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SUMMARY The forms of occurrence of Mn were examined in some acidic surface and sub-soils from areas of permanent grassland using chemical extractants. Despite high total contents of Mn in some of the soils and low pH, only minor proportions occurred as exchangeable Mn2+. Much larger proportions were present as reducible hydrous oxides, e.g. up to 38% and 54% of the total contents in surface and subsoils, respectively, were present as hydroquinone extractable, or easily reducible, Mn. Reducible forms of Mn were poorly correlated with other more mobile forms. Large proportions of the total Mn contents were accounted for when estimates of different fractions were calculated from differences in amounts extracted by different individual extractants, i.e. M NH4OAc, 0.2% hydroquinone, 0.1 M pyrophosphate, and ammonium oxalate. The distribution of Mn amongst the different fractions as determined by a sequential fractionation scheme differed markedly from the distribution calculated by differences. In particular, there was a marked change in form after extraction with pyrophosphate. [ABSTRACT FROM AUTHOR]

In Britain, Lychnis viscaria is restricted to shallow soils on outcrops of basic igneous rocks and, in experiments, seedlings grow well on these soils but fail on soils from outcrops of sandstone, limestone and acid igneous rocks. The growth of seedlings in water-culture with purified salts shows that the species does not require an unusual balance of ions and its response to traceelements is normal. Seedlings will only grow on acid soils (other than on basic igneous rocks) if calcium carbonate, nitrogen, potassium and phosphate are provided, and on calcareous soils if phosphate is provided. There is evidence that L. viscaria can obtain phosphate from soils on basic igneous rocks even though other species show severe deficiency. [ABSTRACT FROM AUTHOR]

A description of the development of a mini wind-tunnel system for the measurement of ammonia volatilisation from grass swards is given. Tunnel design was based on that of Lockyer (1984), but scaled in orderto enable controlled laboratory studies to be carried out and allow investigations of the pathways and mechanisms that control NH3 emission and deposition from grassland swards. The potential of the system was examined by using 15N as a tracer in a study measuringNH3 volatilisation from a source of artificial urine. Deposition along the sward was examined up to 70 cm from the source. Deposition onto the leaf surface and uptake into the leaf via stomata were examined with leaf washing experiments and a compensation point inthe range of 0.5-1.9 Mug m-3 was calculated. [ABSTRACT FROM AUTHOR]

The large input of research effort on aspects of nitrate leaching over the last two decades has produced many innovative scientific and practical results. The MAFF Nitrate Programme has enabled considerableprogress to be made in unravelling much of the complexity of the grassland nitrogen (N) cycle, and identifying gaps as essential first stages in providing improved managements for N in grassland systems. From a practical standpoint, there have been key outputs which have allowed the identification of options for policy, and which should allowgrassland farmers to increase the efficiency of N use throughout their farming system and thereby improve the sustainability of their enterprises. As well as quantifying N transformations, transfers and losses, other important outcomes have been the development of user-friendly models of N cycling (NCYCLE and variants) and an easy to use field kit to determine mineral N in pasture soils. The use of modeling toproduce fertilizer recommendations with a Decision Support System and of new approaches developed within the Programme, in particular system synthesis desk studies, and 'farmlet' investigations to determinethe consequences of modifying N flows and losses, have allowed us toproduce solutions to satisfy the dual aims of meeting environmental and economic production targets. [ABSTRACT FROM AUTHOR]

There has been only a few recent field-based measurements to estimate the impact of excreta from grazing animals on methane (CH 4) exchange. We report measurements of CH 4 exchange from cattle dung and urine deposited in a simulated seasonal grazing pattern. Dung and urine samples were deposited on six separate experimental plots at different times of the year to simulate different stagesof normal grazing under UK conditions to study the effects of environmental factors on CH 4 exchange rates. During all the experiments, dung pats were the main emitter of CH 4 with an estimated mean daily rate of 0.72 (range 0.21 to 1.46) g CH 4-C per cow. Both net emission and consumption of CH 4 from urine patches, however, were observed during the different experiments with a negligible mean daily emission of 0.02 (range -0.05 to 0.15) g CH 4-C per cow. Significant variations were observed between the experiments, despite the similarity of application rates and the composition of the excreta. These variations were mainly due to climatic differences when excreta were deposited: ambient temperature and rainfall were the most important factors. The estimated total annual emission of CH 4 from cattle excreta deposition during the grazing season in the UK ranged between 0.42 and 3.26 (mean = 1.57) kt CH 4-C. Our work confirms other studies that suggest that excreta patches are insignificant sources of CH 4 compared to the rumens of grazing cattle, and that climatic factors have a significant impact on CH 4 emissions. [ABSTRACT FROM AUTHOR]

