Studies on the properties of organic matter in buried humic horizon derived from volcanic ash

To investigate the relationship between age and the sugar composition in hydrolysates of the surface horizon and buried humic horizons with age up to 28,000 years B.P., the neutral sugars and amino sugars in soil hydrolysates were determined.

The ratios of total sugar carbon content to total carbon content of soil ranged from 2.68 to 4.13 percent. These values showed no distinct relationship with age.

Rhamnose, fucose, arabinose, xylose, mannose, galactose, glucose, g1ucosamine and galactosamine were present in the hydrolysates of all soil samples.

The polysaccharides of soil samples which have been buried for shorter periods were dominated by glucose, while those of soil samples buried for longer periods were dominated by mannose.

The proportion of hexoses showed a tendency to increase with age, while that of pentoses showed a tendency to decrease with age.     

Studies on the properties of organic matfer in buried humic horizon derived from volcanic ash

To investigate the relationship between the change of humus property and time factor, the humus composition in the buried humic horizons with the age from 28,000 years B.P. to the present was studied, according to the method presented by Kumada et al. (7).

The fH decreased with the elapse of time and in case of most of humus in the buried humic horizons with the age over 10,000 years, the fH became lower than 40 and were in the form of so-called ‘combined’ humus.

When 3,000-4,000 years have passed since the surface soil buried, the humic acid first moved . to ‘combined form.’ Second, after over 10,000 years, the fulvic acid moved to ‘combined form.’

The humification of ‘free’ humic acid proceeded with the elapse of time till around 5,000 years but of 'combined' humic acid till around 7,000 years. Both the humification-degree of ‘free’ humic acid after around 5,000 years and of ‘combined’ humic acid after around 7,000 years decreased. The humification-degree of ‘free’ and ‘combined’ humic acid from the samples with the age about 15,000 years B.P. to 28,000 years B.P. may be the same.     

Available organic nitrogen in temperate, subtropical, and tropical soils extracted with different solutions

Extraction of organic N by chemical solutions has been used to assess the amount of available N in soil. We tested the efficiency of several solutions in extracting organic N from tropical, subtropical and temperate soils. A conventional 0.067 M phosphate buffer successfully extracted organic N from all 23 soils examined. High-performance size exclusion chromatograms showed a single peak at about 7,800 Da for all phosphate buffer extracts irrespective of soil types. The peak area correlated with the organic N concentration of extracts. Tropical soils had lower retention of organic N than other soils according to the conventional and sequential extraction with phosphate buffer. Organic N extracted with sulfuric acid was significantly (P < 0.001) correlated with the amount of extracted Fe, suggesting that Fe might play a role in the retention of organic N in soil.     

Inorganic nitrogen in a tropical soil with frequent amendments of sewage sludge

Accurate prediction of plant-available N release from sewage sludge is necessary to optimize crop yields and minimize NO₃^– leaching to groundwater. We conducted a 1.5-year study with three maize crops to determine N mineralization from an urban sewage sludge from Barueri, State of São Paulo, Brazil, and its potential to contaminate groundwater with NO₃^–. The soil at the experimental site was a loamy/clayey-textured Dark Red Dystroferric Oxisol. The treatments consisted of: plots without chemical fertilization or sludge, plots with complete chemical fertilization, and plots receiving four different doses of sewage sludge. Dose 1 was calculated at the agronomic N rate, while doses 2, 3 and 4 were, respectively, two, four, and eight times dose 1. The inorganic N addition increased with the rate of biosolid application. The high NO₃^– concentrations in relation to NH₄⁺ were associated with intense soil nitrification. High N losses occurred for the first 27 days after soil sludge incorporation, even at the lowest dose, suggesting that land application of sewage sludge based on the N requirement of the crop may be overestimating the amount of sewage sludge to be applied.     

The distribution of nitrogen in some highly organic tropical volcanic soils

The qualitative and quantitative distribution of N-compounds in 10 tropical soils, and in a number of humic materials extracted from representative samples thereof, was determined after 6 N HCl hydrolysis.Eighty to 98% of the total N in the soils and humic materials was hydrolysable by 6n HCl. Slightly less than one half the hydrolysable N in the soils and humic fractions consisted of amino acids. Well-drained soils and fulvic acids extracted from them contained unusually high concentrations of the acidic amino acids, aspartic and glutamic acids. Between 80 and 95% of the amino acids in the soils was accounted for in the humic materials + NaOH-insoluble organic residues. NH⁺₄-N released by acid hydrolysis was generally higher for the soil samples than for the humic materials. Amino sugar-N constituted relatively small proportions of the total N in the soils and humic fractions.Our data suggest that large quantities of amorphous allophanic materials coupled with relatively high enzymic activity are responsible for the observed accumulation of acidic amino acids in the well-drained tropical volcanic soils.     

