The environment currently has changed. While we have a large grain harvest on the horizon, with the 2022/23 maize harvest estimated at 16,4 million tonnes, the second largest on record, and soybeans at a record 2,8 million tonnes, the prices of these commodities have declined by roughly 15% y/y.
Moreover, agricultural machinery sales have been robust in the past few years.
Therefore, farmers will likely slow the purchases in the future as the need for replacements of older machinery may not be as high.
Moreover, unlike the past few years, where interest rates were more accommodative, the rising interest rates will continue to pressure farmers' finances.
Also worth noting is that the relatively weaker rand/dollar exchange rates will negatively influence the farmers' machinery buying decisions.
Nitrogen is one of the most important nutrients for plant growth and hence heavily applied in agricultural systems via fertilization. Nitrification, that is, the conversion of ammonium via nitrite to nitrate by soil microorganisms, however, leads to nitrate leaching and gaseous nitrous oxide production and as such to an up to 50% loss of nitrogen availability for the plant. Nitrate leaching also results in eutrophication of groundwater, drinking water and recreational waters, toxic algal blooms and biodiversity loss, while nitrous oxide is a greenhouse gas with a global warming potential 300× greater than carbon dioxide. Logically, inhibition of nitrification is an important strategy used in agriculture to reduce nitrogen losses, and contributes to a more environmental-friendly practice. However, recently identified and crucial players in nitrification, that is, ammonia-oxidizing archaea and comammox bacteria, seem to be under-investigated in this respect. In this review, we give an update on the different pathways in ammonia oxidation, the relevance for agriculture and the interaction with nitrification inhibitors. As such, we hope to pinpoint possible strategies to optimize the efficiency of nitrification inhibition.
Nitrification is the step in the nitrogen cycle that links the oxidation of ammonia (produced from the degradation of organic matter) to the loss of fixed nitrogen in the form of dinitrogen gas. It is performed by a few different groups of microorganisms, including the ammonia-oxidizing bacteria, the ammonia-oxidizing archaea, and the nitrite-oxidizing bacteria. These microbes are all aerobes and are predominantly autotrophic. Their specialized metabolism provides them a unique niche, but results in slow and inefficient growth.
Another group of microbes, the anammox organisms, performs the direct anaerobic oxidation of ammonia to nitrogen gas. Conventional nitrification occurs in soils, sediments, and aquatic environments. It is very important in agriculture, where it determines the availability of fertilizer nitrogen, and in wastewater treatment systems, where it participates in the removal of excess nitrogen. In the marine environment, nitrification determines the form of nitrogen available for primary production in the surface layer.
Nitrification is coupled to denitrification in low-oxygen waters and in sediments, where it is an important oxygen sink. In both terrestrial and aquatic systems, nitrifying bacteria are involved in the production of the greenhouse gas, nitrous oxide, probably via a reductive pathway known as nitrifier denitrification. In natural systems, nitrification rates are determined by environmental factors such as salinity, temperature, oxygen, and pH.
