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Quantification of the effects of various soil fumigation treatments on nitrogen mineralization and nitrification in laboratory incubation and field studies
Chemosphere 90 (2013) 1210–1215
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Quantification of the effects of various soil fumigation treatments on nitrogen mineralization and nitrification in laboratory incubation and field studies Dongdong Yan, Qiuxia Wang, Liangang Mao, Wei Li, Hongwei Xie, Meixia Guo, Aocheng Cao ⇑ Department of Pesticides, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, People’s Republic of China
h i g h l i g h t s " Pic significantly increased soil mineral nitrogen during the first 2 weeks. " All four fumigants retarded nitrification in both lab and field studies. " Pic has a stronger inhibitory effect on nitrification compared to other fumigants.
" An S-shaped function described the NO3 N concentrations in lab incubation samples.
a r t i c l e
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Article history: Received 26 March 2012 Received in revised form 31 August 2012 Accepted 12 September 2012 Available online 11 October 2012 Keywords: Chloropicrin Fumigation Mineral nitrogen Mineralization Nitrification inhibition
a b s t r a c t Better quantification of nitrogen mineralization and nitrification after fumigation would indicate if any adjustment is needed in fertilizer application. The effects of chloropicrin (Pic), 1,3-dichloropropene (1,3-D), dimethyl disulfide (DMDS) and metham sodium (MS) fumigation on soil nitrogen dynamics were evaluated in lab incubation and field studies. Although some differences were observed in NHþ 4 N and NO 3 N concentrations in lab incubation and field experiments, both studies led to the same conclusions: (1) Soil fumigation was shown to increase soil mineral nitrogen only during the first 2 weeks after fumigation (WAF). In particular, Pic significantly increased soil mineral nitrogen in both studies at 1 WAF. However, for all fumigant treatments the observed effect was temporary; the soil mineral content of treated samples recovered to the general level observed in the untreated control. (2) All the fumigation treatments depressed nitrification temporarily, although the treatments exhibited significant differences in the duration of nitrification inhibition. In both studies, for a limited period of time, Pic showed a stronger inhibitory effect on nitrification compared to other fumigant treatments. An S-shaped function was fitted to the concentrations of NO 3 N in lab incubation samples. The times of maximum nitrification (tmax) in DMDS and MS treatments were 0.97 week and 1.03 week, which is similar to the untreated control (tmax = 1.02 week). While Pic has the longest effect on nitrifying bacteria, nitrification appears to restart at a later time (tmax = 14.37 week). Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Soil fumigation is a highly effective technique for the control of soil-borne pests (insects, nematodes, weeds, and fungal pathogens) in many vegetable, fruit, nut, ornamental, and nursery crops (Ajwa and Trout, 2004; Minuto et al., 2006; Desaeger et al., 2008; Santos et al., 2009; Haydock et al., 2010). Most fumigants are known to have a broad biocidal activity, killing most soil organisms (Ibekwe et al., 2010). Consequently, fumigants affect the Abbreviations: Pic, chloropicrin; DMDS, dimethyl disulfide; MS, metham sodium; 1,3-D, 1,3-dichloropropene; WAF, week after fumigation; wk, week. ⇑ Corresponding author. Tel.: +86 10 62815940; fax: +86 10 62894863. E-mail address: [email protected] (A. Cao). 0045-6535/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2012.09.041
microbial community and activity of non-target microorganisms, altering nutrient transformation in the soil, and may potentially have effects on soil fertility and the productivity of agricultural systems. Fumigation has a marked effect on N mineralization. It increases mineralization rates, due to the mineralization of microbial biomass killed during fumigation (Lebbink and Kolenbrander, 1974; Shen et al., 1984; De Neve et al., 2004). In addition, it results in partial soil sterilization. Lysis of the dead microbes provides the surviving flora with new substrate, leading to enhanced mineralization (Müller et al., 2003). When soil organic matter decomposes, ammonia is liberated and then converted to nitrate under favorable soil conditions. This process, called nitrification, is significantly reduced by soil fumigation (Duniway, 2002). Fumigants are
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capable of retarding the biological oxidation of ammonia by reducing the activity of the nitrifying bacteria responsible for the first step in nitrification (Yamamoto et al., 2008; Brown and Morra, 2009). The inhibition of nitrification may cause an accumulation of soil ammonium and a reduction in soil nitrate. Indeed, some studies have shown increases in soil ammonium concentration in fumigated soils (Ebbels, 1971; Jenkinson and Powlson, 1976; Shen et al., 1984; MacNish, 1986; Zhang et al., 2011). Where soil mineral nitrogen exists to a large extent in the form of NHþ 4 N it may strongly reduce the accumulation of NO 3 N, thereby decreasing the leaching and denitrification losses of NO 3 N significantly. If substantial or prolonged changes in mineral nitrogen occur after soil fumigation, this would necessitate adjustments in nitrogen fertilizer application to improve nitrogen use efficiency. The overall objective of this study was to quantify the dynamic effects of fumigation on N mineralization and nitrification in laboratory incubation and field studies. 2. Materials and methods 2.1. Lab incubation study Soil samples were collected from the top 20 cm of greenhouse soil in Tongzhou district, southeast of Beijing (34.6% sand, 51.8% silt and 13.6% clay; soil pH 7.1; organic matter 3.1%; bulk density 0.93 g cm3) where the field experiments were conducted. The greenhouse had grown cucumber and tomato in rotation for at least 3 years. The soil was sieved through a 2 mm screen and pre-incubated for 7 d at room temperature in the dark, before any treatments were applied. To study the effects of fumigants on mineral nitrogen in soil, 500 g soil samples were placed in 2.5 L desiccators, treated with 0.25 g (NH4)2SO4 (equivalent to 100 mg N kg1 soil) and mixed thoroughly. The experimental design consisted of four fumigant treatments (chloropicrin, Pic; 1,3-dichloropropene, 1,3-D; dimethyl disulfide, DMDS; metham sodium, MS) and a control in three replicates. Fumigants were added into the desiccators at typical field application rates for each chemical (Pic 53 mg kg1, 1,3-D 39 mg kg1, DMDS 68 mg kg1, MS 54 mg kg1) (Spokas et al., 2006). The desiccators were sealed with vaseline and left for 7 d in the dark at 25 °C. 2.2. Experimental design of field study Field experiments were conducted in the same tomato greenhouse in Tongzhou district, southeast of Beijing (116°440 E, 36°530 N). The field experimental design consisted of four fumigant treatments and an untreated control randomized in a complete block design with three replicated plots. The fumigant treatments, doses and application methods are summarized in Table 1. A drip irrigation system was setup in the experimental area, with emitters 30 cm apart and an emitter flow rate of 1.9 L h1 at 1 atm. The distance between drip tapes was the width of the tomato planting beds (80 cm). Before fumigation, 45 g m2
