Rolf Nieder

Carbon and Nitrogen in the Terrestrial Environment

Introduction.- 1. Carbon and Nitrogen Pools in Terrestrial Ecosystems.- 1.1 Forms and quantities of carbon and nitrogen on earth.- 1.2 Carbon and nitrogen in terrestrial phytomass.- 1.3 Carbon and nitrogen in soils.- 1.4 Global vegetation-soil organic matter interrelationships.- 2. Carbon and Nitrogen Cycles in Terrestrial Ecosystems.- 2.1 The global carbon cycle.- 2.2 The global nitrogen cycle.- 2.3 Carbon and nitrogen cycling in soils.- 2.4 Global climate change and C and N cycling.- 3. Soil Organic Matter Characterization.- 3.1 Chemical characterization of soil organic matter.- 3.2 Physical characterization of soil organic matter.- 3.3 Morphological characterization of soil organic matter.- 4. Organic Matter and Soil Quality.- 4.1 Soil quality.- 4.2 Impact of SOM on soil physical, chemical and biological properties.- 4.3 Evaluation of organic components as soil quality indicators.- 4.4 Use of combined biological parameters for soil quality estimation.- 5. Carbon and Nitrogen Transformations in Soils.- 5.1 Transformations of organic components.- 5.2 Transformations of inorganic components.- 6. Anthropogenic Activities and Soil Carbon and Nitrogen.- 6.1 Land use changes.- 6.2 Agricultural management.- 6.3 Ecosystem disturbance.- 7. Leaching Losses and Groundwater Pollution.- 7.1 Dissolved organic carbon.- 7.2 Dissolved organic nitrogen.- 7.3 Nitrate leaching.- 8. Bidirectional Biosphere-Atmosphere Interactions.- 8.1 Atmospheric Nitrogen Depositions.- 8.2 Carbon fixation via photosynthesis.- 8.3 Biological N2 fixation.- 8.4 Carbon dioxide emission.- 8.5 Methane emission.- 8.6 Emission of oxides of nitrogen: N2O and NO.- 8.7 Ammonia emission.- 8.8 Global climate change and crop yields.- 8.9 Economics of carbon sequestration.- 9. Modelling Carbon and Nitrogen Dynamics in the Soil-Plant-Atmosphere System.- 9.1 Carbon dioxide exchange from soils.- 9.2 Methane emission from rice fields and natural wetlands.- 9.3 Nitrogen trace gas emission.- 9.4 Modelling nitrogen dynamics in soils.- 9.5 Modelling organic matter dynamics in soils.- References.- Index.

Calibration of a simple method for determining ammonia volatilization in the field – comparative measurements in Henan Province, China

The determination of ammonia volatilization with sufficient spatial and temporal resolution requires a simple and versatile in situ measurement technique, particularly in developing countries. Therefore, a simple chamber method for determining ammonia (NH3) volatilization in the field (Dräger-Tube Method; DTM) was calibrated by comparison with simultaneous measurements with a micrometeorological Integrated Horizontal Flux (IHF) method. Five field experiments were conducted following urea fertilization on summer maize and winter wheat plots (1998–1999) at Fengqiu Experimental Station, Central China. The simplicity of the chamber method allowed for measurements to be carried out by trained farmers. The measurements with both methods yielded very similar patterns of NH3 fluxes and similar differences between fertilization treatments. Cumulative NH3 losses determined by the IHF method ranged from 14.6 to 47.9% and from 0.6 to 17.9% of urea-N applied for surface broadcast and incorporated fertilization, respectively. As expected, cumulated NH3 losses were underestimated by the DTM as compared to the IHF by about one order of magnitude. A calibration equation was calculated by multiple linear regression which included NH3 flux data as well as temperature and wind speed values. The calibration model yielded a modelling efficiency c2 of 0.86 resulting in an average estimation error of cumulative NH3 losses of 17%. The equation was validated by comparison of IHF measurements and DTM fluxes not considered in the derivation of the calibration formula. The calibration approach can be used under similar meteorological and field conditions irrespective of the soil characteristics or type of N fertilizer applied.

C and N accumulation in arable soils of West Germany and its influence on the environment : Developments 1970 to 1998

