Wolfgang Zech

Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal - a review

Abstract. Rapid turnover of organic matter leads to a low efficiency of organic fertilizers applied to increase and sequester C in soils of the humid tropics. Charcoal was reported to be responsible for high soil organic matter contents and soil fertility of anthropogenic soils (Terra Preta) found in central Amazonia. Therefore, we reviewed the available information about the physical and chemical properties of charcoal as affected by different combustion procedures, and the effects of its application in agricultural fields on nutrient retention and crop production. Higher nutrient retention and nutrient availability were found after charcoal additions to soil, related to higher exchange capacity, surface area and direct nutrient additions. Higher charring temperatures generally improved exchange properties and surface area of the charcoal. Additionally, charcoal is relatively recalcitrant and can therefore be used as a long-term sink for atmospheric CO2. Several aspects of a charcoal management system remain unclear, such as the role of microorganisms in oxidizing charcoal surfaces and releasing nutrients and the possibilities to improve charcoal properties during production under field conditions. Several research needs were identified, such as field testing of charcoal production in tropical agroecosystems, the investigation of surface properties of the carbonized materials in the soil environment, and the evaluation of the agronomic and economic effectiveness of soil management with charcoal.

Nutrient availability and leaching in an archaeological Anthrosol and a Ferralsol of the Central Amazon basin: fertilizer, manure and charcoal amendments

Soil fertility and leaching losses of nutrients were compared between a Fimic Anthrosol and a Xanthic Ferralsol from Central Amazônia. The Anthrosol was a relict soil from pre-Columbian settlements with high organic C containing large proportions of black carbon. It was further tested whether charcoal additions among other organic and inorganic applications could produce similarly fertile soils as these archaeological Anthrosols. In the first experiment, cowpea (Vigna unguiculata (L.) Walp.) was planted in pots, while in the second experiment lysimeters were used to quantify water and nutrient leaching from soil cropped to rice (Oryza sativa L.). The Anthrosol showed significantly higher P, Ca, Mn, and Zn availability than the Ferralsol increasing biomass production of both cowpea and rice by 38–45% without fertilization (P<0.05). The soil N contents were also higher in the Anthrosol but the wide C-to-N ratios due to high soil C contents led to immobilization of N. Despite the generally high nutrient availability, nutrient leaching was minimal in the Anthrosol, providing an explanation for their sustainable fertility. However, when inorganic nutrients were applied to the Anthrosol, nutrient leaching exceeded the one found in the fertilized Ferralsol. Charcoal additions significantly increased plant growth and nutrition. While N availability in the Ferralsol decreased similar to the Anthrosol, uptake of P, K, Ca, Zn, and Cu by the plants increased with higher charcoal additions. Leaching of applied fertilizer N was significantly reduced by charcoal, and Ca and Mg leaching was delayed. In both the Ferralsol with added charcoal and the Anthrosol, nutrient availability was elevated with the exception of N while nutrient leaching was comparatively low.

Factors controlling humification and mineralization of soil organic matter in the tropics

Abstract The first part of this review focuses on the chemical composition and morphological features that characterize primary and secondary organic resources for humification. The chemical pathways of decomposition and humification of SOM in tropical soils are discussed referring mainly to the chemical structural changes identified by using both solid-state13C nuclear magnetic resonance spectroscopy (13C NMR) of bulk soil samples and liquid-state13C NMR of chemically isolated SOM fractions. The stabilization effects and mechanisms exerted on SOM by clay minerals and sesquioxides in tropical soils are also reviewed. Successively, relevant aspects of organic matter mobilization and dissolved organic matter dynamics in temperate versus tropical ecosystems are examined. In the second part of the review, general and specific aspects of mineralization processes in relation to the chemistry of main SOM pools (labile versus stable SOM components) in the tropics are discussed. Amounts, distribution, and forms of nutrients in SOM, nutrient release from organic versus inorganic sources, nutrient cycling in natural and cultivated soils, and the contribution of SOM to cationic nutrition in tropical soils are reviewed. The final part of the review focuses on the main chemical factors that control CO2 evolution and denitrification processes during SOM mineralization in tropical areas.

Black carbon in density fractions of anthropogenic soils of the Brazilian Amazon region.

