Changes in molecular structure of biodegradable plastics during degradation in soils estimated by FT-IR and NMR

Among the biodegradable plastic specimens (poly-(3-hydroxy-butylate-valerate) (PHB / V), poly-(ε-caprolactone) (PCL), poly-(butylene succinate) (PBS), poly-(butylene succinate and adipate) (PBSA), and poly-lactide (PLA)) that were placed in soils for 1 year at nineteen sites in Japan, plastic specimens with appreciable biodegradation were studied for the transformation of the chemical structure by FT-IR, ¹H-NMR, and ¹³C-NMR. No appreciable differences in the main absorbency-bands of the atomic groups were recognized by FT-IR for any of the plastic specimens tested. However, both ¹H-NMR and ¹³C-NMR analyses suggested that molecular structure of the PHB / V specimens changed after 1 year placement in soils. Based on the assignment of the respective signals of chemical shifts derived from valerate, selective degradation of the valerate moiety in the PHB / V specimens was observed. In contrast, although weight loss, and/or a decrease in tensile strength and elongation were observed after the placement in soils for the PCL, PBS, PBSA, and PLA specimens, the analyses of these specimens by FT-IR, ¹H-NMR, and ¹³C-NMR did not reveal any changes in their molecular structure.     

Degradation of the herbicide sulfentrazone in a Brazilian Typic Hapludox soil

The herbicide sulfentrazone is classified as highly mobile and persistent and this study aimed to examine degradation of this compound on a Typic Hapludox soil that is representative of regions where sulfentrazone is used in Brazil. Soil samples were supplemented with sulfentrazone (0.7 μg active ingredient (a.i.) g^?1 soil), and maintained at 27 °C. Soil moisture was corrected to 30%, 70%, or 100% water-holding capacity (WHC) and maintained constant until the end of the experimental period. Soils without added herbicide were used as controls. Aliquots were taken after 14, 30, 60, 120, 180, and 255 days of incubation for quantitative analysis of sulfentrazone residues by gas chromatography. Another experiment was conducted in soil samples, with and without the herbicide, at different temperatures (15, 30, and 40 °C), with moisture kept constant at 70% of WHC. The sulfentrazone residues were quantified by gas chromatography after 14, 30, 60, and 120 days of incubation. Sulfentrazone degradation was not affected by soil moisture. A significant effect was observed for the temperature factor after 120 days on herbicide degradation, which was higher at 30 °C. A half-life of 146.5 days was recorded. It was observed that the herbicide stimulated growth of actinomycetes, whereas bacterial and fungal growth was not affected. The microorganisms selected as potential sulfentrazone degraders were Rhizobium radiobacter, Ralstonia pickettii, Methylobacterium radiotolerans, Cladosporium sp., Eupenicillium sp., and Paecilomyces sp.     

Reduction in viability of sclerotia of Macrophomina phaseolina with polyethylene mulching of soil

Mulching of Macrophomina phaseolina-inksted soil (moist or dry) with transparent polyethylene sheets during the hot days of May increased temperature of wet soil at 5 cm from 37°C (unmulched) to 52°C (mulched) and of dry soil from 52°C (unmulched) to 65°C (mulched). At 20 cm mulching increased temperature from 30°C to 41°C (wet) and from 38°C to 42°C (dry). In artificially-infested soil. the sclerotia of M. phaseolina were eradicated at 5 cm by a mulch treatment for 1 week and at 20 cm depth 50% sclerotia lost viability in wet soil but were not affected in dry soil. In a naturally infested soil (5–7 sclerotia g^?1), which gave 20% infection on Vigna, the sclerotia were reduced to such an extent that after 1 week mulching no disease was observed on Vigna.     

Interaction study of biochar with phosphate-solubilizing bacterium on phosphorus availability in calcareous soil

A large proportion of phosphate fertilizer applied to calcareous soils reacts with calcium. Changes in soil phosphorus (P) availability after single application of biochar and phosphate-solubilizing bacteria have been reported. However, interaction of biochar (increasing soil pH) and phosphate-solubilizing bacteria (decreasing soil pH) on P availability in calcareous soil is not well known. An incubation experiment was conducted to study how the interactive effects of biochars (produced from wheat straw and cow manure at 300°C and 500°C with residence time of 1, 3 and 6 h) at different rates (0, 5 and 10 t ha^?1) and phosphate-solubilizing Pseudomonas sp. IS8b2 affected on content of soil available P after 0, 60, 120 and 180 days of incubation (DOI) in a calcareous soil. After 60 DOI, the maximum value of available P (50.31 mg kg^?1) was observed in the compound treatment of Pseudomonas sp. IS8b2 and wheat straw biochar (10 t ha^?1) produced at 500°C with residence time of 3 h. We conclude that the combination use of wheat straw biochar and phosphate-solubilizing bacterium is promising to potentially improve soil P availability in calcareous soil, but further research at field scale is needed to confirm this.     

