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Showing papers on "Soil organic matter published in 1975"


Journal ArticleDOI
TL;DR: The relationship between the denitrification capacities of 17 surface soils and the amounts of total organic carbon, mineralizable carbon, and water-soluble organic carbon in these soils was investigated in this article.
Abstract: The relationships between the denitrification capacities of 17 surface soils and the amounts of total organic carbon, mineralizable carbon, and water-soluble organic carbon in these soils were investigated. The soils used differed markedly in pH, texture, and organic-matter content. Denitrification capacity was assessed by determining the N evolved as N2 and N2O on anaerobic incubation of nitrate-treated soil at 20°C for 7 days, and mineralizable carbon was assessed by determining the C evolved as CO2 on aerobic incubation of soil at 20°C for 7 days. The denitrification capacities of the soils studied were significantly correlated (r = 0·77∗∗∗) with total organic carbon and very highly correlated (r = 0·99∗∗∗) with water-soluble organic carbon or mineralizable carbon. The amount of nitrate N lost on anaerobic incubation of nitrate-treated soils for 7 days was very closely related (r = 0·999∗∗∗) to the amount of N evolved as N2 and N2O. The work reported indicates that denitrification in soils under anaerobic conditions is controlled largely by the supply of readily decomposable organic matter and that analysis of soils for mineralizable carbon or water-soluble organic carbon provides a good index of their capacity for denitrification of nitrate.

737 citations


Journal ArticleDOI
TL;DR: In this paper, a theoretical model which gives the rate of microbial decomposition of organic material (plant or animal residues, or soil organic matter) is presented, where explicit equations for the decomposition, mineralization and immobilization are given.
Abstract: A theoretical model which gives the rate of microbial decomposition of organic material (plant or animal residues, or soil organic matter) is presented. Explicit equations for the rate of decomposition, mineralizations and immobilization are given. The main assumption of the model is that the rate of decomposition of any substrate is proportional to the growth rate of its decomposers. The main results of the model are: 1. Addition of extra nitrogen to materials poor in nitrogen increase their rate of decomposition; 2. Addition of extra nitrogen to a substrate whose initial carbon/nitrogen ratio is above a critical ratio (20–30) causes a decrease in the substrate's carbon/nitrogen ratio during its decomposition; 3. If the initial carbon/nitrogen ratio is below the critical one, no change in the substrate's ratio will occur with time; 4. Net mineralization of organic-nitrogen occurs when the substrate being decomposed has an initial carbon/nitrogen ratio which is below the critical one; 5. Addition of ammonium to such a substrate (point 4) will increase the rate of organic-nitrogen mineralization but not necessarily the rate of net mineralization. All the model results are analytical and independent of the values for the various parameters. Nevertheless the application of the model to real field conditions is discussed while presenting a numerical example.

250 citations


Book ChapterDOI
01 Jan 1975
TL;DR: The morphology of humus formations is determined by environmental factors as discussed by the authors, and these differences provide the basis for a division into groups, which are called humus forms, and the morphology of these groups are classified into three categories:
Abstract: Natural humus formations look very different morphologically to the naked eye. These differences provide the basis for a division into groups, which are called humus forms. The morphology of humus forms is determined by environmental factors.

150 citations


Journal ArticleDOI
09 May 1975-Science
TL;DR: The properties and potential of soils of the tropics are poorly understood, and basic concepts about physical and chemical behavior developed in the nonglaciated temperate regions are directly applicable to the Tropics.
Abstract: The properties and potential of soils of the tropics are poorly understood The old idea that laterite is formed when tropical soils are cleared is true of only a small proportion of the area In most features, soils in the tropics are similar or equivalent to soils in the temperate regions Specifically, soil organic matter contents, commonly believed to be low in the tropics, are essentially similar to those of the temperate regions While the basic concepts about physical and chemical behavior developed in the nonglaciated temperate regions are directly applicable to the tropics, the development of soil management practices for sustained food production involves different strategies because of environmental and economic constraints A major distinction is made between the development of high base status and low base status soils With the former, soil management practices should be aimed at maximizing the potential of high-yielding varieties and improving intercropping systems with relatively intensive fertilizer inputs With the low base status soils of the vast savanna and jungle areas energyrelated inputs should be optimized by (i) selecting of crop varieties and species more tolerant to nutritional deficiencies or toxicities, (ii) applying fertilizers at lower rates than those recommended by classic marginal analysis, and (iii) increasing the efficiency of applied fertilizers in such soils

