Importance of fertilizers
Importance of fertilizers
Soil fertility largely depends on its nutrient status: the amounts and rates of nutrient supplies for plant growth. An adequate nutrient supply is an essential factor in plant growth. If there is an adequate supply of nutrients in the soil, plants are likely to grow well and produce high yields. If even one of the nutrients needed is in short supply, plant growth is limited and yields are reduced.
“Law of minimum”
The law of minimum says that one nutrient cannot be substituted for another. Plant growth is limited by the nutrient that is least available when all other elements are present in adequate quantities. The “law of minimum” can be illustrated with a water barrel, with staves of different lengths that represent particular nutrient availability. The barrels capacity to hold water is determined by the shortest stave. Similarly, plant growth is limited by shortages of the least available nutrients. Once the limiting factor (nutrient) has been corrected, yield and growth will increase until the next limiting factor is encountered.
Balanced nutrition is important in obtaining maximum yields. The most usual limitations concern nitrogen, phosphorus and potassium, followed by sulphur.
Nutrients are depleted with each harvest
Where nature is untouched a closed nutrient cycle exists. Plant take up nutrients for growth from soil and release them back during their life cycle so nutrients are maintained in this cycle. When man introduces agriculture this cycle is broken. Nutrients are taken out of the soil together with plants during each harvest.
This loss is partly offset by the decomposition of organic matter in the soil and the gradual accumulation of soil minerals. But this natural process is far too slow. Without an external input, the capacity of the soil to supply plants with nutrients is progressively reduced with every harvest.
Why mineral fertilizers?
Mineral fertilizers supply soil with depleted nutrients
Mineral fertilizers are necessary to replace the nutrients that have been removed from the soil. They can provide an optimal nutrient balance, tailored to the demands of the specific crop, soil and climate conditions, increasing crop yield and quality whilst also minimizing environmental impacts.
Fertilizers ensure the most effective use of both land and water. Where rainfall is low or crops are irrigated, the yield per unit of water used may be substantially increased and the rooting depth of the crop increased through fertilizer application.
Fertilizers help feed the world
The FAO has stated that “after land and water, fertilizers are probably the most important input leading to increased yields”. It is inherently difficult to estimate the share of fertilizers in increasing agricultural output since so many factors are involved. But in the ‘Developed World’, after 150 years of increasing fertilizer use, it is thought that roughly half of the present agricultural output may be attributed to fertilizers.
Between 1961 and 1965 the world cereal area averaged 677 million hectares and annual cereal production was 988 million tonnes. The average area between 2000 and 2008 was 699 million ha and 2100 million tonnes i.e. an increase of 3% in the cereal area and 113% in the production. The benefits of these improvements would not have been realised without fertilizers.
It has been estimated that mineral fertilizers contribute about 40% of the nitrogen taken up by the world’s crops. Since crops provide about 75% of all nitrogen in human protein consumption - either directly, or indirectly through animals - it follows that nearly one third of this protein depends on fertilizers.