Showing papers in "Nutrient Cycling in Agroecosystems in 1998"

Influence of lime, fertilizer and manure applications on soil organic matter content and soil physical conditions: A review

Abstract: The effects of lime, fertilizer and manure applications on soil organic matter status and soil physical properties are of importance to agricultural sustainability. Their effects are complex and many interactions can occur. In the short-term, liming can result in dispersion of clay colloids and formation of surface crusts. As pH is increased the surface negative charge on clay colloids increases and repulsive forces between particles dominate. However, at higher lime rates, Ca2+ concentrations and ionic strength in soil solution increase causing compression of the electrical double layer and renewed flocculation. When present in sufficient quantities, both lime and hydroxy-Al polymers formed by precipitation of exchangeable Al, can act as cementing agents bonding soil particles together and improving soil structure. Liming often causes a temporary flush of soil microbial activity but the effect of this on soil aggregation is unclear. It is suggested that, in the long-term, liming will increase crop yields, organic matter returns, soil organic matter content and thus soil aggregation. There is a need to study these relationships on existing long-term liming trials. Fertilizers are applied to soils in order to maintain or improve crop yields. In the long-term, increased crop yields and organic matter returns with regular fertilizer applications result in a higher soil organic matter content and biological activity being attained than where no fertilizers are applied. As a result, long-term fertilizer applications have been reported, in a number of cases, to cause increases in water stable aggregation, porosity, infiltration capacity and hydraulic conductivity and decreases in bulk density. Fertilizer additions can also have physico-chemical effects which influence soil aggregation. Phosphatic fertilizers and phosphoric acid can favour aggregation by the formation of Al or Ca phosphate binding agents whilst where fertilizer NH4 + accumulates in the soil at high concentrations, dispersion of clay colloids can be favoured. Additions of organic manures result in increased soil organic matter content. Many reports have shown that this results in increased water holding capacity, porosity, infiltration capacity, hydraulic conductivity and water stable aggregation and decreased bulk density and surface crusting. Problems associated with large applications of manure include dispersion caused by accumulated K+, Na+ and NH4 + in the soil and production of water-repellant substances by decomposer fungi.

Closing the global N2O budget: nitrous oxide emissions through the agricultural nitrogen cycle

Abstract: In 1995 a working group was assembled at the request of OECD/IPCC/IEA to revise the methodology for N2O from agriculture for the National Greenhouse Gas Inventories Methodology. The basics of the methodology developed to calculate annual country level nitrous oxide (N2O) emissions from agricultural soils is presented herein. Three sources of N2O are distinguished in the new methodology: (i) direct emissions from agricultural soils, (ii) emissions from animal production, and (iii) N2O emissions indirectly induced by agricultural activities. The methodology is a simple approach which requires only input data that are available from FAO databases. The methodology attempts to relate N2O emissions to the agricultural nitrogen (N) cycle and to systems into which N is transported once it leaves agricultural systems. These estimates are made with the realization that increased utilization of crop nutrients, including N, will be required to meet rapidly growing needs for food and fiber production in our immediate future. Anthropogenic N input into agricultural systems include N from synthetic fertilizer, animal wastes, increased biological N-fixation, cultivation of mineral and organic soils through enhanced organic matter mineralization, and mineralization of crop residue returned to the field. Nitrous oxide may be emitted directly to the atmosphere in agricultural fields, animal confinements or pastoral systems or be transported from agricultural systems into ground and surface waters through surface runoff. Nitrate leaching and runoff and food consumption by humans and introduction into sewage systems transport the N ultimately into surface water (rivers and oceans) where additional N2O is produced. Ammonia and oxides of N (NOx) are also emitted from agricultural systems and may be transported off-site and serve to fertilize other systems which leads to enhanced production of N2O. Eventually, all N that moves through the soil system will be either terminally sequestered in buried sediments or denitrified in aquatic systems. We estimated global N2O–N emissions for the year 1989, using midpoint emission factors from our methodology and the FAO data for 1989. Direct emissions from agricultural soils totaled 2.1 Tg N, direct emissions from animal production totaled 2.1 Tg N and indirect emissions resulting from agricultural N input into the atmosphere and aquatic systems totaled 2.1 Tg N2O–N for an annual total of 6.3 Tg N2O–N. The N2O input to the atmosphere from agricultural production as a whole has apparently been previously underestimated. These new estimates suggest that the missing N2O sources discussed in earlier IPCC reports is likely a biogenic (agricultural) one.