125 citations


Journal ArticleDOI
TL;DR: In this paper, Pot culture experiments are described which attempt to identify the organic fractions of soil sulphur that decompose during the growing season to provide plant-available sulphur, and the effect of moisture stress on the uptake of sulphur by plants is also investigated; this treatment had little effect.
Abstract: Pot culture experiments are described which attempt to identify the organic fractions of soil sulphur that decompose during the growing season to provide plant-available sulphur. Soil organic matter was labelled with 35S by incubating soil with labelled sulphate and several organic sulphur fractions were determined before and after the growth of Sorghum vulgare and following a fallow treatment. The effect of moisture stress on the uptake of sulphur by plants was also investigated; this treatment had little effect. Changes occurred in both hydriodic acid-reducible and carbon-bonded sulphur fractions, 60 per cent of the sulphur taken up by the plants being derived from the latter. The changes in carbon-bonded sulphur involved changes in both Raney nickel-reducible and non-reducible sulphur fractions. All of the sulphur fractions investigated thus contributed available sulphur for plant uptake, and none of them are likely to be of any value for predicting the sulphur requirements of plants.

125 citations


Book ChapterDOI
01 Jan 1975
TL;DR: The manifold importance of organic matter in soil formation and soil fertility has been demonstrated by the experience of agriculture over many centuries and by numerous investigations, in which the role of organic matters in soil processes (weathering, soil profile formation, soil structure formation, etc.) as well as in supplying plants with nutrients and biologically active substances has been elucidated as discussed by the authors.
Abstract: The manifold importance of organic matter in soil formation and soil fertility has been demonstrated by the experience of agriculture over many centuries and by numerous investigations, in which the role of organic matter in soil processes (weathering, soil profile formation, soil structure formation, etc.) as well as in supplying plants with nutrients and biologically active substances has been elucidated.

98 citations


Journal ArticleDOI
TL;DR: In this article, a numerical model based on the transport equations for water and noninteracting solutes and written in IBM S/360 CSMP language was designed to compute the radial movement of water and salts to plant roots.
Abstract: A numerical model, based on the transport equations for water and noninteracting solutes and written in IBM S/360 CSMP language, was designed to compute the radial movement of water and salts to plant roots. The inputs are: the soil's suction and conductivity functions, the soil solution's content and concentration, root density and permeability, and the required uptake rate (whether constant or diurnally fluctuating). The output provides the time-dependent drawdown of matric and osmotic potentials in the immediate vicinity of the root, the gradients and flow rates of water and solutes in the soil, and the plant water potentials needed to maintain different uptake rates. The model is illustrated for various rooting densities and various initial water contents and salt concentrations. The effect of increasing root density and permeability is seen to be similar to the effect of increasing water content or reducing transpirational demand.