diamine phosphate and 1.5 kg m2 organic fertilizer were applied to the soil. All fumigants were applied on 11 July. After fumigation, the soil was covered with 0.04 mm-thick polyethylene film (Hebei Baoshuo Co., Ltd.) for approximately 1 week, and then tilled to disperse the fumigants 1 week before transplanting tomatoes. 2.3. Soil sampling and analysis After 7 d lab fumigation, all the desiccators were taken to a ventilation hood to remove the fumigant gases, and the soil in each desiccator was mixed thoroughly. Soil samples were collected at 0, 1, 2, 4, 8, 12, 16, 20 and 24 weeks after fumigation (WAF; 0 WAF was defined as before fumigation, and 1 WAF was defined as the date when the fumigants were removed). The soil moisture content in each desiccator was maintained gravimetrically after each sampling. In the field experiment, soil samples from the top 20 cm depth were collected at 1, 2, 4, 8, 12 and 16 weeks after fumigation (WAF; 1 WAF was defined as the date when the plastic fumigation film was removed). Weigh 10.00 g of soil samples, add 40 ml of 2 M KCl extraction solution, shake for 0.5 h at room temperature, and filter the soil slurries. Soil mineral nitrogen (defined as NHþ 4 N and NO3 N) were determined by standard automated colorimetric techniques based on the Berthelot reaction, and cadmium reduction method, respectively (using a Futura Continuous Flow Analytical System, Alliance instruments, France). 2.4. Data analysis In previous studies, the percentage inhibition of nitrification by chemicals was calculated from [(C–S)]/C 100, where S = amount of NO 3 N produced in the soil sample treated with chemicals, and C = amount of NO 3 N produced in the control (no chemicals added) (McCarty and Bremner, 1989; Abbasi et al., 2011). The formula may be suitable for our lab study only, because lab incubation is a closed system and soil NO 3 N is unable to move easily. In contrast, soil NO 3 N in field conditions is highly mobile and prone to leaching. So, for the field study, it is more appropriate to calculate the percentage inhibition of nitrification by chemicals in the following manner: [(S–C)]/C 100, where S = amount of NHþ 4 N accumulated in the soil sample treated with chemicals, and C = amount of NHþ 4 N accumulated in the control (no chemicals added). To assess the effect of fumigant treatments on nitrification in our lab incubation study, an S-shaped function was fitted to the NO 3 N concentrations of treated soil samples (Zhang et al., 2000; De Neve et al., 2004) using the following equation:
NO3 NðtÞ ¼ NO3 Nð0Þ þ NA ½1 þ b expðk tÞ1
ð1Þ
where NA (mg N kg1 soil) is the potential amount of N nitrified, b is a dimensionless quantity that determines the position of the inflection point, k is the nitrification rate constant (week1), and
Table 1 Fumigant dose and application method in field study. Soil fumigant
Dose
Chemical structure
Percent a.c.
Application methods
Pic DMDS MS 1,3-D Control
500 kg ha1 800 L ha1 1000 L ha1 200 kg ha1 NA
CCl3NO3 C2H6S2 C2H4NNaS2 C3H4Cl2 NA
99 99.5 42 93 NA
Manual injection Irrigation system Irrigation system Irrigation system NA
Pic = chloropicrin; 1,3-D = 1,3-dichloropropene; DMDS = dimethyl disulfide; MS = metham sodium; a.c = active component; NA = not applicable.
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1 NO ) is the soil NO 3 Nð0Þ (mg N kg 3 N content at the start of the incubation. The time at which maximum nitrification occurred (tmax) was calculated by taking the second order derivative of Eq. (1), yielding: tmax = In b/k. Substitution of tmax in the first-order derivative of Eq. (1) yields the maximum nitrification rate Kmax = NA k. The results were expressed as means of three replicates. The data were subjected to one-way ANOVA for repeated measures to determine the effect of fumigation on mineral nitrogen components in soil at each sampling date. When significant (P < 0.05) treatment differences were observed, protected LSD values were calculated to separate the treatment means. Vertical bars in figures represent LSD values where treatments means are significantly different at P = 0.05. A nonlinear regression model was performed to estimate the parameters (using SPSS Statistics V19) and curves were plotted (using Origin 7.5).
3. Results 3.1. Mineral nitrogen in fumigated soil in lab incubation study The NHþ 4 N and NO3 N concentrations in soil at different sampling dates in the laboratory incubation study are shown in Fig. 1. The treatments affected soil NHþ 4 N content differently at 1 WAF (Fig. 1A). A significant reduction in soil NHþ 4 N content was observed in the untreated control, DMDS and MS treatments, and this reduction was due to the nitrification process occurring in soil during the first week. In contrast, a slight change in soil NHþ 4 N content was observed after Pic and 1,3-D fumigation compared to the untreated control. The soil NHþ 4 N content in the 1,3-D treatment tended to decrease at 2 WAF, falling to the same level as DMDS and MS treatments after the first 2 weeks. After Pic fumigation, little change was observed in soil NHþ 4 N content during the first 12 weeks; and the soil NHþ N reached 4 its normal low value at 16 WAF as a result of recovery of the nitrification process. During the first week of the lab incubation study, soil NO 3 N content increased significantly in DMDS, MS and the untreated control, due to the nitrification process.Soil NO 3 N content in Pic and 1,3-D treatments decreased slightly during the first week, and increased to some extent at 2 WAF, because the conversion of NHþ 4 N to NO3 N was inhibited during the first 2 weeks. After 2 WAF, the NO 3 N content in 1,3-D treated soil rose to the levels observed in DMDS, MS and the control. After Pic
A
fumigation, soil NO 3 N content increased gradually during the first 6 weeks. All of the fumigation treatments depressed nitrification compared with the untreated control, although there were important differences between fumigants in the duration of nitrification inhibition. 3.2. Mineral nitrogen in fumigated soil in field study The NHþ 4 N concentrations in soil at different sampling dates in the field study are shown in Fig. 2A. During the first week, all four fumigants increased the NHþ 4 N content, and a significant increase was observed in the Pic and DMDS treatments compared to the control at 1 WAF. This increment differed from the trend observed in soil NHþ 4 N during the first week of the lab incubation study. After the Pic treatment, soil NHþ 4 N briefly reached a maximum value of 210.0 mg kg1 at 1 WAF, while the control had the 1 lowest soil NHþ . After fumiga4 N concentration of 113.3 mg kg þ tion with DMDS, the soil NH4 N concentration rose temporarily to 153.9 mg kg1, 36% higher than the control. Following 1,3-D and MS fumigation, NHþ 4 N concentrations rose briefly to 133.0 and 128.0 mg kg1, respectively, at 1 WAF (17% and 13% higher than the control). With increasing time, the influence of fumigants þ on soil NHþ 4 N diminished. After 2 WAF, soil NH4 N in all treatments tended to recover to the control level. No significant differences in soil NHþ 4 N concentration were observed at 2, 4, 8, 12, and 16 WAF. The evolution of NO 3 N concentrations in the field study is shown in Fig. 2B. During the first 2 weeks, soil NO 3 N was temporarily higher in the Pic treatment than in the control. After 4 WAF only minor differences in NO 3 N concentration were observed. The concentration of NO 3 N in all field treatments, including the untreated control, generally decreased during the sampling period. This downward trend in the field study differed from the increased NO 3 N concentrations observed in all treatments in the lab study.
