Biol Fertil Soils (2001) 34:79–84 DOI 10.1007/s003740100380
O R I G I N A L PA P E R
Wolfram Zerulla · Thomas Barth · Jürgen Dressel Klaus Erhardt · Klaus Horchler von Locquenghien Gregor Pasda · Matthias Rädle Alexander Heinrich Wissemeier
3,4-Dimethylpyrazole phosphate (DMPP) – a new nitrification inhibitor for agriculture and horticulture An Introduction Received: 17 April 2000 / Published online: 7 June 2001 © Springer-Verlag 2001
Abstract 3,4-Dimethylpyrazole phosphate (DMPP) is a new nitrification inhibitor with highly favourable properties. It has undergone thorough toxicology and ecotoxicology tests and application-technology experiments, and has been shown to have several distinct advantages compared to the currently used nitrification inhibitors. Application rates of 0.5–1.5 kg ha–1 are sufficient to achieve optimal nitrification inhibition. DMPP can significantly reduce NO3– leaching, without being liable to leaching itself. DMPP may reduce N2O emission, apparently without a negative effect on CH4 oxidation of the soil. The use of DMPP-containing fertilizers can improve yield. This offers the possibility of saving mineral fertilizer N, reducing the number of N-application rounds, and obtaining higher crop yields with current fertilizer-N rates. Keywords DMPP · Nitrification inhibitor · Nitrogen losses · 3,4-Dimethylpyrazole phosphate · Nitrogen-use efficiency
that applied (Wiesler 1998), so that, for economic and ecological reasons, an increase in fertilizer-N efficiency continues to be the main objective of N-related research (Trenkel 1997). Results relevant to this are expected from site-specific crop management (Auernhammer 1997), from the use of sensors for N-application monitoring (Wollring et al. 1998), and from the introduction of socalled N-efficient varieties (Spanakakis and Viedt 1990). A further possible means of increasing fertilizer-N utilization rates is the improvement of the fertilizer itself, e.g. by the addition of a nitrification inhibitor (König 1983), particularly together with N in a granulated form (Trenkel 1997). Nitrification inhibitors are compounds that delay the bacterial oxidation of NH4+ to NO2– in the soil (first step of nitrification) for a certain period of time (Fig. 1) by depressing the activities of Nitrosomas bacteria in the soil. The second step of nitrification normally is not influenced.
Advantages of nitrification inhibitors Introduction N plays an essential role in plant production, in regard to both its economic and ecological aspects. On the one hand, N affects yield level and quality like no other plant nutrient, and on the other hand, nitrogenous compounds in the hydrosphere (NO3– accumulation in groundwater) and atmosphere (release of nitrous greenhouse gases) may have numerous unwanted effects on the environment. Even in intensively managed cash crop production, the utilization rate of mineral fertilizer N is only 50–70% of W. Zerulla (✉) · T. Barth · J. Dressel · K. Erhardt · K. Horchler von Locquenghien · G. Pasda · M. Rädle · A.H. Wissemeier BASF Aktiengesellschaft, BASF Agricultural Center Limburgerhof, P.O. Box 120, 67114 Limburgerhof, Germany e-mail:
[email protected] Fax: +49-621-6027260
Guiraud and Marol (1992) found that the amount of NO3– present in the soil during the inhibition period due
Fig. 1 Specific influence of a suitable nitrification inhibitor on the first step (nitritation) of nitrification
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to the addition of nitrification inhibitors was significantly reduced compared to a control without a nitrification inhibitor. Since NO3– is considered to be the source of major processes of N losses (leaching, denitrification), nitrification inhibitors can help to reduce the environmental problems which stem from N application, while increasing fertilizer-N efficiency. Practical advantages of nitrification inhibitors for agriculture and horticulture, as well as for the environment, are: 1. A significant reduction in the risk of NO3– leaching losses from N fertilizers, compared to conventional N fertilizers (Scheffer and Bartels 1998). 2. A decrease in the emission of nitrous greenhouse gases, especially of N2O (Bremner and Yeomans 1987; Michel and Wozniak 1998; Linzmeier et al. 2001; Weiske et al. 2001). 3. Smaller N losses and the temporary NH4+ nutrition of crops, often leading to yield increases (Prasad and Power 1995). 4. Better N utilization by plants (Timmermann and Söchtig 1984; Zerulla and Lutz 1992). 5. A reduction in the work-load of growers due to more flexible timing of fertilizer application, and the possibility of combining or saving application rounds (Munzert 1984; Dachler 1993).