Thermogravimetric evaluation of chitin degradation in soil: implication for the enhancement of ammonification of native organic nitrogen by chitin addition

Degradation of chitin, which is an aminopolysaccharide used as a soil amendment, has been often monitored in soil via its degradation products such as carbon dioxide and ammonium. We report here the applicability of thermogravimetry to measure the amount of chitin added to soil. The maximum pyrolysis rate of the upland surface soil of Brown Forest soil supplemented with chitin was strongly correlated with added chitin content (r = 0.999) when the content exceeded 6.0 g kg^?1. The maximum pyrolysis rates of chitin-added soil (around 385°C) was distinctive from those of soil supplemented with cellulose, chitosan, N-acetylglucosamine, and N,N’-diacetylchitobiose (around 340°C, 300°C, 200°C, and 240°C, respectively), indicating the specific detection of chitin. Soil incubation study demonstrated that 60 g kg^?1 chitin added to the soil declined exponentially (r = 0.993) within days and could not be detected at 90 days after the addition of chitin. Total carbon (C) content also decreased within days whereas total nitrogen (N) remained almost constant over the 90 days. The amount of ammonium-N increased in the initial 30 days after the addition of chitin and reached about 3.6 g kg^?1, which corresponded to the amount of N in the added chitin (4.1 g kg^?1) while the amount of nitrite-N and nitrate-N were below 2.0 and 15 mg kg^?1, respectively. Comparison of the measured ammonium-N and total-C contents with those calculated from the measured chitin-content implied that addition of chitin enhanced degradation of native organic compounds in soil.     

Spatial location of carbon decomposition in the soil pore system

We sought to examine the distribution of carbon (C) decomposition within the framework of the soil pore system. Soils were sampled from a transect having a natural gradient in pore‐size distribution. After the addition of labelled wheat straw (¹³C) the repacked soil columns were incubated (25°C) at soil water matric potentials of either ?75 kPa or ?5 kPa and for either 4 or 90 days. Pore‐size distribution was determined for each soil column after incubation and soils were then analysed for soluble C, label‐derived residual C, label‐derived and native biomass C, nematode abundance, and ergosterol concentration as an indicator of fungal biomass. Overall, the data suggested that pore‐size distribution and its interaction with soil water give rise to a highly stratified biogeography of organisms through the pore system. This results in different rates of decomposition in pores of different size. Added plant material seemed to decompose most rapidly in soils with a relatively large volume of pores with neck diameters c. 15–60 µm and most slowly in soils with large volumes of pores with neck diameters < 4 µm. Regression analysis suggested that at matric potentials of both ?75 kPa and ?5 kPa the fastest decomposition of organic substrate occurred close to the gas–water interface. This analysis also implied that slower rates of decomposition occur in the pore class 60–300 µm. Correlations between the mass of soil biota and the pore volume of each pore class point to the importance of fungi and possibly nematodes in the rapid decomposition of C in the pores c. 15–60 µm during the early stages of decomposition.     

Growth and nitrogenous excretion of a common soil flagellate Spumella sp.—a laboratory experiment

The growth and nitrogenous excretion of a common soil flagellate, Spumella sp., isolated from a Scottish podzol and fed with the common soil bacterium, Pseudomonas fluorescens, were investigated. Video-enhanced light microscopy and transmission electron microscopy were used to study the digestion process. Ingestion of the bacteria occurred rapidly at the base of the two flagella and involved the formation of a small protrusion, which surrounded the prey. The first signs of digestion appeared a few minutes after ingestion with the degradation of the outer membrane of the bacteria. Digestion was complete within 30–60 min, and the indigestible bacterial residues were then released into the medium. Ammonium nitrogen was the major form of nitrogen excreted. Some apparently intact P. fluorescens bacteria were also egested. For each division 130 bacteria were required. No feeding activities were observed at 5°C. Of the total bacterial protein, 42% was incorporated into biomass of flagellates.     

