Mixed Fertilisers In ancient times the farmers discovered the excreta of animals and their decomposing bodies are food for plant life . American Indians used fish and wood ashes for fertiliser. The Chinese have maintained the fertility of their soil for 5000 years by the application of this principle . Manures have been applied on large scale to maintain better plant yields . Before 1900, more than 90 percent of all fertiliser nitrogen was in the form of natural organics ; by 1950, the proportion has decreased to 90 percent. Bones have served to supply phosphorus. The production of and fibre at high rates required by the present large population depends largely upon fertilisers containing multinutrients . Where fertiliser return as much nutrient material to the soil as has been removed by the harvested crops, fertility can be maintained , but in much of ...