica to benzoic, phenyl butyric, phenyl acetic and cinnamic acids significantly reduced their egg laying capacity. Suppression of larval motility was one of the main direct effects of these acids on the nematode. Exposure of tomato roots to different concentrations of phenyl acetic, benzoic, phenyl butyric and cinnamic acids imparted some resistance to invasion by the nematode. In such treated plants fewer larvae could penetrate the roots and develop into mature females and fewer eggs were produced. Research paper No.1455 through the Experiment Station G.B.P.U,A, & T., Pantnagar     

Growth,mineral nutrition and mycorrhizal colonization of red clover and cucumber plants grown in a soil amended with composted urban wastes

The utility of an urban solid waste, either freshly composted or vermicomposted, for improvement of plant growth in a soil B horizon was investigated. Growth, mineral nutrition and arbuscular mycorrhizal (AM) colonization of cucumber and red clover plants were studied in an experiment carried out under controlled growing conditions, using different mixtures of soil and composts as plant substrates. Soil inoculation with the AM fungus Acaulospora sp. did not benefit growth of plants when soil was used as the only substrate, possibly due to its poor fertility. Results showed that neither mycorrhizal plant species grew when soil was mixed with composted urban waste or when compost was used as the only substrate. However, amendment of soil with 10 or 50% vermicompost significantly increased dry matter yields of red clover and cucumber plants, compared to treatments where soil was the only substrate. Addition of vermicompost also increased Olsen-P and other mineral elements in soil and shoot P, Ca, Mg, Cu, Mn and Zn concentrations, but caused a significant reduction on root length colonized by AM fungi in red clover plants. It is concluded that application of high amounts of vermicompost from composted urban wastes to soils might cause a significant reduction of activity of AM fungi, which must be taken into account when using these organic amendments in agricultural systems.     

Influence of [S, S]-EDDS on phytoextraction of copper and zinc by Elsholtzia splendens from metal-contaminated soil

Two pot experiments were conducted to investigate the time course effects of the (S, S)-N, N'-ethylenediamine disuccinic acid (EDDS) addition to contaminated soil on the uptake of Cu and Zn by the Cu accumulator Elsholtzia splendens and on plant Cu and Zn concentrations at different growth stages. EDDS increased the amounts of Cu and Zn soluble in the soil, taken up by plants, concentrated in the xylem sap, and translocated from roots to stems and leaves. The increase in soil-soluble metals, especially Cu, resulted in a corresponding increase in metal concentrations in the xylem sap and leaves. The addition of EDDS to the soil increased plant Cu and Zn concentrations, especially in the leaves, and changed the proportions of Cu and Zn taken up by different plant parts. The proportions of Cu and Zn taken up by the roots were higher than by the leaves of control plants, but EDDS-treated plants showed the opposite trend. EDDS exerted greater effects at the end of the vegetative growth stage than at the start of the flowering or reproductive stages.     

Application of biosolids in mineral sands mine rehabilitation: use of stockpiled topsoil decreases trace element uptake by plants

Mineral sands mining involves stripping topsoil to access heavy-mineral bearing deposits, which are then rehabilitated to their original state, commonly pasture in south-west Western Australia. Organic amendments such as biosolids (digested sewage sludge) can contribute organic carbon to the rehabilitating system and improve soil chemical fertility and physical conditions. Use of biosolids also introduces the risk of contamination of the soil-plant system with heavy metals, but may be a useful source of trace elements to plants if the concentrations of these elements are low in unamended soil. We expected that biosolids amendment of areas mined for mineral sands would result in increased concentrations of metals in soils and plants, and that metal uptake would be decreased by adding stockpiled topsoil or by liming. A glasshouse experiment growing a mixed annual ryegrass (Lolium rigidum)-subterranean clover (Trifolium subterraneum) sward was conducted using two soil materials (residue sand/clay and conserved topsoil) from a mineral sands mine amended with different rates of biosolids (0, 10, 20, 50 dry t/ha), and including a liming treatment (2 t/ha). Total concentrations of metals (As, Cd, Co, Cr, Cu, Ni, Pb and Zn) in soil increased with increasing rate of biosolids application. Metal uptake was generally lower where topsoil was present and was decreased by liming. With increasing biosolids application, plant metal concentrations increased for Cd, Ni and Zn but decreased or were erratic for other elements. In clover, biosolids application removed the Zn deficiency observed where biosolids were not applied. Plant uptake of all elements increased with increasing biosolids application, suggesting dilution by increased plant biomass was responsible for erratic metal concentration results. Despite the observed increases in uptake of metals by plants, metal concentrations in both species were low and below food standard thresholds. It is unlikely that a single application of biosolids in this system posed a threat from heavy metal contamination of soils or plants, and was beneficial in terms of Zn nutrition of T. subterraneum.     