4. Discussion 4.1. Effect of fumigation on mineralization A large portion of organic nitrogen is decomposed to mineral nitrogen by soil microorganisms in a process called mineralization. Soil fumigation has been shown to increase soil mineral nitrogen content due to the decomposition of soil microorganisms after
B
Fig. 1. Evolution of NHþ 4 N (A) and NO3 N (B) soil concentrations of all lab incubation treatments. Vertical bars represent LSD values where treatment means are significantly different at P = 0.05.
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A
B
Fig. 2. Evolution of NHþ 4 N (A) and NO3 N (B) soil concentrations of field study treatments. Vertical bars represent LSD values where treatment means are significantly different at P = 0.05.
fumigation (Gasser and Peachey, 1964; Jenkinson and Powlson, 1976; Shen et al., 1984; De Neve et al., 2004). In our field study, the soil mineral nitrogen content (as the sum of NHþ 4 N and NO 3 N) in all fumigation treatments showed patterns similar to the patterns of NHþ 4 N, whereas the soil mineral nitrogen content in our lab incubation study showed patterns similar to the patterns of NO 3 N (data not shown). Soil mineral nitrogen increased significantly after Pic fumigation in both our lab and field study during the first 2 weeks (Table 2). However, soil fumigation was found to increase soil mineral nitrogen temporarily. In samples taken at longer WAF, the soil mineral content of fumigated soil generally recovered relative to the control. In field conditions, mineralization of the organic nitrogen pool in the soil was larger compared to the lab incubation, and the effect of fumigation on soil mineralization was more marked. Mineralization is a microbial process that depends on the physical and chemical properties of the soil. The different effects of these fumigants on mineral nitrogen are due, at least in part, to their distinct biological activities on soil microorganisms. 4.2. Effect of fumigation on nitrification Nitrification is one of the most important processes among the nitrogen transformations that take place in soil. There is a close relationship between mineralization and immobilization. This occurs because NHþ 4 oxidation at the first step of nitrification is þ responsible for NHþ 4 depletion, and an accumulation of NH4 N clearly indicates a disruption of soil nitrification. Effective inhibition of nitrification should be characterized by a rise in soil NHþ 4 N and concomitant decline in soil NO3 N when compared
with control treatments. The temporary increase in soil NHþ 4 N in all fumigant treatments probably originated from the decomposition of soil organisms following microbial cell death and from metabolism by repopulating microbes (Shen et al., 1984; Yamamoto et al., 2008).Fumigants are capable of retarding the biological oxidation of ammonia by suppressing the activity of the ammonia-oxidizing bacteria responsible for the first step in nitrification (McCarty, 1999). Ammonia oxidation is catalyzed by a complex of membrane-bound proteins that include ammonia monooxygenase (AMO), which can oxidize ammonia to hydroxylamine. A general characteristic of monooxygenase enzymes is a Table 3 Short-term effects of fumigant treatments on nitrification of ammonium in soil samples at 1 WAF. Fumigants
Pic 1,3-D DMDS MS
Inhibition of nitrification (%) Lab incubation
Field study
94.5 84.5 2.4 3.7
85.3 17.4 35.8 13.0
Pic = chloropicrin; 1,3-D = 1,3-dichloropropene; MS = metham sodium.
DMDS = dimethyl
disulfide;
Table 2 Short-term effects of fumigant treatments on nitrogen mineralization in soil. Treatments
Soil mineral nitrogen (mg N kg1) Lab incubation
Pic 1,3-D DMDS MS Control LSD (P 6 0.05)
Field study
1 WAF
2 WAF
1 WAF
2 WAF
244.6 236.3 219.8 232.8 221.6 22.23
273.1 242.2 260.6 268.1 240.3 21.97
295.8 196.6 228.8 177.3 190.2 22.15
183.4 162.4 142.8 145.7 149.8 24.96
Pic = chloropicrin; 1,3-D = 1,3-dichloropropene; DMDS = dimethyl MS = metham sodium; WAF = week after fumigation.
disulfide;
Fig. 3. NO 3 N soil concentrations of all lab incubation treatments with the nitrification model fitted to the data.
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Table 4 Parameters of the nitrification model fitted to the data of lab incubation treatments. Treatment
1 NO 3 Nð0Þ (mg N kg )
R2
NA (mg N kg1)
b
k (week1)
tmax (week)
Kmax (mg N kg1 week1)
Control Pic 1,3-D DMDS MS
158.9 161.1 157.6 158.7 158.7
0.466 0.805 0.873 0.713 0.458
111.2 160.3 103.1 109.3 115.9
3.323 7.108 4.12 108 8.839 12.439
1.178 0.136 9.379 2.256 2.455
1.02 14.37 2.11 0.97 1.03
131.0 21.9 967.0 246.6 284.6
NO 3 Nð0Þ = soil NO3 N content at the start of the incubation; NA = potential amount of N nitrified; b a dimensionless quantity; k = nitrification rate constant; tmax = time at which maximum nitrification occurs; Kmax = maximum nitrification rate.
