INTRODUCTION

During the early part of the nineteenth century, sodium nitrate (Chilean nitrate) and Peruvian guano were imported into Europe, and more significant developments followed. They included the manufacture of superphosphate in England from 1843, by treating first bones and then rock phosphate with sulphuric acid. Two industrial by-products came into importance in the nineteenth century: ammonium sulphate as a by-product in the manufacture of coal gas, and basic slag which contained phosphate from the impure iron oxide used in the steel industry. From 1861 potassium salts became available for use as fertilizer from deposits in Germany, and later from elsewhere. In the twentieth century three important manufacturing processes were (ⅰ) the synthesis of ammonium fertilizers by the Haber–Bosch process, which originated in Germany during the first two decades, (ⅱ) the manufacture of triple superphosphate, which was started by the Tennessee Valley Authority (USA) in the 1930s, and (ⅲ) the manufacture of urea from atmospheric nitrogen and natural gas from oil drilling, which became a cheap and increasingly popular nitrogen fertilizer from the 1950s.

FERTILIZER USE DURING THE TWENTIETH CENTURY

Fertilizer use is essentially a phenomenon of the twentieth century. Many books and thousands of scientific papers have been published on the need for fertilizers and on their uses. The books include those by Cooke (1967, 1982), Sanchez (1976), Wild (1988), Rengel (1998, 1999) and Laegreid et al. (1999).