86 citations


Journal ArticleDOI
TL;DR: A ranking of stands along a soil nutrient gradient, based on field observations and presence data for species, correlated successively less strongly with ordinations computed by similarity—projection, Bray—Curtis method, importance— projection, principal components analysis, and factor analysis.
Abstract: The dwarfed conifer forests occurring on the coastal terraces of Mendocino County, California, are oligotrophic communities containing edaphic endemics as dominants. Species distributions and community characteristics are traced along a gradient in podzolization of the soils from these pygmy conifer stands on highly weathered terrace spodosols, to redwood stands on weakly developed slope spodsols. Vegetation stature, canopy closure, species richness, litter biomass and pH generally decrease along the gradient as podzolization and nutrient impoverishment increase, whereas soil organic matter and available water capacity tend to be highest at the gradient extremes. Analyses of pygmy forest soils show low levels of macro— and micro—nutrients, and high levels of exchangeable aluminum. When ordinations of stands based on vegetational data are compared with rankings based on environmental data, changes in pH of the soil A horizon are found to correlate most highly with vegetation changes. Nutrient loss and acidification, initiated by varying rates of soil weathering in the pygmy forest region, may be aggravated, in the case of pygmy forest soils, by a series of feedback effects, including solubilization of possibly toxic amounts of aluminum by low pH, which may contribute to the observed plant stunting and shrinking pools of nutrients in the biomass. A ranking of stands along a soil nutrient gradient, based on field observations and presence data for species, correlated successively less strongly with ordinations computed by similarity—projection, Bray—Curtis method, importance—projection, principal components analysis, and factor analysis. Although these ordinations were expected to produce distortions in the interstand relations due to the modal and even polymodal nature of species response curves and to the presence of species not spanning the range of the data set, additional distortions due to variability in sample data were also highlighted.

73 citations


Journal ArticleDOI

72 citations


Journal ArticleDOI
TL;DR: In this article, the authors studied the organic matter in three soils from adjacent sites with different long-term treatments: soil I, prolonged arable cultivation, soil II, 17 years under grass after prolonged arability cultivation, and soil III, old pasture.
Abstract: Components of the organic matter have been studied in three soils from adjacent sites with different long-term treatments: soil I, prolonged arable cultivation; soil II, 17 years under grass after prolonged arable cultivation; and soil III, old pasture. Contents of total organic C in the top 15cm were 0.9% in soil I. 1.7% in soil II and 4.8% in soil III. The light fraction, comprising partially decomposed materials with a specific gravity The proportions of the soil organic C released, by hydrolysis, as neutral sugars, uronic acids, amino sugars, amino acids and phenolic acids were generally similar in the three soils, although uronic acids and phenolic acids constituted somewhat greater proportions in soils II and III than in I. The light fractions contained greater proportions of neutral sugars and phenolic acids, and smaller proportions of amino sugars and amino acids than the whole soils.

66 citations



Book ChapterDOI
01 Jan 1975
TL;DR: A relatively simple accommodation to the extraordinarily complex problem of defining and using principles of degradation to predict this aspect of the behavior of pesticides in soil was made by as discussed by the authors. But it is with many scientific endeavors.
Abstract: History will record that eventually there was a relatively simple accommodation to the extraordinarily complex problem of defining and using principles of degradation to predict this aspect of the behavior of pesticides in soil. So it is with many scientific endeavors.

Journal ArticleDOI
TL;DR: In this paper, the most important factors that influence the persistence of pesticides are the chemical stability and physical characteristics of the pesticide; its stability exerting the greatest influence, otherwise volatility being more important in soil and solubility in plants.
Abstract: Some of the factors that influence the persistence of pesticides are common to both plants and soils. These are, firstly, the characteristics of the pesticide, including its over-all stability either as parent compound or metabolites, its volatility, solubility, formulation, and the method and site of application. A second group includes the environmental factors, particularly temperature, precipitation (and humidity) and air movement (wind). The other factors depend on the properties of the plant or soil. Characteristics influencing the persistence of pesticides in plants include the plant species involved, the nature of the harvested crop, the structure of the cuticle, the stage and rate of growth and the general condition of the plant. Corresponding soil characteristics are the soil type and structure, its organic matter content, clay content, acidity or alkalinity, mineral ion content and degree of aggregation and its microbial population. Of these factors, the most important seem to be related to the chemical stability and physical characteristics of the pesticide; its stability exerting the greatest influence, otherwise volatility being more important in soil and solubility in plants. Of the plant characteristics, the species and rate of growth seem most important, and in soil, adsorption on to organic matter or clay minerals, and the populations of soil microorganisms present exert the greatest influence.