broad substrate range (Gvakharia et al., 2007). All four fumigants have been shown to act as substrates of AMO that can competitively inhibit ammonia oxidation (Juliette et al., 1993; Brown and Morra, 2009; Sayavedra-Soto et al., 2010). These fumigants appear to reduce AMO activity primarily by acting as enzyme substrates, but the specific effects of these fumigants may also arise from other unique modes of inhibition. Although some differences were observed between lab and field concentrations of NHþ 4 N at 1 WAF, both NHþ 4 N accumulation or increase clearly reflected a short-term disruption of nitrification processes. All fumigant treatments temporarily retarded nitrification in both lab incubation and field studies. Their inhibition rate at 1 WAF is shown in Table 3. In both the lab and field study, Pic was found to have a stronger inhibitory effect on nitrification compared to other fumigation treatments. An S-shaped function was fitted to the NO 3 N concentrations of treated soil samples (Fig. 3, Table 4). The time of maximum nitrification (tmax) indicates the potential length of the effect of fumigation on nitrification inhibition. When applied to lab incubation results it could be used to predict the effects of fumigant on soil NO 3 N content. In conditions where fumigation has the longest effect on nitrifying bacteria, nitrification appears to restart more gradually (smaller maximum nitrification rate, Pic: Kmax = 21.9 mg N kg1 week1) and at a later time (longer time before maximum nitrification rate is reached, Pic: tmax = 14.37 week). The tmax in DMDS and MS treatments were 0.97 week and 1.03 week, similar to the untreated control (tmax = 1.02 week). The results shown in Table 4 provided additional evidence that Pic can have a stronger inhibitory effect on nitrification of soil NHþ 4 N, while DMDS and MS showed little effect on nitrification. Although the quality of fit was low due to the large variability of mineral nitrogen contents, it provides an illustration of the intensity and duration of the nitrification inhibition by four fumigants at higher-than-normal doses, under lab conditions. Three main processes will affect soil nitrate: ammonia oxidation during nitrification, denitrification, and nitrate leaching (Stevenson, 1986). Soil NO 3 N is repelled from soil particles and highly mobile in field conditions because of its negative charge. And it is also the main form of N taken up by most plants. Tomatoes were planted on the greenhouse during all sampling time. The uptake of soil NO 3 N by plant would be the main reason responsible for the decrease of NO 3 N concentrations in field study. So it is difficult to quantify the effect of fumigation on soil NO 3 N in field conditions. Variable results have also been observed in other studies. Previous studies have reported that NO 3 N concentrations in soil following Pic and methyl bromide fumigation are lower than untreated soil (Draycott and Last, 1971; Rovira, 1976). Conversely, studies have also found that methyl bromide and MS increased soil NO 3 N concentration (Gasser and Peachey, 1964). Variable results were also reported by Müller et al. (2003), who observed a decrease in NO 3 N concentration following fumigation in their laboratory study, but an increase in NO 3 N in their field study.
5. Conclusions Although some differences were observed in NHþ N and NO N between lab and field experiments, both 3 4 studies led to the same conclusions: (1) Pic significantly increased soil mineral nitrogen in both studies and the content of mineral nitrogen was increased by 55.5% and 10.4% after Pic fumigation in field and lab incubation study at 1 WAF, respectively. However, the observed effect was temporary. For longer WAF soil samples, the soil mineral content generally recovered to the level observed in the untreated control. (2) All the fumigation treatments depressed nitrification temporarily, although the fumigants exhibited significant differences in the duration of nitrification inhibition. In both studies, for a limited period of time, Pic showed a stronger inhibitory effect on nitrification compared to the other fumigant treatments. Acknowledgement This work was supported by the National Natural Science Foundation Project of China (NSFC: 40871131). References Abbasi, M.K., Hina, M., Tahir, M.M., 2011. Effect of Azadirachta indica (neem), sodium thiosulphate and calcium chloride on changes in nitrogen transformations and inhibition of nitrification in soil incubated under laboratory conditions. Chemosphere 82, 1629–1635. Ajwa, H.A., Trout, T., 2004. Drip application of alternative fumigants to methyl bromide for strawberry production. HortScience 39, 1707–1715. Brown, P.D., Morra, M.J., 2009. Brassicaceae Tissues as Inhibitors of Nitrification in Soil. J. Agric. Food Chem. 57, 7706–7711. De Neve, S., Csitári, G., Salomez, J., Hofman, G., 2004. Quantification of the effect of fumigation on short- and long-term nitrogen mineralization and nitrification in different soils. J. Environ. Qual. 33, 1647–1652. Desaeger, J.A., Seebold, K.W., Csinos, A.S., 2008. Effect of application timing and method on efficacy and phytotoxicity of 1,3-D, chloropicrin and metam-sodium combinations in squash plasticulture. Pest Manage. Sci. 64, 230–238. Draycott, A.P., Last, P.J., 1971. Some effects of partial sterilization on mineral nitrogen in a light soil. J. Soil Sci. 22, 152–157. Duniway, J.M., 2002. Status of chemical alternatives to methyl bromide for preplant fumigation of soil. Phytopathology 92, 1337–1343. Ebbels, D.L., 1971. Effects of soil fumigation on soil nitrogen and on disease incidence in winter wheat. Ann. Appl. Biol. 67, 235–243. Gasser, J.K.R., Peachey, J.E., 1964. A note on the effects of some soil sterilants on the mineralisation and nitrification of soil-nitrogen. J. Sci. Food Agric. 15, 142–146. Gvakharia, B.O., Permina, E.A., Gelfand, M.S., Bottomley, P.J., Sayavedra-Soto, L.A., Arp, D.J., 2007. Global transcriptional response of nitrosomonas europaea to chloroform and chloromethane. Appl. Environ. Microbiol. 73, 3440–3445. Haydock, P.P.J., Deliopoulos, T., Evans, K., Minnis, S.T., 2010. Effects of the nematicide 1,3-dichloropropene on weed populations and stem canker disease severity in potatoes. Crop Prot. 29, 1084–1090. Ibekwe, A.M., Papiernik, S.K., Grieve, C.M., Yang, C.H., 2010. Influence of fumigants on soil microbial diversity and survival of E. coli O157:H7. J. Environ. Sci. Health, Part B 45, 416–426. Jenkinson, D.S., Powlson, D.S., 1976. The effects of biocidal treatments on metabolism in soil – I. Fumigation with chloroform. Soil Biol. Biochem. 8, 167–177. Juliette, L.Y., Hyman, M.R., Arp, D.J., 1993. Inhibition of ammonia oxidation in nitrosomonas europaea by sulfur compounds: thioethers are oxidized to sulfoxides by ammonia monooxygenase. Appl. Environ. Microbiol. 59, 3718– 3727.
