Evaluation of ecological doses of the nitrification inhibitors 3,4-dimethylpyrazole phosphate (DMPP) and 4-chloromethylpyrazole (ClMP) in comparison to dicyandiamide (DCD) in their effects on dehydrogenase and dimethyl sulfoxide reductase activity in soils

Risk assessment of the nitrification inhibitors (NIs) 3,4-dimethylpyrazole phosphate (DMPP), 4-chloromethylpyrazole (ClMP), and dicyandiamide (DCD) on nontarget microbial activity in soils was determined by measuring dehydrogenase and dimethyl sulfoxide reductase activity (DHA, DRA, respectively) in three differently textured soils under laboratory conditions. Dehydrogenase activity was measured with standard procedure recommended to evaluate side effects of environmental chemicals on general microbial activity in soils. The kinetic of inhibition were obtained by dose–response relationships and used to calculate the no observable effect levels (NOEL values) and the effective doses at 10% and 50% inhibition (ED₁₀ and ED₅₀), respectively. Negative effects on DHA and DRA, respectively, were observed only at rates approximately 40–100 times higher than the concentrations recommended in the field. Both DHA and DRA were affected more in the sandy than in the silty or clayey soil. Consequently, NOEL, ED₁₀, and ED₅₀ values were considerably higher in the clayey than in the silty or sandy soil. The heterocyclic N compounds DMPP and ClMP, respectively, were more effective in inhibiting DHA and DRA than DCD. At application rates used in the field as well as at concentration up to 25 to 90 times higher, the NIs concerned failed to affect general soil microbial activity in soils. Among the three NIs tested, the not marketed ClMP exhibited the strongest negative effects on soil microbial activity. At recommended application rates, the NIs tested should be considered as enviromentally safe.     

Influence of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) in comparison to dicyandiamide (DCD) on nitrous oxide emissions, carbon dioxide fluxes and methane oxidation during 3 years of repeated application in field experiments

In a 3-year field experiment, the effect of the nitrification inhibitor (NI) 3,4-dimethylpyrazole phosphate (DMPP) on the release of N₂O, CO₂, and on CH₄ oxidation, was examined in comparison to that of dicyandiamide (DCD) on N-fertilized and unfertilized experimental sites. Soil samples were analysed simultaneously for the concentrations of N₂O retained in the soil body, NH₄⁺, NO₂^-, NO₃^-, and for the degradation kinetics of DMPP as well as DCD. DMPP decreased the release of N₂O on fertilized plots by 41% (1997), 47% (1998) and 53% (1999) (on average by 49%) while DCD reduced N₂O emissions by 30% (1997), 22% (1998) and 29% (1999) (on average by 26%). In addition, the NIs seemed to decrease the CO₂ emissions of each fertilized treatment. DCD reduced the release of CO₂ by an average of 7% for the 3 years (non-fertilized 10%), and DMPP reduced it by an average of up to 28% (non-fertilized 29%). Furthermore, both NIs failed to affect CH₄ oxidation negatively. The plots that received either DCD or DMPP even seemed to function as enhanced sinks for atmospheric CH₄. DMPP apparently stimulated CH₄ oxidation of N-fertilized plots by ca 28% in comparison to the control. In total, DCD and DMPP reduced the global warming potential of N-fertilized plots by 7% and 30%, respectively. Further, DCD and DMPP diminished the amount of N₂O retained in the soil by 52% and 61%, respectively. The concentrations of NH₄⁺ remained unaffected by both NIs, whereas the amounts of NO₂^- diminished in the plots treated with DCD by 25% and with DMPP by 20%. In both NI treatments NO₃^- concentrations in the soil were 23% lower than in the control. DMPP and DCD did not affect the yields of summer barley, maize and winter wheat significantly. DCD was mineralized more rapidly than DMPP.     

