Soil types with different texture affects development of Rhizoctonia root rot of wheat seedlings

The effect of different soil textures, sandy (97.5% sand, 1.6% silt, 0.9% clay), loamy sand (77% sand, 11% silt, 12% clay) and a sandy clay loam (69% sand, 7% silt, 24% clay), on root rot of wheat caused by Rhizoctonia solani Kühn Anastomosis Group (AG) 8 was studied under glasshouse conditions. The reduction in root and shoot biomass following inoculation with AG-8 was greater in sand than in loamy sand or sandy clay loam. Dry root weight of wheat in the sand, loamy sand and sandy clay loam soils infested with AG-8 was 91%, 55% and 28% less than in control uninfested soils. There was greater moisture retention in the loamy sand and sandy clay loam soils as compared to the sand in the upper 10–20 cm. Root penetration resistance was greater in loamy sand and sandy clay loam than in sand. Root growth in the uninfested soil column was faster in the sand than in the loamy sand and sandy clay loam soils, the roots in the sandy soil being thinner than in the other two soils. Radial spread of the pathogen in these soils in seedling trays was twice as fast in the sand in comparison to the loamy sand which in turn was more than twice that in the sandy clay loam soil. There was no evidence that differences among soils in pathogenicity or soil spread of the pathogen was related to their nutrient status. This behaviour may be related to the severity of the disease in fields with sandy soils as compared to those with loam or clay soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

Impact of Rotylenchulus reniformis on Cotton Yield as Affected by Soil Texture and Irrigation

The effects of soil type, irrigation, and population density of Rotylenchulus reniformis on cotton were evaluated in a two-year microplot experiment. Six soil types, Fuquay sand, Norfolk sandy loam, Portsmouth loamy sand, Muck, Cecil sandy loam, and Cecil sandy clay, were arranged in randomized complete blocks with five replications. Each block had numerous plots previously inoculated with R. reniformis and two or more noninoculated microplots per soil type, one half of which were irrigated in each replicate for a total of 240 plots. Greatest cotton lint yields were achieved in the Muck, Norfolk sandy loam, and Portsmouth loamy sand soils. Cotton yield in the Portsmouth loamy sand did not differ from the Muck soil which averaged the greatest lint yield per plot of all soil types. Cotton yield was negatively related to R. reniformis PI (initial population density) in all soil types except for the Cecil sandy clay which had the highest clay content. Supplemental irrigation increased yields in the higher yielding Muck, Norfolk sandy loam, and Portsmouth loamy sand soils compared to the lower yielding Cecil sandy clay, Cecil sandy loam, and Fuquay sand soils. The Portsmouth sandy loam was among the highest yielding soils, and also supported the greatest R. reniformis population density. Cotton lint yield was affected more by R. reniformis Pi with irrigation in the Portsmouth loamy sand soil with a greater influence of Pi on lint yield in irrigated plots than other soils. A significant first degree PI × irrigation interaction for this soil type confirms this observation.     

Nitrogen mineralisation in soils of varying texture,moisture and organic matter

Summary Estimates of nitrogen availability based on the nitrogen mineralisation potential,N ₀, and the mineralisation rate constant,k, increased within the sequence, loamy sand, coarse sandy loam and loam, and were consistently higher in the high labile organic matter counterparts of the soils. There was a similar trend in the production of inorganic nitrogen at ambient temperatures. Under these conditions, an increase between mid-April and the end of May was followed by a trough in June and July and a second increase from early August to the end of September. Nitrogen production was generally higher where soil moisture was allowed to fluctuate widely in the available range, compared with a moisture regime near field capacity. Results of short-term incubations indicated that net mineralisation was minimal or negative in June and July.There was a significant relationship between values calculated fromN ₀ andk and those obtained near field capacity in the second period of mineralisation when soil temperature was relatively constant, but not in the first period when soil temperature was rising.The time required for mineralisation of 50% ofN ₀ indicated that less than half the potential value would become available in a normal temperature growing season.     

