the role of humus and organo-mineral interactions were central, and which was in line with more recent discoveries from 1990 onwards. Prominent scientists on whom Justus von Liebig drew were Carl Ludwig Sprenger and Hermann Hellriegel. In this field, a 'knowledge erosion' took place, partly driven by an intermingling of economics and research. John Bennet Lawes, an English entrepreneur, began to experiment on the effects of various manures on plants growing in pots in 1837, and a year or two later the experiments were extended to crops in the field. One immediate consequence was that in 1842 he patented a manure formed by treating phosphates with sulfuric acid, and thus was the first to create the artificial manure industry. In the succeeding year he enlisted the services of Joseph Henry Gilbert; together they performed crop experiments at the Institute of Arable Crops Research. The Birkeland–Eyde process was one of the competing industrial processes in the beginning of nitrogen-based fertilizer production. This process was used to fix atmospheric nitrogen (N2) into nitric acid (HNO3), one of several chemical processes generally referred to as nitrogen fixation. The resultant nitric acid was then used as a source of nitrate (NO3−). A factory based on the process was built in Rjukan and Notodden in Norway, combined with the building of large hydroelectric power facilities. The 1910s and 1920s witnessed the rise of the Haber process and the Ostwald process. The Haber process produces ammonia (NH3) from methane (CH4) (natural gas) gas and molecular nitrogen (N2) from the air. The ammonia from the Haber process is then partially converted into nitric acid (HNO3) in the Ostwald process. After World War II, Nitrogen production plants that had ramped up for war-time bomb manufacturing were pivoted towards agriculture uses. The use of synthetic nitrogen fertilizers has increased steadily in the last 50 years, rising almost 20-fold to the current rate of 100 million tonnes of nitrogen per year. The development of synthetic nitrogen fertilizer has significantly supported global population growth — it has been estimated that almost half the people on the Earth are currently fed as a result of synthetic nitrogen fertilizer use. The use of phosphate fertilizers has also increased from 9 million tonnes per year in 1960 to 40 million tonnes per year in 2000. A maize crop yielding 6–9 tonnes of grain per hectare () requires of phosphate fertilizer to be applied; soybean