Toxicity and accumulation of copper and nickel in maize plants cropped on calcareous and acidic field soils

Field experiments in calcareous and acidic field soils were conducted to study the effects of copper (Cu) and nickel (Ni) added to soils on maize growth and metal accumulation in maize plants. The results revealed that the critical concentrations of Cu added to soils that decreased maize grain yield by 10% (EC₁₀) were 711 mg kg^?1 for calcareous soil with a pH of 8.9, and 23 mg kg^?1 for acidic soil with a pH of 5.3. The toxicity thresholds of EC₁₀ did not differ significantly for Cu and Ni. A different pattern of Cu and Ni accumulation in maize plants was also found. The accumulation of Cu in above-ground parts of the plants increased initially as the concentrations of Cu added to soils increased, after which they decreased to a constant level. As the concentrations of Ni added to soils increased, the accumulation of Ni in stems and leaves increased linearly, but the accumulation of Ni in the grains was nonlinear. Additionally, the results revealed that Ni was transported to grains more easily than Cu. The results also showed that the concentrations of Cu and Ni in soil solutions as toxicity predictors and the critical concentrations of Cu and Ni in maize were all soil-dependent.     

Some adverse effects of soil amendment with organic Materials—The case of soils polluted by copper industry phytostabilized with red fescue

The study was aimed to examine the effects of soil amendment with organic waste materials on the growth of red fescue and the uptake of Cu and Zn by this grass, in view of its potential usage for phytostabilization of Cu-polluted soils. Five soils, containing 301–5180 mg/kg Cu, were collected from the surroundings of copper smelter Legnica, and amended with lignite (LG) and limed sewage sludge (SS). Plant growth and the concentrations of Cu and Zn in the shoots and roots of grass were measured in a pot experiment and related to the results of Pytotoxkit and Microtox® tests performed on soil solution. The effects of soil amendment with LG and SS differed greatly, and depended on soil properties. In some cases, the application of alkaline SS resulted in dramatic increase of Cu phytotoxicity and its enhanced uptake by plants, while application of LG to slightly acidic soil caused increased accumulation of Zn in plants, particularly in their roots. The study confirmed good suitability of red fescue for phytostabilization of Cu-contaminated soils except for those extremely polluted. Organic amendments to be used for metal immobilization should be thoroughly examined prior to application.     

Heavy metal absorption status of five plant species in monoculture and intercropping

Absorption ability for heavy metals varies among plant species. This study is to evaluate the absorption characteristics of different plant species and planting patterns for heavy metals. Five plant species (tomato, maize, greengrocery, cabbage, and Japan clover herb) were cultivated in monoculture and in intercropping in soil contaminated with heavy metals (Cd, Pb, Cr, Cu, and Fe), to determine the absorption status. Tomato absorbs greater amounts of heavy metals (especially Cd). Furthermore, accumulation of heavy metals increased when tomato was intercropped with other plant species. Maize accumulates greater amounts of Cr, Cu, and Fe. The heavy metal concentrations were reduced when maize was intercropped. Cd and Pb accumulated more in roots of Japan Clover Herb, and the levels of all five heavy metals decreased when intercropped. Tomato intercropping is a feasible method for phytoremediation of heavy metal-contaminated soil, and maize intercropping is feasible for obtaining safe harvest which can be eaten securely.     