Tillage,crop residue,legume rotation,and green manure effects on sorghum and millet yields in the semiarid tropics of Mali

Alternative soil management practices are needed in semi-arid West Africa to sustain soil fertility and cereal production while reducing the need for extended fallow periods and chemical fertilizers. An experiment was conducted at the Cinzana Station near Segou, Mali to assess the effects of tillage, crop residue incorporation and legume rotation on the growth and yield of sorghum (Sorghum bicolor L. Moench) and pearl millet (Pennisetum glaucum L.) for a period of eight years on a loamy sand and a loam soil. The following treatments were compared under tied ridging and the traditional open ridging: continuous cereal with crop residue removed, continuous cereal with crop residue incorporated, cereal in rotation with cowpea (Vigna unguiculata (L.) Waip.), cereal in rotation with sesbania (Sesbania rostrata Bremek. & Oberm.), and cereal in rotation with dolichos (Dolichos lablab L.). Legumes in rotation were incorporated as green manures except cowpea which was removed after each harvest. Tied ridging improved cereal grain yield from 1022 kg ha⁻¹ with open ridging to 1091 kg ha⁻¹ on the loamy sand and from 1554 kg ha⁻¹ to 1697 kg ha⁻¹ on the loam, when averaged across management regimes and years of cropping. Incorporation of cereal residue at the beginning of the rainy season every other year had only small and inconsistent effects on cereal yield. Rotation with cowpea increased cereal grain and stover yields by 18 and 25%, respectively, on the loamy sand, and by 23% and 27%, respectively, on the loam compared to continuous cereal, when averaged across tillage regimes and years. Sesbania and dolichos performed similarly as green manures on both soils. Incorporation of these legumes as green manure at the end of the rainy season increased cereal grain and stover yields by 37% and 49%, respectively, on the loamy sand, and by 27% and 30%, respectively, on the loam, compared to cereal monoculture without organic amendment, when averaged across tillage regimes and years. A significant linear increase in cereal yield was observed during the eight years of the study on the loam soil when sesbania and dolichos green manures were incorporated. This revised version was published online in June 2006 with corrections to the Cover Date.     

Incubation studies on mineralization of organic sulphur and organic nitrogen

Summary Incubation studies were carried out to investigate the release of sulphur and nitrogen in West Indian soils. Sulphur and nitrogen released or fixed were estimated at 10 days intervals up to 60 days incubation period.All the soils released sulphate when incubated at 30°C. A rapid initial flush of mineralization of both sulphur and nitrogen took place in Cocal fine sand and Montreal sandy loam. In Piarco sandy clay loam and Mayaro sandy loam sulphur mineralization was not accompanied by a concomitant mineralization of nitrogen. An inconsistent pattern of release of sulphur and nitrogen was noticed in Montserrat clay, Akers sandy clay loam, Bellevue sandy clay loam and Soufriere cindery gravelly loamy sand.The release of sulphur does not appear to be related to the total amount of carbon, nitrogen or sulphur. Nitrogen mineralized was significantly correlated with total nitrogen and total sulphur. The correlation between organic matter and nitrogen mineralized was highly significant (r=0.87^**) whereas with sulphur mineralized it did not reach significance. This suggests that nitrogen and sulphur are not mineralized at the same rate in these soils.     