Nitrification inhibitors used worldwide Worldwide, hundreds of nitrification inhibitors are known, which show more or less specific action (Slangen and Kerkhoff 1984; Prasad and Power 1995; McCarty 1999). Thus various workers, e.g. Domsch and Paul (1974), Hauck (1980, 1984), or Winley and San Clemente (1971), have described the nitrification inhibiting effect of various plant-protection products. Wilson (1977a, 1977b) reports on this effect for certain heavy metals. Bremner and McCarty (1993) evaluated the potential of natural plant residues to inhibit nitrification. A nitrificide action is also attributed to a high biuret concentration in urea (Bhargava and Ghosh 1979). However, the practical use of these unspecific nitrification inhibitors is questionable, due to their insufficient activity period, their phytotoxic characteristics, or for environmental reasons. The directed search for specific nitrification inhibitors started in the late 1950s. As early as 1962, nitrapyrin [2-chloro-6(trichloromethyl)pyridine] was introduced as a nitrification inhibitor to the US market (Goring 1962a, 1962b). Dicyandiamide (DCD) gained importance predominantly in Europe (Solansky 1982). Numerous other, mainly heterocyclic, N compounds, though sometimes with excellent nitrification-inhibiting properties (McCarty and Bremner 1989; McCarty 1999), have so far failed to achieve any commercial importance as nitrification inhibitors under practical conditions. The same applies to S compounds (Prasad and Reddy 1977), to urea derivatives (Jung and Dressel 1978) or to acetylene and its derivatives (McCarty 1999).
On a global scale, only two nitrification inhibitors have so far gained importance for practical use; these are DCD in Europe and, to a limited extent, in the US and – exclusively in the US – nitrapyrin.
Disadvantages of DCD and nitrapyrin Besides the advantages specified above, both compounds also have significant disadvantages. DCD is just too expensive for large-scale use in agriculture and horticulture. Also, its efficiency is comparatively low, so that high application rates are needed for sufficient nitrification inhibition [e.g. 15–30 kg DCD ha–1 (independent of the amount of slurry applied) together with a slurry application; Solansky (1982)]. As DCD is highly water soluble, intensive precipitation may lead to its translocation within the soil profile (Teske and Matzel 1988), resulting in the spatial separation of the nitrification inhibitor from the NH4+ to be stabilized. In addition, under certain agroclimatological conditions, DCD use may cause phytotoxicity problems [visible plant damage (Reeves and Touchton 1986)] which, though not leading to reduced yields, affect marketability, e.g. of leaf vegetables. Nitrapyrin has a relative high vapour pressure which excludes its addition to solid fertilizers. Therefore, nitrapyrin is almost exclusively used as an additive to anhydrous NH3 for pre-winter application, as practiced in large areas of the USA. Moreover, this substance belongs to the group of organic chlorine compounds, the release of which into the environment faces increasing opposition. Finally, it is corrosive and explosive and it poses certain toxicology problems (Trenkel 1997).