Some soil-plant and root-shoot relationships of copper,zinc and manganese in white clover and perennial ryegrass

Summary White clover and perennial ryegrass were grown separately, in pots maintained under controlled environment conditions, for a period of 7 months on ten soils. The proportion of the total soil content of each element taken up by the ryegrass, including that in roots, ranged from 0.88 to 2.18% for Cu, from 0.82 to 2.80% for Zn and from 0.25 to 3.15% for Mn. Uptake by the clover was within these ranges for Cu and Zn, but ranged from 0.10 to 1.71% for Mn.After adjustment for the effects of soil contamination, the ratio of root concentration: shoot concentration was always greater than 1 for both Cu and Zn, and for Cu, though not for Zn, it was considerably greater with ryegrass than with clover. For Mn, the ratio of root:shoot concentration was often greater than 1, and differences between clover and grass were not consistent.Concentrations of Cu and Zn in the shoots were always greater in the clover than in the grass, but concentrations of Mn were generally greater in the grass than the clover.     

Distribution of nutrients and phytotoxic metal ions in the soil and in two forest floor plant species of a beech (Fagus sylvatica L.) stand

In a beech (Fagus sylvatica L.) stand in north-west Germany vegetation of two transects (25m:1m and 20m:1m) was mapped and contents of macronutrients (Ca, Mg and K), micronutrients (Fe, Mn, Zn and Cu), and potentially phytotoxic metals (Pb, Cd, Ni and Al) were measured in different soil compartments and in roots, rhizomes, stems and leaves of two forest floor plant species (Mercurialis perennis L. and Polygonatum multiflorum L.). NH₄Cl extractable cation contents, pH and other soil variables were also determined.The highest macronutrient contents could be found in the leaves of M. perennis and P. multiflorum. Heavy metals and Al accumulated in the roots. Correlation analysis suggests a considerable translocation of Zn and Cd between below- and above-ground organs of both investigated forest floor plants. No significant correlation was found between the contents of the other elements in the below- and above-ground parts.Available data indicate a considerable uptake by the plants not only of nutrients, but also of heavy metals from the upper mineral soil. Amounts of heavy metals and Al solubilized in the presence of NH₄Cl increased with decreasing pH, whereas levels of soluble Ca and Mg were maximal at high pH-values of the extracts. It can be concluded that element uptake in the investigated plants is indirectly controlled by the pH of the upper mineral soil.     

Absorption and Distribution of Copper in Plants with Sufficient or Deficient Supplies

Wheat, red clover and ryegrass were grown in flowing solutionculture with sufficient (+ Cu) and deficient (–Cu) suppliesof copper. The rates of Cu absorption (µg g^–1 dryroot day^–1) did not differ greatly between species ineither treatment. Wheat plants, when transferred from the –Cu to the +Cu treatment, absorbed Cu at a much slower rate thanthose which had remained throughout in the + Cu treatment. Inall plants considerable proportions of the absorbed Cu wereretained in the roots, even when the plants were Cu-deficient,and the concentration in roots usually exceeded that in anypart of the shoots in both treatments. Transferring wheat plantsfrom the +Cu to the –Cu treatment decreased the concentrationin all plant parts except old leaves; similarly, transferringfrom the –Cu to +Cu treatment increased the concentrationin all parts of the shoots, execept old leaves, and in the roots. Lolium perenne, Trifolium pratense, Triticum aestivum, ryegrass, red clover, wheat, absorption, copper, flowing solution culture     

Phytoextraction capacity of the Chenopodium album L. grown on soil amended with tannery sludge