Ammonia volatilization from dairy farming systems in temperate areas: a review

Abstract: Ammonia (NH3) emissions from dairy farm systems cause environmental problems. This paper reviews and quantifies the major loss routes of NH3 in dairy farms. Furthermore, management options are discussed that reduce NH3 losses. Losses of NH3 occur during slurry application, housing, slurry storage, grazing, fertilizer application and from crops, in descending order of importance. Animal waste is the major source in four of the six cases. This ranking varies between farms and between countries, depending on environmental conditions and management practices. Total NH3 losses range from 17 to 46 kg N cow yr-1, reflecting the variability in amount and composition of animal excreta (urine + faeces), management of the slurry and soil and environmental conditions. The amount and composition of urine and faeces depend on N tranformations in the digestive track of the cow. Of the major nitrogen compounds excreted urea has the highest potential for NH3 volatilization followed by allantoin, uric acid and creatinine in decreasing order. Creatine, xanthine and hypoxanthine have a low NH3 volatilization potential. Reducing the excretion of urea and urea like products by optimizing N Intake (NI) and N Retention (NR) is one way of decreasing NH3 losses. Improvement is possible since NR is about 20% of NI in practice, whereas 43% is theoretically possible. The second solution is to reduce the rate of NH3 loss by technical means like direct incorporation of slurry into the soil, dilution or acidification of slurry, covering of the slurry storage and/or acidification or dilution of slurry in the storage. These techniques have been known for a long time and now become available on a large scale in practice. Reducing the surface area per cow in the shed and sprinkling floors with water to remove and to dilute urine also decreases NH3 loss. Reducing NH3 loss requires a whole farm system approach, because it shows how intervening in one part may affect NH3 losses in other parts of the system. Reducing NH3 loss may increase nitrate leaching and denitrification. To prevent this, the achieved reduction in NH3 loss should lead to a reduction of total N input of fertilizers, concentrates and forage on the N budget of the farm, which is possible as a reduction of NH3 loss improves the N fertilizing value of slurry. Model calculations showed great scope for reducing NH3 losses on dairy farms by improved management. Up to three fold reductions in NH3 loss are possible together with marked reductions in mineral fertilizer usage. The rate at which improved management techniques, will be introduced in practice depends on legislation, the applicability of new techniques and the expected increase in net production costs. To comply with environmental targets requires a huge effort of farmers with associated high costs.

Comparison of N2O emissions from soils at three temperate agricultural sites: simulations of year-round measurements by four models

Abstract: Nitrous oxide (N2O) flux simulations by four models were compared with year-round field measurements from five temperate agricultural sites in three countries. The field sites included an unfertilized, semi-arid rangeland with low N2O fluxes in eastern Colorado, USA; two fertilizer treatments (urea and nitrate) on a fertilized grass ley cut for silage in Scotland; and two fertilized, cultivated crop fields in Germany where N2O loss during the winter was quite high. The models used were daily trace gas versions of the CENTURY model, DNDC, ExpertN, and the NASA-Ames version of the CASA model. These models included similar components (soil physics, decomposition, plant growth, and nitrogen transformations), but in some cases used very different algorithms for these processes. All models generated similar results for the general cycling of nitrogen through the agro-ecosystems, but simulated nitrogen trace gas fluxes were quite different. In most cases the simulated N2O fluxes were within a factor of about 2 of the observed annual fluxes, but even when models produced similar N2O fluxes they often produced very different estimates of gaseous N loss as nitric oxide (NO), dinitrogen (N2), and ammonia (NH3). Accurate simulation of soil moisture appears to be a key requirement for reliable simulation of N2O emissions. All models simulated the general pattern of low background fluxes with high fluxes following fertilization at the Scottish sites, but they could not (or were not designed to) accurately capture the observed effects of different fertilizer types on N2O flux. None of the models were able to reliably generate large pulses of N2O during brief winter thaws that were observed at the two German sites. All models except DNDC simulated very low N2O fluxes for the dry site in Colorado. The US Trace Gas Network (TRAGNET) has provided a mechanism for this model and site intercomparison. Additional intercomparisons are needed with these and other models and additional data sets; these should include both tropical agro-ecosystems and new agricultural management techniques designed for sustainability.

Nitrous oxide emissions from agricultural fields during winter and spring thaw as affected by management practices

Abstract: Highest rates of N2O emissions from fertilized as well as natural ecosystems have often been measured at spring thaw. But, it is not clear if management practices have an effect on winter and spring thaw emissions, or if measurements conducted over several years would reveal different emission patterns depending on winter conditions. In this study, we present N2O fluxes obtained using the flux-gradient approach over four winter and spring thaw periods, spanning from 1993 to 1996, at two locations in Ontario, Canada. Several agricultural fields (bare soil, barley, soybean, canola, grass, corn) subjected to various management practices (manure and nitrogen fertilizer addition, alfalfa ploughing, fallowing) were monitored. Nitrous oxide emissions from these fields from January to April over four years ranged between 0 and 4.8 kg N ha-1. These thaw emissions are substantial and should be considered in the nitrous oxide budgets in regions where thaw periods occur. Our study indicates that agricultural management can play a role in mitigating these emissions. Our data show that fallowing, manure application and alfalfa incorporation in the fall lead to high spring emissions, while the presence of plants (as in the case of alfalfa or grass) can result in negligible emissions during thaw. This presents an opportunity for mitigation of N2O emissions through the use of over-wintering cover crops.