During the last three decades, large amounts of soil organic matter (SOM) and associated nutrients have been accumulated in arable soils of Western Germany (former FRG) due to deepening of the plough layers (from 35 cm) and to fertilizer application rates which have exceeded the amounts of nutrients removed in harvested crops. Organic carbon and total nitrogen balances (1970—1998) on 120 plots from 16 farms in southern Lower Saxony yielded a cumulative increase of up to 16 t C ha−1 and 1 t N ha−1 in loess soils used for cash crop production and up to 26 t C ha−1 and 2.4 t N ha−1 in sandy soils under livestock production. The buffering capacity for reactive compounds, particularly of C, N, S and P and of other (organic or inorganic) pollutants will reach its limits in the near future, after organic matter ”equilibria” have been re-established. An immediate adaptation of the current fertilizer application rates to the nutrient export by field crops is therefore urgently needed. C- und N-Akkumulation in westdeutschen Ackerboden und ihr Einfluss auf die Umwelt — Entwicklungen 1970 bis 1998 Vertiefung der Ackerkrumen (von 35 cm) und Dunger-Applikationsraten deutlich uber dem Entzug fuhrten wahrend der letzten 3 Jahrzehnte in den Ackerboden Westdeutschlands (ehemalige BRD) zu einer starken Anreicherung der organischen Substanz und der in ihr gebundenen Nahrstoffe. Beispielhafte Bilanzen des organischen Kohlenstoffs und Gesamt-Stickstoffs 1970—1998 auf 120 Schlagen aus 16 Betrieben im sudlichen Niedersachsen zeigten eine kumulative Anreicherung bis zu 16 t C ha−1 und 1 t N ha−1 in Lossboden von Marktfruchtbetrieben und bis zu 26 t C ha−1 und 2,4 t N ha−1 in sandigen Boden von Veredelungsbetrieben. Nach der Wiedereinstellung von ”quasi-stationaren” Gehalten an organischer Substanz wird in naher Zukunft die Pufferkapazitat fur reaktive Verbindungen von C, N, S und P und anderer (organischer und/oder anorganischer) Umweltchemikalien nicht mehr vorhanden sein. Daher ist eine unverzugliche Anpassung der Dunger-Applikationsraten an die Nahrstoffabfuhren vom Feld zwingend erforderlich.

Significance of nitrate leaching and long term N immobilization after deepening the plough layers for the N regime of arable soils in N.W. Germany

Field studies were conducted to assess the turnover and the leaching of nitrogen in arable soils of Lower Saxony (NW Germany). The mean surplus N (difference between N inputs by fertilization and N export by the yield; 146 field plots) from 1985–1988 amounted to 38 kg ha-1 yr-1 in fine textured (clay, loam, silt) and to 98 kg ha-1 yr-1 in coarse (sandy) soils. Leaching of nitrate calculated by a simple functional model for simulation of the N regime over the winter period (i.e. mineralization and leaching) was 16 kg ha-1 in the fine and 63 kg N ha-1 in coarse soils (mean values of the winter periods 1985–1988 from 256 plots).Before the 1960s, the depth of the Ap horizons rarely exceeded 25 cm in arable soils of the former FRG. During the last three decades, ploughing depth has increased to at least 35 cm. The mass balance calculations for total N after ploughing to 35 cm in loess soils of southern Lower Saxony (105 farm plots) yielded a mean increase in total N by about 900 kg ha-1 in 20 years. With respect to soil organic matter equilibria, N accumulation will continue for at least another 10 years on 67% of the examined farm plots. This study suggests that long term N immobilization is one of the most important sinks for nitrogen in arable soils of Germany. For simulation of the N dynamics over the growing season and for long time periods total nitrogen dynamics need to be considered.

Nitrogen transformation in arable soils of North-West Germany during the cereal growing season

In 1991, field experiments on loess (with winter wheat) and sandy soils (with summer barley) were conducted to study N dynamics in the microbial biomass and non-exchangeable NHinf4sup+. The measurements showed a mass change in microbial N, with a maximum increase of 100 kg N ha-1 30 cm-1 from March to July in the loess soil, and a change for only 1 month (May) in the sandy soil. Plots treated with conventional levels of N fertilizer (213 kg N ha-1 on a loess soil to winter wheat and 130 kg ha-1 on the sandy soil to summer barley), reduced levels of N (83% and 62% of the conventional N application), or no N showed no consistent fertilizer N effect on microbial biomass N. From March to July, non-exchangeable NHinf4sup+in loess soils under winter wheat decreased by 110 kg N ha-1 30 cm-1 in conventionally fertilized plots and by 200 kg N ha-1 30 cm-1 in a plot with no N fertilizer. After harvest, the pool of non-exchangeable NHinf4sup+increased due to increasing mineral N concentrations in the soil.

Sources of nitrous and nitric oxides in paddy soils: Nitrification and denitrification

Rice-paddies are regarded as one of the main agricultural sources of N 2O and NO emissions. To date, however, specific N2O and NO production pathways are poorly understood in paddy soils. (15)N-tracing experiments were carried out to investigate the processes responsible for N2O and NO production in two paddy soils with substantially different soil properties. Laboratory incubation experiments were carried out under aerobic conditions at moisture contents corresponding to 60% of water holding capacity. The relative importance of nitrification and denitrification to the flux of N2O was quantified by periodically measuring and comparing the enrichments of the N2O, NH(+)4-N and NO(-)3-N pools. The results showed that both N2O and NO emission rates in an alkaline paddy soil with clayey texture were substantially higher than those in a neutral paddy soil with silty loamy texture. In accordance with most published results, the ammonium N pool was the main source of N2O emission across the soil profiles of the two paddy soils, being responsible for 59.7% to 97.7% of total N2O emissions. The NO(-)3-N pool of N2O emission was relatively less important under the given aerobic conditions. The rates of N2O emission from nitrification (N2On) among different soil layers were significantly different, which could be attributed to both the differences in gross N nitrification rates and to the ratios of nitrified N emitted as N2O among soil layers. Furthermore, NO fluxes were positively correlated with the changes in gross nitrification rates and the ratios of NO/N2O in the two paddy soils were always greater than one (from 1.26 to 6.47). We therefore deduce that, similar to N2O, nitrification was also the dominant source of NO in the tested paddy soils at water contents below 60% water holding capacity.

