Dear Dr. Selva

Some of the upland farmers in the Philippines dont use Nitrification inhibitors because they are less likely to show an economic benefit when high N rates are used in the field. Nitrogen losses at high N application rates are not likely to affect yield as much if lower N rates are applied (fewer bushels per acre are gained with each additional level of N at the high levels).

Though it needs further verification for my statement.

Best Regards,

Wilbert

In sri Lanka also nitrification inhibitors are not in use as rearing cattle in large scale are done by only a few companies. Anyway leaching of nitrates is a problem though no monitoring system is not available.

My professor Dr. Rajendra Prasad and my friend Prakasa Rao, E.V.S. (both RG members) researched extensively on the topic of N leaching in Indian soils under different cropping systems. I suggest you to seek their views by sharing your question with them.

Dear Selva,

In Canada, fertilizers and agronomic supplement products are regulated under the ‘Fertilizers Act and Regulations’.  This ‘act’ stipulates that all regulated fertilizer and supplement products must be effective and safe for human, animal and plant population and for the environment. The Canadian Food Inspection Agency (CFIA) has the mandate to regulate these products.

Nitrification inhibitors fall under the ‘supplements’ category.  Therefore, they are regulated and subject to registration that requires a comprehensive pre-market assessment prior to their sale in Canada.

This pre-market assessment generally includes product safety assessment, efficacy assessment, and thorough scrutiny of other supporting information such as nature of the product, manufacturing method, complete list of ingredients and their source materials.

At present one well known nitrification inhibitor: Dicyandiamide (DCD) is registered to be sale in Canada under the product name ‘Agrotain Plus’, while another product: Nitrapyrin is not registered to be used in Canada.

-SJ

Thank you all for your inputs to date and I hope you will continue your interest on the topic.

Please allow me to expand the context of my question from New Zealand's perspective. DCD has been well researched by our soil scientists in NZ for its efficiency to minimise NO3 leaching and N2O emissions from urine patches. Many papers have already been published (e.g. Agriculture, Ecosystems and Environment). Urine patches (rather than fertiliser-N) had been the focus for our scientists and policy makers since much of the environmental adverse effects have been attributed to N flows resulting from urine deposited by grazing livestock, particularly dairy.

As a result of a series of successful soil research, DCD was promoted to be used on farms in NZ. Unfortunately, minute traces of DCD began to appear in dairy milk which halted the use of DCD in NZ. DCD is not classified as a hazardous substance hence its use is not regulated here. The current and temporary ban has been adhered by the dairy industry voluntarily until DCD is considered as safe to use.

The other key issue is that there are no World Health Organisation (or any other health authority) standards or guidelines for safe DCD residues in food or food products. In the absence of such information food product exporting nations have to be extra cautious hence complete stoppage of DCD use on farms in NZ. You could understand our reaction to the use of DCD in NZ since our farming exports are worth nearly US$25Billion and 50% of this is from dairying.

Another issue we are facing is the potential for DCD entering freshwater systems from farm soils. If enters, DCD could inhibit nitrification in water which could lead to ammonia (NH3) build-up in water which could have more negative effects than NO3 in freshwater systems. Some preliminary work by our freshwater scientists have shown the potential for DCD residues' entry to freshwater systems.

Having said all the above, as I mentioned in my original question, the research on nitrification inhibitors have been in existence for more than 5-6 decades. While continue with this effort we also need to begin to research the pathways of such inhibitors thoroughly before using them widely. If they are safe, I do believe they can be added among our existing environmental mitigation/remediation tools in our sustainability toolbox!

Apart from soil, water and environmental scientists, food-safety and health researchers and regulators also have a responsibility in providing safe threshold levels for food products, without which many useful and well researched chemical/biological tools may not be deployed to improve environmental quality whilst continue to feed the ever growing world.

Please do continue with your useful comments and I hope other experts can also join us in this useful discussion.

Dear Selva,

The additional information about the context of this question was very useful.

As you correctly stated, there is no any International guidelines (such as those from World Health Organization) regarding DCD, perhaps because DCD at the trace levels found was not regarded as food safety issue.

The concern about DCD trace levels in some food products began in North America for a completely different reason, independent from the New Zealand case. 

Some details on that aspect can be found in the paper attached below (which is freely available from the company website).

In Canada, the registered fertilizer product I mentioned previously is a liquid N fertilizer (Urea-Ammonium Nitrate or UAN with DCD as an additive) that is recommended for application by injection into soil, usually as a side-dress application at early stage of growth for grain crops such as maize.  The time lag between this application and the harvest of these crops is 4 to 4.5 months.

-SJ

Dear Susantha

Thank you for the material on tracking DCD residues in food. I found it very useful. The material does refer to the NZ case. It appears that the US company which produced the analytical method was swift and smart to develop very precise methods to detect traces of DCD, melamine and other N based adulterations in food. The melamine (ironically melamine can be produced from DCD) milk powder adulteration case in China was very popular which also implicated NZ because NZ milk powder was used by the culprits on that occasion. Since then NZ & Chinese governments and the respective milk companies had taken stringent steps to avoid similar incidents and the ongoing routine batch analyses provides additional reassurance for the milk powder consumers.