Journal ArticleDOI
TL;DR: In this article, a simple and precise density fractionation of soil mineral-organic complexes, suitable for routine work, is described, with low sample weight, use of glass-fibre paper to collect the lighter fractions, and use of a modified Walkley-Black procedure to determine the carbon content of the light fraction in test tubes.
Abstract: Summary A rapid, simple, and precise density fractionation of soil mineral-organic complexes, suitable for routine work, is described. Special features of the method are: low sample weight, use of glass-fibre paper to collect the lighter fractions, and use of a modified Walkley-Black procedure to determine the carbon content of the light fraction in test tubes. Density-distribution curves of organo-mineral soil complexes are shown to yield useful basic information on degradation processes of soil organic matter caused by cultivation. The results suggest that complexes between clay and organic matter tend to build up preferentially with a certain proportion between the components.

Journal ArticleDOI
TL;DR: Factor analysis of the data revealed that 67 to 81% of the total variance exhibited by all variables per site-sampling period could be accounted for by soil acidity, soil structure, soil fertility, soil moisture, and bacterial factors.
Abstract: Toposequence variations in soil properties were characterized and related to variations in populations of total isolatable bacteria and arthrobacters Increases in soil NO3-N, available phosphorous, NO3-N-producing power, Arthrobacter counts, and the percentage of the total counts represented by arthrobacters were correlated with decreases in soil acidity The total bacterial counts were not correlated with soil acidity but were associated with percentage of soil organic matter and percentage of clay The percentage of the total counts represented by arthrobacters was lowest at the summit position and increased downslope to the highest value in the toeslope position Factor analysis of the data revealed that 67 to 81% of the total variance exhibited by all variables per site-sampling period could be accounted for by soil acidity, soil structure, soil fertility, soil moisture, and bacterial factors A selective medium was developed for soil arthrobacters and tested on a wide variety of central Iowa soils to determine its potential as a medium for enumeration as well as isolation The medium developed in this study was found to be superior to the other available direct-isolation media for soil arthrobacters

Journal ArticleDOI
TL;DR: In this paper, the adsorption/desorption potential of several phenylurea herbicides was studied on representative prairie soils, using slurry-type adaption experiments and the relationship between the k value and the soil organic matter content was found to be of the exponential type.
Abstract: The adsorption/desorption potential of several phenylurea herbicides was studied on representative prairie soils, using slurry-type adsorption experiments. The herbicides showed the following order of increasing tendency to be adsorbed: fenuron < monuron monolinuron < metobromuron < diuron linuron chlorbromuron. The relative adsorption of each herbicide on various soil types was significantly correlated with the soil organic matter content, but not with the clay content. The relationship between the k value and the soil organic matter content was found to be of the exponential type. The extent of adsorption was also inversely related to the order of their water solubilities. The urea herbicides were readily desorbed by water from the low to medium organic matter content sandy loam and heavy clay soils, but not from a loam with very high organic matter content. It is suggested that the relative adsorption/desorption potential of a herbicide may provide a mechanism by which soil applied herbicides can be bi...

Journal ArticleDOI
TL;DR: The effects of acid pre-treatment and fractionation on the molecular weight distribution of OIM Na4P2O7 organic matter extracts were investigated in a chronosequence of weakly weathered soils developed on aeolian sand in New Zealand as mentioned in this paper.
Abstract: Summary Effects of acid pre-treatment and fractionation on the molecular weight distribution of OIM Na4P2O7 organic matter extracts were investigated in a chronosequence of weakly weathered soils developed on aeolian sand in New Zealand. Acid pre-treatment of soils with OIM HCl followed by OIM HCI:03M HF was found to enhance the polydispersion in the nominal molecular weights of the extracts. The same treatment resulted in significant increases in yield and reduction in ash content. However, prolonged standing of extracts in the acids led to acid-induced polymerization, resulting in a predominance of organic matter in the higher nominal molecular weight ranges. Fractionation of organic matter extracts by acid precipitation into humic and fulvic acids did not separate them according to molecular weight as commonly believed. Instead, fulvic acids from most soils were found to have similar nominal molecular weight distributions to those of their humic acid counterparts. A large proportion of soil fulvic acid compounds was in the > 100 000 nominal molecular weight range.