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Quantification of the effects of various soil fumigation treatments on nitrogen mineralization and nitrification in laboratory incubation and field studies Dongdong Yan, Qiuxia Wang, Liangang Mao, Wei Li, Hongwei Xie, Meixia Guo, Aocheng Cao ⇑ Department of Pesticides, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, People’s Republic of China
h i g h l i g h t s " Pic significantly increased soil mineral nitrogen during the first 2 weeks. " All four fumigants retarded nitrification in both lab and field studies. " Pic has a stronger inhibitory effect on nitrification compared to other fumigants.
" An S-shaped function described the NO3 N concentrations in lab incubation samples.
a r t i c l e
i n f o
Article history: Received 26 March 2012 Received in revised form 31 August 2012 Accepted 12 September 2012 Available online 11 October 2012 Keywords: Chloropicrin Fumigation Mineral nitrogen Mineralization Nitrification inhibition
a b s t r a c t Better quantification of nitrogen mineralization and nitrification after fumigation would indicate if any adjustment is needed in fertilizer application. The effects of chloropicrin (Pic), 1,3-dichloropropene (1,3-D), dimethyl disulfide (DMDS) and metham sodium (MS) fumigation on soil nitrogen dynamics were evaluated in lab incubation and field studies. Although some differences were observed in NHþ 4 N and NO 3 N concentrations in lab incubation and field experiments, both studies led to the same conclusions: (1) Soil fumigation was shown to increase soil mineral nitrogen only during the first 2 weeks after fumigation (WAF). In particular, Pic significantly increased soil mineral nitrogen in both studies at 1 WAF. However, for all fumigant treatments the observed effect was temporary; the soil mineral content of treated samples recovered to the general level observed in the untreated control. (2) All the fumigation treatments depressed nitrification temporarily, although the treatments exhibited significant differences in the duration of nitrification inhibition. In both studies, for a limited period of time, Pic showed a stronger inhibitory effect on nitrification compared to other fumigant treatments. An S-shaped function was fitted to the concentrations of NO 3 N in lab incubation samples. The times of maximum nitrification (tmax) in DMDS and MS treatments were 0.97 week and 1.03 week, which is similar to the untreated control (tmax = 1.02 week). While Pic has the longest effect on nitrifying bacteria, nitrification appears to restart at a later time (tmax = 14.37 week). Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Soil fumigation is a highly effective technique for the control of soil-borne pests (insects, nematodes, weeds, and fungal pathogens) in many vegetable, fruit, nut, ornamental, and nursery crops (Ajwa and Trout, 2004; Minuto et al., 2006; Desaeger et al., 2008; Santos et al., 2009; Haydock et al., 2010). Most fumigants are known to have a broad biocidal activity, killing most soil organisms (Ibekwe et al., 2010). Consequently, fumigants affect the Abbreviations: Pic, chloropicrin; DMDS, dimethyl disulfide; MS, metham sodium; 1,3-D, 1,3-dichloropropene; WAF, week after fumigation; wk, week. ⇑ Corresponding author. Tel.: +86 10 62815940; fax: +86 10 62894863. E-mail address: [email protected] (A. Cao). 0045-6535/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2012.09.041
microbial community and activity of non-target microorganisms, altering nutrient transformation in the soil, and may potentially have effects on soil fertility and the productivity of agricultural systems. Fumigation has a marked effect on N mineralization. It increases mineralization rates, due to the mineralization of microbial biomass killed during fumigation (Lebbink and Kolenbrander, 1974; Shen et al., 1984; De Neve et al., 2004). In addition, it results in partial soil sterilization. Lysis of the dead microbes provides the surviving flora with new substrate, leading to enhanced mineralization (Müller et al., 2003). When soil organic matter decomposes, ammonia is liberated and then converted to nitrate under favorable soil conditions. This process, called nitrification, is significantly reduced by soil fumigation (Duniway, 2002). Fumigants are
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capable of retarding the biological oxidation of ammonia by reducing the activity of the nitrifying bacteria responsible for the first step in nitrification (Yamamoto et al., 2008; Brown and Morra, 2009). The inhibition of nitrification may cause an accumulation of soil ammonium and a reduction in soil nitrate. Indeed, some studies have shown increases in soil ammonium concentration in fumigated soils (Ebbels, 1971; Jenkinson and Powlson, 1976; Shen et al., 1984; MacNish, 1986; Zhang et al., 2011). Where soil mineral nitrogen exists to a large extent in the form of NHþ 4 N it may strongly reduce the accumulation of NO 3 N, thereby decreasing the leaching and denitrification losses of NO 3 N significantly. If substantial or prolonged changes in mineral nitrogen occur after soil fumigation, this would necessitate adjustments in nitrogen fertilizer application to improve nitrogen use efficiency. The overall objective of this study was to quantify the dynamic effects of fumigation on N mineralization and nitrification in laboratory incubation and field studies. 2. Materials and methods 2.1. Lab incubation study Soil samples were collected from the top 20 cm of greenhouse soil in Tongzhou district, southeast of Beijing (34.6% sand, 51.8% silt and 13.6% clay; soil pH 7.1; organic matter 3.1%; bulk density 0.93 g cm3) where the field experiments were conducted. The greenhouse had grown cucumber and tomato in rotation for at least 3 years. The soil was sieved through a 2 mm screen and pre-incubated for 7 d at room temperature in the dark, before any treatments were applied. To study the effects of fumigants on mineral nitrogen in soil, 500 g soil samples were placed in 2.5 L desiccators, treated with 0.25 g (NH4)2SO4 (equivalent to 100 mg N kg1 soil) and mixed thoroughly. The experimental design consisted of four fumigant treatments (chloropicrin, Pic; 1,3-dichloropropene, 1,3-D; dimethyl disulfide, DMDS; metham sodium, MS) and a control in three replicates. Fumigants were added into the desiccators at typical field application rates for each chemical (Pic 53 mg kg1, 1,3-D 39 mg kg1, DMDS 68 mg kg1, MS 54 mg kg1) (Spokas et al., 2006). The desiccators were sealed with vaseline and left for 7 d in the dark at 25 °C. 2.2. Experimental design of field study Field experiments were conducted in the same tomato greenhouse in Tongzhou district, southeast of Beijing (116°440 E, 36°530 N). The field experimental design consisted of four fumigant treatments and an untreated control randomized in a complete block design with three replicated plots. The fumigant treatments, doses and application methods are summarized in Table 1. A drip irrigation system was setup in the experimental area, with emitters 30 cm apart and an emitter flow rate of 1.9 L h1 at 1 atm. The distance between drip tapes was the width of the tomato planting beds (80 cm). Before fumigation, 45 g m2