Nitrous oxide emission from soil and from a nitrogen-15-labelled fertilizer with the new nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP)

Mineral-N fertilization can lead to a short-term enhancement of N₂O emission from cultivated land. The aim of this field study was the quantitative determination of the short-term N₂O emission after application of a fertilizer with the new nitrification inhibitor (NI) 3,4-dimethylpyrazole phosphate (DMPP) to winter wheat. NO₃^- and NH₄⁺ fertilizers labelled with ¹⁵N in liquid and granulated form were used in specific fertilizer strategies. N fertilizers with higher NO₃^- contents caused higher N₂O emission than NH₄⁺ fertilizers. For fertilizers with NIs, used in simplified fertilizer strategies with fewer applications and an earlier timing of the N fertilization, the N₂O release was reduced by about 20%. Of the total N₂O emission measured, 10-40% was attributed to fertilizer N and 60-90% originated from soil N. Besides the fertilizer NO₃^--N, the microbial available-N pool in the soil represented a further important source for N₂O losses. Compared to liquid fertilizers, the application in granulated form led to smaller N₂O emissions. For fertilizers with NIs, the decrease in the N₂O emission is mainly due to their low NO₃^--N content and the possibility of reducing the number of applications.     

Effects of 3,4-dimethylpyrazole phosphate (DMPP) on the abundance of ammonia oxidizers and denitrifiers in two different intensive vegetable cultivation soils

Purpose

Nitrification and denitrification in the N cycle are affected by various ammonia oxidizers and denitrifying microbes in intensive vegetable cultivation soils, but our current understanding of the effect these microbes have on N₂O emissions is limited. The nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP), acts by slowing nitrification and is used to improve fertilizer use efficiency and reduce N losses from agricultural systems; however, its effects on nitrifier and denitrifier activities in intensive vegetable cultivation soils are unknown.

Materials and methods

In this study, we measured the impacts of DMPP on N₂O emissions, ammonia oxidizers, and denitrifying microbes in two intensive vegetable cultivation soils: one that had been cultivated for a short term (1 year) and one that had been cultivated over a longer term (29 years). The quantitative PCR technique was used in this study. Three treatments, including control (no fertilizer), urea alone, and urea with DMPP, were included for each soil. The application rates of urea and DMPP were 1800 kg ha^?1 and 0.5% of the urea-N application rate.

Results and discussion

The application of N significantly increased N₂O emissions in both soils. The abundance of ammonia-oxidizing bacteria (AOB) increased significantly with high rate of N fertilizer application in both soils. Conversely, there was no change in the growth rate of ammonia-oxidizing archaea (AOA) in response to the applied urea despite the presence of larger numbers of AOA in these soils. This suggests AOB may play a greater role than AOA in the nitrification process, and N₂O emission in intensive vegetable cultivation soils. The application of DMPP significantly reduced soil NO₃^?-N content and N₂O emission, and delayed ammonia oxidation. It greatly reduced AOB abundance, but not AOA abundance. Moreover, the presence of DMPP was correlated with a significant decrease in the abundance of nitrite reductase (nirS and nirK) genes.

Conclusions

Long-term intensive vegetable cultivation with heavy N fertilization altered AOB and nirS abundance. In vegetable cultivation soils with high N levels, DMPP can be effective in mitigating N₂O emissions by directly inhibiting both ammonia oxidizing and denitrifying microbes.

     

The effect of soil pH and dicyandiamide (DCD) on N2O emissions and ammonia oxidiser abundance in a stimulated grazed pasture soil

Purpose

Nitrous oxide (N₂O) is a potent greenhouse gas which is mainly produced from agricultural soils through the processes of nitrification and denitrification. Although denitrification is usually the major process responsible for N₂O emissions, N₂O production from nitrification can increase under some soil conditions. Soil pH can affect N₂O emissions by altering N transformations and microbial communities. Bacterial (AOB) and archaeal (AOA) ammonia oxidisers are important for N₂O production as they carry out the rate-limiting step of the nitrification process.

