PO 18. Compare and contrast the following approaches for making fertilizer recommendations:

The limiting factor concept is utilized in the sufficiency level method of making nutrient recommendations.  It states that crop yield increases will cease when a nutrient or factor "runs out;" i.e. it cannot promote further increases.  When that factor is supplied, yield will increase until another factor becomes limiting.  The first limiting factor is the component lacking first; the second and third limiting factors are those that only come into play after the first has been amended.  In the below example, each plank of the barrel represents one of the essential components of plant growth.  The fill of the barrel represents yield.  At first, phosphorus is limiting; once there is not enough P to go around, yield cannot increase further.  Once more P has been added, yield can increase until it hits the next-limiting nutrient (in this case, N).