diamine phosphate and 1.5 kg m2 organic fertilizer were applied to the soil. All fumigants were applied on 11 July. After fumigation, the soil was covered with 0.04 mm-thick polyethylene film (Hebei Baoshuo Co., Ltd.) for approximately 1 week, and then tilled to disperse the fumigants 1 week before transplanting tomatoes. 2.3. Soil sampling and analysis After 7 d lab fumigation, all the desiccators were taken to a ventilation hood to remove the fumigant gases, and the soil in each desiccator was mixed thoroughly. Soil samples were collected at 0, 1, 2, 4, 8, 12, 16, 20 and 24 weeks after fumigation (WAF; 0 WAF was defined as before fumigation, and 1 WAF was defined as the date when the fumigants were removed). The soil moisture content in each desiccator was maintained gravimetrically after each sampling. In the field experiment, soil samples from the top 20 cm depth were collected at 1, 2, 4, 8, 12 and 16 weeks after fumigation (WAF; 1 WAF was defined as the date when the plastic fumigation film was removed). Weigh 10.00 g of soil samples, add 40 ml of 2 M KCl extraction solution, shake for 0.5 h at room temperature, and filter the soil slurries. Soil mineral nitrogen (defined as NHþ 4 N and NO3 N) were determined by standard automated colorimetric techniques based on the Berthelot reaction, and cadmium reduction method, respectively (using a Futura Continuous Flow Analytical System, Alliance instruments, France). 2.4. Data analysis In previous studies, the percentage inhibition of nitrification by chemicals was calculated from [(C–S)]/C 100, where S = amount of NO 3 N produced in the soil sample treated with chemicals, and C = amount of NO 3 N produced in the control (no chemicals added) (McCarty and Bremner, 1989; Abbasi et al., 2011). The formula may be suitable for our lab study only, because lab incubation is a closed system and soil NO 3 N is unable to move easily. In contrast, soil NO 3 N in field conditions is highly mobile and prone to leaching. So, for the field study, it is more appropriate to calculate the percentage inhibition of nitrification by chemicals in the following manner: [(S–C)]/C 100, where S = amount of NHþ 4 N accumulated in the soil sample treated with chemicals, and C = amount of NHþ 4 N accumulated in the control (no chemicals added). To assess the effect of fumigant treatments on nitrification in our lab incubation study, an S-shaped function was fitted to the NO 3 N concentrations of treated soil samples (Zhang et al., 2000; De Neve et al., 2004) using the following equation:
NO3 NðtÞ ¼ NO3 Nð0Þ þ NA ½1 þ b expðk tÞ1
ð1Þ
where NA (mg N kg1 soil) is the potential amount of N nitrified, b is a dimensionless quantity that determines the position of the inflection point, k is the nitrification rate constant (week1), and
Table 1 Fumigant dose and application method in field study. Soil fumigant
Dose
Chemical structure
Percent a.c.
Application methods
Pic DMDS MS 1,3-D Control
500 kg ha1 800 L ha1 1000 L ha1 200 kg ha1 NA
CCl3NO3 C2H6S2 C2H4NNaS2 C3H4Cl2 NA
99 99.5 42 93 NA
Manual injection Irrigation system Irrigation system Irrigation system NA
Pic = chloropicrin; 1,3-D = 1,3-dichloropropene; DMDS = dimethyl disulfide; MS = metham sodium; a.c = active component; NA = not applicable.
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1 NO ) is the soil NO 3 Nð0Þ (mg N kg 3 N content at the start of the incubation. The time at which maximum nitrification occurred (tmax) was calculated by taking the second order derivative of Eq. (1), yielding: tmax = In b/k. Substitution of tmax in the first-order derivative of Eq. (1) yields the maximum nitrification rate Kmax = NA k. The results were expressed as means of three replicates. The data were subjected to one-way ANOVA for repeated measures to determine the effect of fumigation on mineral nitrogen components in soil at each sampling date. When significant (P < 0.05) treatment differences were observed, protected LSD values were calculated to separate the treatment means. Vertical bars in figures represent LSD values where treatments means are significantly different at P = 0.05. A nonlinear regression model was performed to estimate the parameters (using SPSS Statistics V19) and curves were plotted (using Origin 7.5).
3. Results 3.1. Mineral nitrogen in fumigated soil in lab incubation study The NHþ 4 N and NO3 N concentrations in soil at different sampling dates in the laboratory incubation study are shown in Fig. 1. The treatments affected soil NHþ 4 N content differently at 1 WAF (Fig. 1A). A significant reduction in soil NHþ 4 N content was observed in the untreated control, DMDS and MS treatments, and this reduction was due to the nitrification process occurring in soil during the first week. In contrast, a slight change in soil NHþ 4 N content was observed after Pic and 1,3-D fumigation compared to the untreated control. The soil NHþ 4 N content in the 1,3-D treatment tended to decrease at 2 WAF, falling to the same level as DMDS and MS treatments after the first 2 weeks. After Pic fumigation, little change was observed in soil NHþ 4 N content during the first 12 weeks; and the soil NHþ N reached 4 its normal low value at 16 WAF as a result of recovery of the nitrification process. During the first week of the lab incubation study, soil NO 3 N content increased significantly in DMDS, MS and the untreated control, due to the nitrification process.Soil NO 3 N content in Pic and 1,3-D treatments decreased slightly during the first week, and increased to some extent at 2 WAF, because the conversion of NHþ 4 N to NO3 N was inhibited during the first 2 weeks. After 2 WAF, the NO 3 N content in 1,3-D treated soil rose to the levels observed in DMDS, MS and the control. After Pic
A
fumigation, soil NO 3 N content increased gradually during the first 6 weeks. All of the fumigation treatments depressed nitrification compared with the untreated control, although there were important differences between fumigants in the duration of nitrification inhibition. 3.2. Mineral nitrogen in fumigated soil in field study The NHþ 4 N concentrations in soil at different sampling dates in the field study are shown in Fig. 2A. During the first week, all four fumigants increased the NHþ 4 N content, and a significant increase was observed in the Pic and DMDS treatments compared to the control at 1 WAF. This increment differed from the trend observed in soil NHþ 4 N during the first week of the lab incubation study. After the Pic treatment, soil NHþ 4 N briefly reached a maximum value of 210.0 mg kg1 at 1 WAF, while the control had the 1 lowest soil NHþ . After fumiga4 N concentration of 113.3 mg kg þ tion with DMDS, the soil NH4 N concentration rose temporarily to 153.9 mg kg1, 36% higher than the control. Following 1,3-D and MS fumigation, NHþ 4 N concentrations rose briefly to 133.0 and 128.0 mg kg1, respectively, at 1 WAF (17% and 13% higher than the control). With increasing time, the influence of fumigants þ on soil NHþ 4 N diminished. After 2 WAF, soil NH4 N in all treatments tended to recover to the control level. No significant differences in soil NHþ 4 N concentration were observed at 2, 4, 8, 12, and 16 WAF. The evolution of NO 3 N concentrations in the field study is shown in Fig. 2B. During the first 2 weeks, soil NO 3 N was temporarily higher in the Pic treatment than in the control. After 4 WAF only minor differences in NO 3 N concentration were observed. The concentration of NO 3 N in all field treatments, including the untreated control, generally decreased during the sampling period. This downward trend in the field study differed from the increased NO 3 N concentrations observed in all treatments in the lab study.
