Decomposition of organic materials from hill soils and pastures: II. Comparative studies on the mineralization of carbon, nitrogen and phosphorus from plant materials and sheep faeces
TL;DR: Grass from monthly cut treatments decomposed more rapidly than annually accumulated grass, and mineralization was greater from Agrostis-Festuca than from Nardus, and more than half of the nitrogen which was mineralized was evolved as NH 3.
Abstract: Four plant materials obtained from Nardus and Agrostis-Festuca hill pastures, and the sheep faeces derived from these materials were incubated at 30°C for periods up to 12 weeks. The evolution of CO 2 and the production of mineral nitrogen and phosphorus were measured: 10–20 per cent and 30–55 per cent of the original carbon was evolved as CO 2 from faeces and plant materials respectively. Of the total original nitrogen, up to 8 per cent was mineralized from faeces, and up to 25 per cent was mineralized from plant materials. Grass from monthly cut treatments decomposed more rapidly than annually accumulated grass, and mineralization was greater from Agrostis-Festuca than from Nardus. More than half of the nitrogen which was mineralized was evolved as NH 3 . Throughout most of the incubation period plant materials immobilized phosphorus while between 3 and 34 per cent of the total phosphorus in faeces was mineralized. The results are discussed in relation to the role of sheep in the soilplant-animal nutrient cycle.
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TL;DR: In this paper, the authors reviewed the progress made in modeling the cycling of nutrients in pasture systems and the major emphasis is on the central role of the grazing animal in influencing soil fertility, particularly in the dung and urine patches.
Abstract: Publisher Summary This chapter reviews the cycling of nutrients within pasture soils. The major emphasis is on the central role of the grazing animal in influencing soil fertility, particularly in the dung and urine patches. In addition, the progress is reviewed that has been made in modeling the cycling of nutrients in pasture systems. Nutrients are partitioned differently between dung and urine, with K being excreted mainly in urine; P, Ca, and Mg are excreted principally in dung and N and S are excreted in both forms. Nutrients returned in excreta can be in inorganic and organic forms, depending on the particular nutrient being considered. For some nutrients (e.g., P and S) significant mineralization of ingested organic forms occurs during passage through the animal, whereas much of the N is excreted in the readily available organic urea form. From the present knowledge of the major nutrient inputs and losses for the grazed pasture system and an understanding of the pathways of nutrient flux within the system and some key measurements, simple mass balance nutrient models for various pasture systems can be constructed. Such simple models have been used to calculate site-specific maintenance fertilizer requirements of pastures based on the amount of nutrient required to replace losses in the soil (e.g., through fixation and leaching) and losses by animal transfer and in animal products.
1,249 citations
TL;DR: In this article, a review deals with methodological approaches, measured rates, and environmental control of two major interdependent processes regulating the structure and function of terrestrial ecosystems, viz., plant decomposition and soil respiration.
Abstract: This review deals with methodological approaches, measured rates, and environmental control of two major interdependent processes regulating the structure and function of terrestrial ecosystems, viz., plant decomposition and soil respiration. Both these processes have been evaluated through indirect assessments as well as through direct measurements under the field conditions. The techniques used suffer in general from difficulties in creating conditions of natural environment during the process of measurement. Generalizations regarding the magnitude of rates in different ecosystems are difficult because of limited results or non-comparability of results from different methods. Temperature and moisture and their interactions markedly influence both the processes. The surface feeders and soil animals have a marked influence on the decomposition. Partitioning of soil respiration into components due to live roots, microbes, and soil fauna has eluded a satisfactory solution so far.
734 citations
TL;DR: This review identifies the mechanisms by which foliar herbivory may indirectly affect the soil biota and associated below-ground processes through affecting plants, so as to better understand the nature of interactions which exist between above-ground and below- ground biota.
