Chlorophyll compounds and nitrogen availability in West Indian soils

Summary The amounts of chlorophyll-type compounds extracted by 90 per cent aqueous acetone from 70 West Indian soils were inversely correlated with soil pH; chlorophyll compounds decomposed when soils were limed to pH 7. Chlorophyll compounds were only significantly correlated with nitrogen used by maize in pot experiments and with mineralizable nitrogen for soils in the pH 5.0 to 5.9 range. Chlorophyll may persist in acid soils because micro-organisms are less active or because the chlorophyll molecule is altered, possibly by the isomorphus replacement of magnesium by reduced iron or manganese.     

Chlorophyll-type compounds in soil

Summary The degradation of chlorophyll-type compounds (chlorophyll and its derivatives) in soil were followed by spectrophotometric and chromatographic techniques to find how closely they represent the bulk of plant material in soil. Tissue enzymes rapidly decomposed chlorophyll in chopped plant material mixed with soil, and decomposition was much slower in material in which the enzymes had been inactivated. This slow decomposition is by micro-organisms which seem to be the important cause of chlorophyll degradation in soil.Micro-organisms decomposed both chlorophyllsa andb in two to four months in field soils; chlorophylla was attacked most. Of the chlorophyll-type compounds, pheophytin, the most closely related derivative of chlorophyll, resisted decomposition largest; chlorophyllide and pehophorbide were found rarely in soil and never in large amounts.Microbiological decomposition increased with increasing moisture content of soil, was fastest at 50 to 60 per cent of the water-holding capacity. Decomposition slowed with increasing soil acidity and was very slow at pH below 4.0. Raising the temperature from 5° to 25°C increased the rate of degradation Neither the species nor quantity of plant material had much effect on the rate of decomposition.     

Chlorophyll-type compounds in soil

Summary The amounts of chlorophyll-type compounds in materials commonly deposited on or in soil were measured and the processes that destroy them in materials on the soil surface, and the ways they may enter the soil, were studied. Of plant material commonly deposited on the soil, freshly-cut ryegrass and lucerne contained most of such compounds and cereal straw least. Faeces from grazing cattle and sheep contained nearly as mush as grass; farmyard manure contained only five per cent as much as fresh faeces.Nine-tenths of the chlorophyll in chopped-up, fresh ryegrass leaves was decomposed in six days; this decomposition was attributed to tissue enzymes and was prevented by boiling, drying, water-logging or freezing. Microorganisms decomposed about sixty per cent of chlorophyll in ryegrass leaves in 90 days.A large amount of chlorophyll-type compounds in faeces on soil leached 4 inches deep into the soil during 90 days in the autumn. Soil under 100-year-old, grazed pasture contained more of these compounds than under grassland that was cut for hay each year.     

Deaminase activity in arable soils

Deamination of 1,2 diamino-4-nitrobenzene (DANB) was assayed in 22 arable soils. Soil texture, pH, total nitrogen and organic matter content were measured, as were the soils' nitrogen mineralisation potentials. Deaminase activity was strongly correlated with clay content, suggesting an association of deaminase with this soil fraction. There was no relationship between deaminase activity and other soil parameters. Deaminase activity was a poor predictor of nitrogen mineralisation potential. This was due to the difference in accessibility of the amino groups in DANB and of native soil organic matter.     

Occurrence of natural organic chlorine in soils for different land uses

Consideration of natural formation of organochlorine compounds in soils is necessary in radioecology in order to understand chlorine radioisotope (³⁶Cl) cycling in various environments for safety assessment purposes, but also in ecotoxicology because certain chlorinated organics in soils are toxic compounds. On the other hand, occurrence of organic chlorine in soils is poorly documented, especially in non-forest ecosystems. We measured total and organic chlorine concentrations in 51 French surface soils sampled from grassland, arable and forest sites on a national scale (French soil quality monitoring network) in order to characterize the variability of organic chlorine concentrations for these different land uses. While previous studies reported that the chlorination of soil organic matter is responsible for chlorine retention in temperate forest ecosystems, this study shows that the non-extractable organohalogen pool accounts for the majority (>80 % on an average) of the total measurable chlorine in grassland and agricultural soils. This suggests that natural chlorination is a widespread phenomenon in all kinds of soils. A multiple linear regression analysis performed on the dataset indicated that retention of organochlorine in soils is related to the organic carbon content, Cl input and soil pH.     