Judging by the Canadian use of DCD and as you pointed out since the time lag is sufficient, any DCD to remain in its original form in the plant tissue is highly unlikely. I think in the NZ case our grazing cycles are frequent which may not allow DCD to fully breakdown in plant tissue. Unlike popular belief, there is sufficient evidence for plants to directly absorb organic-N compounds such as urea from soil hence a simple amide such as DCD can directly enter plant by active absorption. Provided sufficient time is given for the plant metabolic process for amides to be synthesised as protein there should not be any residual issues. It appears that with well disciplined agronomical practices DCD may be used on grazed pasture without residues entering the food chain. However, for this practice to be successful there should be a full co-operation from all participating farms. Then, there is also the issue of DCD residues entering freshwater system. Since in NZ we are targeting urine patches to minimise nitrification soil injection of DCD may not be effective. Canadian practice is correct for the purpose, i.e. efficient use of applied-N.

Selva

Indian research involved the use of natural, biodegradable materials such as neem (Azadirachta indica) and karanj (Pongamia pinnata) seed/kernal oil cakes and essential oils isolated from aromatic plants. Neemcake-coated urea is marketed in India. In addition to being a nitrification inhibitor, neemcake supplies plant nutrients and is a natural pesticide. It also adds organic matter to the soils.

Future research should focus on such natural materials which are environment-friendly, affordable, biodegradable and will not leave any harmful chemicals in the end products.

The Natural nitrification inhibitors like neem work under rainfed conditions unlike the chemical inhibitors. we have observed that vitex leaf coating also is working well under rainfed alfisol conditions.This reduces nitrous oxide emission. 

I think in future we need to try some more plant based materials which work both under irrigated as well as rainfed conditions 

Natural nitrification inhibitors such as neem are organic compounds and how effective would it be to inhibit nitrification of the urine patches?

 DCD is soluble and that is why effective to treat urine patches. The solubility of the product has proved to be its disadvantage - moving into the food stream. 

Improving NUE has been an enigma? Try reducing one loss you end up increasing the other. 

To me a practical solution is regulating the dairy grazing so that there is no concentration of a urine patch in the field.

Dear Desouza

As you pointed out solubility of the inhibitor is important for the inhibitor to be effective. I hope the neem research colleagues can shed some light on the mechanism of neem (particularly solubility) inhibiting nitrification.

As for DCD, my presumption is soluble DCD is entering plant through foliage. Similar to plant absorbed NO3, DCD requires sufficient time to be synthesised into protein. If the grazing commences before full conversion of the DCD into protein it has the potential to leave a residue in dairy milk. May be longer withholding period is the answer or injecting DCD into soil.

As for the high N concentration in urine patches, the challenge is for the animal physiologists/nutritionists to reduce excess NH3 build up in blood (which becomes urea) by low-N :high carbohydrate feed.

Kind regards

Selva

Attached is a paper that gives some details on the Neem. You can also look for other articles by Suri and R. Prasad.

DCD in you conditions (temperate), may persist for longer time and therefore gets into the dairy cows. In the tropics, DCD due to high temperatures is not that effective as an inhibitor. 

In China DCD is not used anymore. Vegetable oil coated controlled release urea is an effective way to increase NUE and to reduce its nitrification as well as nitrite leaching. The coating can be degraded beacuse it comes mainly from vegetable oil. 

Dear Xiao

I am very pleased countries such as India and China have developed their own techniques to improve NUE by using natural products. In NZ, NUE from applied N fertilisers have not been considered as a major issue with the exception of the horticultural industry (e.g. vegetable production) where depleted organic-C in soil due to regular cultivation coupled with large basal dressing of fertilisers appear to drive high N leaching losses. May be NZ horticultural industry could benefit from the use of slow release N fertilisers.

Fertiliser-N is shown to have been utilised efficiently under NZ pastoral system where high instantaneous N immobilisation (NH4 microbial uptake owing to high soil organic matter content) complemented by smaller application rates (25-50 kg/application) and smaller annual N loading (150-200 kg N/ha/year). Good NZ clover-rye grass based pastoral farmers see fertiliser-N as a strategic supplement rather than substitute for clover fixed N of 200 kg/ha/year in NZ.

The major NUE setback for the pastoral farming in NZ lies within the heavily urea laden cow urine patches. The challenge in NZ is to improve NUE in grazed pasture systems, particularly dairying. Owing to smaller urine patches sheep farming has superior NUE than dairying.

NUE in dairying can be improved substantially by indoor feeding of cows, but this is neither practical nor cost effective for NZ farmers. There is also general farming and industry philosophy of supporting outdoor farming. Despite this there have been increasing number of farmers controlling winter grazing leaching by providing temporary housing. There are also added benefits of avoiding soil and pasture damage during wet winters. But the spring and summer leaching of N from cow urine patches still remains as a firm challenge in NZ.

Kind regards

Selva