Measurement of nitrous oxide and di-nitrogen emissions from agricultural soils

Abstract: Nitrous oxide can be produced during nitrification, denitrification, dissimilatory reduction of NO 3 - to NH 4 + and chemo-denitrification. Since soils are a mosaic of aerobic and anaerobic zones, it is likely that multiple processes are contributing simultaneously to N2O production in a soil profile. The N2O produced by all processes may mix to form one pool before being reduced to N2 by denitrification. Reliable methods are needed for measuring the fluxes of N2O and N2 simultaneously from agricultural soils. The C2H2 inhibition and 15N gas-flux methods are suitable for use in undisturbed soils in the field. The main disadvantage of C2H2 is that as well as blocking N2O reductase, it also blocks nitrification and dissimilatory reduction of NO 3 - to NH 4 + . Potentially the 15 N gas-flux method can give reliable measurements of the fluxes of N2O and N2 when all N transformation processes proceed naturally. The analysis of 15N in N2 and N2O is now fully automated by continuous-flow isotope-ratio mass spectrometry for 12-ml gas samples contained in septum-capped vials. Depending on the methodology, the limit of detection ranges from 4 to 11 g N ha-1day-1 for N2 and 4 to 15 g N ha-1day-1 for N2O. By measuring the 15N content and distribution of 15N atoms in the N2O molecules, information can also be obtained to help diagnose the sources of N2O and the processes producing it. Only a limited number of field studies have been done using the 15N gas-flux method on agricultural soils. The measured flux rates and mole fractions of N2O have been highly variable. In rain-fed agricultural soils, soil temperature and water-filled pore space change with the weather and so are difficult to modify. Soil organic C, NO 3 - and pH should be amenable to more control. The effect of organic C depends on the degree of anaerobiosis generated as a result of its metabolism. If conditions for denitrification are not limiting, split applications of organic C will produce more N2O than a single application because of the time lag in the synthesis of N2O reductase. Increasing the NO 3 - concentration above the K m value for NO 3 - reductase, or decreasing soil pH from 7 to 5, will have little effect on denitrification rate but will increase the mole fraction of N2O. The effect of NO 3 - concentration on the mole fraction of N2O is enhanced at low pH. Manipulating the interaction between NO 3 - supply and soil pH offers the best hope for minimising N2O and N2 fluxes.

Atmospheric ammonia and ammonium transport in Europe and critical loads: a review

Abstract: The atmosphere in Europe is polluted by easily available nitrogen (ammonium and nitrate) mainly from livestock (NH3), traffic (NOx) and stationary combustion sources (NOx). The nitrogen emission from various European sources decreases in the order: agriculture, road traffic, stationary sources and other mobile sources (including vehicular emissions from agriculture), with annual emissions of approximately 4.9, 2.7, 2.7 and 0.8 Mt N respectively. The emissions have increased dramatically during the latest decades. In the atmosphere the pollutants are oxidised to more water soluble compounds that are washed out by clouds and eventually brought back to the earth's surface again. Since ammonia is emitted in a highly water soluble form it will also to a substantial degree be dry deposited near the source. Ammonia is, however, the dominant basic compound in the atmosphere and will form salts with acidic gases. These salt particles can be transported long distances especially in the absence of clouds. The deposition close to the source is substantial, but hard to estimate due to interaction with other pollutants. Far from the source the deposition of ammonium is on an annual average halved approximately every 400 km. This short transport distance and the substantial deposition near the source makes it possible for countries to control their ammonium deposition by decreasing their emissions, provided that there is no country with much higher emission in the direction of the prevailing wind trajectory. When the easily available nitrogen is deposited on natural ecosystems (lakes, forests), negative effect can occur. The effect is determined by the magnitude of the deposition and the type of ecosystems (its critical load for nitrogen). In order to reduce the negative effects by controlling the emissions in a cost-efficient way it is necessary to use atmospheric transport models and critical loads.

Compost mulch effects on soil fertility, nutritional status and performance of grapevine

Abstract: Two composts were tested as mulching materials in a vineyard: one was a sewage sludge and bark compost with a low heavy metal content, the other was a municipal solid waste compost with a higher concentration of metals. Both compost mulches increased organic matter content, available phosphorous and exchangeable potassium of soil and improved the porosity and water retention capacity of the soil. They also reduced soil temperature fluctuations, reduced evaporation of soil water, and influenced the levels of some nutrients measured in leaf samples. The data obtained show that the nutrients uptake was more influenced by the physical conditions of the soil (temperature, moisture) than by the availability of nutrients in the soil. The sewage sludge and bark compost did not cause any significant increase in heavy metal levels in soil and plants. In contrast, the municipal solid waste compost led to a notable accumulation of metals in the soil, in the vegetation and in the musts. Both the compost mulch materials had considerable advantages for the soil management on the grapevine rows, by reducing chemical weed control and allowing for the substitution of chemical fertilisers with no loss in vigour, yield or quality of musts.