The metal accumulation potential of Chenopodium album L. grown on various amendments of tannery sludge (TS) was studied after 60 days of sapling planted. The analysis of the results showed that the levels of pH, cation exchange capacity, organic carbon, organic matter and DTPA extractable metals (except Mn) of amendments increased by the addition of tannery sludge ratio. Shoot length of the plant increased by the addition of sludge, whereas, no marked change was observed in root length, fresh and dry weight of the plant. Accumulation of the metals in the plants was found in the order; Fe > Mn > Zn > Cr > Cu > Pb > Ni > Cd. Translocation of toxic metals (Cr, Pb, Cd) in different parts of the tested plant was found in the order; leaves > stems > roots. An increase in the photosynthetic pigments, carotenoid and leaf protein contents of the plants were found to increase with increase in sludge amendments. Correlation analysis between metal accumulation in the plants with DTPA extractable metals emphasized that Mn, Ni, Cr, Pb and Cd showed positive correlation (p < 0.05), whereas, Fe, Zn and Cu showed negative correlation. Transfer factor analysis emphasized that 10% TS amendments were suitable for phytoextraction of Cr. Overall analysis of the data exhibited that the plants may be used for phytoextraction of Cr from tannery waste contaminated soil as most of the metal was accumulated in harvestable part which is a matter of serious concern, whenever used for edible purposes.     

The Application of Soil Amendments to the Retardance of Rainwater-Leached Metals from CCA-Treated Wood Ash in Soil

The burning of wood treated with chromated copper arsenate (CCA) produces an ash that contains high concentrations of copper, chromium, and arsenic. The subsequent leaching of these metals from burn sites can produce soil and water contamination. Soils have varying natural abilities to reduce leaching and impact metals speciation and toxicity by sorption, conversion, and sedimentation-related mechanisms. Recent regulations have resulted in increased quantities of CCA-treated lumber entering the waste stream, making the study of metals leaching from ash, and the amendment of soils to more effectively immobilize metals, important areas of investigation.

The performance of various soil amendments to immobilize or retard Cu, Cr, and As species in soil/CCA-ash mixtures was studied. The amendments evaluated were agricultural lime (CaCO₃/MgCO₃), soil softener (CaSO₄ · 2H₂O), and iron sulfate (FeSO₄). Results of this investigation show that native soil alone retards the mobility of As and Cr, amendments applied alone or in combinations further retard metal mobility compared to the control soil/CCA-ash mixture. The CaSO₄ soil amendment is most effective in reducing the rainwater leaching of Cr and As from CCA-ash in soil reducing the mobility by 72.4% and 77.3%, respectively, compared to the control soil-ash mixture. Cu mobility is increased in the presence of the native soil and by all amendments.     

Response of Plant Parasitic and Free Living Soil Nematodes to Composted Animal Manure Soil Amendments

In an outside pot experiment, dry pig manure processed on pine sawdust litter and fermented for seven days by house fly larvae (fermented manure), and pine sawdust applied alone, and in combination with a spring application of inorganic nitrogen fertilizer were used to determine their effects on plant parasitic and free-living soil nematodes on sugar beets (cv. Antek). Non amended soil was used as a control. All treatments with fermented pig manure and sawdust with nitrogen fertilizer decreased number of plant parasitic nematodes and also root-fungal feeding nematodes compared to the untreated control. Sawdust applied alone had no effect on plant parasitic and root-fungal feeding nematode suppression. Free-living nematodes which were mainly bacteriovores and fungivores were significantly more abundant in soil amended with fermented pig manure, while the sawdust had no effect on these nematodes. The effect of all tested treatments on omnivores-predators was rather random, and in general, the number of these nematodes decreased after soil amendment applications compared to the untreated control.     

Conocarpus biochar as a soil amendment for reducing heavy metal availability and uptake by maize plants