Biochar Decelerates Soil Organic Nitrogen Cycling but Stimulates Soil Nitrification in a Temperate Arable Field Trial

Biochar production and subsequent soil incorporation could provide carbon farming solutions to global climate change and escalating food demand. There is evidence that biochar amendment causes fundamental changes in soil nutrient cycles, often resulting in marked increases in crop production, particularly in acidic and in infertile soils with low soil organic matter contents, although comparable outcomes in temperate soils are variable. We offer insight into the mechanisms underlying these findings by focusing attention on the soil nitrogen (N) cycle, specifically on hitherto unmeasured processes of organic N cycling in arable soils. We here investigated the impacts of biochar addition on soil organic and inorganic N pools and on gross transformation rates of both pools in a biochar field trial on arable land (Chernozem) in Traismauer, Lower Austria. We found that biochar increased total soil organic carbon but decreased the extractable organic C pool and soil nitrate. While gross rates of organic N transformation processes were reduced by 50–80%, gross N mineralization of organic N was not affected. In contrast, biochar promoted soil ammonia-oxidizer populations (bacterial and archaeal nitrifiers) and accelerated gross nitrification rates more than two-fold. Our findings indicate a de-coupling of the soil organic and inorganic N cycles, with a build-up of organic N, and deceleration of inorganic N release from this pool. The results therefore suggest that addition of inorganic fertilizer-N in combination with biochar could compensate for the reduction in organic N mineralization, with plants and microbes drawing on fertilizer-N for growth, in turn fuelling the belowground build-up of organic N. We conclude that combined addition of biochar with fertilizer-N may increase soil organic N in turn enhancing soil carbon sequestration and thereby could play a fundamental role in future soil management strategies.     

东北黑土成土母质培肥过程中土壤肥力变化特征

利用已设置14年的黑土成土母质(表层以下2.0～3.0 m深)培肥定位试验,研究不同农艺措施培肥后土壤肥力指标的变化特征,结合小麦盆栽耗竭试验评估土壤供肥能力,综合评价不同农艺措施对黑土母质培肥的效应。与初始母质相比,黑土母质培肥14年后,土壤总有机碳、全氮、团聚结构稳定性和其他养分含量均不同程度提高,土壤肥力水平的高低直接影响盆栽试验中土壤对小麦的供肥能力。主成分分析发现,母质经过14年的培肥,碳投入量较大的农田秸秆还田处理和苜蓿培肥处理与表层(0～20 cm)黑土更接近,其次是农田有机肥和自然草地培肥处理,农田单施化肥和不施肥处理培肥效果最差。14年连续的外源碳输入通过改善土壤团聚结构和进入土壤的碳分解转化,影响土壤的物理和生物化学性质,促进母质土壤肥力发育。农田秸秆还田、施用有机肥和种植苜蓿对黑土母质肥力提升效果最好,是保证黑土肥力和土壤培肥的有效措施,研究结果可为东北黑土区退化土壤培肥提供理论依据和指导。     

Methane production capacities of different rice soils derived from inherent and exogenous substrates