Plant growth promoting potential of psychrotolerant Dyadobacter sp. for pulses and finger millet and impact of inoculation on soil chemical properties and diazotrophic abundance

Western Indian Himalaya is very rich in biodiversity. Being a cold climatic region, it possesses various psychrotolerant and psychrophilic microorganisms. Psychrotolerant bacterium Dyadobacter sp. was isolated from this region and studied for its plant growth promoting potential against four legumes and finger millet. This bacterium was able to grow at nitrogen (N) deficient medium at both 10°C and 28°C and gave positive nifH amplification that confirms the psychrotolerant and diazotrophic nature of this bacterium. Pot trial-based study showed that this bacterium was able to promote plant growth by fixing atmospheric nitrogen (N₂) and making it available to plants. Agronomical parameters, leaf nitrate reductase activity, and total chlorophyll content were recorded at 30, 45, 60, and 90 days after sowing and found to be increased over their respective controls. The 16S rDNA and nifH genes were quantified by q-PCR to study the dynamics of total bacterial and diazotrophic abundance due to inoculation of Dyadobacter sp. in soil. Soil chemical properties related to soil fertility were also studied at different time intervals after sowing. We found positive correlation among soil pH, soil nifH gene abundance, soil nitrate concentration, and plant leaf nitrate reductase activity. PCR-DGGE was performed to study persistence of Dyadobacter sp. in soil after inoculation, which showed good persistence of plant growth promoting rhizobacteria (PGPR). Hence, it is concluded that Dyadobacter sp. has potential to promote plant growth by fixing atmospheric N₂ and making it available to plant. Further, psychrotolerant nature of this bacterium can be exploited to enhance plant growth in cold climate agriculture due to its ability to fix atmospheric N₂ at low temperature.     

Effect of temperature and flooding duration on phosphate sorption in an acid sulphate soil from Vietnam

Phosphate sorption in soil is controlled largely by Fe-oxihydroxides, and so important changes in P dynamics are expected when the redox potential is modified. Such changes in P sorption when acid soil is flooded, as for rice cultivation, have been evaluated. Samples from an acid sulphate soil in the Mekong Delta of Vietnam were flooded for up to 56 d at 20°C and 30°C. Some of the samples incubated at 30°C were dried in open air for 30 d after flooding. Small redox potential (Eh<0) and pH>6 were rapidly reached in soil flooded at 30°C; less drastic reducing conditions (Eh ?0.2 V) and pH 4–5 occurred at 20°C. Phosphate sorption increased during flooding. The increase was twofold at 20°C, and 10-fold at 30°C. Phosphate sorption index decreased in the soil that was air dried after flooding at 30°C, but still remained two to three times greater than before flooding. These results were compared to the changes in oxalate-extractable Fe, i.e. poorly crystalline or amorphous Fe-oxihydroxides. The increase of P sorption per unit increase of oxalate-Fe was seven to eight fold larger at 30°C than at 20°C.     

百菌清降解菌株H4的分离与表征及其修复污染土壤的潜能研究

A chlorothalonil(CTN)-degrading bacterial strain H4 was isolated in this study from a contaminated soil by continuous enrichment culture to identify its characteristics and to investigate its potential for remediation of CTN in contaminated soil. Based on the morphological, physiological and biochemical tests and 16 S r DNA sequence analysis, the strain was identified as Stenotrophomonas sp. After liquid culture for 7 d, 82.2% of CTN was removed by strain H4. The isolate could degrade CTN over a broad range of temperatures and p H values, and the optimum conditions for H4 degradation were p H 7.0 and 30℃. Reintroduction of the bacteria into artificially contaminated soil resulted in substantial removal of CTN( 50%) after incubation for 14 d. Soil samples treated by H4 showed significant increases(P 0.05) in soil dehydrogenase activity, soil polyphenol oxidase activity, average well-color development obtained by the Biolog Eco plate TM assay and Shannon-Weaver index, compared with the control. Strain H4 might be a promising candidate for application in the bioremediation of CTN-contaminated soils.     