Book ChapterDOI
01 Jan 1975
TL;DR: A survey of the literature pertaining to soil fats, waxes, and resins (often called bitumens or simply lipids) indicates that these substances are probably the least studied of soil organic matter components as discussed by the authors.
Abstract: A survey of the literature pertaining to soil fats, waxes, and resins (often called bitumens or simply lipids) indicates that these substances are probably the least studied of soil organic matter components. Soil organic matter chemists have largely ignored these materials in preference to studies on the true humic materials. This neglect is probably based on the fact that fats, waxes, and resins comprise but a small percentage of the total organic matter of mineral soils (1 to 5%). However, 10 to 20% of the total organic matter of organic soils may come under the lipid classification. Three review articles deal with the soil lipid fraction:HOWARD and HAMER [1960], STEVENSON [1966], and MORRISON [1969]. WOLLRAB and STREIBL [1969] also review the literature on peat and lignite waxes.


Book ChapterDOI
01 Jan 1975
TL;DR: The chemistry and significance of soil organic phosphate, which often accounts for a high proportion of the total phosphate, has been the subject of extensive investigation for well over half a century, and detailed reviews have at intervals summarized the advances achieved as discussed by the authors.
Abstract: The chemistry and significance of soil organic phosphate, which often accounts for a high proportion of the total phosphate, has been the subject of extensive investigation for well over half a century, and detailed reviews have at intervals summarized the advances achieved (e.g., BLACK and GORING [1953], ULRICH and BENZLER [1955]).

Journal ArticleDOI
TL;DR: In a series of experiments, 15N-labeled nitrate fertilizer was used to study the nitrogen balance of a heavy clay soil as discussed by the authors, and only 6 ± 4.5% of the added 15N was not accounted for by soil and plant analysis.
Abstract: In a series of experiments, 15N-labelled nitrate fertilizer was used to study the nitrogen balance of a heavy clay soil. Two of the experiments employed 60-cm deep, 16-cm diameter columns of packed soil. In the first, no added 15N was lost until heavy rain saturated the soil in the undrained columns. Subsequently, fallow and planted columns lost 25% of the 15N added. While denitrification appeared primarily responsible for these losses, some of the 15N may have been lost by weathering of the plants during senescence. This experiment was repeated with precautions to prevent excessive rain saturating the soil. After 16 weeks, only 6 ± 4.5% of the added 15N was not accounted for by soil and plant analysis. In the third experiment, I5N was added to 16-cm diameter confined microplots in situ. The microplots were fallow and were confined by 60-cm deep plastic pipe. After 16 weeks, during which 190 mm of rain fell, 97.7 ± 2.4% of the added 15N was recovered.