3,4-Dimethylpyrazol-phosphate – a new nitrification inhibitor In the framework of a joint research project, BASF, in cooperation with universities and other research institutes, developed a new nitrification inhibitor highly specific in inhibiting nitrification at low concentrations of 0.5–1.0 kg active compound ha–1 (Table 1). This new nitrification inhibitor is 3,4-dimethylpyrazol phosphate (DMPP; ENTEC). For physical and chemical properties the reader is referred to Table 1. According to European legislation, DMPP is recognized as a new substance, and as such has been submitted to extensive standard toxicology and ecotoxicology tests (Andreae 1999; Roll 1999). None of these assays have revealed toxicological or ecotoxicological sideeffects so far. Consequently, neither DMPP-containing fertilizers nor liquid DMPP formulations as additives for urea ammonium nitrate solution or slurry need to be marked as hazardous substances (Andreae 1999; Roll 1999). DMPP has both been declared under the Chemicals Act and been internationally registered according to fertilizer law.
81 Table 1 Chemical structure, physical and chemical properties of 3,4-dimethylpyrazole phosphate (DMPP)
Table 3 Inhibiting effect of DMPP compared to dicyandiamide (DCD) (residual NH4+-N, relative to 8.7 mg NH4+-N in the form of liquid pig manure; incubation experiment with Limburgerhof soil: loamy sand; pH (CaCl2) 6.8; CEC 7.0 mEq 100 g soil–1; Ct 0.8%; total N (Nt) 0.09%. For other abbreviations, see Tables 1 and 2 WAT
DMPP 0
DCD
0.385
0.77
0.96a
0
5
10
12.5a
100 93 39 0 0 0
100 100 73 54 15 4
100 100 76 52 32 16
100 68 3 0 0 0
100 79 18 0 0 0
100 83 37 18 0 0
100 93 47 22 0 0
(%)b 0 1 2 3 4 5
100 68 1 0 0 0
a Application rate of mg DMPP 100 g soil–1 projected to kg DMPP ha–1 b 8.7 mg NH +-N=100% 4
Table 2 Content of NH4+-N and NO3–-N in soil (0–30 cm) after application of ammonium sulphate nitrate (ASN) with DMPP compared to ASN without DMPP [field trial in 1996 near Karlsruhe: annual precipitation 740 mm year–1; average air temperature 10.1°C; sandy loam; pH (CaCl2) 6.5; total C (Ct) 0.8%; NH+4-N and NO3–-N before N application 11 kg ha–1 and 13 kg ha–1, respectively; N application 100 kg N ha–1]. WAT Weeks after treatment WAT
Without N
ASN
ASN+DMPPa
NH4+-N NO3--N
NH4+-N NO3–-N
NH4+-N NO3–-N
52 73 73 64
142 135 96 70
(kg N ha–1) 2 4 6 8
9 25 10 7
9 14 12 18
40 63 70 56
47 30 33 45
a 1% according to the NH +-N content of the basic fertilizer ASN 4 (18.5% NH4+-N, 7.5% NO3–-N)
Properties of DMPP DMPP is effective at very low rates. An application of 0.5–1.5 kg DMPP ha–1 (depending on the amount of applied N) is sufficient under field conditions to securely inhibit nitrification over a period of 4–10 weeks (Table 2). The duration of action depends on climatic conditions (Pasda et al. 2001), site characteristics (Barth et al. 2001; Pasda et al. 2001) and probably the cultivated crop. DMPP is formulated on fertilizer granules (average diameter 3.0–3.6 mm) of straight N fertilizers (e.g. ammonium sulphate nitrate: 18.5% NH4+-N, 75% NO3–-N) and multi-nutrient complex fertilizers (e.g. NPK, 14:3.8:14.1 with 8.5% NH4+-N, 5.5% NO3–-N) with an NH4+ content >55–60% of total fertilizer N. Granules are dissolved easily by rain, giving rise to a mosaic of NH4+ and DMPP concentrations in the topsoil.
