Nitrogen—Inorganic Forms

Most soils contain inorganic nitrogen (N) in the form of ammonium (NHt) and nitrate (NO)"). Nitrite (NOz) also may be present, but the amount is usually too small to warrant its determination, except in cases where NHt or NHt-forming fertilizers are applied to neutral or alkaline soils. Several other forms of inorganic N have been proposed as intermediates during microbial transformations of N in soils, including hydroxylamine (NH20H), hyponitrous acid (H2N20 2), and nitramide (NH2N02), but these compounds are thermodynamically unstable and have not been detected in soil. Until the 1950s, inorganic N was believed to account for <2% of total soil N, on the assumption that NHt and NO)" are completely recovered by extracting soil with a neutral salt solution. The validity of this assumption was challenged by the finding that some soils contain NHt in a form that is not extracted by exchange with other cations (e.g., Rodrigues, 1954; Dhariwal & Stevenson, 1958; Stevenson & Dhariwal, 1959; Bremner & Harada, 1959; Bremner, 1959; Schachtschabel, 1960, 1961; Young, 1962), and by estimates that the proportion of soil N in this form can exceed 50% for some subsurface soils (Stevenson & Dhariwal, 1959; Young, 1962). In such cases, NHt is said to be fixed, and fixed NHt has subsequently been defined as the NHt in soil that cannot be replaced by a neutral potassium salt solution (SSSA, 1987), such as 1 or 2 M KCI or 0.5 M K2S04, in contrast to exchangeable NHt, which is extractable at room temperature with such a solution. Existing information indicates that fixed NHt occurs largely, if not entirely, between the layers of 2: I-type clay minerals, particularly vermiculite and illite (hydrous mica), and that fixation results from entrapment of NHt in ditrigonal voids in the exposed surfaces upon contraction of the clay lattice (Nommik & Vahtras, 1982). The term, nonexchangeable NHt, has been used by Bremner (1965) and Keeney and Nelson (1982) in previous editions of this publication as a more precise alternative to fixed NHt. The same term is used in the present treatment, with specific reference to NHt determined by the method described in "Determination of Nonexchangeable Ammonium," which involves digestion with an HF-HCI solution following treatment of the soil with alkaline KOBr to remove exchangeable NHt and labile organic-N compounds.

Nitrogen - inorganic forms.

Anaerobic digestion (AD) for biogas production leads to several changes in the composition of the resulting digestates compared to the original feedstock (ammonia content, pH, carbon to nitrogen ratio, etc.), which are relevant for the plant availability of macro- and micronutrients after field application. Increased NH4+-N content in digested slurries compared to undigested slurries does not guarantee improved uptake efficiency of slurry nitrogen and increased savings in fertilizer nitrogen. AD of crop residues and cover crops leads to an increase in the total amounts of mobile organic manures within the farming system, resulting in a higher nitrogen use efficiency and an increased scope for target-oriented nitrogen application in time and space, when needed by the crop, as an alternative to the site-bound soil incorporation as green manures. AD of dairy manure appears to reduce the fraction of immediate plant available phosphorus and micronutrients. This does, however, not affect short-term crop availability under field conditions. More studies are needed to improve current knowledge on sulfur losses during AD and fertilizer value of digestates.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/elsc.201100085

Effects of anaerobic digestion on digestate nutrient availability and crop growth: A review

This review of anaerobic metabolism emphasizes aerobic oxidation, because the two processes cannot be separated in a complete treatment of the topic. It is process oriented and highlights the fascinating microorganisms that mediate anaerobic biogeochemistry. We begin this review with a brief discussion of CO 2 assimilation by autotrophs, the source of most of the reducing power on Earth, and then consider the biological processes that harness this potential energy. Energy liberation begins with the decomposition of organic macromolecules to relatively simple compounds, which are simplified further by fermentation. Methanogenesis is considered next because CH 4 is a product of acetate fermentation, and thus completes the catabolism of organic matter, particularly in the absence of inorganic electron acceptors. Finally, the organisms that use nitrogen, manganese, iron, and sulfur for terminal electron acceptors are considered in order of decreasing free-energy yield of the reactions.

Anaerobic Metabolism: Linkages to Trace Gases and Aerobic Processes

A review of the control of odour nuisance from livestock buildings: Part 3, properties of the odorous substances which have been identified in livestock wastes or in the air around them

Evolution of volatile sulfur compounds from soils treated with S-containing amino acids was studied by sensitive gas chromatographic techniques involving use of a flame photometric detector fitted with a sulfur filter. The following volatile sulfur compounds were identified as products of microbial decomposition of S-containing amino acids in soils under aerobic or waterlogged conditions: methyl mercaptan, dimethyl sulfide and dimethyl disulfide (evolved from soils treated with methionine, methionine sulfoxide, methionine sulfone or S-methyl cysteine); ethyl mercaptan, ethyl methyl sulfide and diethyl disulfide (evolved from soils treated with ethionine or S-ethyl cysteine); and carbon disulfide (evolved from soils treated with cystine, cysteine, lanthionine or djenkolic acid). Small amounts of dimethyl sulfide and carbon disulfide were evolved from soils treated with homocystine, and trace amounts of carbonyl sulfide were evolved from soils treated with lanthionine or djenkolic acid. No volatile sulfur compounds were evolved from soils treated with cysteic acid, taurine, or S-methyl methionine. The amounts of sulfur volatilized from soils treated with the 14 S-containing amino acids studied represented from less than 0·1 per cent to more than 50 per cent of the sulfur added as amino acid. Hydrogen sulfide could not be detected as a gaseous product of microbial decomposition of S-containing amino acids in soils under aerobic or waterlogged conditions.

