ALBERT

Notes: Abstract. White rot (Sclerotium cepivorum) causes serious losses in Allium crops throughout the world. The pathogen produces sclerotia which survive for long periods and are the main source of inoculum. Sclerotial germination is stimulated by the host and new sclerotia are produced on the host near the soil surface. Allium crops are cultivated in various systems and environments and no one method of control is effective. There is increasing interest in control strategies based on combinations of treatments which decrease the populations of sclerotia in the soil, thereby improving the effectiveness of present methods of control. Materials and methods being tested for inclusion in programmes of integrated control include germination stimulants, soil fumigants, solar heating, roguing, aerobic composting, microbial control and combined chemical/microbial control with fungicide-resistant micro-organisms.

Notes: Abstract. The relationship between take-all and grain yield was investigated in a first spring wheat crop grown in a field experiment on artificially infested soil. Different incidences and severities of disease were obtained by using different cultivations to incorporate equal amounts of inoculum (killed oat grains colonized by the fungal pathogen) at different depths. The intention of incorporating inoculum at different stages in the same sequence of cultivations to achieve identical soil conditions with inoculum at different depths was not entirely successful because of weather conditions.For most sampling dates and different assessments of disease, there was a strong relationship between yield and disease: regression coefficients were negative and significant (P= 0.01). The linear regression model using logit transformations of disease data from infestations achieved using similar sequences of cultivations accounted for 〉 70% of the variance at all sampling dates, but with untransformed data (percentage plants and percentage roots infected) percentages of variance accounted for were much less at sampling times before anthesis. The plot area affected by premature ripening (whiteheads) also correlated well with yield where similar sequences of cultivations were used, but less well where rotovating to different depths created different soil conditions.The results are discussed in relation to published results from (1) farm surveys, (2) field experiments with natural infection and (3) experiments using different amounts of artificially-produced inoculum. The wider application of artificially-produced inoculum in field experiments on take-all is also considered.

Notes: Abstract. A rotation trial of four years’ pasture followed by two years’ arable was used to study the effect of cropping on the morphological and hydraulic properties of soil. An adjacent paddock in grass for the past 35 years was included as a permanent pasture reference. Initial infiltration and field saturated hydraulic conductivity (Kfs) were least for cultivated soil and increased with increasing time under pasture. This could be explained by the contrasting porosities of resin-impregnated blocks of undisturbed soil which had been infiltrated with methylene blue dye. Small Kfs values for cultivated soil resulted mainly from a thin surface crust, although pore discontinuity at the depth of the cultivation pan (130 mm) could also have contributed. Greater Kfs values under short-term pasture resulted primarily from water flowing through biogenic pores connected to the surface. The greatest Kfs values were in soil that had been under pasture for 35 years (P35). This was attributed to flow through biogenic pores and fissures associated with the strongly-developed subangular blocky structure. The amount of water that infiltrated the two- and four-year pasture soils (P2 and P4) under ponding was 2.5 and 5 times greater, respectively, than the soil that had been cultivated for two years (C2).As irrigation duration cannot be varied under the border-dyking system used on the Canterbury Plains, the interval between irrigations must be varied if the same total amount of water is to be applied to each of these soils through the season. The interval should be less for the cultivated soil than for those under pasture, and should increase with increasing time under pasture (i.e. P35 〉 P4 〉 P2 〉 C2).

Notes: Abstract. N-(n-butyl) thiophosphoric triamide (NBPT) is the most effective compound currently available for retarding hydrolysis of urea fertilizer in soil and for decreasing ammonia volatilization and nitrite e accumulation in soils treated with urea. It is a poor inhibitor of plant or microbial urease, but decomposes quite rapidly in soil with formation of N-(n-butyl) phosphoric triamide, which is a potent inhibitor of urease activity.The adverse effects of urea fertilizers on seed germination and seedling growth in soil are due to ammonia produced through hydrolysis of urea by soil urease. They can be eliminated by addition of a urease inhibitor to these fertilizers.The leaf-burn commonly observed after foliar fertilization of soybeans with urea results from accumulation of toxic amounts of urea in the soybean leaves rather than formation of toxic amounts of ammonia through urea hydrolysis by leaf urease. Leaf-burn is accordingly increased rather than decreased by addition of a urease inhibitor to the urea fertilizer applied.

Notes: Abstract. In most soils of temperate regions nitrate is not held on soil surfaces and moves freely in solution. But when soils carry positive charges, nitrate is held as an exchangeable anion. As a result, leaching of nitrate is delayed relative to the movement of water. The delay can be predicted provided the anion exchange capacity (AEC) can be measured and the concentration of counter-anions is known. For soils with variable charge, the AEC varies with both pH and ionic strength, and the effective AEC should be determined under conditions similar to those in soil solution. A simple leaching method is described which satisfies this requirement. Delays in the leaching of nitrate measured in columns of repacked soil were strongly related to the AEC.

Notes: Abstract. A brief resumé of the organisms involved in the nitrogen cycle is given. Benefits accruing to micro-organisms are considered in two categories: (1) where the reaction product is incorporated into cells (nitrogen-fixing and nitrate assimilating species), (2) where the reaction is used to provide energy for growth (nitrifying and denitrifying species). Some aspects of nitrogen cycling in soils are briefly considered, including inhibition of nitrification, the importance of C/N ratios and nitrate pollution.