Thus, compared to DCD, a comparable if better inhibition effect is achieved with less than one-tenth of the application rate (Table 3). Therefore, mineral fertilizers with DMPP contain only 1% active ingredient, based on their NH4+-N or carbamide-N content. As could be expected, the intensity of nitrification inhibition depends on environmental conditions. The period of time over which nitrification inhibitors are effective strongly depends on soil temperature (Vilsmeier 1980; Slangen and Kerkhoff 1984; Guiraud and Marol 1992). This also applies to DMPP. Incubation studies at constant soil temperatures, using a loess loam without plants, have shown that at 5°C there was practically no nitrification of the NH4+ from ammonium sulphate nitrate to which DMPP had been added, whereas for the control fertilizer without DMPP nitrification was completed within approximately 140 days. At 20°C, and under otherwise unchanged conditions, nitrification for ammonium sulphate nitrate was completed within 7–21 days, compared to 40 days with DMPP (Table 4). Independent of the results cited above, there are indications that several soil parameters directly influence the efficiency of DMPP. However, a monocausal approach cannot give an explanation for the varying intensity of the inhibition effect of DMPP and other nitrification inhibitors. Only the simultaneous observation of several soil parameters can explain the intensity of inhibition of nitrification by DMPP. Barth et al. (2001) showed with multiple regression that the sand content, proton concentration as well as microbiological parameters of soil, such as catalase activity, and the potential nitrification capacity, seem to have a significant influence on the efficiency of DMPP in soils (R2=0.70). It could be shown, both in model experiments as well as in Mitscherlich pots (Table 5) and in lysimeter experiments conducted under adverse environmental conditions in Spain (Serna et al. 2000), that DMPP offers a
82 Table 4 Effect of DMPP on the amount of NH4+-N and NO3–-N in soil incubated at different temperatures (incubation experiment with Hannover soil: loam; pH (CaCl2) 6.4; CEC 11.8 mEq 100 g soil–1; Ct 1.2%; Nt 0.14%; N application 10 mg 100 g soil–1). DAT Days after treatment; for other abbreviations, see Tables 1 and 2 Temperature
DAT
ASN+DMPPa
ASN NH4+-N
NO3–-N
NH4+-N
NO3–-N
3.2 3.3 3.6 5.0 7.3 9.1 2.6 5.2 7.2 7.1 8.9 7.1 10.2 11.9 10.9 11.7
5.2 3.1 4.3 3.7 4.8 4.1 6.6 5.1 4.6 3.8 3.6 4.9 4.4 2.9 0.6 0
2.6 2.5 3.1 2.9 4.0 4.1 2.6 3.2 4.3 4.1 4.6 3.8 5.1 9.5 10.9 10.2
Table 5 NO3– leaching under spinach after application of different nitrification inhibitors [pot trial (four replicates) with Ruchheim soil: loam; pH (CaCl2) 7.6; CEC 14 mEq 100 g soil–1; Ct 1.2%; Nt 0.1%; N application 0.75 g N pot–1]. Values in a row followed by the same letter do not differ significantly (Duncan's test, α=5%). DAF Days after fertilization; for other abbreviations, see Tables 1 and 2 ASN+DMPPa
Irrigation before sampling (mm)
Sampling date DAF
ASN
(% of fertilized N)
20 10 10 Σ40
7 18 22 Σ
10.7 8.3 2.7 21.7
ASN+DCDb
(mg pot–1) 5°C 5°C 5°C 5°C 5°C 5°C 10°C 10°C 10°C 10°C 10°C 20°C 20°C 20°C 20°C 20°C
7 21 42 63 91 140 7 21 42 63 91 7 21 42 63 91
4.7 3.9 2.8 2.9 1.8 0 5.6 4.1 2.4 0.9 0 2.5 0 0 0 0
1% according to the NH4+-N content of the basic fertilizer ASN (18.5% NH4-N, 7.5% NO3-N)
a
better protection against the risk of NO3– leaching than does DCD. Pasda et al. (2001) found that the yield-increasing effect of DMPP was stronger the lighter the soil and the higher the amount of precipitation in the period January–July. This relationship gives an indication of the risk of potential NO3– leaching at a site. The higher this risk, the greater the chance that the addition of a nitrification inhibitor will result in improved N efficiency and thus in a yield increase. DMPP is not translocated within a slightly pseudogleyic brown earth (FAO Gleyic Cambisol); only mechanical incorporation into the ploughed soil layer by soil tillage has been observed (Fettweis et al. 2001). Thus, there seems to be only little spatial separation of the nitrification inhibitor from the fertilizer NH4+. The risk of