Simulation of field scale denitrification losses from soils under grass ley and barley

Denitrification losses from soils under barley and grass ley crops were simulated. The model, which includes the major processes determining inputs, transformations and outputs of nitrogen in arable soils, represents a scale compatible with information generally available in agricultural field research. The denitrification part of the model includes a field potential denitrification rate and functions for the effect of soil aeration status, soil temperature and soil nitrate content. Easily metabolizable organic matter is assumed not to limit denitrification. Simulated values were compared with denitrification measurements made during two growing seasons in the barley and grass ley treatments of a field experiment in central Sweden.Calibration revealed that the optimal parameter values describing the effect of soil aeration on denitrification rates were similar for both treatments. The response function derived agreed well with two data sets found in the literature. The potential denitrification rate constant, derived in the simulations, was higher for grass ley than for barley, which was consistent with the differences in overall rates of carbon and nitrogen turnover found between treatments.The simulated mean denitrification rates for the two seasons were within 20% of the mean of the measured values. However, simulated denitrification showed less temporal variability and a less skewed frequency distribution than measured denitrification. Some of the measured denitrification events not explained by the model could have been due to the stimulating effects of soil drying/wetting and freezing/thawing on microbial activity.     

Supersaturation of soil solutions with respect to gypsum

The products of activities of calcium and sulphate were calculated for solutions of 75 glasshouse soils. The majority of these products was found to be higher than the solubility product of gypsum, thus indicating that these soil solutions were possibly supersaturated. In another investigation, soil solutions were examined to determine whether such high activity products could be really attributed to supersaturation. By means of ultracentrifuging of solutions of glasshouse soils, it could be established that the solutions were practically free of sulphate-bearing colloidal particles. Some solutions contained calcium-bearing colloidal particles, but the quantities of calcium contained in these particles were too small to substantially influence the calcium activity. Addition of gypsum crystals to soil solutions led to crystallization of so much calcium and sulphate that the products of the activities of calcium and sulphate dropped from values that can be listed as high to values approaching the solubility product of gypsum. The results obtained demonstrate the occurrence of supersaturation of soil solutions with respect to gypsum. It is further postulated that the presence of humic substances in the soil solution is responsible for this supersaturation. The possible occurrence of supersaturation with respect to gypsum in soils other than glasshouse soils is discussed.     

Heterogeneity of soil and plant N and C associated with individual plants and openings in North American shortgrass steppe

Small-scale spatial heterogeneity of soil organic matter (SOM) associated with patterns of plant cover can strongly influence population and ecosystem dynamics in dry regions but is not well characterized for semiarid grasslands. We evaluated differences in plant and soil N and C between soil from under individual grass plants and from small openings in shortgrass steppe. In samples from 0 to 5 cm depth, root biomass, root N, total and mineralizable soil N, total and respirable organic C, C:N ratio, fraction of organic C respired, and ratio of respiration to N mineralization were significantly greater for soil under plants than soil from openings. These differences, which were consistent for two sites with contrasting soil textures, indicate strong differentiation of surface soil at the scale of individual plants, with relative enrichment of soil under plants in total and active SOM. Between-microsite differences were substantial relative to previously reported differences associated with landscape position and grazing intensity in shortgrass steppe. We conclude that microscale heterogeneity in shortgrass steppe deserves attention in investigation of controls on ecosystem and population processes and when sampling to estimate properties at plot or site scales.     

Role of magnesium in combination with liming in alleviating acid-soil stress with the aluminium-sensitive sorghum genotype CV323

An experiment to study the effects of Mg nutrition on root and shoot development of the Al-sensitive sorghum (Sorghum bicolor (L.) Moench) genotype CV323 grown in pots of sandy loam under different acid soil stress is reported. This experiment had a factorial design: four rates of liming were combined with four rates of Mg fertilization. When no Mg was added, the pH of the soil solutions (collected in ceramic cups) increased from 4.0 (unlimed) to 4.2, 4.7 and 5.9 at the increasing rates of liming. After 30 days of growth dry matter yields of the limed treatments were 40%, 115% and 199% higher than that of the unlimed treatment. Without liming and at the highest liming rate, adding Mg did not affect plant biomass significantly. At the two intermediate levels of liming, however, 11.3 mg extra Mg per kg soil increased dry matter yield to the same levels as found at the highest liming rate. Concentrations of Mg in the soil solution rose after Mg was added and fell when lime was added, but adding both Mg and lime increased Mg concentrations in the plant shoots. In plants of the limed treatments, dry matter yield was correlated closely with the Mg concentration in the shoot. This was not so in the unlimed treatment. Furthermore, in the unlimed treatments root development was inhibited, but reduced Mg uptake by the plants resulted mainly from the direct effect of Al- (or H-) ions in the soil solution rather than from impaired root development. It is concluded that Mg fertilization counteracted the interfering effects of Al- and H ions on Mg uptake.     

