What is chamic agriculture

History of fertilizers

Natural fertilization is no longer enough

Plants remove nutrients and mineral salts from the soil. The most important elements are nitrogen, phosphorus, potassium, sulfur and calcium. If the plants are not harvested and transported away, these substances end up in the soil again. The plant residues disintegrate and bacteria and small organisms ensure that fertile humus with available minerals is restored from it.

The cultivation of human fields interrupts this cycle. With the harvest, the nutrients are literally carried from the field. Depending on the nutrient richness of the soil, it is depleted after a few harvests. But there is a countermeasure: fertilization.

In China, human excrement was collected thousands of years before the turn of the century and distributed in the fields. The earliest literary mention of fertilization in the West can be found in the "Odyssey" by the Greek poet Homer in the 8th century BC. In Odysseus' farm yard, a heap of dung smelled until the servants distributed it over the fields.

The "green manure" with nitrogen-collecting plants, which were then plowed under, has been known since the Romans at the latest. A fallow land - a year in which the soil is not used - also helps the cultivated area to regenerate. Minerals in the soil dissolve through weathering and are thus available again for agriculture. However, only if there are any left.

This problem worsened in the Middle Ages and early modern times. The word about the "old age of the soil", which the Roman philosopher Seneca (1-65 AD) had already coined, got around. Catastrophic crop failures and famines brought the burning problem into the public focus.

Late medieval alchemists began to research how to artificially increase yields in agriculture. In modern times it became the scientific discipline of so-called agricultural chemistry: the investigation of the nutritional physiology of the plant and the nutrient supply of the soil.

Artificial fertilizer: breakthrough in the 19th century

The Darmstadt-born chemist Justus von Liebig (1803-1873) turned out to be a visionary of agricultural chemistry. As early as 1840 he formulated:

"As a principle of agriculture it must be seen that the soil must fully regain what has been taken from it; in which form this reproduction takes place, whether in the form of excrement, or of ashes or bones, this is probably quite indifferent. It There will come a time when the field, where every plant that you want to achieve on it, is provided with the appropriate fertilizer, which is prepared in chemical factories. "

This credo comes from Liebig's epoch-making work: "Chemistry in its application to agriculture and physiology". Liebig's decisive achievement was that, unlike his contemporaries, he recognized inorganic substances as nutrients in plants: simple salts and acids and uncomplicated organic compounds. This cleared the way for the industrial production of fertilizers. At least in theory.

Further development in the 20th century

But Liebig made a serious mistake. He feared that water-soluble fertilizers would be washed out by rainwater and transported into the depths of the soil where the roots of the plants could not reach. That is why his first large-scale fertilizer based on potash with carbonate of lime was flawed. A compound that did not come off in cold water and remained practically ineffective in the fields.

Nevertheless, Liebig's "Agricultural Chemistry" paved the way for all major discoveries in the fertilizer industry over the next few decades. In this way Adolph Frank (1834-1916) was able to develop potash salt for agriculture. The potassium bound in the potash salt is one of the most important nutrients for plants.

The chemist Wilhelm Ostwald (1853-1932) succeeded in synthesizing ammonia in 1900. However, not in an industrially feasible process. It took another 13 years until ammonia, the important precursor for nitrogen fertilizer, could be produced in sufficient quantities. Nitrogen fertilizer is still the most important mineral fertilizer today and accounts for more than half of the world's fertilizer consumed.

Bioregulators: plant design through chemistry

In the field of classic plant nutrients, which are produced in the fertilizer industry, the decisive discoveries go back many decades. Today, laboratories around the world are researching a new class of active ingredients: what are known as "bioregulators".

While the classic nutrients usually promote the growth of the plant in general, bioregulators have a targeted effect on certain growth processes: for example on the formation of the fruit, the sprouting of the roots, the length growth of the stalks. The plant itself only produces these substances in very low concentrations.

The best-known substance, which has been used extensively for decades, is chlormequat: the stalk shortener. In grain cultivation, it ensures that the growth in length of the stalks is limited.

This has two major advantages. On the one hand, the plant does not waste energy unnecessarily on building up straw; on the other hand, shorter stalks are less prone to breakage caused by wind and rain. Other substances are also used that, for example, allow the fruit to grow faster or ripen at the same time and thus make harvesting more efficient.