Methane production rates were determined at weekly intervals during anaerobic incubation of eleven Philippine rice soils. The average production rates at 25 °C varied in a large range from 0.03 to 13.6 g CH_{4 g(d.w. soil)} ^-1d^-1. The development of methane production rates derived from inherent substrate allowed a grouping of soils in three classes: those with instantaneous development, those with a delay of approximately two weeks, and those with a suppression of methane production of more than eight weeks. Incubation at 30 and 35 °C increased production capacities of all soils, but the grouping of soils was still maintained. The Arrhenius equation provided a good fit for temperature effects on methane production capacities except for those soils with suppressed production. Acetate amendment strongly enhanced methane production rates and disintegrated the grouping. However, the efficiencies in converting acetate to methane differed among soils. Depending on the soil, 16.5–66.7% of the added acetate was utilized within five weeks incubation at 25 °C.Correlation analyses of methane production (over eight weeks) and physico-chemical soil parameters yielded significant correlations for the concentrations of organic carbon (R² = 0.42) and organic nitrogen (R² = 0.52). Correlation indices could substantially be enhanced by using the enriched fraction of organic carbon (R² = 0.94) and organic nitrogen (R² = 0.77), i.e. the differential between topsoil and subsoil concentrations of the respective compounds. The enriched organic material in the topsoil corresponds to the biologically active fraction and thus represents a good indicator of methane production derived from inherent substrate. The best indicators of the conversion rate of acetate in different soils were pH-value (R² = 0.56) and organic carbon content (R² = 0.52).Apparently, soil properties affect methane production through various pathways. Inherent organic substrate represents a considerable source of methane in some soils and is negligible in others. Likewise, soils also differ regarding the response to exogenous substrate. Both mechanisms yield in a distinct spatial variability of methane production in rice soils.     

Possible Mechanism for Spontaneous Establishment of Calluna vulgaris in a Recently Abandoned Agricultural Field

In Western Europe, arable lands have been abandoned to increase the area of nature, such as Calluna vulgaris –dominated heathlands. However, the growth conditions, e.g., nutrient availability and lack of a phenolics-rich organic layer, on ex-arable sandy soils differ markedly from those of heathland and will favor fast-growing plant species. Succession toward Calluna -dominated heathland is expected to take decades unless intensive restoration management is applied. Here, we report a possible mechanism to explain the occurrence of Calluna patches (0.7–2.0 m diameter) in a 10-year abandoned agricultural field within a dominant vegetation of grasses and forbs. All roots sampled from the Calluna patches were colonized by ericoid mycorrhizal (ERM) and other endomycorrhizal fungi. Both nitrogen mineralization of soil organic N and potential nitrogen mineralization (arginine ammonification) were much lower in soil under Calluna patches than in the rest of the ex-arable soil, although other soil characteristics did not differ. The nitrogen to phosphorus ratio in Calluna shoots was much greater than that in shoots of grasses and forbs, indicating that the latter were more N limited. The results indicate that the association with ERM fungi is probably providing the host competitive superiority for nitrogen even in a soil with low organic matter content. Our results suggest that the conversion from arable land into heathland may be accomplished by the immediate establishment of Calluna seedlings and ERM inoculum when agricultural activities are stopped. This needs to be tested in controlled experiments.     

黄土区不同类型土壤可溶性有机氮的含量及特性

测定了黄土高原地区不同生态系统土壤中可溶性有机氮（SON）和游离氨基酸的含量,并分析了其与土壤其他性质之间的关系。结果表明,黑垆土、红油土和淋溶褐土中SON的平均含量分别为24．75、39．10mg／kg和41．80mg／kg,占可溶性总氮（TSN）的51．25％、68．28％和68．57％,分别为土壤全氮的2．54％、3．75％和4．00％;土壤游离氨基酸的含量分别为7．18、7．42mg／kg和7．41mg／kg,分别占SON的30．53％、19．23％和17．50％,占全氮的0．74％、0．71％和0．71％．方差分析结果表明,土壤类型对土壤SON含量及其在TSN和全氮中所占的比例、游离氨基酸在SON中所占的比例有显著影响,而对游离氨基酸的含量及其占土壤全氮比例的影响未达显著水平。枯枝落叶层中SON含量（248．26mg／kg）为农田土壤（24．75mg／kg）的10倍左右,且林地土壤0～20cm土层SON含量（31．03mg／kg）显著的高于当地农田,两种生态系统0～20cm土层土壤中游离氨基酸含量（7．18～7．32mg／kg）相当,但均极显著低于枯枝落叶层中游离氨基酸平均含量（18．57mg／kg）。相关分析结果表明,TSN、SON以及游离氨基酸与全氮、硝态氮、铵态氮、有机质等各养分之间均有极显著的相关性。     