An assessment of human influences on fluxes of nitrogen from the terrestrial landscape to the estuaries and continental shelves of the North Atlantic Ocean

Abstract: Our analysis for the International SCOPE Nitrogen Project shows that the fluxes of nitrogen in rivers to the coast of the North Atlantic Ocean vary markedly among regions, with the lowest fluxes found in northern Canada (76 kg N km−2 yr−1) and the highest fluxes found in the watersheds of the North Sea (1450 kg N km−2 yr−1). Non-point sources of nitrogen dominate the flux in all regions. The flux of nitrogen from the various regions surrounding the North Atlantic is correlated (r2 = 0.73) with human-controlled inputs of nitrogen to the regions (defined as net inputs of nitrogen in food, nitrogen fertilizer, nitrogen fixation by agricultural crops, and atmospheric deposition of oxidized nitrogen), and human activity has clearly increased these nitrogen flows in rivers. On average, only 20% of the human-controlled inputs of nitrogen to a region are exported to the ocean in riverine flows; the majority (80%) of these regional nitrogen inputs is stored in the landscape or denitrified. Of all the nitrogen inputs to regions, atmospheric deposition of NOy is the best predictor of riverine export of nitrogen from non-point sources (r2 = 0.81). Atmospheric deposition of this oxidized nitrogen, most of which derives from fossil-fuel combustion, may be more mobile in the landscape than are regional inputs of nitrogen from fertilizer, nitrogen fixation in agriculture, and nitrogen in foods and feedstocks. Agricultural sources of nitrogen, although larger total inputs to most temperate regions surrounding the North Atlantic Ocean, appear to be more tightly held in the landscape. Deposition of ammonium from the atmosphere appears to be a very good surrogate measure of the leakiness of nitrogen from agricultural sources to surface waters. This suggests a management approach for controlling ‘surplus’ nitrogen used in agricultural systems. The sum of NOy and ammonium deposition proves to be an amazingly powerful predictor of nitrogen fluxes from non-point sources to the coastal North Atlantic Ocean for temperate-zone regions (r2 = 0.92; p = 0.001). By comparing fluxes with some estimates of what occurs in watersheds with minimal human impact, it appears that human activity has increased riverine nitrogen inputs to the ocean by some 11-fold in the North Sea region, by 6-fold for all of Europe, and by 3-fold for all of North America. These increased flows of nitrogen have clearly led to severe eutrophication in many estuaries, and have probably contributed to some eutrophication on the continental shelf in the North Sea and in the Gulf of Mexico. In other regions, however, the input of nitrogen to continental shelves is dominated by cross-shelf advection from deep-Atlantic waters, and the increased inputs from rivers are relatively minor.

Subsoils: chemo-and biological denitrification, N2O and N2 emissions

Abstract: Agricultural practices, soil characteristics and meteorological conditions are responsible for eventual nitrate accumulation in the subsoil There is a lot of evidence that denitrification occurs in the subsoil and rates up to 60–70 kg ha-1 yr-1 might be possible It has also been shown that in the presence of Fe2+ (formed through weathering of minerals) and an alkaline pH, nitrate can be chemically reduced Another possible pathway of disappearance is through the formation of nitrite, which is unstable in acid conditions With regard to the emission of N2O and N2, it can be stated that all conditions whereby the denitrification process becomes marginal are favourable for N2O formation rather than for N2 Because of its high solubility, however, an important amount of N2O might be transported with drainage water

Emmissions of N2O from Scottish agricultural soils, as a function of fertiliser N

Abstract: Potato fields and cut (ungrazed) grassland in SE Scotland gave greater annual N2O emissions per ha (1.0–3.2 kg N2O–N ha-1) than spring barley or winter wheat fields (0.3–0.8 kg N2O–N ha-1), but in terms of emission per unit of N applied the order was potatoes > barley > grass > wheat. On the arable land, especially the potato fields, a large part of the emissions occurred after harvest.

N2o emission from cropland in china

Abstract: Based on the regionalization of uplands and paddy fields in China, the crop intensity in each region and the available field measurements, N2O emission from cropland in China in 1995 was estimated to be 398 Gg N, in which, 310 Gg N was from uplands, accounting for 78% of the total. 88 Gg N–N2O was emitted from paddy fields with 35 Gg N emitted during the rice growing season and 53 Gg N emitted during upland crop season. N2O emission from upland and from paddy field during upland land crop season accounted for 91% of the total emission.

Nitrogen inputs to rivers, estuaries and continental shelves and related nitrous oxide emissions in 1990 and 2050: a global model

Abstract: The purpose of the current paper is to estimate future trends (up to the year 2050) in the global geographical distribution of nitrous oxide (N2O) emissions in rivers, estuaries, and continental shelf regions due to biological processes, particularly as they are affected by anthropogenic nitrogen (N) inputs, and to compare these to 1990 emissions. The methodology used is from Seitzinger and Kroeze (1998) who estimated 1990 emissions assuming that N2O production in these systems is related to nitrification and denitrification. Nitrification and denitrification in rivers and estuaries were related to external inputs of nitrogen to those systems. The model results indicate that between 1990 and 2050 the dissolved inorganic nitrogen (DIN) export by rivers more than doubles to 47.2 Tg N in 2050. This increase results from a growing world population, associated with increases in fertilizer use and atmospheric deposition of nitrogen oxides (NOy). By 2050, 90% of river DIN export can be considered anthropogenic. N2O emissions from rivers, estuaries and continental shelves are calculated to amount to 4.9 (1.3 – 13.0) Tg N in 2050, of which two-thirds are from rivers. Aquatic emissions of N2O are calculated to increase faster than DIN export rates: between 1990 and 2050, estuarine and river emissions increase by a factor of 3 and 4, respectively. Emissions from continental shelves, on the other hand, are calculated to increase by only 12.5%.