Abstract: Studies of the effects of above-ground herbivory on soil organisms and decomposer food webs, as well as the processes that they regulate, have largely concentrated on the effects of non-living inputs into the soil, such as dung, urine, body parts and litter. However, there is an increasing body of information which points to the importance of plant physiological responses to herbivory in regulating soil organisms and therefore, implicitly, key soil processes such as decomposition and nutrient mineralisation. In this review we identify the mechanisms by which foliar herbivory may indirectly affect the soil biota and associated below-ground processes through affecting plants, so as to better understand the nature of interactions which exist between above-ground and below-ground biota. We consider two broad pathways by which above-ground foliar herbivory may affect soil biotic communities. The first of these occurs through herbivore effects on patterns of root exudation and carbon allocation. These effects manifest themselves either as short-term changes in plant C allocation and root exudation or as long-term changes in root biomass and morphology. Evidence suggests that these mechanisms positively influence the size and activity of the soil biotic community and may alter the supply of nutrients in the rhizosphere for plant uptake and regrowth. The second of these involves herbivores influencing soil organisms through altering the quality of input of plant litter. Possible mechanisms by which this occurs are through herbivory enhancing nitrogen contents of root litter, through herbivory affecting production of secondary metabolites and concentrations of nutrients in foliage and thus in leaf litter and through selective foliar feeding causing shifts in plant community structure and thus the nature of litter input to the soil. While the effects of herbivory on soil organisms via plant responses may be extremely important, the directions of these effects are often unpredictable because several mechanisms are often involved and because of the inherently complex nature of soil food-web interactions; this creates obvious difficulties in developing general principles about how herbivory affects soil food-webs. Finally, it is apparent that very little is understood on how responses of soil organisms to herbivory affect those ecosystem-level processes regulated by the soil food-web (e.g. decomposition, nutrient mineralisation) and that such information is essential in developing a balanced understanding about how herbivory affects ecosystem function.
652 citations
TL;DR: It is concluded that short-term responses of soil processes to climate change are more predictable in well-drained grassland and forest soils than in waterlogged soils of the tundra and boreal region.
Abstract: Current models of climate change predict a reduction of area covered by northern coniferous forests and tundra, and an increase in grasslands. These scenarios also indicate a northerly shift in agricultural regions, bringing virgin soils under cultivation. The direct effects of man on tundra, boreal forest, and temperate grassland ecosystems are likely to result in less carbon mobilization from soils and vegetation than from tropical forests. However, as a consequence of climate change, carbon mineralization rates from arctic and sub-arctic soils could be very rapid under warmer and drier conditions because of low stabilization of soil organic matter (SOM) and enhanced microbial responses to small changes in soil moisture and temperature. Predicting the response of these systems to climate change is complicated where the edaphic environment regulating SOM dynamics is not a direct function of macroclimatic conditions. Grasslands contain a greater proportion of highly stabilized SOM than coniferous forests, distributed over greater depth in the soil profile, which is less susceptible to changes in mineralization rates. It is concluded that short-term responses of soil processes to climate change are more predictable in well-drained grassland and forest soils than in waterlogged soils of the tundra and boreal region. Over longer periods of time, however, plant species and soil types will alter in response to new temperature and moisture regimes above- and belowground interacting with the effects of carbon enrichment and changes in nutrient availability. The dynamics of these plant-soil interactions and the future status of soils in different life zones as sources or sinks of carbon is poorly understood. More data are also needed on the distribution of waterlogged forest soils in the boreal zone and responses to warming, which include the production of methane as well as CO2 . The primary recommendation for future research is for integrated studies on plant and soil processes.
325 citations
Cites background from "Decomposition of organic materials ..."
...…materials such as grass litter and most crop residues, with low to moderate lignin content (up to 10-15%), decomposition rates can be predicted from nitrogen concentration or the C/N ratio (Floate 1970, Hunt 1977, Singh and Gupta 1977, Bosatta and Staff 1982, Juma and McGill 1986, Seastedt 1988)....
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TL;DR: A model has been developed to simulate the dynamics of decomposers and substrates in grasslands and the proportion of rapidly decomposing material in a substrate is predicted from its initial nitrogen content.
Abstract: A model has been developed to simulate the dynamics of decomposers and substrates in grasslands. Substrates represented are humic material, feces, and dead plant and animal remains. Except for humic material, substrates are further divided into a rapidly and a slowly decomposing fraction. The proportion of rapidly decomposing material in a substrate is predicted from its initial nitrogen content. The belowground portion of the system is divided into layers because temperature and soil water, the most important driving variables for the model, vary with depth. Decomposition rates are predicted from temperature, water tension, and inorganic nitrogen concentration.
263 citations
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TL;DR: This chapter reviews important papers of research in the field of mineralization of organic nitrogen in soil, beginning with the years preceding World War II.
Abstract: Publisher Summary This chapter reviews important papers of research in the field of mineralization of organic nitrogen in soil, beginning with the years preceding World War II. Although mineralization of nitrogen must consequently be recognized as a very old problem—even the overestimation of the importance of humus for plant nutrition by Albrecht Thaer at the beginning of the 19th century was a result of the conviction of mineralization of organic compounds in soil—it still occupies a prominent position in studies about plant nutrition. The general character of the nitrogen balance in grassland has been investigated long ago, but the spectacular ability of perennial grass to absorb even very high amounts of applied nitrogen and to retain nearly all mineralized and added nitrogen in organically bound form is still considered surprising. Consequently, much attention is paid to this characteristic of grassland and the whole problem of nitrogen mineralization in grassland remains unsolved. Investigations on nitrogen mineralization in uncultivated virgin bogs are very scarce. Cyplenkin and Schilin showed NO3-N formation in the waterlogged peaty soil of the tundra only locally on some hill crests and southbound slopes. Ammonification is much more common in the tundra soil, but is still very slow compared to well-drained neutral soils. Michniewicz determined the rate of nitrogen mineralization and the number of nitrifying organisms in the upper layers of the forest floor and of peat bogs.