A model experiment to study the influence of living plants on the accumulation of soil organic matter in pastures

Summary An attempt has been made to imitate the grassland system by a perfusion apparatus containing a soil-column to which labeled glucose is continuously supplied. Experiments have also been performed with substrate supplied at the start of the experiment to imitate processes occurring in arable land. Deficiency of available nitrogen caused that more of the glucose carbon added to the soil was incorporated into soil organic matter than in the presence of a supplied nitrogen source. Even more glucose carbon was incorporated into soil organic matter when nitrogen deficiency was accompanied by a continous addition of the glucose. The results obtained indicate that the continuous addition of substrate together with nitrogen deficiency as it occurs in permanent pastures are responsible for the accumulation of soil organic matter in these soils.     

Using hydrogel and clay to improve the water status of seedlings for dryland restoration

The decomposition of soil organic matter is mediated by extracellular enzymes. The aim of this work was to identify the factors determining the activity and size of the mobile fraction of extracellular enzymes (laccase, Mn-peroxidase, endocellulase, cellobiohydrolase, ??-glucosidase, endoxylanase, ??-xylosidase, ??-glucosidase, chitinase, arylsulfatase, phosphatase, phosphodiesterase, alanine and leucine aminopeptidase) using a set of soils covering a wide range of physico-chemical properties. Organic matter content had a major effect on enzyme activity both in forest and grassland soils, while the effects of pH and humic compounds content were only important in forest soils, and the molecular mass of humic compounds and Ca content were only important in grasslands. Specific enzyme activity was either comparable between the soil types or higher in grasslands. With the exception of Mn-peroxidase and ??-glucosidase, the specific activities of all enzymes in arable fields under tillage were similar to those in grasslands. Mobility differed among the enzymes and ranged from <1% for arylsulfatase and phosphodiesterase up to 20?C40% for ??-glucosidase and aminopeptidases, with pH being the most important variable. These results demonstrate that the factors regulating enzyme activity are likely to be different in forest soils and grasslands and that enzyme mobility is a characteristic feature of each individual enzyme.     

Changes in soil associated with continuous growth of some vegetation

Summary and conclusions From a study of the composition of the soil and the subsoil under three grasses,Imperata cylindrica, Pennisetum orientale, Pennisetum polystachyum and three legumesTephrosia candida, Medicago sativa andPueraria hirsuta and of those of natural bare soil in the neighbourhood of each, it could be observed that the soils under vegetation contained more moisture, organic matter, organic nitrogen clay and soluble salts but had lower pH values than the bare soils. The soils under grasses had less moisture, lower pH and lower salinity but higher clay content and exhibited greater aggregation than the soils under legumes. Though the soils under grasses had significantly higher quantities of organic matter than the soils under legumes there was no significant difference in the organic nitrogen contents between them.     

霍林河流域湿地土壤碳氮空间分布特征及生态效应

对霍林河流域湿地土壤有机碳及全氮空问分布特征及其生态效应的研究表明,有机碳和全氮的水平分异和垂直分异都十分显著,干湿交替周期是引起分异的关键因子;表层土壤有机碳与全氮含量显著相关(r=0．977),土壤碳氮比基本沿湿度梯度变化;土壤pH值对土壤表层碳氮含量及碳氮比值影响显著;流域湿地土壤与流域草原土壤碳氮比与土壤碳氮含量的相关性差异显著;其生态效应主要表现在生产效应和净化效应两方面．     

