Foliar fertilizer and compound fertilizer are both types of plant nutrition, but they are applied in different ways and have some key differences.

Application method: Foliar fertilizer is applied directly to the leaves of the plant, while compound fertilizer is applied to the soil.

Absorption rate: Because foliar fertilizer is applied directly to the leaves, it is absorbed more quickly by the plant than compound fertilizer. This means that foliar fertilizer can provide quicker results and can be used to correct nutrient deficiencies more quickly.

Nutrient delivery: Foliar fertilizer delivers nutrients directly to the plant, while compound fertilizer delivers nutrients to the soil which then get absorbed by the plant's roots. This means that foliar fertilizer can be more targeted in terms of which specific nutrients the plant receives.

Efficiency: Because foliar fertilizer is applied directly to the leaves, less is required to achieve the same results as soil-applied compound fertilizer. Additionally, foliar fertilizer can be more efficient in cases where the soil is poor or otherwise unable to support healthy growth.

Compatibility: Compound fertilizer can be applied to a wide range of plants and soil types, while foliar fertilizer is more specific and may not be as versatile.

Cost: Foliar fertilizer (per Kg) can be more expensive than compound fertilizer due to the cost of production and application process BUT COST PER NUTRIENT/APPLICATION IS CHEAPER.

Overall, both foliar fertilizer and compound fertilizer have their own advantages and disadvantages and can be used together to achieve optimal plant growth and health. However, in general, compound fertilizer is more common and widely used in agriculture, while foliar fertilizer is used more in horticulture, indoor and container gardening, and for correcting nutrient deficiencies quickly.