Effect of soil type on infectivity and persistence of the entomopathogenic nematodes Steinernema scarabaei, Steinernema glaseri, Heterorhabditis zealandica, and Heterorhabditis bacteriophora

We tested the effect of soil type on the performance of the entomopathogenic pathogenic nematodes Steinernema scarabaei, Steinernema glaseri, Heterorhabditis zealandica, and Heterorhabditis bacteriophora. Soil types used were loamy sand, sandy loam, loam, silt loam, clay loam, acidic sand, and a highly organic potting mix. Infectivity was tested by exposing third-instar Anomala orientalis or Popillia japonica to nematodes in laboratory and greenhouse experiments and determining nematode establishment in the larvae and larval mortality. Infectivity of H. bacteriophora and H. zealandica was the highest in potting mix, did not differ among loamy sand and the loams, and was the lowest in acidic sand. Infectivity of S. glaseri was significantly lower in acidic sand than in loamy sand in a laboratory experiment but not in a greenhouse experiment, and did not differ among the other soils. Infectivity of S. scarabaei was lower in silt loam and clay loam than in loamy sand in a greenhouse experiment but not in a laboratory experiment, but was the lowest in acidic sand and potting mix. Persistence was determined in laboratory experiments by baiting nematode-inoculated soil with Galleria mellonella larvae. Persistence of both Heterorhabditis spp. and S. glaseri was the shortest in potting mix and showed no clear differences among the other substrates. Persistence of S. scarabaei was high in all substrates and its recovery declined significantly over time only in clay loam. In conclusion, generalizations on nematode performance in different soil types have to be done carefully as the effect of soil parameters including soil texture, pH, and organic matter may vary with nematode species.     

Transport of bacterial inoculants through intact cores of two different soils as affected by water percolation and the presence of wheat plants

Abstract Water flow-innduced transport of Burkholderia cepacia strain P2 and Pseudomonas fluorescens strain R2f cells through intact cores of loamy sand and silt loam field soils was measured for two percolation regimes, 0.9 and 4.4 mm h⁻¹, applied daily during 1 hour. For each strain, transport was generally similar between the two water regimes. Translocation of B. cepacia , with 4.4 mm h⁻¹, did occur initially in both soils. In the loamy sand soil, no change in the bacterial distribution occurred during the experiment (51 days). In the silt loam, B. cepacia cell numbers in the lower soil layers were significantly reduced, to levels at or below the limit of detection. Transport of P. fluorescens in both soils also occurred initially and was comparable to that of B. cepacia . Later in the experiment, P. fluorescens was not detectable in the lower soil layers of the loamy sand cores, due to a large decrease in surviving cell numbers. In the silt loam, the inoculant cell distribution did not change with time. Pre-incubation of the inoculated cores before starting percolation reduced B. cepacia inoculant transport in the loamy sand soil measured after 5 days, but not that determined after 54 days. Delayed percolation in the silt loam soil affected bacterial transport only after 54 days. The presence of growing wheat plants overall enhanced bacterial translocation as compared to that in unplanted soil cores, but only with percolating water. Percolation water from silt loam cores appeared the day after the onset of percolation and often contained inoculant bacteria. With loamy sand, percolation water appeared only 5 days after the start of percolation, and no inoculant bacteria were found. The results presented aid in predicting the fate of genetically manipulated bacteria in a field experiment.     

The influence of soil texture on the soil water dynamics and vegetation structure of a shortgrass steppe ecosystem

We analyzed soil water data from three sites with different soil textures in the shortgrass steppe of northeastern Colorado, USA. Our objective was to evaluate the relationship between the occurrence of plant functional types and the effect of soil texture on soil water availability. Soil water availability was greatest in the upper soil layers at all three sites, but the loamy sand site had significantly greater soil water availability than the sandy clay loam and sandy clay sites in wetter years at depths below 60 cm. Calculations of proportional water availability by layer using both field data and fifty-year soil water model simulations, showed that the sandy clay loam and sandy clay soils on average had greater water availability in layers 30 cm and above, but that the loamy sand had the greatest water availability in layers beneath this, particularly at 105 cm. This observation can be linked to the occurrence of a fine textured subsoil at this site. The textural pattern in the loamy sand profile effectively creates two water resources: a shallow pool accessible to all plants; and a deep pool accessible only to deep-rooted plants. This is offered as an explanation for the co-dominance of the two main plant functional types at the loamy sand site. At the other two sites, shallow-rooted shortgrass vegetation dominated, being more consistent with the general pattern for the area. Thus the patterns of vegetation structure at the three sites were consistent with the hypothesis. Aboveground net primary production data for the three sites, along with transpiration estimates from the model simulations, indicated that the additional water availability in the coarse textured soil was associated with higher overall plant productivity.Nomenclature: Taxonomic nomenclature follows R. L. McGregor & T. M. Barkley (1986) Flora of the Great Plains. Great Plains Flora Association. University Press of Kansas, Lawrence.     