Some considerations on methods for spatially aggregating and disaggregating soil information

Abstract: Some possible approaches to the aggregation and disaggregation of soil data and information are presented as an opener to the more detailed discussion The concepts of hierarchy, grain, extent, scale and variability are discussed Slight modifications to the Hoosbeek-Bryant scheme to deal with spatial and temporal scales and various types of quantitative models are suggested Approaches to aggregation or upscaling are reviewed The contributions of representative elementary volume (REV), variograms, fractal theory, multi-resolution analysis using wavelets, critical point phenomena, renormalisation groups and transfer functions are discussed followed by a brief presentation of some ecological approaches including extrapolation by lumping, extrapolation by increasing model extent and extrapolation by explicit integration A clear distinction must be made between additive and non-additive variables The scaling of the former is much less problematic than the latter Corroboration of any approach by testing against the aggregated values seems problematic Methods of disaggregation or downscaling including transfer functions, mass-preserving or pycnophylactic methods are also discussed In order to make quantitative advances, nested sampling or reanalysis of data in land information systems to obtain variance information over a complete range of scales is required Finally an appeal is made for work to begin on a quantitative scale-explicit theory of soil variation

Uncertainty analysis in environmental modelling under a change of spatial scale

Abstract: Although environmental processes at large scales are to a great degree the resultant of processes at smaller scales, models representing these processes can vary considerably from scale to scale. There are three main reasons for this. Firstly, different processes dominate at different scales, and so different processes are ignored in the simplification step of the model development. Secondly, input data are often absent or of a much lower quality at larger scales, which results in a tendency to use simpler, empirical models at the larger scale. Third, the support of the inputs and outputs of a model changes with change of scale, and this affects the relationships between them. Given these reasons for using different models at different scales, application of a model developed at a specific scale to a larger scale should be treated with care. Instead, models should be modified to suit the larger scale, and for this purpose uncertainty analyses can be extremely helpful. If upscaling disturbed the balance between the contributions of input and model error to the output error, then an uncertainty analysis will show this. Uncertainty analysis will also show how to restore the balance. In practice, application of uncertainty analysis is severely hampered by difficulties in the assessment of input and model error. Knowledge of the short distance spatial variability is of paramount importance to input error assessment with a change of support, but current geographical databases rarely convey this type of information. Model error can only be estimated reliably by validation, but this is not easy because the support of model predictions and validation measurements is usually not the same.

Nitrous oxide production in riparian zones and groundwater

Abstract: This paper addresses the question of whether riparian zones and groundwater are ‘hotspots’ of nitrous oxide (N2O) flux in the landscape. First, we describe how riparian zones and groundwater function as transformers of N, with a particular emphasis on mechanisms of N2O production in these ecosystems. We then present specific data on N2O flux in these ecosystems and attempt to reconcile these data with existing regional scale estimates of N flux for Norway and with estimates of N2O flux for Norway produced using the OECD/IPCC/IEA Phase II methodology for calculation of regional and global N2O budgets. While the OECD/IPCC/IEA approach produces estimates of riparian and groundwater N2O flux that are reasonable, given what we know about regional scale N balances and actual data on N2O flux, it does not allow us to determine if riparian zones and groundwater are ‘hotspots’ of N2O production in the landscape. The approach fails to answer this question because it is unable to account for spatially explicit phenomena such as riparian and groundwater processing of excess agricultural N. Research needs that would allow us to address this question are discussed.

Ammonia and nitrous oxide emissions from grass and alfalfa mulches

Abstract: Ammonia (NH3) and nitrous oxide (N-2O) emissions were measured in the field for three months from three different herbage mulches and from bare soil, used as a control. The mulches were grass with a low N-content (1.15% N in DM), grass with a high N-content (2.12% N in DM) and alfalfa with a high N-content (4.33% N in DM). NH3 volatilization was measured using a micrometeorological technique. N-2O emissions were measured using closed chambers. NH3 and N-2O emissions were found to be much higher from the N-rich mulches than from the low-N grass and bare soil, which did not differ significantly. Volatilization losses of NH3 and N-2O occurred mainly during the first month after applying the herbage and were highest from wet material shortly after a rain. The extent of NH3-N losses was difficult to estimate, due to the low frequency of measurements and some problems with the denuder technique, used on the first occasions of measurements. Nevertheless, the results indicate that NH3-N losses from herbage mulch rich in N can be substantial. Estimated losses of NH3-N ranged from the equivalent of 17% of the applied N for alfalfa to 39% for high-N grass. These losses not only represent a reduction in the fertilizer value of the mulch, but also contribute appreciably to atmospheric pollution. The estimated loss of N-2O-N during the measurement period amounted to 1% of the applied N in the N-rich materials, which is equivalent to at least 13 kg N-2O-N ha-1 lost from alfalfa and 6 kg ha-1 lost from high-N grass. These emission values greatly exceed the 0.2 kg N-2O-N ha-1 released from bare soil, and thus contribute to greenhouse gas emissions.

