Denitrification in soil: Effects of insecticides and fungicides

The effects of seven insecticides and six fungicides on denitrification of nitrate in soils were studied by determining the effects of 10 and 50μgg^?1 soil of each pesticide on the amounts of nitrate lost and the amounts of nitrite, N₂O and N₂ produced when soil samples were incubated anaerobically after treatment with nitrate. The insecticides used were lindane, fenitrothion, fonofos, malathion, phorate, terbufos and carbofuran. The fungicides used were mancozeb, maneb, thiram, benomyl, captan and terrazole.None of the insecticides studied had a significant effect on denitrification when applied at the rate of 10 μgg^?1 soil. When applied at the rate of 50μgg^?1 soil, lindane, fonofos and malathion enhanced denitrification in the three soils studied, whereas fenitrothion, phorate, terbufos and carbofuran either had no appreciable effect on denitrification in these soils, or enhanced denitrification in at least one of the soils.None of the fungicides studied had an appreciable effect on denitrification when applied at the rate of 10μgg^?1 soil, but thiram increased the ratio of N₂ to N₂O in the gaseous products of denitrification. Captan inhibited denitrification in two of three soils studied when applied at the rate of 50μgg^?1 soil. The other five fungicides either had no significant effect on denitrification, or enhanced denitrification, when applied at this rate. Reports that maneb, thiram and terrazole inhibit denitrification in soil were not confirmed.     

Denitrification and fermentation in plant-residue-amended soil

Summary Nitrous oxide production (denitrification) during anaerobic incubation of ground-alfalfa-, red-clover-, wheat-straw-, and cornstover-amended soil was positively related to the initial water-soluble C content of the residue- amended soil. The water-soluble C concentration decreased in all treatments during the first 2 days, then increased in the alfalfa-, red-clover-, and wheat-straw-amended soil until the end of the experiment at 15 days. An accumulation of acetate, propionate, and butyrate was partly responsible for the increased water-soluble C concentration. Denitrification rates were much higher in the alfalfa-and red-clover-amended soil, but NO ₃ ^– was not fully recovered as N₂O in these treatments. Supported by earlier experiments in our laboratory, we conclude that some of the NO ₃ ^– was reduced to NH ₄ ⁺ through fermentative NO ₃ ^– reduction, otherwise known as dissimilatory NO ₃ ^– reduction to NH ₄ ⁺ . Acetate, the primary product of anaerobic fermentation, accumulated in the alfalfa- and red-clover-amended soil in the presence of NO ₃ ^– , supporting previous observations that the processes of denitrification and fermentation occur simultaneously in C-amended soil. The partitioning of NO ₃ ^– between denitrification and fermentative NO ₃ ^– reduction to NH ₄ ⁺ depends on the activity of the denitrifying and fermentative bacterial populations. NO₂ concentration may be a key in the partitioning of NO ₃ ^– between these two processes.     

Sugar beet herbicides and soil nitrification

The effects of phenmedipham, propham, carbetamide, lenacil and benzthiazuron on soil nitrification was studied in the laboratory using a perfusion technique. The nitrification process was markedly retarded at a phenmedipham concentration of 50–500μg g^?1 soil, so that 55–150 days were required for complete oxidation of supplied NH⁺₄-N as compared with 33 days for the untreated control. Phenmedipham caused a reduction in both the maximum population and the proliferation rate of nitrifying organisms, as evaluated from kinetic parameters. These inhibitory effects showed a low persistance probably due to herbicide breakdown. The effects of 100 μg g^?1 soil of propham, carbetamide, lenacil or benzthiazuron on the nitrification process was very weak, although the kinetics of the nitrification process was affected by all these herbicides.     

Denitrification in a cultivated soil: Optimal glucose and nitrate concentrations

An experiment was conducted in the laboratory on a cultivated soil incubated in serum bottles with a range of C-to-nitrate concentrations. C was added in form of glucose and nitrate in form of Ca(NO₃)₂. It was shown that an C-N concentration of respectively 500 μg C (glucose-equivalent, Glc-Eq.) and 36 μg N g⁻ dry soil was optimal for denitrification. Results obtained either in the laboratory, in soil columns or in the field were in good agreement with one another. In particular, the root zone was shown to be favorable for denitrifying activity because the water-soluble C (Glc-Eq.) and N concentrations were more favorable than in bare soil. Furthermore, the water-soluble extractable Glc-Eq. appeared to be closely related to the denitrification rate and is thus likely to represent the energetic C pool supporting denitrification.

This was related to an inhibiting effect of increasing NO₃⁻ and NO₂⁻ concentrations on NO₃⁻ loss and N₂O production. Such inhibition can affect short-term measurements of denitrification in the field.     

