Final answer:
The statement is false; fertilizer efficiency generally decreases when soil pH drops below 6.0 because nutrient availability is negatively affected in more acidic soils.
Step-by-step explanation:
The statement 'Fertilizer efficiency increases as soil pH decreases below 6.0' is false. This is because most plants prefer a soil pH between 6.0 and 7.0, where nutrients are most readily available for plant uptake. When soil pH drops below 6.0, meaning the soil becomes more acidic, certain nutrients become less available and others may reach toxic levels, thereby reducing fertilizer efficiency. Additionally, extreme soil acidity can negatively affect soil microbiology and plant root systems.