What's the difference between soil and foliar micronutrient applications?

Soil applications and foliage sprays rectify micronutrient deficiencies, albeit in different ways. Soil amendments such as zinc sulfate become available to the root systems of plants, allowing for a more gradual correction that could take several months. Conversely, a foliage spray delivers nutrients directly to the leaves, and while it can eliminate yellowing in soybeans within 48 hours, it is only a temporary fix that will require several applications to sustain the corrected nutrient deficiency.

Soil amendments require a pH of under 6.5 for iron to be available. In Missouri, a corn farm treated manganese deficiency by banding 10 lb/acre of manganese sulfate ahead of planting. The crop showed the effects fully within 6 weeks of application. Applying foliar sprays would have required 4 applications to achieve the same level of effectiveness. When using amendments, select a method that fits the crop's tolerance level and operator's budget.

Foliar sprays can eliminate all the soil chemistry. I once saved flowering soybeans after a soil pH locked out iron and other nutrients with many 0.5% iron chelate sprays. In the past, they showed the green back within 72 hours but needed bi-weekly and/or weekly repeat sprays. For crops like apples, follow up with both: pre-bloom soil zinc and then spray the boron once the petals shed or drop.

Timing is important. Apply soil micronutrients 4 weeks before planting (or up to 2 weeks after planting). Plants will have a comparatively better distribution of micronutrients in the soil before planting. Foliar sprays are more effective at dawn when stomata open wider for increased absorption. A Georgia pecan grower increased yield by 25% after he began to apply zinc around 5 AM during kernel formation instead of in the middle of the day.

Read the full article: 7 Essential Micronutrients for Plants: Complete Guide