Scale issues in agroecological research chains

Abstract: Translating information about soil characteristics and qualities across different spatial and temporal scales has emerged as a major theme in soil science. The interest in scale has developed as our understanding of processes operating at scales larger (e.g. landscape, regional) or smaller (molecular, aggregate) than the field plot has increased. As next steps are considered in this area, an examination of the ecological literature presents some valuable philosophical and practical concepts pertaining to the translation of information across scales. The concepts of hierarchy and the holon are particularly relevant to the study of soil as a component of an ecosystem. The experience of the ecologists over the last 30 years suggests both opportunities and constraints for the study of soil systems at different spatial and temporal scales. As an example, our ability to predict soil processes at the small scale given large scale information (“down” scaling) is much worse than our ability to scale “up”. Moreover, while there have been several successful efforts to scale up certain types of information, we have been unable to predict large-scale phenomena given small scale information in several important instances. Ecological studies provide relevant insight. Different approaches to scale translation, and the successes and failures of these different approaches, have important implications for soil characterization and identification of land qualities as we address contemporary environmental problems at different scales. It is suggested that current scale translation efforts of all types fail for one of two main reasons; (1) either a key controlling process or characteristic has been overlooked, or (2) when multiple factors interact to create unique phenomena.

Long term effects of inorganic fertilizer inputs on crop productivity in a rice-wheat cropping system

Abstract: Three levels of N (40,80,120 kg N ha-1) and P (0,17.5,35 kg P ha-1), and 2 levels of K (0,33 kg K ha-1) were tested for 19 years in rice and wheat crops of a rice-wheat cropping system in a fixed layout of 3×2×2 factorial partially confounded design along with one control and 3 replications. From this trial, data of 7 treatments, i.e. 0-0-0, 40-35-33, 80-35-33, 120-35-33, 120-0-0, 120-35-0 and 120-0-33 kg ha-1 N-P-K respectively were compared for yield trends, changes in response functions, soil organic -C and available N,P,K status. Soil organic - C decreased in unfertilized plots by 62% (over initial value of 0.45%) but increased by 44, 40 and 36% in plots receiving 120-35-33, 120-35-0 and 80-35-33 kg ha-1 N-P-K respectively. Available N was also greatest in these same three treatments. Available soil P increased by about 5 fold in 15 years in treatments supplied with fertilizer P, but no significant change was detected in treatments without P addition. Yields of rice and wheat exhibited linear declining trend in all treatments. The highest rate of decline (89 kg ha-1 year-1 in rice and 175 kg ha-1 year-1 in wheat), however, was found when 120 kg ha-1 N was applied alone. The least rate of decline of 20 kg ha-1 year-1 in rice and 58 kg ha-1 year-1 in wheat was observed when 40-35-33 kg ha-1 N-P-K respectively was applied to both the crops. At currently recommended levels of NPK (120-35-33 kg ha-1), the rate of decline in yields was 25 kg ha-1 year-1 for rice and 62 kg ha-1 year-1 for wheat. Possible causes of these yield declines are discussed.

Influence of nitrogen nutrition and metabolism on ammonia volatilization in plants

Abstract: Barley (Hordeum vulgare L. cv. Golf) was grown in solution culture with controlled nitrogen availability in order to study the influence of nitrogen nutrition on ammonia emission from the leaves. Ammonia emission measured in cuvettes connected to an automatic NH3 monitor was close to zero for nitrate grown plants but increased to 0.9–1.3 nmol NH3 m-2 leaf area s-1 after 3–5 days of ammonium nutrition. Increasing concentrations from 0.5 to 10 mM NH4+ in the root medium increased NH3 emission from the shoots, root glutamine synthetase activity and NH4+ concentrations in apoplast, xylem sap and bulk tissue, while apoplastic pH values decreased.

Research on soil fertility decline in tropical environments: integration of spatial scales.

Abstract: Soil nutrient depletion is increasingly regarded as a major constraint to sustainable food production in tropical environments. Research in the recent past focused on different scales, but few attempts were made to link them. In this paper, two cases are elaborated in Central America (CA) and Sub-Saharan Africa (SSA), in which the integration of different scales has been studied. Soil nutrient depletion has been calculated for fields, and has then been aggregated to farms, regions, and subcontinents. Key problems on aggregation of field nutrient balances to farms include nutrient flows between fields. Aggregation of farms to regions requires a generalization of individual farms into a farm typology. Aggregation of regions into subcontinents implies that the farm typology concept can mostly not be maintained, resulting in a generalized calculation based on national soil, climate and land use data bases. The field-farm step proved complicated for SSA due to the occurrence of a wide variety of nutrient flows between fields, whereas in CA these flows were much less pronounced; the farm-region step turned out to be manageable for both CA and SSA as farm typology adequately covered observed variation; the region-subcontinent step proved difficult for CA due to the considerable variation in management and input levels in farming systems, whereas this was less the case in SSA. The study shows that integration of spatial scales is constrained by both data availability (the tropical parameter crisis) and by scale-specific variability.