The objective of this study was to assess the use of Concarpus biochar as a soil amendment for reducing heavy metal accessibility and uptake by maize plants (Zea mays L.). The impacts of biochar rates (0.0, 1.0, 3.0, and 5.0% w/w) and two soil moisture levels (75% and 100% of field capacity, FC) on immobilization and availability of Fe, Mn, Zn, Cd, Cu and Pb to maize plants as well as its application effects on soil pH, EC, bulk density, and moisture content were evaluated using heavy metal-contaminated soil collected from mining area. The biochar addition significantly decreased the bulk density and increased moisture content of soil. Applying biochar significantly reduced NH₄OAc- or AB-DTPA-extractable heavy metal concentrations of soils, indicating metal immobilization. Conocarpus biochar increased shoot dry biomass of maize plants by 54.5–102% at 75% FC and 133–266% at 100% FC. Moreover, applying biochar significantly reduced shoot heavy metal concentrations in maize plants (except for Fe at 75% FC) in response to increasing application rates, with a highest decrease of 51.3% and 60.5% for Mn, 28% and 21.2% for Zn, 60% and 29.5% for Cu, 53.2% and 47.2% for Cd at soil moisture levels of 75% FC and 100% FC, respectively. The results suggest that biochar may be effectively used as a soil amendment for heavy metal immobilization and in reducing its phytotoxicity.     

Bioaccumulation of heavy metals in Dactylis glomerata L. growing in a calcareous soil amended with sewage sludge

The total and DTPA-extractable concentrations of Pb, Ni, Zn, Cu, Cr and Cd were measured in a calcareous soil amended with different doses of sewage sludge under field conditions. The same metals were also measured in the roots and leaves of Dactylis glomerata at the end of the first vegetative period after the sludge was added. The root concentrations of all the metals were unrelated to their concentrations in the soil. Leaf concentrations of Zn and Cr correlated with total (Zn) and DTPA-extractable (Zn and Cr) concentrations in the soil. DTPA extraction did not appear to be very useful for evaluating the bioavailability of metals in this kind of soil as it gave very low correlation coefficients with leaf content (r = 0.684, P = 0.0049 for Zn and r = 0.557, P = 0.0249 for Cr). Concentrations of Pb, Ni, Cu, and Cd in roots and leaves of Dactylis glomerata were unrelated to the total or DTPA-extractable concentrations in the sludge-amended soil.     

Plant Nutrient Partitioning in Coffee Infected with Meloidogyne konaensis

Two experiments were conducted to assess nutrient partitioning in coffee (Coffea arabica cv. Typica land race Guatemala) infected with Meloidogyne konaensis. Nutrient levels were quantified from soil, roots, and leaves. In the first experiment, 500-cm3 aliquants of a Kealakekua Andisol were infested with four initial population densities of M. konaensis ranging from 0 to 1,500 freshly hatched second-stage juveniles. Coffee plants (~3 months old) were transplanted into the soil and grown for 25 weeks. Plants responded to nematode infection with decreases (P < 0.05) in concentrations of Ca, Mg, P, and B and increases (P < 0.05) in concentrations of Mn, Cu, Zn, and Ca/B in the roots. Mn and Cu uptake by roots was decreased (P < 0.05) by nematode infection even though concentrations of Mn and Cu increased (P < 0.05) in the roots. Concentrations of Ca and Mg also decreased (P < 0.05) in the leaves, whereas the concentration of Zn increased (P < 0.05). In the second experiment, the soil was amended with Zn at 0 or 5 mg/kg soil and infested with M. konaensis at 0, 100, 1,000 or 10,000 eggs/1,200 cm³ soil. Three-month-old coffee seedlings of similar height were weighed and transplanted into pots and then placed in a greenhouse and grown under 50% shade for 23 weeks. Concentrations of P, K, Ca, Mg, Mn, B, and Zn increased in roots of nematode-free plants growing in Zn-amended soil. The beneficial effects due to the Zn amendment were not apparent in nematode-infected plants. Mn, B, and Zn uptake by coffee roots and P and B concentrations in coffee leaves responded similarly. Management of M. konaensis is necessary to achieve optimal nutrient management in coffee.     