Dynamics of nitrogen after deeper tillage in arable loess soils of West Germany

SummaryThe depth of ploughing has increased in West Germany during the last three decades. Before the 1960s, the depth of the Ap horizon rarely exceeded 25 cm; in the early 1980s it reached about 35 cm on average but it has remained constant since that time. In 1989, the total N content of 105 plots in the southern Niedersachsen loess area was measured after deepening of the plough layers. The N content of the samples was compared with that of earlier samplings (1) before deeper tillage in the 1960s, the 1970s, and the 1980s; and (2) in 1983. Directly after the deeper ploughing, the N content of the topsoil decreased, presumably due to dilution with the subsoil material. Mass balance calculations for total N in 1989 showed that the phase of N accumulation can take 20 years or more. Within two decades, up to 2000 kg N ha-1 was immobilized in the soil organic matter. Recent incubation experiments with disturbed soil indicated that the N mineralization capacity was reestablished in all soils and is now similar to that of the early (1960s and 1970s) and more recent (1980s) deepened plough layers. Undisturbed soil material incubated in plastic tubes showed a significantly reduced net mineralization at water contents above 65% of the waterholding capacity, particularly in the lower part (15–30 cm) of the Ap horizon. This study suggests that N accumulated in the deep plough layers cannot contribute noticeably to net N mineralization in loess soils during the growing season.

Stability of buried carbon in deep-ploughed forest and cropland soils - implications for carbon stocks

Accumulation of soil organic carbon (SOC) may play a key role in climate change mitigation and adaptation. In particular, subsoil provides a great potential for additional SOC storage due to the assumed higher stability of subsoil SOC. The fastest way in which SOC reaches the subsoil is via burial, e.g. via erosion or deep ploughing. We assessed the effect of active SOC burial through deep ploughing on long-term SOC stocks and stability in forest and cropland subsoil. After 25–48 years, deep-ploughed subsoil contained significantly more SOC than reference subsoils, in both forest soil (+48%) and cropland (+67%). However, total SOC stocks down to 100 cm in deep-ploughed soil were greater than in reference soil only in cropland, and not in forests. This was explained by slower SOC accumulation in topsoil of deep-ploughed forest soils. Buried SOC was on average 32% more stable than reference SOC, as revealed by long-term incubation. Moreover, buried subsoil SOC had higher apparent radiocarbon ages indicating that it is largely isolated from exchange with atmospheric CO2. We concluded that deep ploughing increased subsoil SOC storage and that the higher subsoil SOC stability is not only a result of selective preservation of more stable SOC fractions.

Beitrag der Landwirtschaft zu diffusen N-Einträgen

Seit den 1950er Jahren wird auf der landwirtschaftlich genutzten Flache (LF) in Deutschland mehr Stickstoff (N) ausgebracht als mit den Ernteprodukten abgefahren. Der kumulative N-Uberschuss betragt von 1950 bis heute in den Alten Bundeslandern uber 4 000 kg/(ha LF). Zurzeit umfasst der mittlere N-Uberhang in Deutschland mindestens 85 kg N/(ha · a) und durfte zum uberwiegenden Teil in die Gewasser bzw. in die Atmosphare gelangen.

Soil Quality and Human Health

Protecting soil and preserving its overall quality has become a key international goal. Early concepts of soil quality dealt mainly with soil properties that contribute to soil productivity, with little consideration for environment regulation and human health. It is only recently that studies integrating soil and human health have been initiated. While soil performs several important functions related to ecosystem services, the most significant functions for human health are production of safe and nutritious food and protecting from environmental pollution. Human health is greatly dependent on the soil-water-air continuum which is strongly moderated by processes in the soil. The functions of soil such as filtering, buffering and transformation help in protecting the environment, including human beings against the contamination of groundwater and the food chain. Human activities impact several processes in soil that could lead to physical (accelerated erosion, deterioration of soil structure, crusting, compaction, hard-setting), chemical (nutrient depletion and imbalance, acidification, salinization) and biological (depletion of soil organic matter, loss of biodiversity) degradation of soil. Soil degradation directly affects food security through reduction in crop yields, decline in their nutritional quality and reduced input use efficiency. Plant availability of mineral nutrients in the soil is the main source of mineral supply to human beings. Plants, which absorb minerals from soil, are either eaten directly by humans or fed to animals that are then included in human diet. Therefore, any deficiency in plant products could manifest in human beings. Global warming associated with altered rainfall pattern could subject soils to significant risk of climate induced physical and chemical degradation. Therefore, it is imperative to manage soils to minimize soil degradation and to derive benefits for human health. In this chapter, land as a resource for supporting global population and the role it plays in performing ecosystem functions vis-a-vis soil quality, and the impact of anthropogenic activities on soil quality, plant and animal products and human health are discussed.