Denitrification in drained and undrained arable clay soil

Emissions of nitrous oxide (N₂O) and nitrogen gas (N₂) from denitrification were measured using the acetylene inhibition method on drained and undrained clay soil during November 1980-June 1981. Drainage limited denitrification to about 65% of losses from undrained soil. Emissions from the undrained soil were in the range 1 to 12 g N ha^–1 h^–1 while those from the drained soil ranged from 0.5 to 6 g N ha^–1 h^–1 giving estimated total losses (N₂O + N₂) of 14 and 9 kgN ha^–1.
Drainage also changed the fraction of nitrous oxide in the total denitrification product. During December, emissions from the drained soil (1.8±0.6 gN ha^–1 h^–1) were composed entirely of nitrous oxide, but losses from the undrained soil (2.7 ± 1.1 g N ha^–1 h^–1) were almost entirely in the form of nitrogen gas (the fraction of N₂O in the total loss was 0.02). In February denitrification declined in colder conditions and the emission of nitrous oxide from drained soil declined relative to nitrogen gas so that the fraction of N₂O was 0.03 on both drainage treatments. The delayed onset of N₂O reduction in the drained soil was related to oxygen and nitrate concentrations. Fertilizer applications in the spring gave rise to maximum rates of emission (5–12g N ha^–1 h^–1) with the balance shifting towards nitrous oxide production, so that the fraction of N₂O was 0.2–0.8 in April and May.     

Sorption-desorption of "aged" sulfonylaminocarbonyltriazolinone herbicides in soil

Sorption-desorption interactions of pesticides with soil determine the availability of pesticides in soil for transport, plant uptake, and microbial degradation. These interactions are affected by the physical and chemical properties of the pesticide and soil, and for some pesticides, their residence time in the soil. The objective of this study was to characterize sorption-desorption of two sulfonylaminocarbonyltriazolinone herbicides incubated in soils at different soil moisture potentials. The chemicals were incubated in clay loam and loamy sand soils for up to 12 wks at -33 kPa and at water contents equivalent to 50 and 75% of that at -33 kPa. Chemicals were extracted sequentially with 0.01 N CaCl(2) and aqueous acetonitrile, and sorption coefficients were calculated. Sufficient sulfonylaminocarbonyltriazolinone herbicides remained (>40% of that applied) during incubation to allow calculation of sorption coefficients. Aging significantly increased sorption as indicated by increased sorption coefficients. For instance, for sulfonylaminocarbonyltriazolinone remaining after a 12-wk incubation at -33 kPa, K(d) increased by a factor of 4.5 in the clay loam soils and by 6.6 in the loamy sand as compared to freshly treated soils. There was no effect of moisture potential on sorption K(d) values. These data show the importance of characterization of sorption-desorption in aged herbicide residues in soil, particularly in the case of prediction of herbicide transport in soil. In this case, potential transport of sulfonylaminocarbonyltriazolinone herbicides would be over-predicted if freshly treated soil K(d) values were used to predict transport.     

Effect of some herbicides on microbial activity in soil

The effect of 25 herbicides and herbicide combinations, in amounts comparable to those used in agriculture, on microbial activity in two soil types was determined in the laboratory. Herbicides did not affect respiration, assayed by CO₂ evolution and dehydrogenase activity, in either silty clay loam or loamy sand. Organic matter decomposition, determined by the amount of CO₂ evolved and inorganic N formed from decomposing alfalfa tissue, was also not affected. Alteration in soil pH or moisture content did not affect herbicide action. Addition of herbicides 3 weeks before amendment, or fertilizer application, also did not influence herbicide activity. Selected herbicides (trifluralin, linuron, dinoseb) at concentrations 100-fold higher than the recommended rates did not affect alfalfa decomposition. Solubilization of Ca₃(PO₄)₂ in soil was not affected by herbicides. S oxidation to SO^2?₄ in soil, however, was increased by most herbicides. In silty clay loam, 18 of the 25 herbicides and herbicide combinations increased S oxidation almost up to 3-fold. Results in loamy sand were similar. Dinoseb effectively reduced the algal population in loamy sand by more than 90%. Trifluralin, linuron, and metribuzin did not inhibit algal populations.     