Soil Washing Enhanced by Humic Substances and Biodegradable Chelating Agents

Industrial timber treatment sites have resulted in widespread soil contamination by Cu, Cr, and As, presenting potential long-term liability and associated risks to human health and the environment. This study evaluated the roles of natural humic substances (lignite-derived humic substances, standard and commercially available humic acids) and biodegradable chelating agents (ethylenediamine-N,N-disuccinic acid (EDDS) and glutamic-N,N-diacetic acid (GLDA)) for soil washing. Batch kinetic experiments revealed that humic substances promoted Cu extraction at pH 8, but they were significantly adsorbed on the soil at pH 4, possibly posing impediment to soil remediation. The metal extraction by EDDS and GLDA was comparable to that of EDTA (ethylenediamine-tetraacetic acid), and it was more effective at pH 4 than pH 8, probably due to acidic dissolution of metal precipitates and oxides. Metal distribution analysis indicated that the carbonate fraction of Cu and the oxide fraction of As and Cr were mainly extracted, while the exchangeable fraction of Cu increased. The residual leachability tests showed that humic substances reduced the Cu and As leachability but the reduction was insufficient. In contrast, EDDS was able to reduce the leachate concentrations of Cu and As to below 5 mg L^?1, meeting the waste acceptance criteria for landfill disposal. Nevertheless, soil washing methods and remediation strategy may need further modifications to facilitate site restoration and promote soil recycling.     

Bioavailability and crop uptake of trace elements in soil columns amended with sewage sludge products

In order to assess the potential impact of long-term sewage sludge application on soil health, the equivalent of about 25 years of agronomic applications of low-metal (`EQ') sewage sludge products were made to greenhouse soil columns. After a 6-year period of `equilibration', during which time successive crops were grown with irrigation by simulated acid rain, the plant-available quantities of trace elements were estimated in the soils by extraction with 0.01 M CaCl₂ at 90 °C, and measured directly by uptake into a crop of red clover (Trifolium pratense L.). Soil pH had a strong influence on the level of extractable and plant-available metals, and because the tested sludge products affected soil pH differently, pH was directly factored into the comparison of different sludge treatments with controls. CaCl₂-extractable levels of several metals (Cu, Zn, Mo), sulfur and phosphorus were found to be higher in the soils amended with organic-rich sludge products than in the control soils. However, extractable Cd and Ni were not significantly elevated by the sludge amendments, presumably because of the low total loading of these metals. Copper, Zn and Mo applied in the form of sludge ash had low soil extractability, suggesting that these trace metals were trapped in high-temperature mineral phases formed during sludge incineration, and resisted subsequent weathering in the soil environment. Extractable soil metals in the alkaline-stabilized sludge treatment were also generally low. Phytotoxicity from the sludge metal loadings (Zn≤125, Cu≤135 kg/ha), was not clearly indicated as long as soil pH was maintained in the 6–7 range by lime amendment. Nevertheless, unexplained depressions in yield were noted with some of the sludge products applied, particularly the dewatered and composted materials. On limed soil columns, the most consistent effect of sludge product amendment on red clover composition was a marked increase in plant Mo.     

The effects of micro-organisms on plant growth

Summary Subterranean clover, tomato, phalaris, and radiata pine were grown with a complete plant- nutrient solution in sterile sand and agar and inoculated with soil suspensions prepared from unsterilized and from sterilized soil.The presence of micro-organisms reduced primary-root growth in all plants and total root growth in most plants. The total numbers of secondary roots were lower in non-sterile treatments but there was a tendency for an increase in the concentrations of secondary roots with the non-sterile plants. Under the test conditions only radiata pine grown in sterile sand produced significantly greater top growth than those grown in the presence of micro-organisms. Root-stunting micro-organisms were shown to occur in each of four different soil types used in the studies but the extent of stunting varied with the soil. In agar, root stunting was observed at 5 days and 9 days after planting (and inoculation) with subterranean clover and tomato respectively.Production and growth of root hairs by subterranean clover was markedly reduced by organisms from all four soils tested, the reduction varying with the soil. In contrast to root-stunting organisms, root-hair suppressing micro-organisms were abundant in soil. Root-hair suppression was apparent in sand after 3 days and is an inhibition of root-hair development rather than microbial digestion of existing root hairs. Only slight root-hair reduction was observed for tomato and phalaris.