Notes: Abstract. Autotrophic nitrifiers such as Nitrosomonas use ammonia mono-oxygenase for the initial stage of ammonia oxidation. Nitrification inhibitors have this enzyme as their site of action. Their mechanisms include alternative substrates, suicide substrates and cuprous copper chelators.In heterotrophs, organic nitrogen is normally in the fully reduced state, but a few cell metabolites contain N-O bonds. The synthesis and breakdown of such compounds provides a mechanism for heterotrophic nitrification. A non-enzymic mechanism for nitrogen-oxidation involves hydroxyl radicals produced by the Fenton reaction. Heterotrophic nitrification is particularly important in woodland soils, where wood-rotting fungi use free radicals to break down lignin. Tests for a radical mechanism are described.

Notes: Abstract. The workshops covered various aspects of nitrogen in the environment, with special emphasis on the problems posed by nitrogenous compounds as pollutants.

Notes: Abstract. The standard of English in papers submitted to Soil Use and Management varies from excellent to disgraceful. Good scientific English is direct and simple in structure. It uses familiar words in their correct sense and order with the minimum of qualification. Slovenly prose may imply slipshod research, and prolixity an inability to think clearly.Make your meaning plain. Express itSo we'll know, not merely guess it.(G.V. Jacks, The Summary)

Notes: Abstract. Machinery was designed specifically for relay-cropping on permanent raised beds (150 mm high and 1.5 m wide) in northern Victoria. This machinery enabled maize (Zea mays) to be successfully sown at 2, 4 and 5 weeks before harvest, and 1 day after harvest (Control), of wheat (Triticum aestivum). The sowing equipment consisted of a four-row cultivator, behind which were four precision seeders. The wheels (250 mm in diameter) were spaced at 1.5 m to track along the base of the furrows. In one pass on each bed, the sowing equipment tilled two strips (each 50 mm wide, 30 mm deep and 50 mm from the outer row of wheat) and sowed maize, with little damage to the wheat crop. We extended the axle of the trailed harvester so that the wheels (250 mm in diameter) were 3 m apart, and moved the drawbar 300 mm to one side so that all wheels ran along the base of the furrows. There were no significant differences between treatments in yield (mean 2.9 t ha-1) of dryland wheat, in final emergence percentage (mean 89%) or in early growth of irrigated maize. The maize yielded significantly less grain in the treatment sown at 5 weeks (9.6 t ha-1), but not 2 or 4 weeks (mean 10.6 t ha-1) before the wheat was harvested, than in the Control (10.8 t ha-1). The wheat and maize yielded more grain than those grown traditionally as sole crops in northern Victoria.

Notes: Abstract. Wet and droughty soils and those on steep slopes are now marginal for agriculture in Denmark. A nation-wide map of these soil types has therefore been made to show their distributions. This was based on an existing soil database containing maps and analytical data. The paper describes the methods used to extract and display the data.

Notes: Abstract The co-regionalization between relative elevation and zinc concentration was used to map zinc concentration in the soil of the Geul floodplain in the southern Netherlands by co-kriging from 154 observations. Point co-kriging and point kriging for estimating zinc content in the soil were compared in terms of kriging variances. Another 45 samples were used to compare the precision of the estimated values in terms of squared and absolute estimation errors. Point co-kriging produced better estimates of zinc concentration than either simple point kriging or linear regression from the relative elevation data alone. Moreover, the estimation variances for co-kriging are substantially smaller than those for kriging. The results suggest that knowledge of geomorphological processes can often improve the quality of interpolation maps of properties that are expensive to measure.

Notes: Abstract. Disjunctive kriging provides minimum variance estimates of properties from non-linear combinations of spatially correlated sample data. In addition it can be used to estimate the conditional probability that some critical threshold is exceeded or that there is a deficit at unsampled points. The technique has been applied to estimate and map the salinity of the soil in the Bet Shean Valley of Israel from measurements of electrical conductivity. In November 1985 the estimated electrical conductivity of the soil exceeded 4 mS per centimetre throughout most of the region, and in only a small area was the probability of salinity less than 0.2. By March 1986 the electrical conductivity had declined everywhere to less than 4 mS per centimetre, and the conditional probability of exceeding this value nowhere exceeded 0.25. Despite the fluctuation in salinity farmers seem to have it under control. The results suggest that winter wheat is likely to germinate poorly in the saltier parts of the region and that lucerne (alfalfa, Medicago sativa) is unlikely to yield its maximum over most of it. Cotton, a summer crop sown in spring, should not suffer.

Notes: Abstract. To allow land planners and managers to assess erosion under alternative management practices a model has been developed. It is based on the universal soil loss equation but uses subfactors for crop cover and management. Readily available agronomic data and field expert opinion were used in formulating the method. Locally-derived data are used to validate the model which is then applied to agricultural systems in New South Wales, ranking the relative erosion hazard associated with crop and land management practices.