Abstract Frequent charcoal findings together with black carbon concentrations in the soil organic matter (SOM) of up to 35% provided evidence that black carbon is important for the SOM stability in Terra Preta soils. This paper aims to investigate whether black carbon is additionally stabilised by organo-mineral complexation. For this purpose black carbon was analysed in density fractions using benzenecarboxylic acids as molecular markers. Density fractions were also studied by scanning electron microscopy and energy dispersive X-ray spectroscopy. Concentrations and total amounts of black carbon were generally highest in the light fraction indicating that a major part of black carbon is not chemically stabilised but intrinsically refractory. On the other hand, a large part of black carbon was also found in the heavier fractions, where it was partly embedded within plaques of iron and aluminium oxides on mineral surfaces. The major part of black carbon in the medium fraction seemed to be organo-mineral complexed because we found amounts of black carbon in this fraction by wet chemical analysis but not by scanning electron microscopy and energy dispersive X-ray spectroscopy. The spectroscopic analysis can only detect particulate black carbon. Black carbon was particularly enriched in 30–40 cm soil depth, and in all fractions of Terra Preta soils compared to adjacent Oxisols. The occurrence of particulate black carbon together with potsherds in the subsoil horizons of Terra Preta soils indicate that this might be due to turbation processes or the soils were covered by earthworm or termite activities. Further research, however, is needed to clarify the transport mechanisms of black carbon into deeper soil horizons.

Sorption of DOM and DOM fractions to forest soils

The sorption of total, hydrophilic, and hydrophobic dissolved organic matter (DOM) on 125 forest soil samples was studied in batch experiments. The soil samples represented the main soil orders of temperate climatic zones: Entisols, Inceptisols, Alfisols, Mollisols, and Spodosols. In general, sorption was adequately described by the linear initial mass isotherm. At zero addition of DOM, the release of dissolved organic carbon (DOC) into solutions depended on the soil organic C (OC) content. The DOC released was comprised primarily of hydrophilic substances (61–100%). High contents of OC reduced DOC sorption, notably that of hydrophilic DOC. In soils free of carbonates, sorption was related to oxalate-extractable aluminum (Alo) and dithionite-extractable iron (Fed); however, in carbonatec soils DOC retention was correlated with Fed only. Consequently, soils with high OC content and/or low contents of extractable Al and Fe showed low DOC retention (e.g. E horizons), whereas subsoil horizons had high DOC sorption capacities. The majority of the soils preferentially sorbed hydrophobic DOC. This was caused by the higher affinity of hydrophobic DOC to oxide/hydroxide soil components. There was also a strong competition effect between hydrophilic and hydrophobic DOC, especially in soils with a limited number of binding sites. sorption of hydrophobic DOC in some soils was even accompanied by the displacement of indigenous hydrophilic substances. In carbonate-free soils, multiple regression analysis including Alo, Fed, and OC explained 75 and 77% of the variance of the partition coefficient (m) of the initial mass isotherm for the sorption of total and hydrophobic DOC, respectively. Due to the competitive effect of hydrophobic DOC on hydrophilic DOC retention, the relation was weaker for the hydrophilic fraction. In the carbonate-containing soils, multiple regression analysis including Fed and OC explained 67, 58, and 59% of the variance of m for total, hydrophilic, and hydrophobic DOC, respectively.

Formation and mobilization pathways of dissolved organic matter: evidence from chemical structural studies of organic matter fractions in acid forest floor solutions

Dissolved organic matter (DOM) is well recognized to influence the geochemistry of ecosystems. This study was conducted to determine the pathways of DOC mobilization in the forest floor of coniferous forests. DOM from the forest floor of two acid forest soils in the Fichtelgebirge (Germany) was fractionated into hydrophobic acids and neutrals, and hydrophilic acids and neutrals. Carbon distribution at both sites was similar: 53 and 52% hydrophobic acids, 23 and 22% hydrophilic acids, 10 and 11% hydrophobic neutrals, and 7 and 8% hydrophilic neutrals, respectively. Structural composition of the DOM fractions was determined using chemical degradation, FT-IR and 13C NMR spectroscopy, as well as pyrolysis-field ionization mass spectrometry. Results indicate different chemical composition of the DOM fractions within each site. Hydrophobic acids show high concentrations of carboxyl and hydroxyl groups, and a high ratio of vanillic acid to vanillin (ca 1.0), both indicating a high degree of biodegradation of plant-derived compounds. Carbohydrates are covalently bound to apolar moieties and from carbohydrate composition a lignocellulose nature of the hydrophobic acid fraction is suggested. Hydrophilic acids can be differentiated from the hydrophobic acids by their higher degree of oxidative biodegradation. The hydrophilic acid fraction also exhibits a higher ratio of microbially released polysaccharides versus plant-derived polysaccharides. Hydrophobic neutrals show the closest relationships to the refractory soil humin, with less degraded dimeric ‘condensed’ lignin subunits and relatively high contents of non-carbohydrate aliphatics. Hydrophilic neutrals are enriched in carbohydrates mobilized by enzymatic cellulose and hemicellulose breakdown, as well as from microbial origin. We conclude that DOM release into forest floor solution is related to microbial activity by oxidative degradation of plant-derived organic matter (e.g. water-soluble lignin and lignocellulose fragments) and by production of microbial metabolites (e.g. polysaccharides). Overall evidence suggests that hydrophobic acids (i) represent intermediates in organic matter decomposition, which can be further degraded to hydrophilic acids and CO2, and (ii) are precursors of humic substances in illuvial horizons after precipitation/adsorption.