Impact of soil types on chemical composition of essential oil of purple basil

Purple basil is among the most important basil varieties and its essential oil is used for several purposes including medicinal and aromatic uses. Soil types may impact the plant growth, development, and essential oil composition. Hence, it is important to find the most suitable soil type which may produce basil plants having essential oil with the best composition and concentration. For this reason, plant samples of purple basil that were grown in areas with clay, loamy sand, and sandy-clay loam soil types were collected and evaluated to determine the changes in the yield and essential oil components. Essential oil contents were determined with the Clevenger Device, and essential oil compositions were determined by using GC and GC/MS analysis. The highest essential oil yield according to soil types was obtained from the plant samples that were grown in the loamy sand soil. It was also found that the main compounds present in Arapgir town purple basil were methylcinnamate and linalool that was also present in all Turkish purple basil under all types of soil. According to the soil types, the highest concentration (46.03%) of methylcinnamate was observed in loamy sand soils, and the lowest (42.33%) was obtained from sandy-clay loam soils and found to be significantly different. Data regarding correlations between soil types and essential oil ratios showed that organic matter and P₂O₅ had a significant negative correlation with methylcinnamate. The present study will help researchers and farmers to choose the most suitable soil type to achieve maximum essential oil production from purple basil.     

Transfer of plasmid RP4 between pseudomonads after introduction into soil; influence of spatial and temporal aspects of inoculation

Abstract Transfer of plasmid RP4 between introduced strains of Pseudomonas fluorescens was studied in 2 soils, Ede loamy sand and Guelph loam, in non-rhizosphere and rhizosphere soil using soil chambers and microcosm systems. Short-term organism survival was generally at high levels (> 10⁶/g dry soil), in both soils, whereas long-term survival was poorer, particularly in the loamy sand. Amendment of this soil with bentonite clay improved bacterial survival. Plasmid transfer between donor and recipient strains freshly introduced into separate portions of Ede loamy sand, which were subsequently mixed, was only detected in the vicinity of growing wheat roots, suggesting roots stimulate bacterial migration and/or growth. However, no transfer was detected between resident donor and recipient cell populations (introduced 48 days previously), due to poor organism survival. Plasmid transfer was detected in the rhizosphere between established, resident donor cell populations, and newly-introduced recipients, and vice-versa, in both soils. These data suggested that plant roots enhance the frequency of bacterial matings not only between organisms present in the same niches, but also between organisms from different niches, or in different conditions of stress, probably by stimulating bacterial migration and/or growth, or by providing additional surfaces for cell-to-cell contact.     

Quantifying the effect of soil moisture content on segmenting root system architecture in X-ray computed tomography images

Aims

A commonly accepted challenge when visualising plant roots in X-ray micro Computed Tomography (μCT) images is the similar X-ray attenuation of plant roots and soil phases. Soil moisture content remains a recognised, yet currently uncharacterised source of segmentation error. This work sought to quantify the effect of soil moisture content on the ability to segment roots from soil in μCT images.

Methods

Rice (Oryza sativa) plants grown in contrasting soils (loamy sand and clay loam) were μCT scanned daily for nine days whilst drying from saturation. Root volumes were segmented from μCT images and compared with volumes derived by root washing.