Thermal analysis in the evaluation of compost stability : a comparison with humification parameters

Abstract: Characterization of organic matter of six composts from agroindustrial wastes was carried out by both chemical analysis and thermal analysis in order to assess their level of stability. Degree of humification (DH%) and index of humification (HI) were calculated after extraction, fractionation and analysis of the organic carbon from composts. Differential Scanning Calorimetry (DSC) and thermogravimetry (TG) were simultaneously performed in oxidizing conditions on whole ground composts. Thermoanalitical data resulted to be useful in integrating quantitative information coming from chemical analysis of humified fraction of compost organic matter. Particularly, DSC curves allow to distinguish between well and poor stabilized composts, and information deriving from weight losses, registered by TG curves, permits to individuate a thermoanalytical parameter (R1) that resulted to be well correlated to humification parameters DH% and HI.

Treatment of solid animal manures : identification of low nh3 emission practices

Abstract: Cattle and pig dung and poultry excreta were used in laboratory experiments to study the effect of different solid manure treatments concerning NH3 losses during storage and after application to soil. Aerobic decomposition (composting) during incubation (storage) resulted in drastically higher NH3 emissions compared with anaerobic decomposition conditions. Application of the aerobically treated materials to soil resulted in low NH3 losses, as NH4-N concentrations were low in these materials. Anaerobically treated materials and non-decomposed poultry excreta gave rise to significant NH3-N emissions as a result of highly increased ammoniacal N concentrations in soil, if applied on the soil surface. Rates of NH3-N volatilization from soil surface-applied manures were closely related to the pH changes taking place on the surface. Maximum pH values attained explained 79% of the variance in the extent of NH3 volatilization. Incorporation of animal dung into soil to 5 cm depth or below reduced ammonia volatilization by 80% compared with surface application.

Phosphorus and potassium soil test and nitrogen leaf analysis as a base for citrus fertilization

Abstract: A network of six NPK long-term field trials was carried out on different soils of citrus-producing regions of Sao Paulo state, Brazil, in order to estimate quantitative relations of fruit yield to NPK fertilization and to determine parameters for fertilizer recommendation based on soil testing and leaf analysis The experiments were set up in an incomplete factorial design 1/2 43 with 32 treatments, with four yearly rates of N (30, 100, 170 and 240 kg N/ha), P (9, 27, 45 and 63 kg P/ha) and K (25, 91, 157 and 223 kg K/ha) Four to seven harvests were recorded for the six experiments Response surfaces of the type y = bo + b1N + b11N2 + b2P + b22P2 + b3K + b33K2 + b12NP + b13NK + b23PK were adjusted to the average yields of each trial Correlation were established for yield increases, expressed as relative yields, and results of soil analysis of P and K, and leaf analysis of N Soil samples taken at 0-20 cm depth in the beginning of each experiment were analyzed for resin extractable P and exchangeable K using an ion-exchange resin procedure Yield responses for phosphorus and potassium applications were observed respectively in soils with less than 20 mg dm-3 of P and 20 mmolc dm-3 of K+ Yield responses to nitrogen were related to the total content of nitrogen in leaves, being largest for N values of 23 g kg-1 and smallest for N of 28 kg-1 With these field information, a practical approach for fertilizer recommendation for citrus, based on soil analysis for P and K and leaf analysis for N, was developed

Technical measures to reduce ammonia losses after spreading of animal manure

Abstract: During the years 1992-1995, field trials were conducted at the Swedish Institute of Agricultural Engineering (JTI) to investigate the efficiency of different techniques to reduce ammonia emissions after spreading of liquid and solid manures (i.e. slurries and farmyard manures). Ammonia emissions were measured with passive diffusion samplers. Results clearly show that the most effective way to reduce ammonia emissions is to inject or incorporate the manure into the soil. When applying slurry in a growing crop, band spreading gives a lower emission than broadcasting. Irrigation after spreading also reduces ammonia emissions. Solid manure can give rise to substantially greater ammonia emissions than slurry when applied at the same rate under identical environmental conditions and should not generally be considered as a low-concentrated N fertilizer.

Fertilizers, agronomy and N2O

Abstract: N2O is emitted from agricultural soils due to microbial transformation of N from fertilizers, manures and soil N reserves. N2O also derives from N lost from agriculture to other ecosystems: as NH3 or through NO3- leaching. Increased efficiency in crop N uptake and reduction of N losses should in principle diminish the amount of N2O from agricultural sources. Precision in crop nutrient management is developing rapidly and should increase this efficiency. It should be possible to design guidelines on good agricultural practices for low N2O emissions in special situations, e.g. irrigated agriculture, and for special operations, e.g. deep placement of fertilizers and manures. However, current information is insufficient for such guidelines. Slow-release fertilizers and fertilizers with inhibitors of soil enzymatic processes show promise as products which give reduced N2O emissions, but they are expensive and have had little market penetration. Benefits and possible problems with their use needs further clarification.