Notes: Abstract. The 296 soil associations of the National Soil Map of England and Wales are placed into five categories of erosion risk. These are based on land use, landform and soil properties and take into account the extent of erosion in the uplands, and its frequency, extent and rates in the lowlands. Erosion of arable land is by water or wind, but in the uplands frost action and disturbance by sheep are also important. A large proportion of arable England (36%) is at moderate to very high risk of erosion, including much of the better drained and more easily worked land, especially sandy soils. In the uplands thin soils or deep peats are most at risk. If land use changes, because of increasing intensification of agriculture or in response to climatic changes, many soil associations will become more at risk of erosion.

Notes: Abstract. Four lithological types of chalk are recognized. Normal white chalk has 34–50% porosity, nearly all of which holds water conventionally‘available’to plants. Hard chalk and grey chalk have less porosity and available water; chalk marl has very little available water. Significant capillary rise from below the root zone can be expected in normal white chalk only, and is not halted by fragmentation. Chalk has little N and usually little P. Only grey chalk and chalk marl have much ettractable K and Mg. These also slake, impeding roots. Thus, fertilized plants tolerant of high pH can grow well on normal white chalk debris, but on raw chalk marl, e.g. Channel Tunnel spoil, they need irrigation. Interesting plants volunteer on chalk debris, even on slaked chalk marl by the sea.

Notes: Abstract. Tillage and mulching effects on the environment of the seed zone and on growth of cowpea (Vigna unguiculata) seedlings in the humid tropics were studied at Ibadan, southwestern Nigeria, in the 1987 and 1988 late cropping seasons. The split-plot design experiment had conventional tillage (ploughing and harrowing), reduced tillage (ploughing only), zero tillage and grass mulch treatments. Conventional and reduced tillage practices decreased initial bulk density and increased seedling emergence, root growth, dry matter yield and overall seedling performance. Addition of mulch increased the soil moisture in the root zone and significantly decreased maximum soil temperatures and diurnal fluctuations in temperature. This provided a more stable environment for seedling establishment and growth than the unmulched soil.

Notes: Book reviewed in this article.Heavy Metals in Soils Editor B.J. Alloway.F.A.O. Soils Bulletin 61: Radioactive fallout in soils, crops and food By F.P.W. Winteringham.Dynamics of soil organic matter in tropical ecosystems Edited by D.C. Coleman, J.M. Oades and G. Uehara.Agroforestry for soil conservation By A. Young.

Notes: Abstract. One direct measurement and two indirect estimates suggest that 35–40 kg nitrogen per hectare are deposited on arable land from the atmosphere each year in the south and east of England. This could contribute markedly to nitrate leaching and soil acidification. It may also change the flora and fauna of ‘natural’ ecosystems, as such amounts are likely to exceed the critical load.

Notes: Abstract. Four bullock-drawn tillage implements (mouldboard plough, chisel plough, sweeps, and shovels) were evaluated on a hard-setting Alfisol. Measurements included draft requirement, bulk density, cone index, soil crust strength, water content of the plough-layer and crop yield. Changes in bulk density and cone index due to tillage decreased with time and were negligible by the end of the growing season. After tillage with a mouldboard plough the crust was stronger than after tillage with other implements. The shovel cultivator enabled the soil to store more water, and required least draft per unit effective area of cut.

Notes: Abstract. During 1986 erosion on soil mulched with 6 t ha-1 of straw was compared with that on soil maintained bare by herbicides in a mature apple orchard. The orchard was on well-drained soil with a sandy loam top on a slope of 2°. Erosion was greatest in the alleys between the trees, where traffic had compacted and smoothed the soil. The mean annual soil loss on bare ground in the alleys was 0.45 t ha-1; straw mulch reduced this by 85%. Erosion was worst between July and October, when rainfall 〉 10 mm h-1 was most frequent. However, differences in soil moisture and resistance to infiltration may have also contributed to differences in erosion throughout the year.

Notes: Abstract. Biological control by manipulating agricultural practices has been used for thousands of years. In the more restricted sense, of adding antagonistic micro-organisms, biological control is still a very small part of the chemical pesticide market, but reliable products are becoming available. Achieving consistent results in realistic agricultural conditions is a problem, but there is a good possibility of controlling root diseases, especially where the soil characteristics or the environmental conditions can be controlled. The use of biological control in integrated control is successful, and in the long-term genetic engineering techniques will be important in the development of biological control. Environmental safety and effective patent protection are still being developed, but there seem to be no insuperable problems.

Notes: Abstract. The recent spread of sugar-beet rhizomania and barley yellow mosaic virus in Europe has stimulated fresh interest in plant viruses with soil-borne fungal vectors. Although there are at least 20 such viruses, most of which cause diseases of important field crops, there are many gaps in our knowledge of their epidemiology because much research has concentrated exclusively on the viruses. The vectors are lower fungi that are obligate parasites of plant roots and are therefore difficult to study experimentally. Resting spores containing virus can survive indefinitely in soils but effects of rotation have not been greatly studied. There is no quantitative information relating inoculum levels of fungus and virus to disease development. Only limited information is available about inoculum distribution in soil and factors affecting its potency. The diseases are mostly dispersed by soil movement during agricultural operations but some features of disease distribution in infested fields await adequate explanation. Little is known about interactions with other micro-organisms.