Results

At saturation the overlapping attenuation values of root material, water-filled soil pores and soil organic matter significantly hindered segmentation. However, in dry soil (ca. six days of drying post-saturation) the air-filled pores increased image noise adjacent to roots and impeded accurate visualisation of root material. The root volume was most accurately segmented at field capacity.

Conclusions

Root volumes can be accurately segmented from μCT images of undisturbed soil without compromising the growth requirements of the plant providing soil moisture content is kept at field capacity. We propose all future studies in this area should consider the error associated with scanning at different soil moisture contents.     

The influence of fertilizers,soil organic matter and soil compaction on maize yields on the Surinam ‘Zanderij’ soils

Summary In connection with the growing interest in Surinam to exploit the soils in the hinterland, some trials were carried out on Zanderij soils to study productivity, fertilizer need and influence of some special soil factors on yield. The test crop was maize. The yields were generally low which might partly be attributed to the relative dry weather conditions during the trials. On all soils investigated, yield responses to phosphate application were high. On loamy soils there was sometimes a response to nitrogen and on sandy soils to potassium. Yields on sands were lower than on loamy sands and sandy loams. The most important yield determining soil factor proved to be organic matter. On compacted soils yields were considerably lower which was due to increased mechanical impedance for root growth and in some cases to inadequate aeration. Also published as Bulletin of the Agricultural Experiment Station, Paramaribo, Surinam. Also published as Bulletin of the Agricultural Experiment Station, Paramaribo, Surinam.     

Recovery of soil respiration after drying

Soils are frequently exposed to drying and wetting events and previous studies have shown that rewetting results in a strong but short-lived flush of microbial activity. The aim of this study was to determine the effect of the water content during the dry period on the size and duration of the flush and on the rate of recovery. Two soils (a sand and a sandy loam) were maintained at different water contents (WC) 30, 28 and 25 g water kg^?1 soil (sand) and 130, 105 and 95 g water kg^?1 soil (sandy loam) for 14 days, then rewet to the water content at which respiration was optimal [WC 35 (sand), WC200 (sandy loam)] and maintained at this level until day 68. Ground pea straw (C/N 26) was added and incorporated on day 1. The controls were maintained at the optimal water content throughout the 68 days. Respiration rates during the dry phase (days 1?C14) decreased with decreasing water content. The flush of respiration after rewetting peaked on day 15 in the sandy loam and on day 16 in the sand; it was greatest in the soils that had been maintained at the lowest water content [WC25 (sand) and WC95 (sandy loam)]. Cumulative respiration during the remainder of the incubation period in which all soils were maintained at optimal water content increased more strongly in the soils that had been dry compared to the constantly moist control. On the final day of the dry period (day 14), cumulative respiration in the dry soils was 29?C65% (sand) and 67?C94% (sandy loam) of the constantly moist control whereas on day 68 it was 80?C84% (sand) and 86?C96% (sandy loam). The greater increase in cumulative respiration in the previously dry soils can be explained by the reduced decomposition rates during the dry period which resulted in higher substrate availability on day 14 compared to the constantly moist control. Microbial community structure assessed by phospholipid fatty acid analyses changed over time in all treatments but was less affected by water content than respiration; it differed only between the highest and the lowest water content. These differences were maintained throughout the incubation period in the sandy loam and transiently in the sand. It can be concluded that the soil water content during the dry phase affects the size of the flush in microbial activity upon rewetting and that microbial activity in previously dried soils may not be fully restored even after 54 days of moist incubation, suggesting that drying of soil can have a significant and long-lasting impact on microbial functioning.     

