BASF: Reducing nitrogen losses (Part 2)

Can technology provide the key to smarter nitrogen use? Recently three fertilizer experts Dr. Markus Schmid, Dr. Wolfram Zerulla, Dr. Gregor Pasda from BASF received invitation from Agropages to share their professional viewpoints on this question. After describing in the first part the benefits of nitrogen fertilization as well as the environmental problems related to the application of nitrogen containing organic and mineral fertilizers, BASF focus in this second part on measures to reduce nitrogen losses in form of ammonia (NH3), nitrate (NO3-) and nitrous oxide (N2O).


Part 2: Reducing nitrogen losses

Farmers have lots of possible measures available to apply nitrogen fertilizers in a sustainable way. Already the first decision, the selection of the right fertilizer type, defines the loss potential during the growing season: For example, if they select a urea-based fertilizer the potential of ammonia loss is much higher compared to ammonium nitrate-based fertilizers. If they use a nitrate fertilizer under tropical conditions nitrate leaching can be anticipated.

So choosing the right fertilizer can help make a difference in nitrogen losses, although options aren’t always available. In China, more than 80 percent of nitrogen fertilizers are urea-based. Due to production focus and distribution channel issues, most farmers are forced to use urea-based fertilizers.

Once a fertilizer type is selected, farmers can minimize nitrogen losses by utilizing appropriate application methods and timing. With the right information and tools, there is an opportunity to reduce nitrogen losses to processes such as volatilization, leaching and denitrification.

Minimizing Volatilization

One method for applying urea to minimize losses is to incorporate it into the soil. Lab and field trials in Europe and the U.S. showed that incorporating urea into the soil at a depth of 5 centimeters is not effective in reducing NH3 emissions. Emissions are significantly reduced when the urea is “buried” at least 10 cm deep (Tab. 1). Urea soil incorporation before seeding can be done with spring crops, such as corn and malting barley, so that crops will not be disturbed. However, it’s not possible in other crops, such as winter cereals, pasture and winter oilseed rape, which need an over-top application of fertilizers.

Table 1: Ammonia losses from urea applied on top soil or incorporated into the soil.

A simple and cost-effective option for managing volatility and reducing ammonia losses from urea-based fertilizers is to use a urease inhibitor, such as Limus® nitrogen management from BASF. Limus® is the latest development in urease inhibitors, and is the only urease inhibitor on the market offering two active ingredients for broad protection against nitrogen loss and formulation stability. Additional details and technical information related to Limus® are addressed in more detail in part 3.

Reducing the Risk of Leaching

Ammonium sulfate and ammonium nitrate fertilizers like ammonium nitrate, calcium ammonium nitrate and NPK fertilizers based on ammonium nitrate compounds are rapidly transferred into nitrate under normal weather and soil conditions (see first part of the publication). Because nitrate as well as soils are negatively charged, nitrate can be translocated easily and can also be leached into the groundwater.

Leaching occurs when there is too much precipitation or irrigation after fertilization. A reliable weather forecast regarding high rainfall on farmer´s site hardly exists. There are also no agricultural measures known to avoid leaching under high rainfall conditions. Neither incorporation of the fertilizer into the soil nor a fertilizer placement helps to avoid such losses.

One approach for reducing the likelihood of leaching is to split the application of nitrogen fertilizers, although this can impact a farmer’s investment by increasing the time, machinery and energy to make multiple applications.

Another option is to consider nitrification inhibitors, which can reduce the risk of leaching for a substantial amount of time following fertilizer applications. Nitrification inhibitors influence the metabolism of the bacteria Nitrosomonas, which is responsible for the transformation of ammonium into nitrite. DMPP (3,4-dimethylpyrazole phosphate) is one example of a nitrification inhibitor, and is available from BASF. Additional details and technical information related to DMPP are addressed in more detail in part 3.

Dentrification

N2O-emissions arise from denitrification or during the nitrification process (see first part). Few options existed for managing denitrification, except for reducing the amount of fertilizer applied – with obvious impacts to overall yield. Nitrification inhibitors, such as those discussed in the previous part, can reduce N2O-emissions by an average of 50 percent (AKIYAMA et al. 2010; RUSER and SCHULZ, 2015).

Other Tools

There are many tools available for farmers to define the right amount of nitrogen fertilizer needed for the specific crop: Soil analysis, for example, helps to detect the amount of nitrogen available to plants in the soil in spring or during the vegetation period. This allows farmers to adjust the amount of supplemental fertilizer required to meet the plants’ needs.

Plant tissue analysis can help farmers determine if plants are optimally nourished. Using optical and spectral methods, it is possible to measure the nitrogen status of a crop as it is growing, with opportunities to be very site-specific for those farmers who employ precision agriculture techniques. It also allows farmers to be more precise in determining when to time a second nitrogen application. Both are well-established measures to avoid over-fertilization.

While most farmers would agree that their goal is to balance nitrogen application and crop uptake, uncertainties related to weather, pests and unmeasured nitrogen losses often lead to over-application as farmers try to avoid undernourished crops.

So it is obvious that the selection of the right fertilizer is key for a sustainable nitrogen fertilization. Besides the already described technology of urease and nitrification inhibitors, slow release and controlled release fertilizers are also a tool to reduce losses. However, they are very expensive to produce and therefore up to now not suitable for common agriculture from a price perspective. Also the release patterns do not fit perfectly with the requirements of fast growing annual crops. The market for such fertilizers are therefore ornamentals, nurseries and lawns.

With so much complexity in farming, many of these options are overlooked as farmers face so many other decisions and operational costs. However, as the need for nitrogen use efficiency moves up in priority, more and more farmers are turning to new technologies to realize the economic and environmental benefits of smart nitrogen use.