Notes: Abstract. Root diseases are often hard to identify or quantify visually, particularly by the inexperienced, so several modern methods of diagnosis from other branches of biology have been modified for soil-borne plant pathogens. Though very sensitive, most of these techniques are slower and more laborious than the routine inspection of plants for disease symptoms, yet they need less expertise and are consistently accurate. Apart from immunology, most laboratory diagnostic procedures have so far proved ill-suited for field use, as they are neither sufficiently flexible nor portable. Despite the rapid detection and identification of numerous viruses by routine enzyme-linked immunosorbent assays (ELISA), there have been until recently few suitable protocols adapted for fungi. DNA hybridization forms the basis of another group of fairly rapid diagnostic techniques which will probably be restricted to the laboratory for some while yet. Nevertheless, DNA techniques have proved valuable in various investigations, such as unravelling the phylogeny of some species of soil-borne pathogens. For the foreseeable future methods based on antibodies and DNA probes are likely to extend their domination of detection and diagnosis techniques. By making recognition easier, these techniques play complementary roles in expanding our understanding of the biology, taxonomy and ecology of soil-borne pathogens.

Notes: Abstract . There are many records of mycorrhizae, particularly ectomycorrhizae, protecting roots against soil-borne plant pathogens, though fungal or viral diseases of the green parts are usually more severe in mycorrhizal plants. There are various mechanisms by which mycorrhizae protect themselves against soil-borne diseases. The occurrence and ecological significance of these mechanisms are discussed in relation to environmental factors. Mycorrhizae will probably become a very effective means of biological control once we have learned how to manage them.

Notes: Abstract. The most important root diseases of wheat in southern Australia are take-all, rhizoctonia bare patch and cereal cyst nematode. Control of grasses in annual pastures in the year preceding wheat crops decreased take-all on wheat and the amount of the take-all fungus in soil, decreased the damage caused by Rhizoctonia, and gave yield increases. Fumigation of cereal-growing soils gave yield increases in wheat of 0.75 to 2.8 tonnes per hectare, indicating that in southern Australia soil-borne root diseases impose a major constraint on productivity. Residues of the herbicide chlorsulfuron one year after application to an alkaline soil increased root damage by Rhizoctonia in barley and decreased grain yields by 1.5 tonnes per hectare. Root damage by cereal cyst nematode was decreased by direct drilling wheat and also by having a barley cultivar resistant to the pathogen as a preceding crop. The number of cysts of cereal cyst nematode on wheat roots was increased by the application of superphosphate in bands with the seed. These results show that in southern Australia soil management strategies which decrease the levels of root disease greatly increase grain yields.

Notes: Abstract. Farm livestock typically retain 5–23% of dietary nitrogen, and consequently excrete large amounts of nitrogen, mainly in urine. Areas affected by cattle urine may receive the equivalent of several hundred kg nitrogen per hectare. Urea is usually hydrolysed to ammonium carbonate within a few days. This increases the soil pH and thereby assists volatilization of ammonia. Volatilization is also increased by soil warmth and by small soil cation exchange capacities. Over the grazing season in lowland UK about 15% of the nitrogen in urine is likely to be volatilized as ammonia, but only 1–5% of the nitrogen in dung is lost in this way.Substantial volatilization of ammonia probably occurs from animal houses and after spreading of slurry in the field. About 3–4% of fertilizer nitrogen used in the UK is lost as gaseous ammonia. Cut grass herbage also loses ammonia by volatilization, if allowed to remain in the field in wet conditions. Total annual emissions of nitrogen as ammonia from grassland and livestock in UK are probably 320 000–420 000 tonnes.

Notes: Abstract. Public perceptions of agriculture as a contributor to environmental stress are resulting in changes within agricultural production systems. Increasingly, these systems will need to be economically viable, environmentally sound, socially and politically acceptable, and conserving of natural resources-the characteristics that describe a sustainable agriculture. Improving and maintaining agricultural production systems with these characteristics must continue to be the objectives of agricultural research. Nitrogen research has contributed markedly to meeting the production and economic goals of agriculture, but it has not yet focused enough on answering socially and politically sensitive questions. Questions are posed about the environmental effects of various nitrogen management practices and the research needed to answer them is outlined. Emphasis is put on immobilization-mineralization as affected by use of nitrification inhibitors and split-application, release of nitrogen from animal manures, legumes, and other crop residues, and establishing acceptable yield goals.

Notes: Book review in this ArticleManagement Systems to Reduce Impact of Nitrates. Editor J.C. Germon

Notes: Abstract. ALES, the Automated Land Evaluation System, is a microcomputer program that allows land evaluators to build their own knowledge-based systems with which they can compute the physical and economic suitability of land map units, in accordance with the FAO's Framework for Land Evaluation. The economic suitability of a land mapping unit for a land utilization type is determined from the predicted annual gross margin per unit area. Increasing limitations result in increased costs of production, decreased yields, or both. Evaluators build decision trees to express inferences from land characteristics to land qualities, from land qualities to predicted yields, and from land qualities to overall physical suitability. A representative model is described.

Notes: Abstract. After restructuring of a heavy saline gypsum containing clay soil by intensive subsoiling to 0.7 m depth, it was possible to leach 60% of the leachable salts from the restructured soil in 28 days by inducing a lateral flow of leaching water through the soil profile.