Journal ArticleDOI
TL;DR: In this paper, the authors evaluated the changes in chemical and physical properties of a Keith silt loam (fine-silty, mixed, mesic, Aridic Argiustolls) that may be attributed to cropping.
Abstract: from various cropping systems and the uniqueness of a longThe need to document further the changes in soil properties time cultivated field adjacent to huffdograss (Buehloe dactyloides) pasture prompted us to evaluate sail-property changes of a Keith silt loam ( fine-silty, mixed, mesic, Aridic Argiustolls 1, characteristic of that pasture and field. In the fall of 1973, we ples were obtained from the pasture (newly broken sod) and brake the sod of the buffalograss pasture for analysis. Soil samthe adjacent cultivated field. The wet aggregates from the pasture were stabler as mmpared with the cultivated field for both flash and vacuum wetting. However, the dry aggregates from the cultivated field were slightly stabler than those from the pasture. The average clod densities were 1.7 and 1.3 g a 3 from the tilled and pasture soils, respectively. The pasture soil was also much more permeable. The constant infiltration rate (after 6 hours of infiltration) averaged 0.95 and 0.13 of the general deterioration of many of the physical properties cm hr-1 for pasture and cultivated soils, respectively. Because of its soil, the cultivated field will require special management Consideration. Additional Indez Words: tillage, soil structure, infiltration, organic matter. s . . . OIL'S PHYSICAL PROPERTIES generally deteriorate if a Soil 1s mtenslvely cultivated. Page and Willard (1946) found cultivation resulted in a loss of pore space and a corresponding increase in weight per unit-volume of soil. Other workers (van Bavel and Schaller, 1950; Wilson and Browning, 1945) observed decreased aggregation of soil under continuous corn. Olmstead (1946), who compared aggregation of soil from virgin buffalograss pasture with that of plots broken from virgin buffalograss (Buchloe ducfyzone the tilled plots had lost approximately 80% of their hides) prairie about 1902, found that in the surface-tilled initial aggregation-a decrease sufficient to account for decreased crop yields. Harris et al. (1966) summarized their review of "Dynamics of Soil Aggregation" by reporting that a soil's aggregate status usually deteriorates rapidly if the soil is repeatedly cropped with annuals that supply little organic matter to the soil, require extensive cultivation, and provide minimal vegetative cover. deteriorated soil structure (Cary and Hayden, 1973.) MidHowever, not all continuous row-cropping systems have dleton (1952) reported tilling the soil at its most favorable moisture content usually will improve (or change very little) its structure because the aggregates formed from the joining of individual particles then will tend to countereration with the Kansas Agric. Exp. Sta. Dept. of Agronomy 'Contribution from the Agric. Res. Serv., USDA, in coopContribution no. 1461: Colby Branch Sta. no. 54. Paper presented before Div. S6 , Soil Sci. Soc. Am., Chicago, Ill. November 1974. Received 20 Jan. 1975. Approved 14 Mar. 1975. zSoil Scientist and Engineering Technician, USDA, ARS, NCR, Manhattan, Kansas, and Superintendent, Colhy Exp. Sta., Colby, Kansas. balance those disrupted by implement action. Harris et al. (1966) concluded grasses and perennial crops with extensive root systems, a continuous supply of readily decomposable organic matter, and effective protective coverage improve soil aggregation. The change in soil properties from various cropping systems needs to he further documented. In this study, we evaluated the changes in chemical and physical properties of a Keith silt loam (fine-silty, mixed, mesic, Aridic Argiustolls) that may be attributable to cropping. The study was possible because a field cultivated for many years is adjacent o the buffalograss pasture being brought under cultivation. METHODS AND PROCEDURE The newly broken sod, cultivated for a few years about the native pasture continuously. The main plant species (and apturn of the century (from 1913 or 1914 until 1973), was in proximate percentages) in the pasture included: 55% buffalograss, 20% western wheatgrass (Agropyron smithir), 17% red three-awn (Arisfidn longiseta), 5% tall dropseed (Sporobolus), laneous weeds-prairieconeflower (Ratibida Raf.), gumweed 1% little barley (Hordeum pusillum Nutt.), and 2% miscel(Grindelia Willd.), fetid marigold (Dyssodia papposa (vent.) Hitche.), and firewied (Epilobium angrrsrifolirrm L.). In the fall of 1973, the sod was chiseled 83 cm on center, approximately 20 cm deep. After chiseling, the soil was prepared for plowing by disking twice-io level the area and break up sod clumps-and then plowed 15 cm deep and left for the winter, In early spring of 1974, a roller packer was used twice to level and prepare a seedbed for spring barley, planted in late February. The cultivated field has been cropped for more than 60 years. Early cropping sequence included forage sorghum (Sorghum wheat fallow. Starting in 1959 the sequence has been: bicolor (L..) Moench.), wheat (Triticum aestivum L.), and 1959-summer-fallow 1960-fallowed wheat 1967-summer-fallow 1961-summer-fallow 1968-fallowed Lancer wheat 1962-fallowed wheat 1969-summer-fallow 1963-summer-fallow 1970-fallowed Shawnee wheat 1964-fallowed grain sorghum 1972-nonirrigated spring barley 1971-irrigatedsugar beet 1965--summer-fallow 1973-irrigated corn 1966-fallowed Scout wheat Sails from the field with a long-time cropping history and from the field previously in grass pasture will be referred to as "tilled" and "sod." ple from both sod and tilled fields at 0to 15-, 15to 30-, and We obtained a composite (at least 10 suhsamples) soil sam30to 60-cm depths. The samples were analyzed for chemical properties at the Kansas State Univ. Soil Testing Laboratory. cultivated and grassed sites were allowed to air-dry, we deterAfter about 10 kg of soil obtained from the plow layer of the mined their dry-aggregate stability and size distribution by dry sieving according to Chepil's method (1951, 1952, 1958), using a sieve described by Lyles et al. (1970). To determine wet-aggregate stability (of soil wetted both by vacuum and by direct immersion) of the 2.0and 0.84-mm size fraction obtained from the dry sieving, we used the method described by Kemper (1965). except we used a 15.2-cm-diameter sieve and a 30-g soil sample. Our mechanical sieving machine lowered and raised the sieve holder throngh a distance of 2.7 cm 25 X each minute. 964 965 S ~ I D M O R E ET AL. : SOIL CHANGES RESULTING FROM CROPPING Table 1-Chemical properties of the sod and tilled Keith soils, fall 1973 c-15 1,210 I4 IS30 770 6 750 0.35 11.2 0.6 Ll.0 1.5 7 . 9 13.6 3&60 613 0.71 11.4 0.5 20.6 3.0 7.5 13.7 800 13 838 0.31 2. 22 6. 4 0. 6 2. 21 8. 2 1.7 7. 8 14. 9 0. 42

