Nitrification inhibitors.
This is the first part of our blog on slow release fertilizers: nitrification inhibitors (NI) in turf. The second covers urease inhibitors (UI). Turf fertilizers that contain nitrogen inhibitors like DMPP and Didin, are often termed nitrogen stabilizers. Products such as these offer an alternative to slow release fertilizers like Sirflor 38.
- NI reduce emission of nitrous oxide (N2O) from the soil, and reduce leaching of soil nitrate (NO3–) out of the root zone.
- UI decrease ammonia (NH3) losses after urea hydrolysis.
Both NI and UI slow down nitrogen losses, and give turf more time to take up nitrogen. This means when you feed your turf it is giving it the best chance to take up N.
What is Nitrification?
Nitrification is the action of microbes to convert ammonia to nitrate, and is an important step in the nitrogen cycle in the soil.
The nitrification rate depends on several factors. These include:
- The soil temperature;
- The presence or absence of soil oxygen;
- The soil moisture content;
- pH, and
- The actual fertilizer you use.
How do Nitrification Inhibitors work?
Nitrification inhibitors (NI) like Didin, temporarily slow Nitrosomonas bacteria in the soil. These microbes are responsible for the conversion of ammonium N to nitrite. Nitrobacter, amongst other bacteria, then convert this nitrite to nitrate in the soil. When soil temperatures are greater than 10°C, nitrification takes around two to four weeks, and as the soil temperature increases the nitrification rate increases.
Nitrification inhibitors reduce nitrate leaching, keep nitrogen in the ammonia form longer, and increase nitrogen efficiency. Do realsie that if a turf canopy intercepts an inhibitor before it reaches the soil, there is a good chance that nitrification and denitrification will continue. These need to reach the soil to work effectively and so placement is very important. 1Bell, M.J., Rees, R.M., Cloy, J.M., Topp, C.F.E., Bagnall, A. and Chadwick, D.R. (2015b) Nitrous oxide emissions from cattle excreta applied to a Scottish grassland: Effects of soil and climatic conditions and a nitrification inhibitor. Science of the Total Environment, 508, pp.343- 353. If this occurs then using these is a waste of time and money.
Temperature Effect on Nitrification
Nitrification is very temperature dependent, and slows to virtually nothing at soil temperatures below 10°C. Above 23°C, and the nitrification rate is at its maximum.
In fact, soil temperature is the major factor influencing how long NIs work in the soil. For example, DCD and DMPP are not as efficient when you use these above a temperature of 16°C2Chen, D., Suter, H., Islam, A., Edis, R., Freney, J.R. and Walker, C.N. (2008). Prospects of improving efficiency of fertiliser nitrogen in Australian agriculture: a review of enhanced efficiency fertilisers. Australian Journal of Soil Research 46, 289-301..
Nitrification and Soil Oxygen.
Oxygen is needed for nitrification to occur, and a water-filled pore space above 60% has a negative impact. After heavy rainfall the water filled pore space increases but nitrification resumes, once oxygen levels increase when free water drains from the soil profile. The entire process stops due to a lack of oxygen if a soil floods or becomes waterlogged. Ironically, a lack of water also has a negative impact on this process.
So be aware that nitrification is fastest in well-aerated soils, that are close to field capacity.
Inhibitors and soil pH.
Turf can also take up nitrogen as ammonium. When turf takes up nitrogen as ammonium it causes an increase in P uptake and of micronutrients such as Mn and Fe3Marschner H, 1995. Mineral Nutrition of Higher Plants. https://doi.org/10.1016/B978-0-12-473542-2.X5000-7.
As a soil pH increases, DCD and DMPP are less effective 4Guardia G, Marsden KA, Vallejo A, Jones DL and Chadwick DR. 2018. Determining the influence of environmental and edaphic factors on the fate of the nitrification inhibitors DCD and DMPP in soil. Science of the total environment, 624: 1202-1212..
Reduce nitrogen leaching.