Notes: Abstract. This paper describes experiments on the inhibitory effects of hydroquinone (HQ), phenylphos-phorodiamidate (PPDA) and N-butyl phosphorothioic triamide (NBPT) on the nitrification in soil. Incubations were carried out at 2/3 field capacity at 25°C of soil samples to which either ammonium or nitrite was added together with inhibitors. Addition of PPDA or NBPT did not influence the oxidation of ammonium. HQ. however, retarded the process significantly, and also the accumulation of nitrite. This was confirmed in experiments whereby added nitrite was followed. Some of the differences could be explained by changes in the soil pH. During incubation the evolution of the total mineral nitrogen was not importantly altered by addition of the inhibitors.

Notes: Abstract. The properties of soil under 15-year-old plantations of gmelina (Gmelina arborea) and teak (Tectona grandis) were compared with logged forest soil in south-western Nigeria. The soil was significantly denser in the 0–10 cm layer of plantation soil and total porosity less than that of forest soil. Organic carbon was significantly greater in the 0–10 cm layer of forest soil. Similarly, the concentrations of total N, exchangeable Ca, Mg and K were greater under forest soil, but the concentrations of available P were similar under all three ecosystems. The smaller organic carbon and nutrient content of plantation soil is mainly due to its more open organic matter and nutrient cycles and nutrient immobilization in the fast-growing exotics.

Notes: Abstract. The soil has been investigated at a long-term experiment examining the silvicultural and site-related effects of four tree species (Scots pine, Norway spruce, oak, common alder), planted pure or in mixtures. The experiment is located in Gisburn Forest, Yorkshire, and commenced in 1955. After 32 years, small significant differences were found for soil properties relating to soil organic matter accumulation and incorporation; the soil under the conifers and alder was slightly more acid than that under oak and grass control plots, and the conifers had thicker F and H but thinner A horizons. There was also some evidence that the conifers and alder has retarded the formation of a grey iron-deficient B horizon. Some mixed plots were differentiated from pure ones by canonical variate analysis. Soil pH has declined under all plots since 1954; the effect of mixing species on this property is discussed.

Notes: Abstract. Nutrient manipulation through fertilization or modification of the soil environment to influence nutrient availability is an important cultural control for plant disease and an integral component of production agriculture. Fertilization decreases soil-borne diseases by maximizing the inherent disease resistance of plants, by facilitating disease escape through increased nutrient availability or stimulated plant growth, and by altering the external environment to influence the survival, germination and penetration of pathogens. The flexibility in most disease-nutrient interactions permits a much broader utilization of this cultural control in decreasing disease severity than is presently practised. It is clear that the severity of most diseases can be decreased and the chemical, biological or genetic control of many plant pathogens enhanced by proper fertilization. Breeding nutrient-efficient or disease-tolerant crops and establishing cultivar requirements should further improve production efficiency.

Notes: Abstract. The aluminium (Al), iron (Fe) and Dissolved Organic Carbon (DOC) contents of the soil solution were monitored in two upland grassland and afforested podzol soils in Mid-Wales. Al organo-metallic complexes predominated in the O horizon leachates of the grassland soil, whereas inorganic monomeric Al forms dominated in the lower mineral horizons. Dissolved organic matter determines the chemistry, solubility, and transport of Al and Fe in the O horizon, and these are under strong biological control. The distributions of organic-Al, Fe and DOC within the soil profile were consistent with traditional podzolization theory. Observed increases in the molar ratios of Al:DOC in solution in the lower soil horizons may be responsible for the small solubility of Al organo-metallic complexes in those horizons. Afforestation increased the concentrations of organic-Al and Fe in the soil solution as compared with the concentrations observed for the grassland soil. Clearcutting further significantly mobilized Al and Fe from the upper soil horizon, primarily by increasing the DOC concentration in the soil water.

Notes: Abstract. Current estimates are tabulated for the quantities of nitrogen circulating in the global nitrogen cycle. Five gases, NH3, N2O, NO, NO2 and N2, dominate the movement of nitrogen between the earth's surface and the atmosphere. The input of combined nitrogen to the land surface of the earth is tentatively estimated at 290 million tonnes per year, a total which includes 74 million tonnes from fertilizers. Known outputs from land (as gaseous NH3, N2O and NOX, and as inorganic nitrogen carried to the sea by rivers) are much less, totalling 130 million tonnes per year. Emissions of N2 gas probably account for most of the difference. There has been an increase in the use of nitrogen of about 5% per year over the last ten years. The demand for fertilizer nitrogen is likely to continue to grow if the population of the world continues to increase.

Notes: Abstract. The methods available for measurement of nitrogen fixation by field grown Phaseolus vulgaris are reviewed. Phaseolus is generally considered to have little ability to fix nitrogen. This is discussed in the light of research on host genotypes and Rhizobium strains, and the influences of environment on these in isolation and in symbiosis.

