A nutrient elements such as nitrogen or zinc is referred to as an essential element if it satisfies the three conditions stated below:
The deficiency of the nutrient must make it impossible for the plant to complete both its vegetative and reproductive stages of growth.
The deficiency of the element cannot be corrected by substituting another element. For example, the deficiency of Sodium (Na) could be corrected by supplying potassium (K); therefore, Na is not an essential element in plants.
The deficiency symptoms of the element must be demonstrable for a wide variety of species and families. That is to say that the deficiency symptoms of the element must be the same in a number of plant species. As the symptom appears on maize, it should also show on rice and beans, and so on.
Scientists have been using mathematical models to describe growth. Such mathematical models could be used in predicting the number of crop yields expected from the supply of an amount of an element or growth factor.
Growth is related to time whether measured in terms of height, dry weight, etc.
This equation was developed to relate growth to the supply of plant nutrients. Mitschelich’s equation expresses that if all but one of the plant nutrients are supplied in adequate amounts to a plant, its growth is proportional to the amount of this one limiting element that was supplied to the soil.
Mathematically, it is expressed as:
|(A – y)C
|increase in yield resulting from growth factor dx.
|increment in growth factor x.
|The maximum possible yield obtained by supplying
|the optimum amount of all the growth factors.
|Proportionality constant (depends on growth
Value of C for N, P & K
N = 0.122, P205 = 0.6, K20 = 0.40. However, C is in variance with different crops.
This is expressed as y = M (I – Rx)
Where y = amount of growth produced by a given quality of the growth factor, x.
|quantity of growth factor
|Maximum growth (yield) when all growth factors are
|present at optimum levels.
Both Mitscherlich’s and Spillman’s equations could be reduced to
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