Relevance of scale dependent approaches for integrating biophysical and socio-economic information and development of agroecological indicators

Abstract: Issues of environmental sustainability, limits to growth and opportunity, introduction of new technology, and the economic and social costs of resource degradation have forced more proactive integration of biophysical and socio-economic data Natural resources management, including soil, water and land quality, involve balancing the often conflicting objectives of food and fibre production under scenarios of increasing demand, while increasing economic efficiency and maintaining the quality of the environment It involves integration of data from several disparate disciplines, scaling the data to make them compatible on input, identifying strategic indicators, criteria and thresholds with which to assess the state and performance of the system, and the application of biophysical and economic optimisation models to examine the impacts and trade-offs of alternate management options However, some basic questions of scales and hierarchies still have to be resolved, eg how to “scale-up” the biophysical data to the level at which public policy is formulated without losing the integrity of the data This paper examines these and related issues by discussing the theories and principles of spatial and temporal hierarchies and scales, and providing some examples of application

The mycorrhizal fungus Glomus mosseae enhances growth, yield and chemical composition of a durum wheat variety in 10 different soils

Abstract: The effect of the vesicular arbuscularmycorrhizal fungus (VAMF) Glomus mosseae ongrowth, yield and nutrients' uptake of the durum wheatvariety ‘Sifnos’ was investigated in ten differentsoils. Inoculation had a positive effect on tillering,improved plant growth up to 11.6 times and increasedgrain yield up to 5.4 times as compared tonon-inoculated plants. The thousand kernels weight wasimproved by up to 60%. The analysis of shoot tissue ofthe mycorrhizal plants showed that P concentration wasincreased up to 4 fold, while the K, Ca and Mg uptakewas similar for both mycorrhizal and non-mycorrhizalplants. The concentrations of the trace elements Mn,Zn, Fe and Cu were lower in the mycorrhizal plantscompared to that of non-inoculated ones. The P and Mgconcentration of the grains produced by the inoculatedplants was increased while the Ca concentration wasdecreased. The concentration of the heavy metals waseither decreased ( Mn, Fe, Co, Cr, Ni, Pb) or remainedunchanged (Zn, Cu). The colonization in the roots ranged from 23 to 78%.

Can organic farming help to reduce n-losses? experiences from denmark

Abstract: This study is in two parts. In the first part, nitrogen (N) losses per unit of milk and meat in Danish conventional and organic pig and dairy farming were compared on the basis of farm data. In the second part, organic and conventional dairy farming were compared in detail, using modelling. N-surpluses at different livestock densities, fodder intensities, and soil types were simulated. Finally, simulated N-surpluses were used in national scenarios for conversion to organic dairy farming in Denmark. In Part one, pig farming was found to have a higher N-efficiency than dairy farming. Organic pig production had a lower N-efficiency and a higher N-surplus per kg meat than conventional pig production. The possibilities to reduce N-loss by conversion to organic pig production therefore appear to be poor. Organic dairy farming had a higher N-efficiency and a lower N-surplus per kg milk than conventional dairy farming. Conversion from conventional to organic dairy farming may therefore reduce N-losses. In Part two, a positive correlation between livestock density and N-surplus ha-1 was found for dairy farming. For all simulated livestock densities, fodder feeding intensities and soil types, organic systems showed a lower N-surplus per unit of milk produced than conventional systems. National scenarios for dairy farming showed that the present Danish milk production could be achieved with a 24% lower total N-surplus if converted from intensive conventional farming to extensive organic farming. At the same time, N-surplus ha-1 and N-surplus (t milk)-1 would be lowered by 50% and 25% respectively. Changing from intensive to extensive conventional dairy farming with a livestock density equal to that in the organic scenario resulted in a reduction in N-surplus ha-1 of 15%. It was concluded that a reduction in total N-loss from agriculture is possible by converting from conventional to organic dairy farming but at the cost of either lower production on the present dairy farm area, or the current production on a substantially larger area.

Global use and trade of feedstuffs and consequences for the nitrogen cycle

Abstract: This paper presents an estimate of the amount of nitrogen involved in the use and trade of feedstuffs for a number of world regions Livestock production has shown a steady increase world-wide as a result of an annual increase of 14% in developing countries and 09% in developed countries during the period 1960–1990 Particularly in developing countries, the strong growth of animal production and a tendency towards decreasing reliance on grazing and increasing importance of fodder crops and feed concentrates, cause a major increase in the consumption of feedstuffs Cereals form the major feedstuff world-wide The current global use of cereals for feed is about 30% of the total use (57% in developed countries and 17% in developing countries) Net trade of cereals and other feedstuffs represents 4–8 Tg N per year, which is only 4–7% of the total N consumption by the world's animal population A strong growth of the per capita food consumption, a relative increase of meat consumption, coupled with a strong population growth, may cause a strong increase of the net trade of cereals In particular the countries of the Middle East, North Africa and China may become important importers of cereals In future, the N transport between regions in the form of feedstuffs may become an important component in the global N cycle