Superphosphate is an artificial fertiliser, and is the most important fertiliser used in New Zealand. Farmers often shorten its name to ‘super’.
Improving plant growth
Most soils contain some nutrients and can support plant growth, even if this is slow. For faster plant growth, as long as soil is moist enough, extra nutrients can be added by applying fertiliser.
The main nutrients in superphosphate fertiliser are:
- calcium (about 20%)
- sulfur (11–12%)
- phosphorus (9–10%).
Phosphorus, commonly called phosphate, comes from rock phosphate. It is needed for pasture and crop growth on New Zealand soils. It increases the strike rate of seedlings, stimulates root development and flowering, and improves plant growth.
Superphosphate is effective in a range of soils and climates, and does not affect the acidity of soil.
Early agricultural chemists
In the early 1800s, there were two important figures in the new science of agricultural chemistry.
The first was a French chemist, J. B. Boussingault, who around 1834 began an innovative series of experiments on his farm in Alsace. He created a nutrient balance sheet, comparing the total nutrients applied to a crop with the total taken up by the crop.
The second was Justus von Liebig, a German chemist, who patented an original, artificial manure. However, this failed in practice because the manufacturing process made the phosphate unavailable to plants.
The invention of superphosphate
These two threads of research soon came together, leading to the invention of superphosphate.
In 1843, entrepreneur and agricultural chemist John Bennet Lawes used Boussingault’s methods on his Rothamsted estate near London. Aware of Liebig’s failure, he made his own phosphate manure using a process he had patented in 1842. This involved treating mineral phosphates with sulfuric acid to make superphosphate. In this form, phosphate is rapidly released into the soil, where it can be used by plants. The fertiliser was first advertised for sale on 1 July 1843.
Early New Zealand
The British settlers who arrived in the 1840s and 1850s to take up farming would have heard about the new science of agricultural chemistry, and wondered how much of it was relevant to New Zealand conditions. They pressed for institutions that would offer agricultural education.
Canterbury Agricultural College
Canterbury Agricultural College was founded at Lincoln in 1878. One of the earliest moves by staff was to import superphosphate. It probably came from Adelaide, Australia, which had the first superphosphate manufacturing plant in the southern hemisphere. From then on, superphosphate set the pace for the development of agriculture in New Zealand.