375 citations
TL;DR: In this article, the chemical changes which take place in a urine patch have been studied using urine from wethers and to a small extent from cows, and the results showed that the hold up of urine on leaf surfaces of pastures was shown to amount to as much as 12·5% of the green weight of herbage.
Abstract: 1. The chemical changes which take place in a urine patch have been studied using urine from wethers and to a small extent from cows.2. The sizes of individual urine patches vary considerably, depending mainly on the volume of the urination. The average from wethers is about 45 sq.in.3. The volume of urine per wether per day averages 2880 ml. with a nitrogen content of 0·92%, of which about 75% was in the form of urea; 4·1% as allantoin; 2·6% as hippuric acid; 1·5% as creatine-creatinine; and 12·4% as amino-nitrogen.4. Improved herbage growth results in twice the area actually wetted with urine. The total area affected averaged 100 sq.in.5. The probable area wetted with urine from cow urinations was about 650 sq.in. with a further 200 sq.in. affected indirectly.6. With wethers the average rate of nitrogen application on a urine patch amounts to 432 lb. of nitrogen per acre.7. The rate of hydrolysis of urea in laboratory experiments is affected by temperature and is increased by small amounts of hippuric acid but not by the other urinary constituents tried. The hydrolysis rate is greater at soil moisture content of 24% than at higher moisture levels.8. Urea hydrolysis in soil (both in laboratory and in the field) is accompanied by pronounced increase in pH (up to pH 9·2 with urea equivalent to that applied to a urine patch).9. The rate of nitrification is greatly affected by the pH changes. At pH values in excess of 8 nitrites accumulate and nitrate formation is retarded.10. Heteroauxin and allantoin were both found to stimulate nitrification in laboratory experiments when used at levels found in urine. Other urinary constituents were without effect.11. The hold up of urine on leaf surfaces of pastures was shown to amount to as much as 12·5% of the green weight of herbage.12. Ammonia in considerable amounts may be lost to the air both from herbage and from soil.13. Field experiments are in complete agreement with laboratory experiments and no essential difference of wether and cow urine was noticed.14. The fate of the nitrogenous constituents is briefly considered and shown schematically.
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TL;DR: Organic matter, in the form of plant residues, will be produced quicker than it can be destroyed by microorganisms, while certain higher plants grow readily in waterlogged soils, due to the prevailing anaerobic conditions.
Abstract: Climate markedly modifies the nature and rapidity of decomposition of plant remains in the soil and thus exerts all important influence upon the nature and abundance of the organic matter, or so-called " humus." It is an entirely wrong assumption that this " humus," simply because it is dark in color and is found in the soil, always comprises the same constituents, in terms of definite chemical complexes. The chemical nature of the " humus " will depend upon: (I) the chemical nature of the plant residues; (2) the soil conditions, such as reaction, aeration, abundance of available minerals, etc., all of which modify the nature of the microscopic population of the soil which bring about the decomposition processes; (3) the environmental or climatic conditions, especially temperature and moisture supply, which modify not only the nature of the microrganisms but also the rate of the decomposition processes; (4) finally the type of microorganisms active in the decomposition of the plant residues, as influenced by the above factors. The problems commonly considered in the study of decomposition of plant residues, as influenced by climatic conditions, comprise: (i) the decomposition of the organic residues as a whole, as well as of the various chemical constituents; (2) the accumulation of " humus " which is more resistant to further decomposition than the fresh plant residues; (3) the rate of evolution of the plant nutrients in an available form. According to Mohr ('22), no organic matter accumulates in well aerated soils at an average temperature of 250 C. and higher. When the mean temperature is below 250 C., organic matter accumulates even in fully aerated soils. The lower the temperature the greater will be the accumulation of organic matter in the soil, within certain limits. This he explained by the relative influence of the temperature upon the growth of higher plants and upon the development of microorganisms which destroy the plant residues. The lower temperatures check the growth of the latter more than of the former. As a result, organic matter, in the form of plant residues, will be produced quicker than it can be destroyed by microorganisms. In waterlogged soils, the aerobic fungi and bacteria are unable to develop, due to the prevailing anaerobic conditions, while certain higher plants grow readily.
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