WAEC Agriculture 2011 Paper

Concept:Yellowing of older lower leaves is a classic sign of deficiency in a mobile nutrient like $\text{nitrogen}$.Explanation:$\text{Nitrogen}$ is mobile inside the maize plant.When the soil lacks enough $\text{nitrogen}$, the plant moves it from older lower leaves to younger upper leaves.This causes the lower leaves to lose chlorophyll and become yellow.In contrast, $\text{phosphorus}$ deficiency gives purplish leaves, $\text{zinc}$ deficiency causes interveinal mottling, and $\text{potassium}$ deficiency affects leaf margins.Thus, the yellowing of lower leaves is best explained by nitrogen deficiency.Answer:D. $\text{nitrogen}$