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Soil and fertilisers

Themes: Food and Fertilisers | Nutrient pollution | Balancing nutrient pools | Quiz

Increasingly there is a tendency to increase the amount of fertiliser added to soils to improve productivity, especially in the developed world. Fertilisers can be added by hand or from aeroplanes as here in New Zealand. Farming has changed greatly over the centuries that humans have inhabited the world. Initially there were few people and their needs for food were largely met by hunting wild animals and gathering foods that grew naturally in the countryside. Gradually from this way of life there evolved groups around the world who began to domesticate plants, develop crops and lead a more sedentary existence. This was really the beginning of the evolution towards farming as we know it today. Initially, the need for fertilisers was not recognised and fertility of the soil was maintained by moving to a new patch and leaving the one just used to regenerate naturally. Eventually it was realised that soil fertility could be regenerated more quickly by using manures from livestock, and mixed farming came into being in which there was a symbiosis between the cropped land on the one hand and the farm animals which provided the manure to maintain its fertility on the other. Now agriculture has been revolutionised in many parts of the world with the discovery of artificial fertilisers and these are now being used to provide extra nutrients which have enabled yields to increase enormously.

Today, in the more developed parts of the world, farming is very sophisticated. It relies on the use of high-technology equipment to prepare the soil for crops, fertilisers to enable the crops to grow well, pesticides to keep away the pests and diseases, and huge combine harvesters to harvest the crop. By using fertilisers and manures the yields of crops have increased threefold in developed parts of the world. There are two main types of fertiliser and manures in use today. Firstly there are the organic manures which are mainly animal wastes. The source of these is therefore livestock farms or farms which have a mixture of livestock and arable farming. Sludge from sewage works can also be used though these have in the past been linked with the addition of undesirable chemical elements to the land. These organic manures contain less nitrogen, phosphorus and potassium than most artificial fertilisers but they represent an important re-use of waste materials. They also have the advantage, particularly when mixed with straw, of adding valuable organic material to the soil. Their drawback is that organic manures are normally added to land in autumn when plants need them least and they take time to breakdown and release nutrients.

Artificial fertilisers are now by far the most widely used. These have been manufactured for many years but there has been a dramatic rise in their use in the last few decades. For example, it is estimated that use of nitrogen fertilisers increased by fifteenfold in the last 50 years, giving rise to a threefold increase in yields of cereals such as wheat. There is little doubt that the use of artificial fertilisers has dramatically increased the yield of crops in the developed world. There are a wide range of artificial fertilisers now available. Most contain nitrogen, phosphorus and potassium but the proportions vary. Given a knowledge of the nutrient status of soils it is possible now to prescribe the type of fertiliser and the composition of it to meet a crop's requirement on a particular soil. In a sense, we can have prescription agriculture - just as we humans might go to the chemist to obtain a tonic. The use of these fertilisers enables the loss of nutrients taken off in a crop each year to be completely replaced and hence soil fertility to be maintained. Their use also reduces the cost of food production.

Themes: Food and Fertilisers | Nutrient pollution | Balancing nutrient pools | Quiz