4. Discussion 4.1. Effect of fumigation on mineralization A large portion of organic nitrogen is decomposed to mineral nitrogen by soil microorganisms in a process called mineralization. Soil fumigation has been shown to increase soil mineral nitrogen content due to the decomposition of soil microorganisms after
B
Fig. 1. Evolution of NHþ 4 N (A) and NO3 N (B) soil concentrations of all lab incubation treatments. Vertical bars represent LSD values where treatment means are significantly different at P = 0.05.
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A
B
Fig. 2. Evolution of NHþ 4 N (A) and NO3 N (B) soil concentrations of field study treatments. Vertical bars represent LSD values where treatment means are significantly different at P = 0.05.
fumigation (Gasser and Peachey, 1964; Jenkinson and Powlson, 1976; Shen et al., 1984; De Neve et al., 2004). In our field study, the soil mineral nitrogen content (as the sum of NHþ 4 N and NO 3 N) in all fumigation treatments showed patterns similar to the patterns of NHþ 4 N, whereas the soil mineral nitrogen content in our lab incubation study showed patterns similar to the patterns of NO 3 N (data not shown). Soil mineral nitrogen increased significantly after Pic fumigation in both our lab and field study during the first 2 weeks (Table 2). However, soil fumigation was found to increase soil mineral nitrogen temporarily. In samples taken at longer WAF, the soil mineral content of fumigated soil generally recovered relative to the control. In field conditions, mineralization of the organic nitrogen pool in the soil was larger compared to the lab incubation, and the effect of fumigation on soil mineralization was more marked. Mineralization is a microbial process that depends on the physical and chemical properties of the soil. The different effects of these fumigants on mineral nitrogen are due, at least in part, to their distinct biological activities on soil microorganisms. 4.2. Effect of fumigation on nitrification Nitrification is one of the most important processes among the nitrogen transformations that take place in soil. There is a close relationship between mineralization and immobilization. This occurs because NHþ 4 oxidation at the first step of nitrification is þ responsible for NHþ 4 depletion, and an accumulation of NH4 N clearly indicates a disruption of soil nitrification. Effective inhibition of nitrification should be characterized by a rise in soil NHþ 4 N and concomitant decline in soil NO3 N when compared
with control treatments. The temporary increase in soil NHþ 4 N in all fumigant treatments probably originated from the decomposition of soil organisms following microbial cell death and from metabolism by repopulating microbes (Shen et al., 1984; Yamamoto et al., 2008).Fumigants are capable of retarding the biological oxidation of ammonia by suppressing the activity of the ammonia-oxidizing bacteria responsible for the first step in nitrification (McCarty, 1999). Ammonia oxidation is catalyzed by a complex of membrane-bound proteins that include ammonia monooxygenase (AMO), which can oxidize ammonia to hydroxylamine. A general characteristic of monooxygenase enzymes is a Table 3 Short-term effects of fumigant treatments on nitrification of ammonium in soil samples at 1 WAF. Fumigants
Pic 1,3-D DMDS MS
Inhibition of nitrification (%) Lab incubation
Field study
94.5 84.5 2.4 3.7
85.3 17.4 35.8 13.0
Pic = chloropicrin; 1,3-D = 1,3-dichloropropene; MS = metham sodium.
DMDS = dimethyl
disulfide;
Table 2 Short-term effects of fumigant treatments on nitrogen mineralization in soil. Treatments
Soil mineral nitrogen (mg N kg1) Lab incubation
Pic 1,3-D DMDS MS Control LSD (P 6 0.05)
Field study
1 WAF
2 WAF
1 WAF
2 WAF
244.6 236.3 219.8 232.8 221.6 22.23
273.1 242.2 260.6 268.1 240.3 21.97
295.8 196.6 228.8 177.3 190.2 22.15
183.4 162.4 142.8 145.7 149.8 24.96
Pic = chloropicrin; 1,3-D = 1,3-dichloropropene; DMDS = dimethyl MS = metham sodium; WAF = week after fumigation.
disulfide;
Fig. 3. NO 3 N soil concentrations of all lab incubation treatments with the nitrification model fitted to the data.
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Table 4 Parameters of the nitrification model fitted to the data of lab incubation treatments. Treatment
1 NO 3 Nð0Þ (mg N kg )
R2
NA (mg N kg1)
b
k (week1)
tmax (week)
Kmax (mg N kg1 week1)
Control Pic 1,3-D DMDS MS
158.9 161.1 157.6 158.7 158.7
0.466 0.805 0.873 0.713 0.458
111.2 160.3 103.1 109.3 115.9
3.323 7.108 4.12 108 8.839 12.439
1.178 0.136 9.379 2.256 2.455
1.02 14.37 2.11 0.97 1.03
131.0 21.9 967.0 246.6 284.6
NO 3 Nð0Þ = soil NO3 N content at the start of the incubation; NA = potential amount of N nitrified; b a dimensionless quantity; k = nitrification rate constant; tmax = time at which maximum nitrification occurs; Kmax = maximum nitrification rate.