Micro flora related to the nitrogen cycle in the tropical upland farm soils

Samples of upland-farm surface soils (0–10 em in depth) belonging to various great soil groups were collected in 28 upland sites in Thailand during the rainy season.

Among the microbes related to the transformation of nitrogen, namely ammonifiers, ammonia oxidizers, nitrite oxidizers and denitrifiers, the count of denitrifier showed the maximum value amounting to 10⁴ to 10⁵ per 1 g of dry soil, followed byammonifier. The population level of nitrogen-fixing blue green algae was unexpectedly high, being 10³ to 10¹

The microbial counts in Brown Forest Soils, Rendzinas and Grumusols with high content of organic matter, available phosphorus and exchangeable potassium tended to be high.

Non-calcic Brown Soils, Reddish Brown Lateritic Soils, Alluvial Soils, Red-Yellow Podzolic Soils and Gray Podzolic Soils which lack in some nutrients showed intermediate levels of microbial populations, while the counts of nitrogen-fixing blue green algae in Alluvial Soils and those of denitrifier in Red-Yellow Podzolic Soils were markedly high. In the case of Low Humic Gley Soils and Regosols with low content of organic matter, available phosphorus and available potassium, the population of microbes was generally small.

The relationship between the organic matter content and the microbial population of soils was positively significant at 0.1 % level only in the case of fungal population (r=0.551), while the relationship between the available phosphorus content and the microbial population was positively significant at 0.1% level only in the case of Azotobacter (r=0.682).

The relationships between the total nitrogen, the exchangeable potassium, the amount of NH₄+^-N, the amount NO₂ ^--N, or the amount of NH₄ ⁺-N+NO₂ ^--N and each microbial population were not significant in any microbial groups.

The count of denitrifiers in upland farm soils of Thailand was 9 times as high as that in non-volcanic upland-farm soils of Japan and was 23 times higher than that in volcanic soils though large variations were seen among the great soil groups of Thailand. Conversely, the population of non-spore-forming nitrite oxidizers in the upland farm soils of Thailand was 1/100 that in non-volcanic soils of Japan and 1/280 that in volcanic soils. In the case of Azotobacter, the count in upland farm soils of Thailand averaged 2,800 per 1 g of dry soil. while that in non-volcanic upland farm soils of Japan was 77 on the average.

The ratio of aerobic bacteria to actinomycetes in upland farm soils of Thailand was 2.31, while that of non-volcanic soils of Japan was 7.28.     

Adsorption and translocation of sulfur in some tropical acid soils

In view of growing concern about sulfur (S) deficiency, we attempted to study the effect of soil characteristics on the adsorption and translocation of S in soils. Laboratory experiments were conducted with five surface soils collected from three regions in the state of Orissa (Eastern India). In an adsorption study, all the soils were equilibrated with graded doses of potassium sulfate (K₂SO₄). Freundlich adsorption isotherms provided good fit to S adsorption data. Free Fe₂O₃ and Al₂O₃ in the soils were primarily responsible for retaining added S in soils. Further, studies on the movement of sulfate‐S in 30‐cm plexiglass columns, where radio‐labeled S along with water (5 cm) was applied as gypsum and K₂SO₄, showed that K₂SO₄‐S migrated deeper than gypsum‐S. Sulfur moved deeper in case of initially water‐saturated soils than in initially air‐dry soils.     

Integrated Soil Fertility Management: Aggregate carbon and nitrogen stabilization in differently textured tropical soils

Soil organic matter is important to improve and sustain soil fertility in tropical agroecosystems. The combined use of organic residue and fertilizer inputs is advocated for its positive effects on short-term nutrient supply, but the effect of the integrated use on long-term stabilization of soil organic C and N is still unclear. We conducted a 1.5-y soil incubation experiment with maize (Zea mays) residue and urea fertilizer to examine the stabilization of C and N in four Sub-Saharan African soils differing in texture (sand, sandy loam, clay loam, and clay). The inputs were enriched with ¹³C and ¹⁵N in a mirror-labelling design to trace the fate of residue-C and N, and fertilizer-N in combination. We hypothesized that combining inputs would enhance the stabilization of C and N relative to either input alone across a range of soil textures. The treatments were destructively sampled after 0.25, 0.5, and 1.5 y to assess input-derived C and N stabilization in soil macro- and microaggregate fractions. The combination treatment had a significant but small (2% of residue-applied C) increase in residue-C stabilized in the total soil after 0.25 y, but this increase did not persist after 0.5 and 1.5 y. While combining residue and fertilizer decreased the amount of residue-N stabilized within 53- to 2000-μm sized soil aggregates (e.g., 7% less at 1.5 y), it increased the stabilization of fertilizer-N at all sampling times (e.g., 20% more at 1.5 y). The increased amount of fertilizer-N stabilized was significantly greater than the amount of residue-N lost in the combined input treatments in the three finer textured soils at 1.5 y, indicating an interactive increase in the stabilization of new N. Our results indicate that combining residue with fertilizer inputs can increase the short-term stabilization of N, which has the potential to improve soil fertility. However, benefits to N stabilization from combining organic residues and fertilizer seem to be less in coarser-textured soils.     