Metabolism of fluoroacetate by a soil Pseudomonas SP. and Fusarium solani

Enzymes (haloacetate halidohydrolases) capable of cleaving the C-F bond of fluoroacetate and some other organofluorine compounds have been isolated and partially purified from a soil pseudomonad and from the common soil fungus Fusarium solani. Both enzymes readily released F^? from monofluoroacetate and fluoroacetamide but were without effect on a wide range of other organic F-compounds. The enzymes also cleaved the C-Cl and C-Br bonds in mono-chloroacetate and monobromoacetate. Inorganic F^? acted as a competitive inhibitor of the enzymes. The molecular weights of both enzymes were about 62,000. Thus the properties of the halidohydrolases from both organisms were similar in many respects but the bacterial enzyme was more stable at 55°C and exhibited an unusual difference in temperature coefficient (Q₁₀ value) over its higher (30–55°C) and lower (15–30°C) temperature ranges.     

14C-labelled maleic hydrazide degradation in soil: Influence of temperature,moisture, clay and organic material

¹⁴C-labelled maleic hydrazide (MH) was added to each of three soils at a concentration of 4 mg kg^?1, and its degradation measured by the release of ¹⁴CO₂ after 2 days. Between 1 and 30°C, at a constant moisture content (full field capacity), the mean degradation rate increased by a factor of 3 for each temperature increment of 10°C (Q₁₀ = 3). The mean activation energy was 78 kJ mol^?1. Above 35°C, the degradation rate decreased.At soil moisture contents between wilting point and 80–90% of field capacity, the degradation rate doubled with an increase in moisture content of 50% of field capacity (constant temperature, 25°C). Above field capacity, the degradation rate was either unchanged or decreased. Below wilting point the degradation was very slow, even after 2 months.The rate of decomposition of MH at all temperatures and moisture contents was lowest in the soil with the highest content of organic matter and the lowest clay content. This soil had the highest Freundlich K value, and presumably adsorbed MH the most strongly, although the lower clay content may also play a role in the lower decomposing capacity of this soil.     

Growth of Gaeumannomyces graminis var. tritici in soil: Effects of temperature and water potential

The effects of temperature and water on the growth of the take-all fungus, Gaeumannomyces graminis var. tritici (Ggt), were examined in two factorial experiments. The first examined the effects of temperature and water potential on the growth of two isolates of Ggt on agar media, using osmotically-adjusted water potentials. The second experiment was concerned with the growth of the Ggt isolates in one sterile and two natural soils at two water regimes in the absence of a living host. Three temperatures (10, 18 and 26°C) were used in these experiments. A third experiment determined growth through soil.Growth was greatest at high temperatures and low water potential in axenic culture, but in unsterile soil growth at different temperatures and water potentials was strongly influenced by competition from the soil biota. The best temperature for growth in unsterile soil was 18°C. Growth at 26°C in unsterile soil was greatly reduced, this being attributed to more intense microbial competition. In sterile soil Ggt grew equally well at 18 and 26°C. At 10°C, both isolates of Ggt grew better in unsterile soil than in sterile soil.Under suitable conditions Ggt grew out readily from infected straw into unsterile soil (up to 5 cm in 10 days) in the absence of a host plant, forming melanized, hyaline and branched hyphae. These hyphae were infectious after dry storage for 5 months in the laboratory. Ggt thus appears to be a more successful soil inhabitant than is widely believed. Our experiments could explain many of the host-based concepts related to field expression of disease.The technique presented here could be of value for testing the suppressiveness or conduciveness of soils by measuring fungal growth in soil.     

Microbial and non-biological decomposition of chlorophenols and phenol in soil

The aerobic and anaerobic degradation of phenol and selected chlorophenols was examined in a clay loam soil containing no added nutrients. A simple, efficient procedure based on the high solubility of these compounds in 95% ethanol was developed for extracting phenol and chlorophenol residues from soil. Analysis of soil extracts with UV spectrophotometry showed that phenol,o-chlorophenol,p-chlorophenol, 2,4-dichlorophenol, 2,6-dichlorophenol and 2,4,6-trichlorophenol were rapidly degraded, whilem-chlorophenol, 3,4-dichlorophenol, 2,4,5-trichlorophenol and pentachlorophenol were degraded very slowly by microorganisms in aerobically-incubated soil at 23°C. Both 3,4,5-trichlorophenol and 2,3,4,5-tetra chlorophenol appeared to be more resistant to degradation by aerobic soil microorganisms at 23°C. None of the compounds examined were degraded by microorganisms in anaerobically-incubated soil at 23°C. Direct microscopic observation revealed that phenol and selected chlorophenols stimulated aerobic and to a lesser extent, anaerobic microbial growth in soil, and aerobic soil bacteria were responsible for the degradation of 2,4-dichlorophenol in aerobically-incubated soil at 23°C. Phenol,o-chlorophenol,m-chlorophenol,p-chlorophenol and 2,4-dichlorophenol underwent rapid non-biological degradation in sterile silica sand. Non-biological decomposition contributed, perhaps substantially, to the removal of some chlorophenols from sterile aerobically-incubated soil and both sterile and non-sterile anaerobically-incubated soil.     