Bioavailability of triazine herbicides in a sandy soil profile

The bioavailability of atrazine was evaluated in a Danish soil profile (Drengsted) using a combination of soil sorption, transport and mineralisation methods as well as inoculation using Pseudomonas ADP. Sorption of atrazine decreased markedly with depth as indicated by K_d values of 5.2 l kg^-1 for the upper soil and 0.1 l kg^-1 for the subsoils. The transport of atrazine was evaluated using soil TLC plates and the resulting R_f values were 0.1 for the upper soil and 0.9 for the subsoil. Only a relatively small amount of atrazine leached through undisturbed soil columns taken from the upper 60 cm. Inoculating with Pseudomonas strain ADP (1᎒⁶ CFU g^-1 dry weight soil) revealed that the degradation of 0.01 ppm atrazine was fully completed (80% mineralisation) within 10 days in the subsoil, while it reached less than 15% in the upper soil. Over a period of 500 days, a total mineralisation of 37% of added atrazine in the upper soil was found (2 mg kg^-1 incubated at 20° C). However, in the subsurface soil where 0.02 mg kg^-1 of atrazine was incubated at 10°C, the degradation was slower, only reaching about 12%. Terbuthylazine mineralisation was found to be temperature-dependent and low (less than 5%) in the upper soil and very much lower in the subsoil. Desethylterbuthylazine was the most frequently found metabolite. Finally, Pseudomonas strain ADP inoculated into soils from different depths increased the mineralisation of terbuthylazine dramatically. Modelling using a "two-compartment model" indicated that desorption of terbuthylazine is the limiting step for its mineralisation.     

Effects of preemergence and postemergence herbicides on urea hydrolysis and nitrification of urea nitrogen in soil

The influence of 5 and 50 mg active ingredient kg^-1 soil of nine preemergence and nine postemergence herbicides on transformations of urea N in soil was studied in samples of two coarse-textured and two fine-textured soils incubated aerobically at 20°C. The effects of each herbicide on soil urea transformations was measured by determining the amounts of urea hydrolyzed and the amounts of NO _inf3 ^sup- and NO _inf2 ^sup- produced at various times after treatment with urea. Applied at the rate of 5 mg active ingredient kg^-1 soil, none of the herbicides retarded urea hydrolysis in the four soils used, but four of the postemergence herbicides (acifluorfen, diclofop methyl, fenoxaprop ethyl) retarded urea hydrolysis in the two coarse-textured soils. All the herbicides tested except siduron retarded nitrification in the two coarse-textured soils when applied at 50 mg of urea N active ingredient kg^-1 soil, and fenoxaprop ethyl and tridiphane markedly retarded nitrification of urea N in all four of the soils when applied at this rate. One-way analysis of variance and correlation analyses indicated that the inhibitory effects of the 18 herbicides tested on nitrification of urea N in soil increased with a decrease in the organic-matter content and an increase in the sand content of the soil. Present address: Department of Soil and Environmental Sciences, University of California, Riverside, CA 92521, USA     

两种除草剂的土壤生态效应及其对后茬作物生长的影响

采用盆栽试验,研究了分别施用低剂量和高剂量的苄.丁和二氯喹啉酸对水稻田土壤环境以及紫云英生长的影响。结果表明：施用除草剂苄.丁和二氯喹啉酸均不利于后茬冬季绿肥作物紫云英植株干物质的累积,而且施用量越多,干物质累积越少。低剂量的苄.丁显著降低了紫云英植株中N素累积量,而二氯喹啉酸降低紫云英植株中N和K累积量;施用高剂量苄.丁和二氯喹啉酸则降低紫云英植株中N、P和K累积量。无论是施用低剂量还是高剂量的苄.丁和二氯喹啉酸均降低土壤中N、K养分的有效性。低剂量二氯喹啉酸对土壤中有效P含量影响不显著,而施用高剂量二氯喹啉酸显著降低P素养分有效性。施用低剂量苄.丁对土壤中过氧化氢酶、蔗糖酶和尿酶活性的影响均不显著,而低剂量二氯喹啉酸则显著抑制了过氧化氢酶活性。施用高剂量苄.丁和二氯喹啉酸对土壤中蔗糖酶活性影响不显著,但均抑制了过氧化氢酶和尿酶活性。此外,施用低剂量和高剂量苄.丁增加了土壤中细菌数量,而二氯喹啉酸则正好相反。两种剂量的苄.丁和二氯喹啉酸均减少了土壤中放线菌数量,但对真菌数量变化不显著。由此可见,稻田施用二氯喹啉酸对稻田土壤环境以及后茬冬季紫云英作物的药害大于苄.丁。     

Denitrification enzyme activity is limited by soil aeration in a wastewater-irrigated forest soil