Nitrate is much more mobile than ammonium in the soil. In soils low in clay and high in sand (modern-day sports turf constructions), NIs reduce N leaching. 5Ferguson RB., Cahoon JE, Hergert GW, Peterson TA, Gotway CA, and Hartford AH. 1995. Managing spatial variability with furrow irrigation to increase nitrogen use efficiency. p. 443–464. In P.C. Robert et al. (ed.) Site-specific management for agricultural systems. ASA, CSSA, and SSSA, Madison, WI
Better Colour.
When you use NIs on turf you tend to see a dark green colour response. There are two reasons for this:
- Turf has to take up the N as ammonium, which gives a dark green colour and
- The lower soil pH around the roots, means iron and manganese are more available for uptake.
What’s on the market?
- Nitrapyrin is the most popular Nitrogen Inhibitor in agriculture, but is volatile and needs to be placed into the soil. Also, the nitrogen inhibitor, Nitrapyrin is a bactericide, and it kills microbes in the soil. It is persistent in cold soils in comparison to warm soils, where it lasts 6-8 weeks.
- DCD or Didin lasts 25-55 days and quickly moves out of the root zone after rainfall or irrigation. In Australia, Didin is the most popular Nitrogen Inhibitor in turf and you find this in Umaxx and Uflexx. The rate of Didin is 2-10% of the total N content. It comprises 65% N, and contributes to soil organic nitrogen.
- DCD is more mobile than DMPP because it is very soluble in water. In sandy soils and in high rainfall areas, DCD is likely to leach, but it tends not to move in soils with a high CEC and organic matter content.
- DMPP is in the Entec range of fertilizers. It is active for 25-70 days, immobile in the soil, but less effective at high temperatures. DMPP claims to be 15-30x more efficient than DCD, and stays in the top 150mm of the root zone. Inhibition occurs at rates of 0.5–1.5 kg/Ha and it reduces nitrate leaching without leaching itself.
- Piadin contains a mixture of 1H-1,2,4-triazole and 3-MP, and is a stand alone liquid NI. You can use this in several ways. For example, you can use this as a pre or post fertilizer spray to a turf surface. Alternatively, you can add this to a spray tank and turn a urea or ammonium based liquid or soluble into an inhibited fertilizer. This high flexibility means that you are not tied to prefomulated products that contain an NI.
What Nitrification Inhibitor works best?
The highest N losses are on sandy soils, poorly drained soils, and in these cases, NI’s give good results.
In heavier soils, like push up greens or fairways and sports grounds, Didin is the best option but in sandy greens or sports grounds, DMPP and Piadin work best6Guo Y, Naeem A and Mühling KH. 2021. Comparative Effectiveness of Four Nitrification Inhibitors for Mitigating Carbon Dioxide and Nitrous Oxide Emissions from Three Different Textured Soils. Nitrogen 2021, 2(2), 155-166; https://doi.org/10.3390/nitrogen2020011.
Examples of Inhibitors | ||
Common Name | Chemical Name | Activity |
DCD, Didin | Dicyandiamide | Nitrification Inhibitor |
DMPP, Entec | 3,4-dimethylpyrazole phosphate | Nitrification Inhibitor |
Nitrapyrin, N-Serve | 2-chloro-6-(trichloromethyl)-pyridine | Nitrification Inhibitor |
DMPSA | 2-(3,4-dimethyl-1H-pyrazol-1-yl) succinic acid isomeric mixture | Nitrification Inhibitor |
NPPT | N-(2-Nitrophenyl) phosphoric triamide | Urease Inhibitor |
NBPT, NBPT, nBTPT, or Agrotain | N-(n-butyl) thiophosphoric triamide | Urease Inhibitor |
PPD, PPDA | phenyl phosphorodiamidate | Urease Inhibitor |
References
Graduated from Newcastle University with an Hons Degree in Soil Science in 1988, Jerry then worked for the Sports Turf Research Institute (STRI) as a turf agronomist before emigrating to Australia in 1993.
He followed this by gaining a Grad Dip in Business Management from UTS. He has worked in a number of management roles for companies as diverse as Samsung Australia, Arthur Yates and Paton Fertilizers.
He has always had a strong affinity with the Australian sports turf industry and as a result he established Gilba Solutions as an independent sports turf consultancy in 1993. Jerry has written over 100 articles and two books on a wide range of topics such as Turf Pesticides and Nutrition which have been published in Australia and overseas.