Formation of volatile sulfur compounds by microbial decomposition of sulfur-containing amino acids in soils

Interference and recovery tests reported indicate that the Orion ammonia electrode can be used satisfactorily for determination of ammonium in soil extracts and water samples. The electrode method of analysis described is rapid, simple, and precise, and its results agree closely with those obtained by a distillation‐titration method of determining ammonium in soil extracts and water samples.

Determination of ammonium in soil extracts and water samples by an ammonia electrode

Release of volatile S compounds from soils treated with S-containing organic materials was studied by sensitive gas chromatographic techniques. Methyl mercaptan, dimethyl sulfide, dimethyl disulfide, carbonyl sulfide and carbon disulfide were identified as gaseous products of decomposition of animal manures, sewage sludges and plant materials in soils under aerobic or waterlogged conditions. No release of hydrogen sulfide was detected. Most of the S volatilized from soils treated with sludges was in the form of dimethyl sulfide and dimethyl disulfide. whereas most of the S volatilized from soils treated with manures and plant materials was in the form of methyl mercaptan and dimethyl sulfide. More S compounds were released, and more S was volatilized, by decomposition of manures, sludges or plant materials in soils under waterlogged conditions than by decomposition under aerobic conditions. When calculated as a percentage of the S added as organic material, the average amount of S volatilized under aerobic or waterlogged conditions was

Evolution of volatile sulfur compounds from soils treated with sulfur-containing organic materials

Gas Chromatographie studies showed that air-dry and moist soils have the capacity to sorb dimethyl sulfide (CH 3 SCH 3 ), dimethyl disulfide (CH 3 SSCH 3 ). carbonyl sulfide (COS) and carbon disulfide (CS 2 ), but do not sorb sulfur hexafluoride (SF 6 ). Moist soils sorb larger amounts of CH 3 SCH 3 . CH 3 SSCH 3 . COS or CS 2 , than do air-dry soils, but the capacity of moist (or air-dry) soils for Sorption of these gases is much smaller than their capacity for sorption of H 2 S. SO 2 or CH 3 SH. The ability of moist soils to sorb COS is considerably greater than their ability to sorb CH 3 SCH 3 , CH 3 SSCH 3 or CS 2 . and sorption of COS by moist soils is accompanied by release of small amounts of CS 2 . Experiments with sterilized (autoclaved) soils indicated that soil microorganisms are partly responsible for the sorption of CH 3 SCH 3 . CH 3 SSCH 3 . COS and CS 2 by moist soils. Support for this conclusion was obtained from experiments showing that the rate of sorption of these gases by moist soils increases with time. The work reported provides further evidence that soil is an important natural sink for gaseous atmospheric pollutants, but indicates that soils have little, if any, potential value for removal of CH 3 SCH 3 . CH 3 SSCH 3 . COS or CS 2 , from industrial emissions polluted by these gases. The finding that soils have no capacity for sorption of SF 6 is significant in relation to use of this gas as a tracer for atmospheric research and as an internal standard for gas Chromatographie studies of evolution and sorption of gases by soils.

Sorption of sulfur gases by soils

Evolution of volatile sulfur compounds from animal manures [beef cattle (Bos taurus), dairy cattle (Bos taurus), poultry (Gallus domesticus), sheep (Ovis aries), and swine (Sus scrofa)] was studied by gas chromatographic techniques permitting detection and identification of trace (nanogram) amounts of sulfur gases in the presence of nonsulfur gases known to be released through microbial decomposition of organic materials. All manures studied released hydrogen sulfide (H₂S), methyl mercaptan (CH₃SH), and dimethyl sulfide (CH₃SCH₃) when incubated under anaerobic conditions, and some released dimethyl disulfide (CH₃SSCH₃), carbonyl sulfide (COS), and/or carbon disulfide (CS₂). Only trace amounts of one sulfur gas (dimethyl sulfide) could be detected in the gaseous products of decomposition of manures under aerobic conditions, and no evidence could be obtained that sulfur gases contribute to the odors of dried manures. Most of the sulfur volatilized when manures were incubated under anaerobic conditions was in the form of hydrogen sulfide and methyl mercaptan, and the amount of sulfur volatilized in 1 month at 23C represented < 1% of the total sulfur in the manures studied.

W.L. Banwart

Papers

Formation of volatile sulfur compounds by microbial decomposition of sulfur-containing amino acids in soils

Determination of ammonium in soil extracts and water samples by an ammonia electrode

Evolution of volatile sulfur compounds from soils treated with sulfur-containing organic materials

Sorption of sulfur gases by soils

Identification of Sulfur Gases Evolved from Animal Manures