Viewpoints from BASF: Can technology provide the key to smarter nitrogen use? (Part 1)

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. The question is handled in three parts. The first part will answer why nitrogen use efficiency has to be increased. Part two will give an overview about possible measures to improve nitrogen use efficiency. Finally the latest technologies to increase nitrogen use efficiency offered by BASF are described in part three.

Dr. Markus Schmid  After earning his PhD in chemistry, Markus Schmid joined BASF as a Lab Team Leader in Polymer Research. After various job assignments in R&D and Strategy Development, he took over responsibility as Head of R&D Solutions beyond Crop Protection at BASF’s Crop Protection Division in Limburgerhof and is now responsible for the group of technical marketing and the product introduction of Limus .

Dr. Wolfram Zerulla  Agronomist, more than 30 years with BASF, fertilizer specialist especially in enhanced efficiency fertilizers, member of International Fertilizer Industry Association (IFA), Fertilizers Europe (FE) and Industrieverband Agrar (IVA, Germany)

Dr. Gregor Pasda   Agronomist, more than 20 years with BASF, fertilizer specialist especially in nitrification and urease inhibitors

Part 1: The Urgent Case for Increasing Nitrogen Use Efficiency

Nitrogen is essential for plant growth, development and reproduction. Deficiencies in nitrogen can stunt growth, weaken plants and reduce crop yields.

Plants require large amounts of nitrogen for healthy growth, and they receive that nitrogen from many sources. While it’s one of the most abundant elements on earth, nitrogen delivered to plants by the atmosphere, precipitation, soil and decaying raw materials (such as crop residues and animal manure), is not enough to ensure sufficient nitrogen nutrition for crops. Modern agricultural production requires more.

In the early 1900s, scientists at BASF set out to find a way to make the manufacture of ammonia feasible on a large scale to better meet the nitrogen needs of commercial agriculture. German physical chemist Fritz Haber and industrial chemist Carl Bosch each played a role in developing the Haber-Bosch process, a method of directly synthesizing ammonia from hydrogen and nitrogen. Each received Nobel prizes for their scientific achievements, and the process they developed still ensure the protein supply for about 50 percent of the world’s population (ERISMAN et al. 2008).

Despite all of the contributions that nitrogen fertilizer has made to crop production, it is possible to have too much of a good thing. Over-application and inefficient use due to unmanaged nitrogen losses can have far-reaching effects.

• Diminished nitrogen nutrition reduces yield potential, resulting in economic losses for farmers
• Ecological effects include acidification of soil, reduced biodiversity and eutrophication of soil and water
• Effects on human health can include the negative impacts of air pollution and smog

The primary goal of nitrogen best management practices is attaining high nitrogen use efficiency, ensuring the most effective use of nitrogen fertilizer – optimizing crop yields while minimizing nitrogen losses to the environment.

Finding Balance in the Nitrogen Cycle

Nitrogen exists in various forms in soil and transforms from one form to another (see figure 1) as it moves through the soil to crop, water and the air. Whether nitrogen is naturally present in or added to the soil, transformative processes including mineralization and nitrification increase the availability of nitrogen to plants. Other processes, such as fixation, volatilization, denitrification and leaching result in nitrogen losses from the area where it would be available to plants (i.e. the root zone).

Figure 1: nitrogen cycle

Elementary nitrogen (N2) can be transferred into reactive nitrogen by lightning, symbiotic bacteria in legume roots and technical processes like the above-mentioned Haber-Bosch process.

Organic bound nitrogen, such as is present in crop residues, animal manure and soil organic matter, is converted to inorganic nitrogen through the process of mineralization. Ammonium, the first molecule of this natural process, is further transferred by soil bacteria into nitrite (NO2-) and finally to nitrate (NO3-) in another process called nitrification. Under specific soil conditions (mainly oxygen deficiency), nitrate is transferred into gaseous nitrogen components like NOx, N2O and elementary nitrogen through the de-nitrification process. With the last compound, the nitrogen cycle is complete.

During these conversions nitrogen losses occur. Unfortunately these losses increase with increasing amounts of applied fertilizers independent if they are of organic or mineral origin. Therefore agriculture in general and intensive agriculture in particular (which is necessary to produce enough food) leads to higher nitrogen losses compared to a natural unaffected environment.

These losses involve compounds (ammonia, nitrate and nitrous oxide) that have been shown to have negative impacts on the environment and human health.

Ammonia (NH3): Main sources of these gaseous losses are storage and application of organic manure, the application of ammonium containing fertilizers on alkaline soils and of urea based fertilizers respectively which are the dominant nitrogen sources globally.