Nitrogen balance studies for different Egyptian soils cropped with corn

Summary The nitrogen balance for four different Egyptian soils cropped with corn and fertilized with increasing amounts of ammonium sulphate was studied in pot experiments. The tested soils were clay loam, calcareous sandy loam, sandy loam and sand. Nitrogen added as seeds, fertilizers, irrigation water and insecticides, nitrogen removed by the plants including thinned plants and fallen leaves and the nitrogen content of the soils before sowing and after the harvest were determined and used to draw the balance sheet.The obtained results showed that nitrogen loss ranged between 6.8 and 51.5 per cent depending mainly on soil type and to some extent on the rate of applied ammonium sulphate. Nitrogen uptake by the corn plants was lowest from the clay loam soil and highest from the sandy soil. In all cases it increased slightly with the addition of nitrogen fertilizer. re]19720918     

Habitable pore space and survival ofRhizobium leguminosarum biovartrifolii introduced into soil

The hypothesis that the population size of introduced bacteria is affected by habitable pore space was studied by varying moisture content and bulk density in sterilized, as well as in natural loamy sand and silt loam. The soils were inoculated withRhizobium leguminosarum biovartrifolii and established and maintained at soil water potentials between –5 and –20 kPa (pF 1.7 and 2.3). Rhizobial cells were enumerated when population sizes were expected to be more or less stable. In sterilized soils, the rhizobial numbers were not affected or decreased only slightly when water potentials increased from –20 to –5 kPa. In natural soils, the decrease in rhizobial numbers with increasing water potentials was more pronounced. Bulk density had only minor effects on the population sizes of rhizobia or total bacteria. Soil water retention curves of both soils were used to calculate volume and surface area of pores from different diameter classes, and an estimation of the habitable pore space was made. Combining these values of the theoretical habitable pore space with the measured rhizobial numbers showed that only 0.37 and 0.44% of the habitable pore space was occupied in the sterilized loamy sand and silt loam, respectively. The situation in natural soil is more complicated, since a whole variety of microorganisms is present. Nevertheless, it was suggested that, in general, pore space does not limit proliferation and growth of soil microorganisms.     

Modeling long-term compost application effects on nitrate leaching

Application of compost to agricultural soils may be beneficial for crop production by increasing soil fertility and supplying plant nutrients, however, any raise of the soil organic matter content may increase the potential for unintended groundwater contamination by nitrate leaching. In this paper, the effect of long-term compost applications on nitrate leaching, soil organic matter content, and crop production is analyzed using results of simulation scenarios for agricultural sites with loamy and sandy soils. Simulations were carried out using the Danish Nitrogen Simulation System (DAISY) which describes the nitrogen balance in a one-dimensional soil-plant-atmosphere system and considers compost type and application rate as well as management and cropping practice. Estimations of hydraulic and solute transport parameters are based on pedotransfer functions. Data from a 4.5-year period of field experiments with compost applications in northern Germany as well as from laboratory experiments with compost amended soil are used for model calibration. Simulation results suggest that: (i) with respect to nitrogen turnover the differences between compost types (i.e., non-matured and matured) are small compared to site-specific properties (i.e., soil temperature and water balance) and management practices (i.e., crop rotation) when considering a compost application period of 50 years; (ii) with respect to nitrate leaching the effect of different compost application scenarios is highly sensitive at the sand and relatively small at the loam site; and (iii) relatively high crop yields and acceptably low nitrate concentrations in the drainage water are obtained at the sand site when applying a combination of 10 t compost/ha/yr and soil- N_min adjusted mineral nitrogen additions of about 20 kg/ha/yr to a winter-grain dominated crop rotation. Further optimization may be possible by applying reduced rates of the (economically interesting) non-matured compost. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

Response of Soybean to Heterodera glycines Races 1 and 2 in Different Soil Types

Experiments were conducted for 3 years at four locations and 1 year with six soil types at a common location in North Carolina to determine damage and control-cost functions for Heterodera glycines races 1 and 2 on soybean. In the experiments on native loamy sand and sandy soils, tolerance limits for initial population densities were 0 or very low, whereas in a muck, the tolerance limit was 315 eggs/500 cm³ soil. The aggressive race 2 was more damaging than race 1 in Lakeland sand and Norfolk loamy sand. The crop response was not different between races in the Appling sandy clay loam and Belhaven muck. Soybean yield responses to H. glycines were linear in six soil types in microplots at a common site. The amount of damage varied among these soil types, with lowest yields in the muck because of severe drought stress in this soil. An exponential function adequately described soybean yield response relative to nematode control with increasing rates of aldicarb in Norfolk loamy sand. Treatment with aldicarb in the Lakeland sand decreased the effective egg population of H. glycines but had only a minor effect in the muck.     