Control of early seedling growth in varietal lines of hexaploid wheat (Triticum aestivum), durum wheat (Triticum durum), and barley (Hordeum vulgare) in response to the phthalimide growth regulant,AC 94,377

AC 94,377 caused elongation of seedlings of Triticum aestivum, Triticum durum, and Hordeum vulgare when applied to the soil, or the soil plus seed at planting. Affected were the leaf sheathes and the coleoptiles, and at high compound rates there was premature elongation of the stem internodes. As exemplified by the response of T. aestivum var. Fidel, the influence on coleoptile elongation was greatest under conditions whereby the coleoptile was naturally stimulated to elongate, i.e., when growth was in the dark and temperatures were cool (15°C). All of the stem internodes were capable of elongation except the one below the coleoptile node. The effect on leaf sheath elongation was prolonged when compared to activity of gibberellic acid.Several varieties of the three cereal species were examined in the greenhouse for sensitivity to AC 94,377 in order to evaluate the extent of the response. All of the barley varieties examined were sensitive to AC 94,377, elongating regardless of the planting conditions. Two such conditions were established, including incubation under warm (28/20°C) conditions following planting the grains 1 cm deep, and incubation under cool (22/16°C) conditions following planting the grains 6 cm deep. Wheat varieties distributed into two general categories, those which were sensitive and those which were not. The insensitivity correlated well to the presence of the reduced height (Rht) and GA-insensitive (Gai) genes in Triticum aestivum and Triticum durum, respectively. Thus, AC 94,377 can be used conveniently to evaluate varietal lines for the presence of this phenotype. This correlation also lends support to the notion that the Rht/Gai mutations in wheat are either at the level of a gibberellin receptor or at a step in the signal transduction pathway.     

A field study on the fate of 15N-ammonium to demonstrate nitrification of atmospheric ammonium in an acid forest soil

To demonstrate the contribution of atmospheric ammonium to soil acidification in acid forest soils, a field study with¹³N-ammonium as tracer was performed in an oak-birch forest soil. Monitoring and analysis of soil solutions from various depths on the¹³N-ammonium and¹⁵N-nitrate contents, showed that about 54% of the applied¹⁵N-ammonium was oxidized to nitrate in the forest floor. Over a period of one year about 20% of the¹⁵N remained as organic nitrogen in this layer. The percentage¹⁵N enrichment in ammonium and nitrate were in the same range in all the forest floor percolates, indicating that even in extremely acid forest soils (pH < 4) nitrate formation from ammonium can occur. Clearly, atmospheric ammonium can contribute to soil acidification even at low soil pH.     

Restoration and creation of freshwater wetlands using seed banks

The minimum information about a seed bank needed for a wetland restoration or creation project is a species list. There are two basic techniques for determining the composition of seed banks: (1) mechanical separation of seeds from a volume of soil and (2) germination of seeds from a volume of soil under appropriate environmental conditions. The latter method always gives biased results. It is best to collect as many random samples as possible when sampling a wetland seed bank. These can be combined as needed for processing. Field studies in India have demonstrated that vestigial seed banks can be used to re-establish a former vegetation type in a monsoonal wet-land that had become overgrown by a species of grass. In less than a year, 9 of 1 I species in the vestigial seed bank were found growing in areas cleared of the grass. Vestigial seed banks of drained prairie wetlands in the northcentral United States contained a few wetland species after 70 years, although species diversity and seed density declined significantly after 20 to 30 years of drainage and cultivation. In Florida, U.S.A., wetlands have been established in strip-mined areas using donor soils from existing wetlands. Newly established wetlands quickly developed a dense cover of vegetation, although this vegetation often lacked many desirable wetland species. Experimental studies of soil moisture conditions using a seed bank from the Delta Marsh, Canada, demonstrated that soil moisture affected both the total number of seeds, and the relative proportion of seeds of each species that germinated from a seed bank. The density of seedlings of emergent wetland species in the treatments was directly proportional to soil moisture, while that of terrestrial annuals was inversely proportional. Emergent species made up nearly 90% of the seedlings in the wettest treatment and 0% in the driest.From a paper presented at the Third International Wetlands Conference, 19–23 September, 1988, University of Rennes, France.     

Application of good laboratory practice (GLP) to culture collections of microbial and cell cultures

Although the principles and the necessity for good laboratory practice (GLP) guidelines to confirm the credibility, integrity, and quality of non-clinical laboratory studies have been known for more than a decade, culture collection activities are not subject to them. Because of recent advances in biotechnology, culture collections face increased demands not only for quality cultures but also current information. When applied in culture collections, GLP guidelines prove to be an excellent management tool as well as a cost-effective system of providing authentic and reliable microbial and cell cultures and associated data.     

Changes in soil microflora associated with control of Sclerotium Rolfsii by Furfuraldehyde

The efficacy of 2‐furfuraldehyde for control of Sclerotium rolfsii was studied in laboratory and greenhouse experiments. Mycelial growth of the fungus was reduced proportionally with concentrations of 0.1–0.5 ml furfuraldehyde l^‐1 agar medium, and viability of sclerotia diminished on exposure to 2‐furfuraldehyde vapours. Detectable populations of bacteria and fungi, including Trichoderma spp., were reduced significantly (9=0.05) when furfuraldehyde was added to the agar used for soil dilution plates of untreated soil. Repeated treatments of natural soil with the fumigant significantly increased populations of Trichoderma spp. and bacteria, but diminished numbers of actinomycetes. Increasing dosages applied to soil artificially infested with S. rolfsii caused a reduction of disease on lentil, Lens culinaris. Results indicate that the compound, when applied to field soil, changes the composition of soil microflora and has potential for integrated control of S. rolfsii.     

根分泌物及其生态效应

根分泌物是个古老而年轻的研究领域。早在18,19世纪,人们(Plenk,1795;Decandolle,1830)就观察到根分泌物对邻近植株的促生和抑制作用,1904年Hilter提出“根际”的概念,标志着人们对根分泌物及其生态效应的进一步认识。此后人们对根分泌物研究逐步展开。Lyon和Willson(1920)发现,生长于无菌水培液中的植物能释放有机物,为深入研究奠定了基础。但很长一段时间这个研究领域一