Material and methods

A field study was conducted to investigate the effect of soil pH changes on N₂O emissions, AOB and AOA community abundance, and the efficacy of a nitrification inhibitor, dicyandiamide (DCD), at reducing N₂O emissions from animal urine applied to soil. The effect of three pH treatments, namely alkaline treatment (CaO/NaOH), acid treatment (HCl) and native (water) and four urine and DCD treatments as control (no urine or DCD), urine-only, DCD-only and urine + DCD were assessed in terms of their effect on N₂O emissions and ammonia oxidiser community growth.

Results and discussion

Results showed that total N₂O emissions were increased when the soil was acidified by the acid treatment. This was probably due to incomplete denitrification caused by the inhibition of the assembly of the N₂O reductase enzyme under acidic conditions. AOB population abundance increased when the pH was increased in the alkaline treatment, particularly when animal urine was applied. In contrast, AOA grew in the acid treatment, once the initial inhibitory effect of the urine had subsided. The addition of DCD decreased total N₂O emissions significantly in the acid treatment and decreased peak N₂O emissions in all pH treatments. DCD also inhibited AOB growth in both the alkaline and native pH treatments and inhibited AOA growth in the acid treatment.

Conclusions

These results show that N₂O emissions increase when soil pH decreases. AOB and AOA prefer different soil pH environments to grow: AOB growth is favoured in an alkaline pH and AOA growth favoured in more acidic soils. DCD was effective in inhibiting AOB and AOA when they were actively growing under the different soil pH conditions.     

Effect of fertilizers with the new nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate) on yield and quality of agricultural and horticultural crops

In 1997-1999, 136 field trials were conducted under various soil-climatic conditions in western and southern Europe in order to assess the effects of N fertilizers with the new nitrification inhibitor (NI) 3,4-dimethylpyrazole phosphate (DMPP) on the yield and quality of various agricultural and horticultural crops. Results show that DMPP may increase the mean crop yield (grain yield, winter wheat +0.25 t ha^-1, wetland rice +0.29 t ha^-1, grain maize +0.24 t ha^-1; tuber yield, potatoes +1.9 t ha^-1; corrected sugar yield, sugar beets +0.24 t ha^-1; biomass, carrots +4.9 t ha^-1, lambs' lettuce +1.9 t ha^-1, onions +0.5 t ha^-1, radish +4.6 t ha^-1, lettuce +1.4 t ha^-1, cauliflower +5.2 t ha^-1, leek +1.7 t ha^-1, celeriac +2.2 t ha^-1) and/or improve crop quality (e.g. reduced NO₃^- concentration in leafy vegetables). In some crops, the same yield level as obtained with the control (fertilizer without DMPP) was achieved with one fewer applications of N, or with a reduced N application rate. The positive effect of DMPP on crop yield was especially pronounced at sites with a high precipitation rate or intensive irrigation, and/or light sandy soil. DMPP had a negative effect on the crude protein concentration of winter wheat and on the biomass yield of spring-grown spinach.     

A lysimeter study of nitrate leaching from grazed grassland as affected by a nitrification inhibitor,dicyandiamide, and relationships with ammonia oxidizing bacteria and archaea