Ammonia as a gas is transported over long distances and can react with other atmospheric compounds to form aerosols, which can result in smog. Ammonia is also deposited to natural biotopes and effects there an unwanted nitrogen fertilization and acidification of the soils. Both of these effects can decrease biodiversity (BOBBNIK et al. 1998) and negatively impact human health (ANONYMUS 2014).

Nitrate (NO3-) is the dominant nitrogen form involved in nitrogen nutrition. Due to its negative charge it cannot bind to the negative charge of soil particles which makes nitrate highly mobile in soil, causing it to leach into ground and surface water. Sources of nitrate include many kinds of organic and mineral fertilizers because all applied nitrogen eventually converts into nitrate. Excess nitrate can lead to eutrophication of waterbodies, negatively impacting water quality and biodiversity.

A direct negative impact of nitrate on human health is hardly reported. However, recent investigations show that nitrate seems to be important for energy transport in human bodies (PRESLEY et al. 2011). Problems occur if nitrate is converted into nitrite by bacteria. Therefore the threshold value for drinking water is low to avoid “blue baby syndrome” or the danger of stomach cancer due to bacteria-contaminated drinking water with high contents of nitrate.

Nitrous oxide (N₂O) is another gaseous compound that might be emitted during the nitrification and denitrification process. It has a very high greenhouse gas potential (296 times more so than CO₂) and therefore contributes to climate change.

Many countries have recognized these issues. Governments try to limit the negative impacts of nitrogen in its different forms by legislation and international conventions. Examples of efforts to address these issues include the Gothenburg Protocol (involving multiple countries and the European Union), and the National Emission Ceilings (NEC) directive in Europe regarding ammonia emissions, the nitrate-directive in Europe, “Clean water act” in the USA regarding nitrate leaching and the UN Framework Convention on climate change regarding N₂O emissions.

Intensive fertilization remains a critical step in maximizing crop yields to nourish the ever-increasing world population. The ultimate goal of nutrient management, then, is to maximize nitrogen use efficiency by applying adequate amounts at the appropriate times, while minimizing nitrogen losses to the environment.

Optimizing nitrogen use efficiency is an approach that has great potential for helping achieve this balance between maximizing agricultural production while minimizing environmental impacts. In regions such as the Americas, Europe and Asia, the ideal outcome would see reductions in nitrogen application rates without yield loss. In developing regions, such as Africa, increasing nitrogen use efficiency has the potential to allow for increased nitrogen fertilization, resulting in higher yields. As we look to the future, we must strive to achieve this balance.

Nitrogen Use Challenges: The Chinese Dilemma

In the short span of two decades, China experienced a transformation from a net importer of food to a more balanced situation. This has been a significant achievement, considering that the country’s history includes periods of malnutrition and famine, where it was unable to sufficiently feed its people.

The credit for this massive shift is intensification of agriculture. An important part of this intensification was the increase of mineral nitrogen fertilizer production and use. Today, China is the world’s largest mineral fertilizer producer (2013: 36,8 Mio t/year, 16,6 Mio t P2O5, 4,6 Mio t K2O; ANONYMUS 2016) and the country with the highest rate of nitrogen application per crop (ZHENLING et al. 2010).

The primary mineral nitrogen fertilizers produced in China are urea and NPK-fertilizers in which the nitrogen component is also based on urea. Urea is cost-effective, has a high nitrogen content, and is considered safer and easier to store than many other fertilizer options in common use. For those reasons, it is used extensively as a nitrogen source in agriculture, and accounts for more than 50 percent of the world’s nitrogen-based fertilizers.

Urea-based fertilizers are recognized as a contributing source of ammonia emissions. The only mineral fertilizer that shows higher ammonia emission rates is ammonium bicarbonate, which is still on the Chinese market.

China is facing huge environmental challenges based on ammonia emissions, primarily originating from agriculture (LIU et al. 2014). These emissions can contribute to a number of issues, including smog, contamination and eutrophication of ground and surface water bodies due to nitrogen input, plant damage and toxicological problems for the population. Additionally, nitrate leaching from arable soils and N₂O emissions during nitrogen turnover in the soil impacts the environment in a negative way.

For a future sustainable development of the country a reduction of all these emissions are therefore necessary. A reduction of these emissions and as a consequence a reduction of the nitrogen application rate is the only way to improve nitrogen use efficiency.

This problem is also recognized and addressed by the Chinese agricultural science and considered already in the five years plan 2013 of the Chinese government. The goal for the future therefore is to improve nitrogen use efficiency significantly without reducing the yield potential of Chinese agriculture (CHEN 2013).