Growth variations of Common beech (Fagus sylvatica L.) under different climatic and environmental conditions in Europe—a dendroecological study

Abstract With increased growth potential on the one hand, but on the other hand a high percentage of trees exhibiting visible damages and the apparent regional decline in Common beech (Fagus sylvatica L.) stands in Europe, new questions arise about the sensitivity and resistance of this tree species to current environmental changes. In order to obtain more relevant information about this, 36 beech stands under different climatic and environmental conditions throughout Europe were selected and investigated by dendroecological methods. The variation of tree ring widths of Common beech was found to be a very sensitive indicator, reflecting clearly the signals of environmental influences. A high statistical quality of tree ring chronologies demonstrates a high suitability for dendroecological analysis. The investigation of long-term growth variations results in site-dependent and especially elevation-dependent growth trends. Since 1950, at lower altitude sites in Central Europe mainly increased growth trends are obvious. At higher altitude sites, however, almost all sites show a slightly decreased growth potential during the last decades. It seems that at higher altitudes in Central Europe, environmental changes in the recent past with negative effects on cambial activity are the predominant growth influences. This is also reflected in short-term growth disturbances and growth depressions after 1975 in tree ring series of beech trees growing on higher altitude sites. The investigation of climate–growth relations by different dendroecological methods results in distinct altitude-dependent growth-limiting factors. The comparison of chronologies demonstrates a high resistance of beech at sites where water supply is the main growth controlling factor. Strong disturbances and depressions in radial increment, however, were found at higher altitude sites in Central Europe especially at the end of the 1970s. Comparisons with reactions in preceding years demonstrate an increased sensitivity or an affected ‘ecological fitness’. Site factors modify the intensity of damage symptoms, but cannot be regarded as primary causes. Recent environmental changes may be responsible for the reduced ‘ecological fitness’ of Common beech in higher altitude sites. The spatial and temporal distribution of the detected growth disturbances leads to the assumption that increased tropospheric ozone concentrations are involved in the process of a changed sensitivity and resistance.

Seasonal variations in the chemical composition of dissolved organic matter in organic forest floor layer leachates of old-growth Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) stands in northeastern Bavaria, Germany