Nitrate (NO₃^?) can contribute to surface water eutrophication and is deemed harmful to human health if present at high concentrations in the drinking water. In grazed grassland, most of the NO₃^?‐N leaching occurs from animal urine‐N returns. The objective of this study was to determine the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO₃^? leaching in three different soils from different regions of New Zealand under two different rainfall conditions (1260 mm and 2145 mm p.a.), and explore the relationships between NO₃^?‐N leaching loss and ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA). The DCD nitrification inhibitor was found to be highly effective in decreasing NO₃^?‐N leaching losses from all three soils under both rainfall conditions. Total NO₃^?‐N leaching losses from the urine patch areas were decreased from 67.7–457.0 kg NO₃^?‐N/ha to 29.7–257.4 kg NO₃^?‐N/ha by the DCD treatment, giving an average decrease of 59%. The total NO₃^?‐N leaching losses were not significantly affected by the two different rainfall treatments. The total NO₃^?‐N leaching loss was significantly related to the amoA gene copy numbers of the AOB DNA and to nitrification rate in the soil but not to that of the AOA. These results suggest that the DCD nitrification inhibitor is highly effective in decreasing NO₃^? leaching under these different soil and rainfall conditions and that the amount of NO₃^?‐N leached is mainly related to the growth of the AOB population in the nitrogen rich urine patch soils of grazed grassland.     

Influence of temperature on mineralization kinetics with a nitrification inhibitor (mixture of dicyandiamide and ammonium thiosulphate)

Summary The influence of temperature on the action of a dicyandiamide nitrification inhibitor was studied during a laboratory incubation after the addition of ammonium sulphate labelled with ¹⁵N. In the control treatment, nitrification was only slightly affected by temperature and was rapid; on the 42nd day, two-thirds of the ¹⁵N was incorporated into the nitrate fraction while no further tracer was found in ammoniacal form. With the addition of dicyandiamide, the process was slowed down considerably when the temperature was maintained at 10°C, and only about 10% of the ¹⁵N was nitrified in 6 months. After 1 month of incubation at 10°C, a temperature increase to 15°C for 4 weeks modified the nitrification kinetics only slightly. However, as soon as the temperature reached 20°C, the beginning of dicyandiamide decomposition and an increase in the quantity of NO ₃ ^- -N was observed. The inhibition was measured by the nitrification index, which was greater than 80% as long as the temperature did not exceed 15°C, and decreased to 10% after 6 months; this value was reached only after 1 year in soil maintained at 10°C. The half-life of the NH ₄ ⁺ was decreased by raising the temperature. In the experimental conditions described, nitrification was inhibited by the dicyandiamide for at least 6 months provided the temperature did not exceed 15°C.     

Effects of biochar and 3,4-dimethylpyrazole phosphate (DMPP) on soil ammonia-oxidizing bacteria and nosZ-N2O reducers in the mitigation of N2O emissions from paddy soils

Purpose

Paddy fields are an important source of nitrous oxide (N₂O) emission. The application of biochar or the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) to paddy soils have been proposed as technologies to mitigate N₂O emissions, but their mechanisms remain poorly understood.

Methods

An experiment was undertaken to study the combined and individual effects of biochar and DMPP on N₂O emission from a paddy field. Changes in soil microbial community composition were investigated. Four fertilized treatments were established as follows: fertilizer only, biochar, DMPP, and biochar combined with DMPP; along with an unfertilized control.

Results

The application of biochar and/or DMPP decreased N₂O emission by 18.9–39.6% compared with fertilizer only. The combination of biochar and DMPP exhibited higher efficiency at suppressing N₂O emission than biochar alone but not as effective as DMPP alone. Biochar promoted the growth of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), while DMPP suppressed AOB and increased AOA. Applying biochar with DMPP reduced the impact of DMPP on AOB. The nirS-/nirK- denitrifiers were decreased and nosZ-N₂O reducers were increased by DMPP and the combination of DMPP and biochar. The abundance of the nirK gene was increased by biochar at the elongation and heading stages of rice development. Compared with fertilizer only, the application of biochar and/or DMPP promoted the abundance of nosZ genes.

Conclusion

These results suggest that applying biochar and/or DMPP to rice paddy fields is a promising strategy to reduce N₂O emissions by regulating the dynamics of ammonia oxidizers and N₂O reducers.

