Economic optima in fertilizer response curve refers to:

Correct option is B

· Economic optimum = fertilizer rate where value of additional yield = cost of added fertilizer.
· Lies below biological maximum yield because maximum yield is not always economical.
Why other options are wrong
· (a) Maximum yield = biological optimum, not economic.
· (c) Recommended dose is generalized, may not equal economic optimum.
· (d) Deliberately low dose ≠ optimum.