土地利用变化对沙地土壤全氮空间分布格局的影响

利用经典统计学和地统计学相结合的方法,分析了科尔沁沙地东南缘草地和8年前开垦的耕地土壤全氮含量和空间分布格局．结果表明,草地与耕地表层(O～10cm)土壤全氮含量差异不显著,亚表层(10～20cm)含量差异显著(P     

Nitrogen Pool in Northern-Taiga Larch Forests of Central Siberia

The pools of nitrogen in different blocks of forest ecosystems and its cycle in the soil are considered. It is shown that the bulk of nitrogen concentrates in the soil and dead organic matter (necromass) of an ecosystem. The nitrogen pool of forest litters and soils consists by 83–93% of the inert compounds that cannot be involved in the biological cycle. Mineralization of organic nitrogen-containing substances in the litters and soils usually yields ammonium as an end product. The amount of nitrogen mineralized over the growing season is partially expended for annual plant increment (30–65%) and immobilization (12–17%), with its large proportion being found in the soil.     

Do soil aggregates really protect encapsulated organic matter against microbial decomposition?

Soil aggregates can provide an effective protection of organic matter against microbial decomposition as reported by several macroaggregate disruption studies. However, research on the role of aggregation for carbon mineralization was mainly focused on arable soils. In the present study we aim to clarify the impact of aggregation on organic matter protection by measuring carbon mineralization in terms of microbial respiration rates of intact macroaggregates (2–4 and 4–8 mm) and corresponding crushed aggregates from seven topsoil horizons from both arable and forest sites. For two arable and one forest soil we found a significantly (P < 0.001) lower carbon mineralization from intact aggregates as compared to the corresponding crushed material. The portion of aggregate protected carbon reached up to 30% for a grassland soil. For the other arable and forest soils no significant effect of aggregation was found. Similarly, no clear trend could be found for the protective capacity of different size fractions. We conclude that protection by aggregation is effective primarily for soils with a large pool of labile organic matter regardless of their usage as arable land or forest.     

Nitrification and organic nitrogen formation in soils

Summary The formation of mineral nitrogen species and of organic nitrogen was studied in three different types of soils in relation to the application of the nitrification inhibitor nitrapyrin. The results indicate that nitrification brings about a deficit in total mineral nitrogen and a concomitant surplus in non biomass organic nitrogen. This phenomenon increases with increasing levels of applied ammonium nitrogen and soil organic matter. The phenomenon is considered to be due to the reaction of the transient nitrite formed with soil phenolic compounds and appears to be of significance in all soils in which nitrification occurs, even neutral to alkaline and low carbon soils.     

Initial decay of woody fragments in soil is influenced by size, vertical position, nitrogen availability and soil origin

Fast-growing bacteria and fungi are expected to cause the initial stage of decomposition of woody fragments in and on soils, i.e. the respiration of sugars, organic acids, pectin and easily accessible cellulose and hemi-cellulose. However, little is known about the factors regulating initial wood decomposition. We examined the effect of wood fragment size, vertical position, nitrogen addition and soil origin on initial wood decay and on the relative importance of fungi and bacteria therein. Two fractions of birch wood were used in microcosm experiments, namely wood blocks (dimensions: 3 × 0.5 × 0.5 cm) and sawdust (dimensions: 0.5–2 mm). The woody fragments were enclosed in nylon bags and placed on top of- or buried in an abandoned arable soil and in a heathland soil. After 15, 25 and 40 weeks of incubation, fungal biomass was quantified (as ergosterol and chitin content) and bacterial numbers were determined. The results indicated that initial wood decay was mostly caused by fungi; bacteria were only contributing in sawdust in/on abandoned arable soil. Larger fragment size, burial of fragments and nitrogen addition positively influenced fungal biomass and activity. Fungal biomass and decay activities were much lower in woody fragments incubated in/on heathland soil than in those incubated in/on abandoned arable soil, indicating that soil origin is also an important factor determining initial wood decay.     

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 A_p 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.