     

Effects of concentration,incubation temperature,and repeated applications on degradation kinetics of dicyandiamide (DCD) in model experiments with a silt loam soil

Summary The kinetics of dicyandiamide (DCD) decomposition were studied (at 80% water-holding capacity) in pretreated and non-pretreated soils, using model experiments. DCD was added in different concentrations (6.7, 16.7, and 33.3 g DCD-N g^–1 dry soil) and incubated at various temperatures (10°, 20°, and 30°C). Additionally, DCD decomposition was examined in sterile soil (with or without Fe₂O₃) after inoculation with a DCD-enrichment culture. In the sterile variant, (30°C)the applied dicyandiamide concentration remained constant, even after 36 days. In the sterilized and reinoculated variant, DCD disappeared within 7 days. Addition of Fe₂O₃ powder to the sterilized soil had no effect on DCD degradation. In the pretreated soils, DCD mineralization started immediately at all temperatures and concentrations without a lag phase. A temperature increase of 10°C doubled the mineralization rate. The mineralization rates were independent of the initial concentrations. In the non-pretreated soils (except at 30°C with 16.7 and 33.3 g DCD-N g^–1 dry soil) DCD decreased only after a short (30°C) or a long (10°C) lag phase. These results suggest that an inducible metabolic degradation occurred, following zeroorder kinetics.     

Elemental status (Cu,Mo, Co,B, S and Zn) of Scottish agricultural soils compared with a soil‐based risk assessment

Concentrations of six elements copper (Cu), molybdenum (Mo), cobalt (Co), boron (B), sulphur (S) and zinc (Zn) are summarized for Scottish advisory soil samples collected during the period 1996–2008. Accompanying cropping information indicated that the majority of samples collected for Co analysis were from grassland compared with B, S and Zn where sampling was predominantly prior to either potatoes or vegetables. The proportion of samples measured as potentially deficient [very low (VL) or low categories] were 80% for Co, compared with 50, 40, 38, 25 and 18% for Mo, S, Zn, Cu and B, respectively. Only S displayed a significant decline (ca. 2 mg S/kg) over this 13‐year period. However, comparison of Cu and Co data with some collected from an earlier time period (1973–1980) suggested little difference for Cu but a smaller number of VL and low Co status samples. A predicted risk assessment using soil parent material, texture and drainage status suggested that 22, 38 and 40% of the agricultural area of Scotland were at a high, medium and low risk of Cu deficiency; comparable numbers for Co were 48, 30 and 22%. The reliability of the risk assessment was tested using a sub‐set of advisory samples with specific information on soil series. Of the soils predicted to have a high risk of Cu deficiency, 52% actually fell into the ‘deficient’ status. A similar comparison for Co indicated 90% of the samples predicted as having a high risk of deficiency were measured as VL or low.     

The uptake of nutrients by sunflower plants (Helianthus annum) growing in a continuous flowing culture system,supplied with nitrate or ammonium as nitrogen source

Sunflower plants (Helianthus annuus) were grown in a continuous flow nutrient system, in which nitrogen was supplied, under controlled pH conditions, in either the NO₃-or NH₄-form. Nutrient uptake and distribution, as well as dry matter production of the plants, was followed over the growth period. The results obtained may be summarized as follows: 1. At all stages in development, growth was somewhat greater in the plants of the NO₃-treatment, but the difference between the two treatments was not large. The similarity in the behaviour of plants in the two nitrogen treatments is discussed in relation to the maintenance of a high pH in the nutrient medium. 2. The mean rates of uptake of Ca, Mg, K, and Na, expressed per unit root length, were all higher in the NO₃-fed plants. For P, the mean rate of uptake was higher in the NH₄-fed plants. 3. The levels of K, Ca, Mg, and Na, per unit dry weight, were higher in the NO₃-fed plants, but for P the converse was true. 4. The higher uptake of Ca and Mg by NO₃-fed plants was reflected in the higher concentrations of these elements in the leaves. In the case of K, accumulation occurred in the roots. 5. From the results of selected harvests, it was found that total nitrogen uptake was higher in the NO₃-fed plants.