Urea transformation in some tropical soils

The effects of incubation at 20°, 30° and 40°C and urea concentrations of 0, 50, 100 and 200 μg N/g soil on urea hydrolysis and nitrification were investigated in three Nigerian soils. At constant temperature urea hydrolysis and rate of NO₃^? accumulation increased with increasing rate of urea addition. Urea was rapidly hydrolyzed within 1 week of incubation. Nitrification in Apomu soil increased with increasing incubation temperature. Nitrification was slow in acid Nkpologu soil (pH 4.7). Texture, cation exchange capacity and C:N ratios of the soils were not related to urea hydrolysis or nitrification. Nitrite accumulation in these soils was insignificant. Soil pH was decreased by nitrification of hydrolyzed urea-N.     

Inhibition of nitrate accumulation in tropical grassland soils: effect of nitrogen fertilization and soil disturbance

In acid soils in the Eastern Plains of Colombia, forage grasses planted on land prepared before the previous dry season produced 40–50% more dry matter than when land was prepared immediately before planting. Virtually no NO₃⁻ accumulated in surface (0–10 cm) soil from three native undisturbed savanna sites. Where land was ploughed before the dry season, NO₃⁻ levels increased gradually after a 2–3 month lag, and dropped at the beginning of the rains. In samples incubated for 4 weeks, more NO₃⁻ accumulated in the wet than the dry season. A similar 2–3-month lag occurred when land was ploughed after the dry season. NH₄⁺ levels were higher in ploughed than savanna soils, and rose in all soils at the beginning of the rains. More NO₃⁻ and NH₄⁺ accumulated on incubation in pots than in soil cores. Forage grasses inhibited NO₃⁻ accumulation in the soil, relative to plant-free plots, and legumes stimulated it. N fertilization overcame this inhibition except in the case of Brachiaria humidicola .     

Nitrogen-fixing microorganisms in paddy soils (Part 1) Characteristics of the nitrogen fixation in paddy soils

In most paddy soils, as is already well-known, the crop yield goes on decreasing just for the first few years and then stabilizes at a comparatively high level with no supply of fertilizer or manure.     

凋落物中次生代谢物对森林土壤可溶性氮的影响

通过外加性质不同的凋落物以及不同浓度的单宁酸,于武夷山不同海拔高度的森林土壤中进行培养,研究森林凋落物中次生代谢物对土壤可溶性氮(N)的影响。结果显示,土壤经加入凋落物处理,其可溶性N含量降低。加入杉木凋落物使红壤可溶性N含量降低12.0%～27.5%,杉木较竹叶凋落物处理降低作用显著(p0.05);对黄红壤添加不同浓度单宁酸处理显示,与对照比较,高浓度单宁酸可显著(p0.001)降低土壤可溶性N含量,降低幅度在40.6%～48.1%,而低浓度单宁酸对土壤可溶性N的影响不显著。表明植物凋落物,尤其是杉木对土壤可溶性N的影响很可能与其本身单宁酸含量差异有关,从而影响了土壤可溶性有机N和无机N的转化。     

Decomposition of rice residue in tropical soils

Nitrogen mineralization and immobilization of rice residue in Maahas clay soil under lowland and upland conditions were investigated by using ¹⁵N-labelled rice straw. The mineralization of residue-nitrogen was taking place even though the net mineralization was depressed by incorporation of rice residue.

There were some significant differences in the pattern of nitrogen transformation between lowland and upland soil conditions. The nitrogen transformation measured by mineralization of soil nitrogen and rice-residue nitrogen and the nitrogen immobilization into rice residue were more active under lowland conditions than under upland conditions, during the earlier period of residue decomposition.     

Trace elements in tropical Asian paddy soils

Attempts were made to evaluate correlations of total trace elements with various soil characters in the hope that such correlations would allow prediction of the trace element status of paddy soils in Tropical Asia.

Among the 11 trace elements studied, Ni and Cr showed by far the highest correlation, followed by the pairs of V and Zn, Ni and Zn, and Cr and Zn.

High positive correlations of trace elements with soil characters were found for the following pairs: total Fe₂O³, and V and Zn, total K₂0 and Rb, total CaO and Sr, total TiO₂, and V, total Al₂0³ and Zn, 10 Å clay content and Rb, clay and V, and sand and Zr. Among the negative correlations, the highest was between total SiO₂ and V, followed by those between total SiO₂ and Zn and sand and Zn.