DMPP being leached into the groundwater seems to be very low. However, more research is required. In lysimeter studies, set up according to the guidelines of the German Federal Biological Research Centre for Agriculture and Forestry (1990), using a slightly pseudogleyic brown earth from aeolic sand, conducted at the Jülich Research Centre over a 3-year period, no DMPP concentrations above the detection limit of 0.5 µg l–1 could be found in the leachate (Fettweis et al. 2001). An additional important environmental advantage of nitrification inhibitors can be seen in the repeatedly documented reduction of N2O losses after a N application (Skiba et al. 1993; Anonymous 1996). It seems that DMPP is especially effective in this respect. At a loamy soil site near Giessen, Germany, DMPP reduced the
a a a a
4.5 2.6 0.5 7.6
a b b b
12.1 3.5 0.5 16.1
a b b ab
a 1.6% according to the NH +-N content of the basic fertilizer ASN 4 (18.5% NH4+-N, 7.5% NO3–-N) b 13% according to the NH +-N content of the basic fertilizer ASN 4 (18.5% NH4+-N, 7.5% NO3–-N)
emission of N2O considerably more than DCD, without having a negative effect on CH4 oxidation of the soil (Weiske et al. 2001). A decrease in C mineralization, as was observed in these field experiments, could not be confirmed in model experiments. Because of an effective and specific inhibition of nitritation by DMPP, NH4+ was stabilized for a period of several weeks of nitrification, but the addition of this nitrification inhibitor did not lead to higher NH3 losses when compared to the control (Linzmeier et al. 1999). These results, however, may depend on soil properties and the soil pH in particular. As the choice of a fertilizer is primarily a question of cost, a nitrification inhibitor should offer practical advantages for the farmer in addition to the advantages specified above. Frequently claimed advantages for the use of a fertilizer with nitrification inhibitors are increases in yields, the possibility of saving fertilizer N and reducing the number of fertilizer applications (Trenkel 1997; Wozniak et al. 1997). These advantages have also been obtained with the use of DMPP-containing fertilizers in numerous experiments under western and southern European conditions (Ebertseder and Kurpjuweit 1999; Pasda et al. 1999, 2001; Hähndel and Zerulla 2000). For most crops, significant yield increases compared to the control fertilizer without nitrification inhibitor were obtained when averaging the results of application-technology experiments. The number of application rounds could always be decreased. In many experiments with vegetables, the use of DMPP resulted in a reduced NO3– concentration in the fresh matter, and plants frequently had a more intense green colour. The positive effects of a DMPP application could be found even in perennial crops such as citrus fruits (Serna et al. 2000). DMPP proved to be highly plant compatible (no phytotoxic damage). So far, there have been no reported field experiments in which the application of DMPP caused a phytotoxic reaction. Even an overdose of DMPP, achieved by applying eightfold the recommended
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Fig. 2 Photograph showing compatibility of DCD and DMPP with lettuce plants. Left DCD dose eightfold the recommended concentration, right DMPP dose eightfold the recommended concentration
application rate, did not lead to any symptoms in the plants, whereas an overdose of DCD caused pronounced symptoms (Fig. 2). When residues were analysed – with extremely rare exceptions – only traces of DMPP could be detected in plants such as winter wheat, potatoes, lettuce and red cabbage, while DCD seems liable to be taken up by plants at higher concentrations (Reeves and Touchton 1986). More broad-scale research is required with a great variety of crops in order to confirm the results obtained so far. Acknowledgements The authors wish to thank the Federal Ministry of Education, Science, Research and Technology, Bonn, Germany, for supporting the project "Ökoeffiziente Dünger – Entwicklung zur Minimierung von Stickstoffemissionen in Wasser und Luft”.
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