 In land-based wastewater treatment systems (LTS), denitrification is an important nitrogen removal process. We investigated the factors limiting the denitrifying population in a forested LTS, by studying the individual and combined effects of soil aeration, water content, nitrate and carbon on denitrification enzyme activity (DEA). The size of the soil denitrifying population in the LTS appeared to be limited by soil aeration, and limiting oxygen availability increased the denitrifying population above that observed in the field. Furthermore, we found that wastewater irrigation altered the short-term response of denitrifiers to anaerobic soil conditions. Under low oxygen conditions, denitrifiers in the wastewater-irrigated soils produced enzymes sooner and at a greater rate than soils without a history of wastewater irrigation. We propose that the size of the denitrifying population cannot be expected to be large in free-draining, coarsely textured soils even when provided with additional nitrogen and water inputs. Received: 11 October 1999     

Denitrification rate relationships with soil parameters in the field

Abstract

It has been recently shown that there is a large spatial variability in denltrification rates measured in the field. The objective of this study was to assign this variability to twelve measurable or determined soil parameters known or suspected to be Important to denitrification during the early part of the growing season. Relationships were sought with 16 cores at a grid spacing of 25 cm on three sites (dates) within a 0.07 ha area of a cultivated silt loam soil. The denitrification rate was estimated from the N₂O production rate with the acetylene blockage technique.

Only few statistical significant relationships were found with simple and multiple regression analyses and there was a lack of consistency from site to site. Plotting the data revealed a tentative negative relationship between the N₂O production rate and percent air‐filled porosity. A few cores at each site showed a much greater N₂O production rate for no discernable reason, but these rates were also negatively related to percent air‐filled porosity. Tentative positive relationships between N₂O production rate and total organic carbon or water‐soluble carbon were similarly found.     

Structural influences in relative sorptivity of chloroacetanilide herbicides on soil

Adsorption of the chloroacetanilide herbicides acetochlor, alachlor, metolachlor, and propachlor was determined on soils and soil components, and their structural differences were used to explain their sorptivity orders. On all soils and soil humic acids, adsorption decreased in the order: metolachlor > acetochlor > propachlor > alachlor. On Ca(2+)-saturated montmorillonite, the order changed to metolachlor > acetochlor > alachlor > propachlor. FT-IR differential spectra of herbicide-clay or herbicide-humic acid-clay showed possible formation of hydrogen bonds and charge-transfer bonds between herbicides and adsorbents. The different substitutions and their spatial arrangement in the herbicide molecule were found to affect the relative sorptivity of these herbicides by influencing the reactivity of functional groups participating in these bond interactions. It was further suggested that structural characteristics of pesticides from the same class could be used to improve prediction of pesticide adsorption on soil.     

除草剂配施安全剂对土壤酶活性与糜子根系生理代谢的影响

为探究安全剂与除草剂复配施用对除草剂药害的缓解以及对糜子田土壤酶活性、根系活性氧代谢和糜子生长发育的影响。于2019年5-10月在陕西省榆林市小杂粮试验示范站进行试验,选用糜子品种‘榆糜2号’为试验材料,选取苗前除草剂:谷友(10%单嘧磺隆,2.4 kg/hm2)与3种安全剂:芸苔素(300 mL/hm2)、赤霉素(300 mL/hm2)、奈安(1.2 kg/hm2)复配使用,设置清水不除草对照与人工除草对照。测定杂草鲜重防效、药害指数、根际土壤酶活性、糜子根系抗氧化酶活性与丙二醛含量及糜子农艺性状与产量。结果表明:1)芸苔素、赤霉素、奈安与单嘧磺隆复配后药害指数显著下降,分别降低了20.27%、21.63%、20.94%;2)单嘧磺隆处理(H1)的土壤蔗糖酶、脲酶活性在施药后7～42 d时相较于不除草处理CK1被显著抑制,活性抑制率随时间降低,添加安全剂后土壤蔗糖酶和脲酶活性显著提升,抑制率显著降低;3)与单施除草剂相比,安全剂复配施用的糜子根系超氧化物歧化酶活性在施药后14～28 d时显著升高;过氧化氢酶活性显著降低;丙二醛含量明显降低;4)单嘧磺隆导致糜子株高、穗长、主穗质量降低...     