The influence of soil type and moisture on pupal survival of Bactrocera tryoni (Froggatt) (Diptera: Tephritidae)

Abstract  Larvae of the Queensland fruit fly, Bactrocera tryoni , pupate in the soil, but the influence of soil variables on B. tryoni pupal mortality is not known. For other tropical tephritid species, soil moisture has been identified as a major pupal mortality factor. In the laboratory, we tested the effects of soil moisture and soil type on pupal survival through a factorial experiment which used three soil types (loamy sand, loam, sandy clay) and seven soil moisture levels (0%, 10%, 25%, 50%, 75%, 90% and 100%). Minor, but significant, differences in pupal mortality were observed between the soil types, but the most significant factor affecting pupae was extremes of soil moisture. Eighty-five percent pupal mortality occurred at 0% soil moisture and 30% mortality at 100% soil moisture: very low levels of mortality occurred at all intermediate levels. We detected a significant interaction between soil type and moisture level but cannot explain it. In a follow-up experiment, we demonstrated that prepupal wandering larvae of B. tryoni could discriminate between different moisture levels, with significantly greater pupation in loam soil at 75% soil moisture than at either 0% or 100% soil moisture. Results are used to modify a pupal mortality/soil moisture equation used in a recently published DYMEX model of B. tryoni population dynamics .     

An experimental study of old-field succession in relation to different environmental factors

From 1984 to 1986, old-field succession on sterilized sand and loam was studied under different water- and nutrient regimes. Within one month, moss and phanerogam species appeared on all experimental plots but further succession was rather varied. Salix species established quickly on loam and formed within 3 years a shrub layer up to 3 m in height. On sand, woody plant species were observed only at a high ground-water level. On loam, the well-known old-field succession from short-living therophytes to long-living phanerophytes of clearings and woodlands proceeded very quickly. In contrast, on sand, therophytes, hemicryptophytes and herbaceous chamaephytes of ruderal- and grassland communities were still dominant after three years. A high ground-water level as well as mineral fertilization had sometimes positive, sometimes negative effects on this succession. Periodic estimates of cover, made during the succession were supplemented at the end of the experiment by the measurements of phytomass and bioelement storage. The highest amount of biomass was measured on the three loamy soils where shrub layers were well developed. In comparison with data published elsewhere, the above-ground biomass of 2.2–2.8 kg dry matter m^-2 and the below-ground biomass up to 7.2 kg dry matter m^-2 were both extraordinarily high. Over the three years, the vegetation on sandy soils accumulated between 1.2 and 5.1 g N m^-2 yr^-1 and on loamy soils between 17.1 and 24.7 g N m^-2 yr^-1.     

Anhydrobiotic Coiling of Nematodes in Soil

Nematodes of three genera (Acrobeloides sp., Aphelenchus avenae, and Scutellonema brachyurum) were induced to coil and enter anhydrobiosis in drying soil of two types: sandy loam and loamy sand. Coiling was studied in relationship to soil moisture characteristics. Coiling and the physiological state of anhydrobiosis occurred before the water in sandy soils reached a water potential of -15 bars. Coiling was maximum at 3-6 bars, depending on the soil type and nematode species. It appeared that induction of coiling and anhydrohiosis were determined by the physical forces exerted by the water film surrounding the nematode, which, for these three species, was 6-9 monomolecular layers of water, rather than the % moisture and relative humidity of the soil per se.