Ethion degradation and its correlation with microbial and biochemical parameters of tea soils

Ethion, a highly persistent insecticide in soil, is extensively used in tea cultivation in the tropics. The studies on the environmental impact of ethion in tea soil ecosystems are scanty. Silty loam and sandy loam soils from tea fields of Dooars (Typic Uderthents) and Hill (Typic Dystrudepts), respectively, were investigated for the degradation and effect of ethion application on soil microbial and biochemical variables under controlled laboratory conditions. Ethion degraded faster in the Hill soil than in the Dooars soil. Higher temperature (30°C) aided in faster degradation due to the increased microbial activity in the soils. Ethion application at field rate (FR) had lower half-lives (70 days at 20°C and 42.3 days at 30°C for Dooars soil; 65.4 days at 20°C and 39 days at 30°C for Hill soil) than at ten times FR (10FR; 75.2 days at 20°C and 44.2 days at 30°C for Dooars soil; 70 days at 20°C and 41.8 days at 30°C for Hill soil). Soil microbial biomass carbon, ergosterol content, fluorescein diacetate hydrolyzing and β-glucosidase activities declined in all the treatment combinations up to day 60 for both FR and 10FR doses at 20°C, irrespective of the soil types. At 30°C, the decreasing trend was observed up to day 30 for both the soils. The toxicological effect of ethion on microbiological and biochemical parameters persisted till their corresponding half-lives. The microbial metabolic quotient and microbial respiration quotient were altered, but was short-lived, indicating ethion induced disturbances. The recovery of the depressive action at 10FR ethion spiking on the studied variables was of slightly longer duration than noticed at FR application, although the depressive effect was overcoming after the respective half-lives of ethion. The microbial and biochemical soil parameters were negatively correlated with application of ethion up to day 60 of incubation.     

Effect of soil solarization on subsequent nitrification activity at elevated temperatures

Soil solarization is a nonchemical method of soil disinfection achieved by covering the soil surface with sheets of vinyl plastic to generate elevated soil temperature, generally over 45°C. Such elevated temperatures may be detrimental to some nitrifying microorganisms and favorable to others. However, little information exists to indicate how nitrification activity in soil is affected after solarization. We performed several experiments to investigate the effects of soil solarization on nitrification activity. We found that: (1) if a soil was subjected to pretreatment of 45 or 50°C for as little as 1 d, nitrification activity in a subsequent incubation at 30°C was less than that of a soil that did not receive any high-temperature pretreatment. However, if a soil received pretreatments of 45 or 50°C for more than 7 d, nitrification activity in a subsequent incubation at 45 or 50°C was greater than that of soil that did not receive high temperature pretreatment. (2) Nitrification activity in three kinds of soil taken from 0–5 cm depth after solarization treatment was greater at 45°C than 30°C. (3) Nitrification activity at 45°C in soil that had received solarization in the preceding year was greater than that in soil that had not been subjected to solarization. This was consistent with the fact that the population densities of ammonia oxidizers were greater in soils that had been subjected to solarization. These results suggest that soil solarization induces nitrifying microorganisms that are more active at 45–50°C than they are at 30°C, and that the effect of solarization on nitrification persists until the next crop season.     

Temperature effects on N mineralization: changes in soil solution composition and determination of temperature coefficients by TDR