Ammonia is a reactive pollutant emitted primarily by agricultural sources near ground level in the rural environment. The consequence of these factors is that, in addition to the effects of long-range pollutant transport, ammonia has major effects at a local scale, with emission and receptor areas often closely located in the rural landscape.There is a substantial local spatial variability that needs to be considered in effects assessments, while variations in local depositionmay affect the amount of ammonia available for impacts further afield. The wide-ranging UK program ADEPT (Ammonia Distribution and Effects ProjecT) has addressed these issues through a combination of measurement and modeling activities concerning the distribution of emissions, atmospheric transport, deposition and effects assessment. The results are illustrated here by summarizing the findings of a joint experiment at Burrington Moor, Devon, and wider modeling contrasting the variability at a field scale with 5 km resolution estimates for the UK. The fraction of emitted NH3 deposited locally is shown to depend critically on the downwind land-cover, with fluxes being dependent on interactions with the ammonia compensation point. This willrestrict deposition back to agricultural land, but may mean that non-conservation woodlands could be of benefit to recapture a significant fraction of emissions. The generalized models demonstrate the high spatial variability of ammonia impacts, with a case study being used to show the consequences at a field scale. In source regions substantial variability occurs at sub-1 km levels and this will have major consequences for the emission reduction targets needed to protect ecosystems. [ABSTRACT FROM AUTHOR]

Ammonia volatilization from nitrogen (N) fertilizer applied throughout the year to two soil types was measured using a system of small wind tunnels. Losses from urea ranged from 12 to 46% of the applied N. Small losses, averaging less than 1%, were measured from ammonium nitrate (AN) and calcium nitrate applications. Factors influencing theselosses are discussed. Using these results and those from other workers, emission factors for urea and AN applications to grass land in the UK were determined as 23.0 and 1.6% of the applied N, respectively.Emission factors for these fertilizers when applied to arable land were estimated as 11.8 and 0.8%, respectively. The emission factor forall other applied N (as straight and compound fertilizers) was assumed to be similar to that for AN. Calculations showed that fertilizer applications to agricultural land in the UK contributes 34 kt NH3-N per year, equivalent to 17% of the total annual NH3 emission. [ABSTRACT FROM AUTHOR]

Grazing animals on managed pastures and rangelands have been identified recently as significant contributors to the global N2Obudget. This paper summarizes relevant literature data on N2O emissions from dung, urine and grazed grassland, and provides anestimate of the contribution of grazing animals to the global N2O budget. The effects of grazing animals on N2O emission are brought about by the concentration of herbage N in urine and dung patches, and by the compaction of the soil due to treading andtrampling. The limited amount of experimental data indicates that 0.1 to 0.7% of the N in dung and 0.1 to 3.8% of the N in urine is emitted to the atmosphere as N2O. There are no pertinent data about the effects of compaction by treading cattle on N2O emission yet. Integral effects of grazing animals have been obtained by comparing grazed pastures with mown-only grassland. Grazing derivedemissions, expressed as per cent of the amount of N excreted by grazing animals in dung and urine, range from 0.2 to 9.9%, with an overall mean of 2%. Using this emission factor and data statistics from FAOfor numbers of animals, the global contribution of grazing animals was estimated at 1.55 Tg N2O-N per year. This is slightly more than 10% of the global budget. [ABSTRACT FROM AUTHOR]

Before decreasing yield significantly, copper deficiency affected the amounts of phenolic compounds released (by treatment with sodium hydroxide) from the cell walls separated from young leaves of wheat. Effects of changes in copper supply on the amounts of phenolic compounds released followed closely its effect on copper concentration in the plant parts. More ferulic and less p-coumaric acid was released from the walls of young leaves of copper-deficient plants than from those of copper-adequate ones; these differences were less marked in older than in younger leaves. Copper deficiency decreased the lignin, hemicellulose and acetyl contents of cell walls only in severely deficient plants. [ABSTRACT FROM AUTHOR]