broad substrate range (Gvakharia et al., 2007). All four fumigants have been shown to act as substrates of AMO that can competitively inhibit ammonia oxidation (Juliette et al., 1993; Brown and Morra, 2009; Sayavedra-Soto et al., 2010). These fumigants appear to reduce AMO activity primarily by acting as enzyme substrates, but the specific effects of these fumigants may also arise from other unique modes of inhibition. Although some differences were observed between lab and field concentrations of NHþ 4 N at 1 WAF, both NHþ 4 N accumulation or increase clearly reflected a short-term disruption of nitrification processes. All fumigant treatments temporarily retarded nitrification in both lab incubation and field studies. Their inhibition rate at 1 WAF is shown in Table 3. In both the lab and field study, Pic was found to have a stronger inhibitory effect on nitrification compared to other fumigation treatments. An S-shaped function was fitted to the NO 3 N concentrations of treated soil samples (Fig. 3, Table 4). The time of maximum nitrification (tmax) indicates the potential length of the effect of fumigation on nitrification inhibition. When applied to lab incubation results it could be used to predict the effects of fumigant on soil NO 3 N content. In conditions where fumigation has the longest effect on nitrifying bacteria, nitrification appears to restart more gradually (smaller maximum nitrification rate, Pic: Kmax = 21.9 mg N kg1 week1) and at a later time (longer time before maximum nitrification rate is reached, Pic: tmax = 14.37 week). The tmax in DMDS and MS treatments were 0.97 week and 1.03 week, similar to the untreated control (tmax = 1.02 week). The results shown in Table 4 provided additional evidence that Pic can have a stronger inhibitory effect on nitrification of soil NHþ 4 N, while DMDS and MS showed little effect on nitrification. Although the quality of fit was low due to the large variability of mineral nitrogen contents, it provides an illustration of the intensity and duration of the nitrification inhibition by four fumigants at higher-than-normal doses, under lab conditions. Three main processes will affect soil nitrate: ammonia oxidation during nitrification, denitrification, and nitrate leaching (Stevenson, 1986). Soil NO 3 N is repelled from soil particles and highly mobile in field conditions because of its negative charge. And it is also the main form of N taken up by most plants. Tomatoes were planted on the greenhouse during all sampling time. The uptake of soil NO 3 N by plant would be the main reason responsible for the decrease of NO 3 N concentrations in field study. So it is difficult to quantify the effect of fumigation on soil NO 3 N in field conditions. Variable results have also been observed in other studies. Previous studies have reported that NO 3 N concentrations in soil following Pic and methyl bromide fumigation are lower than untreated soil (Draycott and Last, 1971; Rovira, 1976). Conversely, studies have also found that methyl bromide and MS increased soil NO 3 N concentration (Gasser and Peachey, 1964). Variable results were also reported by Müller et al. (2003), who observed a decrease in NO 3 N concentration following fumigation in their laboratory study, but an increase in NO 3 N in their field study.
5. Conclusions Although some differences were observed in NHþ N and NO N between lab and field experiments, both 3 4 studies led to the same conclusions: (1) Pic significantly increased soil mineral nitrogen in both studies and the content of mineral nitrogen was increased by 55.5% and 10.4% after Pic fumigation in field and lab incubation study at 1 WAF, respectively. However, the observed effect was temporary. For longer WAF soil samples, the soil mineral content generally recovered to the level observed in the untreated control. (2) All the fumigation treatments depressed nitrification temporarily, although the fumigants exhibited significant differences in the duration of nitrification inhibition. In both studies, for a limited period of time, Pic showed a stronger inhibitory effect on nitrification compared to the other fumigant treatments. Acknowledgement This work was supported by the National Natural Science Foundation Project of China (NSFC: 40871131). References Abbasi, M.K., Hina, M., Tahir, M.M., 2011. Effect of Azadirachta indica (neem), sodium thiosulphate and calcium chloride on changes in nitrogen transformations and inhibition of nitrification in soil incubated under laboratory conditions. Chemosphere 82, 1629–1635. Ajwa, H.A., Trout, T., 2004. Drip application of alternative fumigants to methyl bromide for strawberry production. HortScience 39, 1707–1715. Brown, P.D., Morra, M.J., 2009. Brassicaceae Tissues as Inhibitors of Nitrification in Soil. J. Agric. Food Chem. 57, 7706–7711. De Neve, S., Csitári, G., Salomez, J., Hofman, G., 2004. Quantification of the effect of fumigation on short- and long-term nitrogen mineralization and nitrification in different soils. J. Environ. Qual. 33, 1647–1652. Desaeger, J.A., Seebold, K.W., Csinos, A.S., 2008. Effect of application timing and method on efficacy and phytotoxicity of 1,3-D, chloropicrin and metam-sodium combinations in squash plasticulture. Pest Manage. Sci. 64, 230–238. Draycott, A.P., Last, P.J., 1971. Some effects of partial sterilization on mineral nitrogen in a light soil. J. Soil Sci. 22, 152–157. Duniway, J.M., 2002. Status of chemical alternatives to methyl bromide for preplant fumigation of soil. Phytopathology 92, 1337–1343. Ebbels, D.L., 1971. Effects of soil fumigation on soil nitrogen and on disease incidence in winter wheat. Ann. Appl. Biol. 67, 235–243. Gasser, J.K.R., Peachey, J.E., 1964. A note on the effects of some soil sterilants on the mineralisation and nitrification of soil-nitrogen. J. Sci. Food Agric. 15, 142–146. Gvakharia, B.O., Permina, E.A., Gelfand, M.S., Bottomley, P.J., Sayavedra-Soto, L.A., Arp, D.J., 2007. Global transcriptional response of nitrosomonas europaea to chloroform and chloromethane. Appl. Environ. Microbiol. 73, 3440–3445. Haydock, P.P.J., Deliopoulos, T., Evans, K., Minnis, S.T., 2010. Effects of the nematicide 1,3-dichloropropene on weed populations and stem canker disease severity in potatoes. Crop Prot. 29, 1084–1090. Ibekwe, A.M., Papiernik, S.K., Grieve, C.M., Yang, C.H., 2010. Influence of fumigants on soil microbial diversity and survival of E. coli O157:H7. J. Environ. Sci. Health, Part B 45, 416–426. Jenkinson, D.S., Powlson, D.S., 1976. The effects of biocidal treatments on metabolism in soil – I. Fumigation with chloroform. Soil Biol. Biochem. 8, 167–177. Juliette, L.Y., Hyman, M.R., Arp, D.J., 1993. Inhibition of ammonia oxidation in nitrosomonas europaea by sulfur compounds: thioethers are oxidized to sulfoxides by ammonia monooxygenase. Appl. Environ. Microbiol. 59, 3718– 3727.
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