We studied the changes in composition of the soil solution following mineralization of N at different temperatures, with a view to using TDR to calculate temperature coefficients for the mineralization of N. Mineralization from soil organic nitrogen was measured during aerobic incubation under controlled conditions at six temperatures ranging from 5.5 to 30°C, and at constant water content in a loamy sand soil. We also monitored during the incubation the concentrations of SO₄^2–, Cl^–, HCO₃^–, Ca²⁺, K⁺, Mg²⁺ and Na⁺, and the pH and the electrical conductivity in 1:2 soil:water extracts. Zero‐order N mineralization rates ranged between 0.164 at 5.5°C and 0.865 mg N kg^?1 soil day^?1 at 30°C. There was a significant decrease in soil pH during incubation, of up to 0.6 pH units at the end of the incubation at 30°C. The electrical conductivity of the soil extracts increased significantly at all temperatures (the increase between the start and the end of the incubation was 4‐fold at 30°C) and was strongly correlated with N mineralization. The ratio of bivalent to monovalent cations increased markedly during mineralization (from 2.2 to 5.9 at 30°C), and this increase influenced the evolution of the electrical conductivity of the soil solution through the differences in molar‐limiting ion conductivity between mainly Ca²⁺ and K⁺. Zero‐order mineralization rate constants, k, for NO₃^– concentrations calculated from TDR varied between 0.070 (at 5.5°C) and 0.734 mg N kg^?1 soil day^?1 (at 30°C), which were slightly smaller, but in the same range, as the measured rates. Underestimation of the measured N mineralization rates was due, at least in part, to differences in cation composition of the soil solution between calibration and mineralization experiments. A temperature‐dependence model for N mineralization from soil organic matter was fitted to both the measured and the TDR‐calculated mineralization rates, k and k_TDR, respectively. There were no significant differences between the model parameters from the two. Our results are promising for further use of TDR to monitor soil organic N mineralization. However, the influence of changing cation ratios will also have to be taken into account when trying to predict N mineralization from measured electrical conductivities.     

Influence of soil temperature and soil compaction on growth and P uptake of sugar beet

Sugar beet growth is often impaired by cold and compacted soil. The aim of this study was to determine the effect of soil temperature and soil compaction on the growth and function of sugar beet roots. For this purpose a pot experiment with sugar beet (Beta vulgaris) was conducted in a growth chamber in which the soil temperature was kept constant either at 10°C or 20°C and air temperature at 20°C. The soil was uncompacted (1.30 g cm^?3) or compacted to a bulk density of 1.65 g cm^?3. In order to find out whether growth restriction was caused by insufficient P supply of the plant the experiment was run without and with P application (300 mg per kg soil). Root growth was much smaller at 10°C compared to 20°C, whereas root/shoot ratio was not affected by soil temperature. Hence, root and shoot growth was inhibited to the same extent. P content of the plants was not reduced, neither by cold nor by compacted soil, although parameters of acquisition such as root length and morphological root properties were altered. Soil temperature strongly affected P influx, whereas compaction did not. The calculation with a simulation model showed that at 10°C soil temperature the predicted P uptake of the plants agreed with the measured P uptake irrespective of compaction and P application. However, at 20°C the model underestimated the P influx at low soil P availability even if allowance was made for root hairs. It is concluded that under conditions of high shoot P demand and low P availability in soil P has been mobilized by mechanisms not taken into account by the model.     

Polyethylene mulching of soil to reduce viability of sclerotia of Sclerotium oryzae

Mulching of Sclerotium oryzae infested soil (moist or dry) with polyethylene sheets during hot summer days of May and June increased the soil temperature at 5 cm from 36°C (unmulched) to 48°C (wet) and from 44 to 52°C (dry) and at 20cm from 32 to 38°C (wet) and from 35 to 39°C (dry). In artificially-infested soil, the sclerotia were not eradicated but 95–100% loss in viability was observed at 5 cm by a mulch treatment for 1 week and at 20 cm by mulching for 8 weeks. Mulching effects were not influenced by moisture content of soil or by amendments with lucerne or wheat straw. Mulching of naturally-infested soil at a second site did not eradicate S. oryzae but reduced sclerotial viability by 93%.     

Inoculation with phosphate-solubilizing microorganisms and a vesicular-arbuscular mycorrhizal fungus improves dry matter yield and nutrient uptake by wheat grown in a sandy soil

 The effect of inoculating wheat (Triticum aestivum L.) with the PO₄ ^3–-solubilizing microorganisms (PSM) Bacillus circulans and Cladosporium herbarum and the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus sp. 88 with or without Mussoorie rock phosphate (MRP) amendment in a nutrient-deficient natural sandy soil was studied. In the sandy soil of low fertility root colonization by VAM fungi was low. Inoculation with Glomus sp. 88 improved root colonization. At maturity, grain and straw yields as well as N and P uptake improved significantly following inoculation with PSM or the VAM fungus. These increases were higher on combined inoculation of PSM and the VAM fungus with MRP amendment. In general, a larger population of PSM was maintained in the rhizosphere of wheat in treatments with VAM fungal inoculation and MRP amendment. The results suggest that combined inoculation with PSM and a VAM fungus along with MRP amendment can improve crop yields in nutrient-deficient soils. Received: 4 September 1997