Soil material classes and inherent potentiality ratings previously established were found to have some value for the prediction of the status of certain trace elements in soil.     

Buffer Ph methods for estimation of lime requirement of tropical acid soils

Abstract

Lime requirements (LR) of 26 agricultural acid soils were estimated using the following buffer methods: Shoemaker‐McLean‐Pratt (SMP) single buffer (SMP‐SB), SMP double buffer (SMP‐DB), Mehlich buffer method for crops with high LR (MEHLICH I), and Mehlich buffer methods for crops with low LR (MEHLICH II). The LR were determined to three pH targets (6.5, 6.0 and 5.5). The LR values were then evaluated through regression analysis using LR values obtained by the Ca(OH)₂ titration (for the 6.5 pH target) and moist CaCO₃‐incubation (for the 6.0 and 5.5 pH targets) as reference methods. All the buffer methods were well correlated with the reference methods but the SMP‐DB gave the best results for both high and low LR soils, and was particularly impressive at the lowest pH target.     

洞庭湖水稻土有机氮组分及其与可矿化氮的关系特征

为深入理解土壤有机氮有效性,利用Bremner酸解法测定了洞庭湖区典型水稻土有机氮组分,采用淹水生物培养法测定了土壤可矿化氮,并分析了二者间的内在关系。结果表明,酸解氮是土壤有机氮素的主要存在形式,其占土壤全氮的比例为58.6%～83.8%,不同类型水稻土酸解氮含量总体上依潴育性水稻土、潜育性水稻土、淹育性水稻土的次序逐渐降低;酸解氮中,氨基酸氮、氨基糖氮、氨态氮与未知氮占土壤全氮的比例分别为25.6%～43.1%、2.6%～9.0%、11.9%～22.3%和8.0%～25.3%。土壤可矿化氮数量变化主要受有机碳、全氮及粘粒含量的影响。酸解氮各组分均与土壤可矿化氮显著正相关(R=0.427～0.858,P0.05),但多元逐步回归和通径分析表明,氨基酸氮是对可矿化氮有直接重要贡献的组分,是可矿化氮的主要来源。氨基酸氮、氨基糖氮、氨态氮、未知氮与氮矿化势的通径分析决策系数分别为0.685、0.251、0.028、-0.050,表明提升有机氮中除未知氮外的其它酸解组分特别是氨基酸氮的分配比例有利于增加土壤可矿化氮供应容量。     

Soluble organic nitrogen in agricultural soils

 The existence of soluble organic forms of N in rain and drainage waters has been known for many years, but these have not been generally regarded as significant pools of N in agricultural soils. We review the size and function of both soluble organic N extracted from soils (SON) and dissolved organic N present in soil solution and drainage waters (DON) in arable agricultural soils. SON is of the same order of magnitude as mineral N and of equal size in many cases; 20–30 kg SON-N ha^–1 is present in a wide range of arable agricultural soils from England. Its dynamics are affected by mineralisation, immobilisation, leaching and plant uptake in the same way as those of mineral N, but its pool size is more constant than that of mineral N. DON can be sampled from soil solution using suction cups and collected in drainage waters. Significant amounts of DON are leached, but this comprises only about one-tenth of the SON extracted from the same soil. Leached DON may take with it nutrients, chelated or complexed metals and pesticides. SON/DON is clearly an important pool in N transformations and plant uptake, but there are still many gaps in our understanding. Received: 10 June 1999     

Effects of nitrogen source and aluminum on growth of tropical tree seedlings adapted to low pH soils

The effects of N-source and Al on the growth of seedlings of Melastoma malabathricum, Acacia mangium, and Melaleuca cajuputi, which are tropical woody plants and are very tolerant to Al, and barley (Hordeum vulgare), which is a typical Al-sensitive plant, were investigated. The Al and N treatments consisted of the application of either 0 or 0.5 mM Al, and 2 mM NH₄ ⁺ or N0₃ ^-, respectively. Growth of the tropical plants was enhanced by Al and NH₄ application. In all the plant species, the pH of the culture solution decreased and the concentrations of soluble Al and P increased with the + NH₄ treatment, which positively affected the growth of the tropical plant species. Excised roots of M. malabathricum dissolved insoluble Al with NH₄ application and absorbed Al mainly from root tips. Al did not affect the leaf N concentration except in the case of barley. Roots of M. cajuputi exuded a large amount of citrate, which slightly increased by the + Al treatment. In A. mangium, the reactivity of soluble Al to PCV (pyrocatecholviolet) decreased in the culture solution of the + Al + NH₄. treatment and Al concentration of roots in this treatment was very low. Roots of M. malabathricum released H+ along with Al uptake as well as NH₄ ⁺ uptake. It is concluded that Al and NH₄ ⁺ exert beneficial effects on the growth of tropical tree seedlings.