Notes: Abstract. Nitrogen-fixing micro-organisms contain the metalloenzyme nitrogenase, which can be separated into two proteins with molecular weights of approximately 58000 and 220000. Molybdenum held with iron and sulphide atoms in the cofactor (FeMoco) cluster of the larger protein is probably responsible for binding and reduction of dinitrogen (N2). X-ray absorption spectroscopy indicates that the moybdenum is surrounded by three oxygen (or nitrogen) atoms, three irons and three sulphurs. Synthetic clusters with similar X-ray absorption structures to FeMoco do not, however, interact with dinitrogen. Many metal compounds, such as those with tertiary phosphines as co-ligands, can bind dinitrogen, and some containing molybdenum can also reduce it in acidic solution to produce ammonia via several intermediate compounds. These may be developed for production of ammonia fertilizer.

Notes: Abstract. 15N2 was used in a sealed controlled environment chamber to investigate the transfer of fixed nitrogen from white clover to perennial ryegrass growing in soil in pots. There was no difference in the 15N content of roots and shoots of clover plants after exposure to 15N. No labelled fixed nitrogen was detected in ryegrass plants growing with the clover plants for a period of 129 days. There was therefore no evidence of rapid direct transfer (excretion) of fixed nitrogen from clover to ryegrass.

Notes: Abstract. Microbial osmoregulation as a factor regulating the nitrogen and carbon contents of soil microbial biomass was studied in two experiments. In the first the percentages of the carbon and nitrogen occurring in the cytoplasm of Aspergillus flavus and Pseudomonas sp. were shown to be strongly influenced by osmotic stress. In the second, biomass carbon and nitrogen initially increased with increasing water stress (osmotic and matric) up to −1.0 and −1.5 MPa, respectively, but declined under greater osmotic stress. As the soil microbial carbon and nitrogen pools are affected by these stresses, allowance must be made for them when interpreting biomass measurements in water-stressed soils.

Notes: Abstract. Nematodes and protozoa assist nitrogen mineralization by consuming bacteria, and this may increase the amount of nitrogen taken up by plants so that it exceeds the amount lost by root exudation. One of the methods used to determine bacterial consumption by protozoan grazers in aquatic ecosystems, namely progressive dilution of the grazing pressure, was tested in a sandy soil. The result suggests that a basic assumption of the technique, that grazing is directly proportional to the dilution factor, is untrue for soils, possibly because the increase in moisture content with increasing dilution enhances grazer activity.

Notes: Abstract. Samples of peat were incubated with 15N-labelled ammonium sulphate, urea, wheat straw and glycine and divided into six size fractions of solid components and a water-soluble fraction. The fractions were analysed by NMR spectroscopy to study the formation of humic substances and rind how fertilizer nitrogen is immobilized in peaty soils. After six months' incubation about half of the ammonium sulphate nitrogen was still present as ammonium in the soluble fraction, the urea had been entirely metabolized to ammonium and various organic compounds, about half the straw had been decomposed to ammonium and amino acid or peptide materials, and most of the glycine had been transformed to ammonium, amide and aliphatic amine.

Notes: Effects of sowing date, fungicide seed treatments, and the head smut fungus Ustilago bullata Berk, on establishment, herbage, and seed production of prairie grass cv. Grasslands Matua (Bromus willdenowii Kunth) were measured in autumn- and spring-sown field trials in New Zealand.Autumn seedling establishment from thiram-treated seed relative to untreated seed was increased by 27% from the earliest sowing (early March), and by 65% from the latest sowing 8 weeks later. Infestation of seed with ustilospores of U. bullata reduced seedling establishment at all but the latest autumn sowing. Fungicide seed treatments had little effect on spring seedling establishment, but V. bullata infestation of seed reduced establishment compared with healthy seed, particularly after late sowings (early November).Herbage production was greater from early than from late sowings in both autumn and spring, and was less in plants grown from U. bullata infested seed than in plants from healthy seed. Enhanced autumn establishment from thiram-treated seed led to improved herbage production when plants were young, but this effect disappeared about 18 weeks after late autumn sowing. Overall herbage production from spring sowing was more than twice that from autumn sowing.A 6-week delay in autumn sowing led to a 58% reduction in seed production the following summer.Early autumn and spring sowings, together with adequate control of seedling diseases, are likely to give optimum herbage and seed production from prairie grass.

Notes: Herbage production and quality of swards of brome grass (Bromus carinatus. Hook and Am) were compared with other commonly sown grasses at two sites in Scotland. At Ayr, the comparison was with perennial ryegrass (Lolium perenne L.), cocksfoot (Dactylis glomerata L.) and timothy (Phleum pratense L.) under 6-cut (experiment 1) and 4-cut (experiment 2) regimes over 3 years with 360 kg ha−1 fertilizer N applied annually in each experiment. At Edinburgh, brome grass was compared over 3 years with perennial ryegrass and cocksfoot under a 7-cut system given 3(X)-35O kg N ha−1 year−1 (experiment 3) and with perennial ryegrass, cocksfoot and Italian ryegrass (Lolium multiflorum Lam.) under a 4-cut system given 250–325 kg N ha−1 annually (experiment 4).Over the 3 years, brome grass gave 1.18, 6.19 and 1.3% less dry matter (DM) production than the other grasses in experiments 1, 2 and 3 respectively; in experiment 4, it was 1 % less productive than Italian ryegrass but 1.2% more productive than the other grasses. The organic matter digestibility (OMD) of brome grass was lower than that of perennial ryegrass but higher than timothy at Ayr, similar to perennial and Italian ryegrasses at Edinburgh but markedly superior to cocksfoot at both sites. N concentrations in brome grass were higher than in the ryegrasses but lower than in cocksfoot. Mineral composition data showed brome grass to be high in P and K, low in Ca and Mg and very low in Na compared with corresponding concentrations in the other grasses.The variable performance of this brome grass species (B. carinatus) against commonly used grasses in the reported experiments, together with similar evidence from the literature, leads to the conclusion that it is unlikely to be suitable for widespread use in the UK; nevertheless, it has shown some promise in drought-prone situations.

