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Browse the 1966 Encyclopaedia of New Zealand
Graphic: An Encyclopaedia of New Zealand 1966.


This information was published in 1966 in An Encyclopaedia of New Zealand, edited by A. H. McLintock. It has not been corrected and will not be updated.

Up-to-date information can be found elsewhere in Te Ara.



Artificial Fertiliser Cycle—Clover Plants and Nitrogen Supply

The chain of events started on a farm by the application of artificial fertilisers is quite a complex one. Usually the fertilisers chosen are those supplying such additional plant nutrients as may be required to fulfil the needs of the clovers. One way in which clovers differ from grasses is their ability to support certain bacteria which grow in nodular colonies on their roots and have the ability to fix atmospheric nitrogen. The host clover plants utilise this supply of nitrogen which is a nutrient essential for plant growth. With their nitrogen provided by the bacteria, and other nutrients by the fertilisers and the soil itself, the clovers are able to grow. Under grazing conditions the next stage occurs when the clover plants are eaten by stock. From their food, stock extract nitrogen and minerals useful for their needs and void the balance in their excrements. Usually the smaller portions are retained and the greater amounts voided and returned to the soil. Again, when clovers are eaten by stock, some of their nitrogen is liberated in dung and urine, and grass plants, which have no nitrogen-fixing bacteria of their own, are now able to use this secondhand nitrogen and grow along with the clovers in the pasture. Grasses also have access to nitrogen when clover roots rot underground and liberate some of their supply. Continued applications of fertiliser accompanied by the sowing of clovers and the subsequent utilisation of growth by grazing stock, builds up the supply of plant nutrients in the soil. Organic matter also slowly increases and soil structure improves. Where such practices are incorporated into a system of agriculture, soil fertility is enhanced and profitable farming at high levels of production usually achieved. These fertility principles apply not only to dairying but also to other systems of grasslands farming. Among these, fat-lamb production is of great importance and is the greatest competitor of dairying for land. Whether sheep or dairy cows are run on an area depends partly on an assessment of which type of stock is likely to prove the more profitable. Climate influences production costs, and is therefore a factor determining profits.