Journal ArticleDOI
TL;DR: In this article, the stable isotope 15N was used to study the fate of nitrogen fertilizers applied to a black earth growing wheat, and the results showed that 15N-labeled ammonium and nitrate were almost completely recovered by soil and plant analysis.
Abstract: The stable isotope 15N was used to study the fate of nitrogen fertilizers applied to a black earth growing wheat. In a glasshouse experiment using soil packed at 56 % moisture (pF 2) into pots, added nitrate was almost completely recovered (mean, 98.8 ± 2.3 %) by soil and plant analysis. This experiment was repeated using 15N-labelled ammonium as well as nitrate; mean recoveries at 15 weeks were 96.8 and 97% respectively (± 2.2% at P < 0.05). A series of pots with soil wetter than pF 2 (at 63% moisture) was also included in an attempt to favour denitrification. Again, virtually complete recovery of added 15N was measured, 97 and 96.8% at 56 and 63% moisture respectively. Fallow and planted systems were then studied in a gas lysimeter. During experiments lasting up to 14 weeks, gaseous losses as 15N-labelled denitrification products were less than the equivalent of 0.2 µg nitrogen/g soil (the lower limit of detection with a mass spectrometer). Although analysis of plant and soil from the lysimeter in two experiments showed virtually quantitative recovery (99.7 and 97.05%), small (0.16%) losses of labelled ammonia into the lysimeter atmosphere were detected. The significance of these results is discussed in relation to the common finding of large deficits in nitrogen balance studies.

Journal ArticleDOI
TL;DR: Carrot was the crop showing the greatest reduction in yield after 4 yr cropping without the addition of commercial fertilizers, and potassium as the primary nutrient to be first in short supply for celery, carrot and lettuce.
Abstract: Vegetable response to fertilizer treatments of a well decomposed organic soil over a 4-yr period showed potassium as the primary nutrient to be first in short supply for celery (Apium graveolens L....

Journal ArticleDOI
TL;DR: In this paper, the tracer technique was used to measure the amount of nitrogen trapped in the Maahas clay soil to which no organic material was added, and it was found that 20% of the fertilizer nitrogen added as basal to the soil was immobilized in submerged soils.
Abstract: Greenhouse experiments using the tracer technique showed that about 20 per cent of the fertilizer nitrogen added as basal to the Maahas clay soil wa11 immobilized in submerged soils to which no organic material was added. The addition of organic matter to the soil increases the amount of nitrogen immobilized and the magnitude depends on the carbon to nitrogen ratio of the materials added. More fertilizer nitrogen waa immobilized in the soils under upland and alternate wet-and-dry conditions than under submerged soil conditions. The uptake of fertilizer nitrogen by rice plants growing under submerged soil conditions ceased at the vegetative stage of growth because only a small amou11t of available nitrogen remains in the soil at this time, but the rice plant continued to absorb gradually untagged nitrogen from the soil throughout the reproductive etages of growth. Losses of fertilizer nitrogen were great under the alternate wet-and-dry conditions (submerged-upland). The loss of nitrogen from the s...

