Rare Earth Elements, REEs, are used in a wide range of applications but there are some which are not so popular such as agriculture and plant growth. In the early 19th century some reports were published on the action of rare earths on plant growth which reported mostly positive effects. In 1972, China started to research in this field and the results were so extraordinary that shortly afterwards the commercial use if rare earths in Chinese agriculture was started.
Research in China and its application
Today the use of REEs as trace elements in fertilisers in China is common, since in 1972 it started a systematic research including both laboratory and field experiments. Such a big application of REEs requires more information to understand its impact by answering questions such as how extended is this application in China, how the application process is, and which is the influence of REEs on the yield of plant and trees.
Over the last 30 years, the treated area with rare earths constantly increased from a minor area of 1330 ha in 1980 to 16 million ha in 1995 as it can be seen in the following Table. It means that by 1995, the treated surface with fertilisers containing REEs was 160.000 km2, which supposes an area bigger than Greece and almost as big as Tunisia.
The increases of land treated with REE containing fertilisers in China1
After research started, different REE containing fertilizers were developed. There are basically three kinds of fertilisers: (1) Nongle, which contains RE chlorides, (2) Changles, which contains RE oxides as well as plant growth elements and (3) MAR, which consists of RE compounds mixed with amino acids. However, Changle is the most widely used of the fertilisers above. Although its composition, shown in the next Table, presents a total amount of rare earth oxides, REO, of 32.19 wt.%, some manufacturers increase it to values above 38 wt.%2.
There are several methods to apply the fertiliser to the plant. For example, it can be used as root fertiliser, which means that it is directly applied to the soil. Besides soil application, other common methods are practised such as seed soaking, foliar spraying and seed dressing. The application stage depends on the growth stage and the specie of the plant; and it has to be continued every year to be effective. In the following appears a summary with some species, the amount of rare earths that has to be applied as well as the method to use it.
To date, an increase in the yield of about 50 plant species such as cereal, sugar or vegetables as well as for more than 20 species trees and pasture grasses have been reported. In addition to the increase of the amount produced during harvest, there are betterments in product quality. In example, sugar content in sugar increases or increased vitamin C content in apples.
If the effects of REEs on agriculture are so amazing, why arenât they used abroad China?
Research in Western countries and contradictions
Clear understanding of the results reported in China is hard due to the either the access to the source is difficult, or most reports are not available in English, or the papers are often lacking details of experimental method and statistical treatment. Therefore, it is crystal clear that basic and wide research on this field needs to be carried out outside China to verify those results and to provide more information.
From the 1930s to the 1980s, only a few papers on the effects of rare earth elements on plants were published outside China, in which positive effects were the general trend but there were also some authors reporting detrimental results. It was after and during the 1990s when Western countries interest on this field increased again after some Chinese papers became accessible.
Today, studies carried out in different countries such as Australia or Germany show conflicting results with both beneficial and detrimental results. Hence, most of investigations canât confirm the great effects of rare earths on yields as well as other properties reported in China.
Consequently, there is a need for further well conducted and properly documented experiments on REEs influence on plants. Rigorous statistical treatment of data is also recommended in order to extrapolate and compare the results from different reports. Although there are many questions left unanswered regarding REE effect on plant yield and growth, more detailed reports might open up agricultural use of rare earths to other countries beyond China.
Besides studying the effect on plant growth, there is a need of reports on the effects of rare earths on human consuming rare earth containing diets and their effect on all parts of the food chain as well as on the environment.
1. Redling, K., 2006. Rare Earth Elements in Agriculture with Emphasis on Animal Husbandry. PhD Thesis, Ludwig-Maximilians MĂŒnchen University.
2.Â Grirem Advanced Materials, http://www.chinarem.com/eng/english/products/clu.htm, consulted on 28/01/2015.
3. Pang, X., Li, D. C., Peng, A., 2002. Application of Rare-earth elements in the Agriculture of China and its Environmental Behaviour in Soil. Environmental Science and Pollution Research, 9, p143-148.