Organic matter dissolved in thepercolation water of forest soils contributeslargely to element cycling and transport ofnatural and anthropogenic compounds. The wayand extent to which these processes areaffected depends on the amount and the chemicalcomposition of soluble organic matter. Becausethe amount of soluble organic matter variesseasonally with changes in the microbialactivity in soil, it seems reasonable to assumethat there may be also seasonal changes in thechemical composition of dissolved organicmatter. We examined dissolved organic matter inthe seepage waters of organic forest floorlayers over a 27-month period (1997–1999) intwo forest ecosystems, a 160-year-old Scotspine (Pinus sylvestris L.) stand and a90-year-old European beech (Fagussylvatica L.) forest. The forest floorleachates were analysed for bulk dissolvedorganic C, C in hydrophilic and hydrophobicdissolved organic matter fractions,lignin-derived phenols (CuO oxidation),hydrolysable neutral carbohydrates and uronicacids, hydrolysable amino sugars, and stablecarbon isotope composition. In addition, westudied the samples by use of liquid-state13C-nuclear magnetic resonance (NMR)spectroscopy.For both investigated forest sites we foundthat the dissolved organic carbonconcentrations in forest floor leachates werelargest during summer. They peaked after rainstorms following short dry periods (106–145 mgdissolved organic C l−1). The proportionsof C in the hydrophilic fractions were largestin winter and spring whereas in summer andautumn more C was found in the hydrophobicfraction. According to liquid-state 13C-NMR spectroscopy, summer and autumn samples hadlarger abundances of aromatic and aliphaticstructures as well as larger proportions ofcarboxyl groups whereas the winter and springsamples were dominated by resonances indicatingcarbohydrates. Wet-chemical analyses confirmedthese results. Winter and spring samples wererich in neutral carbohydrates and amino sugars.The summer and autumn samples contained morelignin-derived phenols which were also strongeroxidised than those in the winter and springsamples. Seasonal changes of δ13C valueswere found to reflect the changes in thechemical composition of dissolved organicmatter. Most negative values occurred whenisotopically light lignin-derived compoundswere abundant and less negative values whencarbohydrates predominated.The different vegetation, age of thestands, and underlying mineral soils resultedin different concentrations of dissolvedorganic carbon and in differences in thedistribution between hydrophobic andhydrophilic organic carbon. Despite of this,the results suggest that the trends in temporalvariations in the composition of dissolvedorganic matter in forest floor seepage waterwere remarkably similar for both sites.Dissolved organic matter in winter and springseems to be mainly controlled by leaching offresh disrupted biomass debris with a largecontribution of bacterial and fungal-derivedcarbohydrates and amino sugars. Dissolvedorganic matter leached from the forest floor insummer and autumn is controlled by thedecomposition processes in the forest floorresulting in the production of stronglyoxidised, water-soluble aromatic and aliphaticcompounds. The chemical composition ofdissolved organic matter in forest floorseepage water in winter and spring indicateslarger mobility, larger biodegradability, andless interaction with metals and organicpollutants than that released during summer andautumn. Thus, the impact of dissolved organicmatter on transport processes may varythroughout the year due to changes in itscomposition.

Black carbon—possible source of highly aromatic components of soil humic acids

Abstract Structural features and chemical composition of highly aromatic soil humic acids strongly suggest that these humic acids are derived from black carbon (charred plant residues, soot) and not from native plant materials. Humic acids from laboratory-oxidized black carbon show remarkable similarities to highly aromatic soil humic acids in their spectroscopic properties and chemical composition. Thus, black carbon is considered to be a possible source of the chemically most stable, aromatic soil carbon pool.

Magnesiummangel, einer der Gründe für das Fichten- und Tannensterben in NO-Bayern

ZusammenfassungAuf sauren Granit- und Phyllitstandorten stocken in den Hochlagen der NO-bayerischen Mittelgebirge weitverbreitet Fichten und Tannen, die unabhängig vom Alter gelbspitzige Nadeln aufweisen. Die Erkrankung endet vielfach mit dem Absterben der Bäume. Die Nadelanalyse macht deutlich, daß in erster Linie sichtbarer Mg-Mangel vorliegt. Nach unseren Erfahrungen ist außerdem die Zn-Versorgung unzureichend, was ebenfalls gelbe und nekrotische Nadelspitzen verursacht. Die entsprechenden Nadelspiegelwerte lauten: Da die Erkrankung großflächig erst seit einigen Jahren auftritt, vermuten wir einen Zusammenhang mit dem atmogenen Säureeintrag. Dieser ruft vorrangig eine Verarmung an basisch wirkenden Kationen hervor, wie Beregnungsexperimente beweisen. Da unsere Standorte besonders Mg- und Zn-arm sind, kommt die Versorgung der Bäume mit diesen beiden Nährstoffen zuerst ins Minimum. Die Folgen sind Gelbspitzigkeit, Nekrosen und Abfallen der Nadeln, was zum Tod der Fichten und Tannen führt. Die Applikation von Mg-haltigen Verbindungen über dem Boden bzw. über die Nadeln bewirkt eine Revitalisierung.SummaryOn acid soils in northeastern Bavaria,Picea abies andAbies alba are developing symptoms of yellow and brown needle tips, especially on the older needles. Even the whole tree may die. Needle analysis indicates Mg- and Zn-deficiency: Since these symptoms are mainly restricted to the higher parts of the mountains where ten years ago no affected trees have been observed, we suppose that this kind of injury is the result of acid input. Experiments with acid precipitation have proven a decrease of cations like Ca, Mg. Since our sites are poor in Mg and Zn, acid input first reduces the uptake of the two. The result is Mg- and Zn-deficiencies, causing yellow and brown needle tips and even dying of the trees.The application of fertilizers containing Mg on the soil or by spraying on the foliage brings about a revitalization.