Journal ArticleDOI
TL;DR: The feedback effect of plant residues on soil organic matter is of current interest in many agricultural systems due to recent large increases in crop yields as mentioned in this paper, and computer-based numerical methods which fit differential equations to data allow the plant yield-soil organic matter relations in crop sequential experiments to be examined more fully.
Abstract: The feedback effect of plant residues on soil organic matter is of current interest in many agricultural systems due to recent large increases in crop yields. Computer-based numerical methods which fit differential equations to data allow the plant yield-soil organic matter relations in crop sequential experiments to be examined more fully. The equation dN/dt = -K1(t)*N + K2 + K3(t)*Y(t) where N is soil organic nitrogen, Y(t) is plant yield at time t, K2 is a constant noncrop addition term, and K1(t) and K3(t) are decomposition and addition crop coefficients which vary with the stage of the sequential experiment, has been fitted to soil and plant yield data from the Morrow and Sanborn plots. Coefficients of the above model and three restricted variants of it were estimated by least squares, using soil nitrogen and crop yield data over 50 to 63 years. Statistical comparisons of the models were also made. From the equations the relationships between equilibrium soil levels and crop yields were calculated and the feedback effect of increasing crop yield on soil nitrogen level was estimated. At Morrow, increasing corn yields in a continuous corn system had negligible feedback effects on soil N level. However, some feedback effects were shown by oats and clover. At Sanborn, oats had the greatest feedback effect of the four crops examined. In this experiment timothy had the least feedback effect. Manure in both experiments substantially increased soil equilibrium levels. The value of quantitative estimates of feedback effects and the need for additional soil data in understanding changes in agricultural ecosystems are discussed.

Journal ArticleDOI
TL;DR: In this article, continued application of fertilizer to a pasture soil over a 4-year period, increased the phosphate extractable, the bicarbonate extractable and the total sulphur contents.
Abstract: Continued application of fertilizer to a pasture soil over a 4 year period, increased the phosphate extractable, the bicarbonate extractable, and the total sulphur contents. Where the same level of sulphur had been applied during this period, the phosphate extractable sulphur declined exponentially with time since the last fertilizer application. No such relation with bicarbonate extractable sulphur was established. Under a pasture regime, there was an increase in the carbon bonded sulphur fraction with increasing level of sulphur applied. Evidence from cropped soils showed that sulphur in the carbon bonded form was not a permanent sink for soil sulphur. On cropping, more sulphur was withdrawn from the carbon bonded than from the hydriodic acid reducible form. The similarity in composition between new additions to the soil sulphur and that already there, and the mobility of the element between the forms examined, will make it difficult to devise a satisfactory soil test for the sulphur status of a soil.

Journal ArticleDOI
TL;DR: In this article, an automatic CHN analyzer was used to determine the organic and inorganic carbon content of soils, and the results showed that at 500°C complete oxidation of soil organic matter occurs without appreciable decomposition of carbonates.
Abstract: Differential thermal analysis shows that in soils organic matter and carbonates react in very different temperature ranges. An automatic CHN Analyzer was therefore used to determine the organic and inorganic carbon content of soils. At 500°C complete oxidation of soil organic matter occurs without appreciable decomposition of carbonates. Because only elemental carbon is determined, interferences due to weight losses from structural water in clays are eliminated. Decomposition of carbonates begins above 500° and always is concluded before 1100°C. Total organic and inorganic carbon in soils thus may be determined by running replicates at 500° and 1100°C with the Analyzer.


Journal ArticleDOI
01 Mar 1975-Geoderma
TL;DR: In this article, the alkali-soluble organic matter of soil with a cation-exchange resin resin (Amberlite IR 120, H + form) was treated with cation exchange resins.