Notes: Book reviews in this article: Advances in Nitrogen Cycling in Agricultural Ecosystems Edited by J.R. Wilson Ruminant nutrition. Recommended allowances & feed tables Edited by R. Jarrige Soil Husbandry Tom Batey Evaluation of straws in ruminant feeding Edited by M. Chenost and P. Reiniger

Notes: An experiment was conducted to examine the effect of concentrate supplementation on the performance of suckling lambs while grazing at variable levels of herbage allowance. Twenty-four ewes suckling twin lambs were allocated 55 d after lambing between four grazing treatments (two levels of herbage allowance × two levels of supplementation) in a 2×2 factorial design. The sward consisted of Tall Fescue and was grazed rotationally.Daily herbage organic matter (OM) allowances were 57.0 (H) and 38.5 (L) g OM kg LW−1 above 1·5 cm cutting height. Lambs were either supplemented (S) ad libitum with high-moisture whole maize grain or unsupplemented (U).Supplement intake during the 60-d grazing period was 16 kg DM and 17.5 kg DM respectively for LS and HS lambs. The effect of supplementation on lamb growth rate differed significantly between allowances: at the low allowance level, supplementation increased growth rate (287 g d−1 vs 226 g d−1), whereas it had no effect at the high level (277 g d−1 vs 276 g d−1). Growth rate of unsupplemented lambs was significantly reduced at the low level of allowance compared to the high level (226 g d−1 vs 276 g d−1). The effect of sward height on time spent grazing by unsupplemented lambs is described during the defoliation of a plot.

Notes: This study evaluated the relationships between legume proportion and dry matter (DM) yield, N yield, and herbage N concentration for three binary legume-grass mixtures In Uruguay. Two identical trials were established, one in 1983 (Trial 1) and another in 1984 (Trial 2) and were evaluated for 2 years. Treatments were white clover (Trifolium repens L.) (WC), red clover (Trifolium pratense L.) (RC), and birds-foot trefoil (Lotus corniculatus L.) (BT), each grown with tall fescue (Festuca arundinacea Schreb.) (TF) at four legume proportions, plus pure stands of TF. In Trial 1, annual DM yields of RC-TF were greater than yields of WC-TF or BT-TF and in Trial 2 RC-TF and BT-TF yielded more than WC-TF. The N concentration of either the legume or TF components usually was greater for WC-TF than other mixtures in both trials. Annual DM yields in Trial 1 were optimized by legume proportions of 47 to 59% for WC, 62 to 67% for RC-TF, and 57 to 100% for BT-TF; and N yields were optimized by 70% of WC or RC, and by 100% BT. In Trial 2, which had greater soil-N availability than Trial 1, optimum DM or N yields were achieved at lower WC proportions than in Trial 1. Changes in legume proportion did not affect legume N concentrations, but N concentration of TF in mixture was always positively and linearly related with legume proportion. It is concluded that DM yields for the first 2 years after seeding were greater for RC-TF and BT-TF than for WC-based mixtures. Herbage DM and N yields of WC-TF were optimized by lower legume proportions than for RC-TF and BT-TF. The N concentration of TF increased linearly with increasing proportions of any of the three legumes.

Notes: The numbers of lactic acid bacteria (LAB), as measured by Rogosa SL agar, on lucerne (Medicago sativa) chopped for ensiling were predicted using two methods. The first prediction method consisted of regression equations developed from two previous harvesting seasons and required inputs of wilting time between mowing and chopping, average wilting temperature and moisture content of the lucerne at chopping. The second method simulated the growth of LAB on the lucerne during wilting and needed similar inputs. The former method predicted LAB counts within one order of magnitude more than 95% of the time except for lucerne samples drier than 60% dry matter. The prediction of the simulation model had more variation than those of the regression equations, but the simulation model was applicable over a wider range of conditions. These results, together with earlier studies, provide a preliminary basis for determining when a silage inoculant containing LAB will be most beneficial.

Notes: The occurrence of Listeria spp. in pasture grass and grass silage made with various additives and preservation techniques is reported. Silage samples were collected three times (in November, February and May) from eighty dairy farms. The prevalence of Listeria spp. in pasture grass samples was 0.647 and in silage samples 0.227. Only two species, L. monocytogenes and L. innocua were observed. Listeria spp. Were isolated from the silage at least once at thirtynine farms (0.488), and L. monocytogenes at twenty-seven farms (0.338). The occurrence of Listeria was highest among the silage samples collected in November (0.288). Silages preserved with acids had the lowest prevalence of Listeria (0.194). Silages preserved in tower silos were most often free of Listeria, only 0.056 being positive. The highest prevalence of the Listeria spp. (0.324) was detected in clamp silage. The results of chemical analyses of silage statistically reflect the frequency of Listeria.