Denitrification activity in the root zone of a sludge-amended desert soil

Summary We evaluated potential NO _inf3 ^sup- losses from organic and inorganic N sources applied to improve the growth of cotton (Gossypium hirsutum) on a Pima clay loam soil (Typic Torrifluvent). An initial set of soil cores (April 1989) was collected to a depth of 270 cm from sites in a cotton field previously amended with anaerobically digested sewage sludge or an inorganic N fertilizer. The denitrification potential was estimated in all soil samples by measuring N₂O with gas chromatography. Soils amended with a low or high rate of sludge showed increased denitrification activity over soil samples amended with a low rate or inorganic N fertilizer. All amended samples showed greater denitrification activity than control soils. The denitrification decreased with soil depth in all treatments, and was only evident as deep as 90 cm in the soils treated with the high sludge rate. However, when soils collected from depths greater than 90 cm were amended with a C substrate, significant denitrification activity occurred. These date imply that organisms capable of denitrification were present in all soil samples, even those at depths far beneath the root zone. Hence, denitrification was C-substrate limited. A second series of soil cores taken later in the growing season (July 1989) confirmed these data. Denitrification losses (under laboratory conditions) to a soil depth of 270 cm represented 1–4% of total soil N depending on treatment, when the activity was C-substrate limited. With additional C substrate, the denitrification losses increased to 15–22% of the total soil N.     

Effect of soil on urease inhibition by substituted urea herbicides

The effects of some substituted urea herbicides, fenuron, monuron, diuron and linuron, on soil urease were investigated. All herbicides are soil urease mixed inhibitors and the same inhibition mechanism is presumed. A kinetic relationship, which takes into account herbicide adsorption, is developed in order to calculate the inhibition constants of soil urease from adsorption constants. A linear relationship between Hammett sigma values and log K_i for fenuron, monuron and diuron is obtained, from which the formation of a complex between herbicides and enzyme is proposed By comparing kinetic constants for soil urease with those obtained for jack bean, in the presence of the same herbicides, a possible effect of the soil matrix on the enzyme-herbicide complex is also suggested.     

除草剂对不同种植年限柑橘园土壤氮转化过程及温室气体排放的影响

为探讨除草剂施用对柑橘园土壤氮转化及温室气体排放的影响,在实验室培养条件下,研究了0年(林地)、种植10年和30年的柑橘园土壤中分别添加除草剂草甘膦和丁草胺后,尿素态氮含量、硝化和反硝化作用以及温室气体排放的变化。研究结果表明,橘园土壤中尿素第1 d的水解率、氮肥硝化率、反硝化作用损失总量以及N_2O和CO_2排放量显著高于林地土壤(P0.05)。与10年橘园土壤相比,30年橘园土壤显著增加了尿素的水解速率、氮肥硝化率和CO_2排放量(P0.05),但二者的反硝化损失量没有显著差异。施用草甘膦和丁草胺都显著促进了林地土壤的尿素水解(P0.05),第1 d尿素态氮含量分别降低11.20%和12.43%;但对3种土壤氮肥的硝化率均没有明显影响。施用丁草胺显著降低了林地土壤的CO_2排放量(P0.05),对两种橘园土壤的CO_2排放没有明显影响,但明显增加了两种橘园土壤的N_2O排放总量(P0.05),分别比不施除草剂增加56.27%和85.41%;施用草甘膦对3种土壤的N_2O和CO_2排放均没有明显影响。可见,草甘膦和丁草胺的施用不会对柑橘园土壤的氮转化过程产生影响,但丁草胺显著增加了柑橘园土壤的N_2O排放。     

Contrasting soil microbial responses to fertilizers and herbicides in a canola-barley rotation

The combination of high input costs and low commodity prices is forcing some farmers to consider reducing crop inputs like seed, fertilizer and herbicides. In a field trial in which different canola (Brassica napus L.) and barley (Hordeum vulgare L.) inputs were subtracted from a full package, or added to an empty package, we studied the effects of full or reduced fertilizer and herbicide inputs on soil microbiological characteristics at two sites from 2005 to 2008. The full package consisted of a high-yielding crop variety seeded at an optimum rate, with fertilizers and herbicides applied at recommended rates. The empty package consisted of a less expensive, low-yielding crop variety seeded at a low rate, with no fertilizer or herbicide applied. Between these two extremes were treatments in which fertilizers or herbicides were applied at 50% of recommended rates or not at all. Each treatment was repeated year after year in the same plot, i.e., treatment effects were cumulative. Fertilizer effects on soil microbial biomass C (MBC), β-glucosidase enzyme activity and bacterial functional diversity (based on community-level physiological profiles) were usually positive. Reduced fertilizer application rates reduced the beneficial fertilizer effects. Significant herbicide effects on soil microbiological properties occurred less often, were smaller in magnitude than fertilizer effects, and were mostly negative. Reduced herbicide rates reduced the deleterious herbicide effects. These significant fertilizer and herbicide effects were observed in canola more than barley, and mostly in the final year of the study, indicating the cumulative nature of treatment effects over time. Therefore, repeated applications of agricultural inputs like fertilizers and herbicides can have more significant effects on soil biology and biological processes than single applications indicate.