Notes: An ultrasonic rangefinder (sonic sward stick) was developed for rapidly measuring and recording the undisturbed surface height of swards. HFRO and ultrasonic sward stick measurements of undisturbed sward height over continuously grazed pasture were closely related. The measurements obtained with both instruments were related to the sward mass; the distribution of that mass between leaf, stem and dead material had little effect.

Notes: A mathematical model is presented that predicts the time-course of aerobic deterioration in grass and whole-crop maize silages. The model predicts the stability of the silage taking into account the buffering capacity of the silage, the initial contents of organic acids and ethanol, pH, the initial temperature and the initial populations of the microorganisms. The specific processes simulated include the growth of yeast and acetic acid bacteria, the oxidation of fermentation products, the consumption of oxygen and the production of carbon dioxide, the rise in temperature. and the increase in pH.The deterioration of silage is seen to be initiated by acetic acid bacteria or by yeast, or by both groups together. The factors that determine which groups will prevail are the dry matter contents and the chemical composition of the silage. The output of the model is validated by comparison of the simulated data with data from published work on the deterioration of silage.

Notes: In experiment 1, a mixture of perennial ryegrass and white clover (176 g DM kg−1) was ensiled with no addition, or with the application of Lactobacillus plantarum, 3 × 106(g fresh weight of herbage)−1 or enterobacteria, 3 × 106 (g fresh weight of herbage)−1 or both of these inoculants. Silos were incubated at either 18°C or 26°C for 7 d and sealing of half of the silos was delayed for 48 h. In experiment 2, cocksfoot (247 g DM kg−1) was ensiled with no additive, with the application of L. plantarum, 4 × 106 (g fresh weight of herbage)−1 enterobacteria, 4 × 106 (g fresh weight of herbage)−1 or ammonium nitrate, 5 g (kg herbage)−1. Silos were incubated at 18°C and sealing was delayed for 48 h.In neither experiment were the untreated silages of satisfactory quality after 35 d ensilage, having pH's of 4·3 and 6·4. and ammonia-N concentrations of 139 and 209 g N (kg total N)−1 in experiments 1 and 2 respectively. The poorer fermentation in experiment 2 reflected the lower water-soluble carbohydrate (WSC) content of the ensiled herbage (136 and 53 g WSC (kg DM)−1 in experiments 1 and 2 respectively). Inoculation with L. plantarum significantly reduced silage pH and the concentrations of ammonia-N (experiment 1 only) and ethanol and increased lactic acid concentrations. Inoculation with enterobacteria had only minor effects in each experiment.In experiment 1, incubation at 26°C increased the rate of fermentation in the silos as pH was significantly lower after 7d incubation at 26°C than at 18°C, but this effect had largely disappeared after 35 d incubation. When sealing of the silos was delayed for 48 h, the resulting silages had significantly higher pH and ammonia-N contents than silages from silos that had been sealed immediately after filling.In experiment 2, addition of ammonium nitrate significantly reduced the concentrations of ethanol and acetic acid in silages opened after 7 d. After 35 d the concentrations of ethanol were significantly reduced and those of ammonia-N increased by the addition of ammonium nitrate. There were marked increases in silage pH between 7 and 35 d ensilage and in the concentrations of ammonia-N and acetic acid in the silages that had been inoculated with ammonium nitrate at ensilage.

Notes: Measurements of rates of growth and senescence of leaf lamina per tiller and of changes in tiller population densities were made in three experiments designed to investigate the influence of sward slate on leaf turnover and net production under continuous stocking.In each experiment initially uniform swards were fenced to provide four plots on which animal numbers were adjusted twice weekly to give a series of swards maintained as nearly as possible in a steady state with respect to sward surface height (range 1.1–6.4 cm) and herbage mass (range 440–2690 kg OM ha−1). Two experiments were carried out in July–September on vegetative swards and one in May–June on a reproductive sward. Measurements were begun 3–7 weeks after treatments were started and were repeated weekly during 3–4 week measurement periods.In all three experiments the rate of lamina growth per tiller increased linearly with an increase in sward surface height and herbage mass. In the two experiments conducted in July–August this relationship was partially offset by a linear increase in the rate of senescence per tiller but net production per tiller also increased linearly in relation to sward height and mass. In the experiment conducted in May–June the rates of growth and senescence per tiller increased in parallel so that net production per tiller showed no relationship with sward condition.Tiller population densities in the July–August experiments were highest in swards maintained between 2 and 3 cm surface height and declined in swards maintained above and below this height. In the experiment in May–June tiller numbers were similar in all treatments prior to the summer solstice but diverged in a manner similar to the other experiments later in the year.The rate of lamina growth per unit area increased in a manner consistent with an asymptotic relationship and the rate of senescence increased linearly with increasing sward height and mass in all three experiments. Net production per unit area was reduced on swards below about 2.5 cm in height but was insensitive to variation in sward surface height between 2.5 and 6.0 cm (approximately 1000–2500 kg OM ha−1 herbage mass).The effectiveness of adjustments in tiller numbers and production per tiller and of changes in the balance between growth and senescence as mechanisms of sward homeostatis, together with their implications in the scope for manipulating herbage production by grazing management are discussed briefly.