The number of vegetable growers who are either curious about foliar feeding or using the practice routinely has risen in recent years. Foliar feeding has become a major component of the crop management plans of some vegetable growers while other people are concerned that too many growers rely too heavily on the practice. Let’s review some basic information specific to the process to improve decision-making about it.
1. It is true that plants can absorb nutrients through their leaves. However, it is also true that absorption differs with leaf age and condition, among individual nutrients, and based on other factors. Overall, young leaves tend to take-in nutrients more readily than older ones but are also more easily damaged by caustic solutions. Also, while micronutrients are absorbed at higher rates than macronutrients, micronutrients are present at sufficient levels in most complete soil-applied fertilizers or can be added to them effectively. Similarly, nutrients must reach specific locations in the plant regardless of where they enter it and may be less likely to do so at needed levels after entering through leaves instead of roots. Finally, nutrients entering through leaves and moving within the plant does not guarantee that the application will affect it in ways increasing profit. So, consider the following when asking what role, if any, foliar feeding will have in your comprehensive nutrient management plan: a) relative need for various nutrients, and b) nutrient absorption/uptake rates, mobility, effects once in the plant based on where they enter, and availability in different fertilizers.
2. Proponents of foliar feeding mention that it can: a) be highly tailored, b) bypass soil-based issues, c) lessen the potential for leaching or other losses, and d) create quick responses that may boost crop quality and/or reduce or help plants recover from stress. However, it is also important to consider major concerns with foliar feeding as a primary, routine practice, including how it: a) can damage leaves and fruits, create nutrient imbalances, facilitate the onset and/or progression of foliar disease, and contribute to runoff, b) usually has only short-term effects (requiring repeated use), c) should be done during specific environmental conditions which may not occur during large portions of the season, and d) requires great care to balance risks/rewards and costs.
Therefore, on balance, it is best to:
1. Consider “foliar feeding” as a supplement to, NOT a replacement for a comprehensive nutrient management program in which nearly all fertilizer is applied to the root zone. Strengthening root zone-based delivery programs will address the clear majority of nutrient management questions and challenges. Focus on specific and unique situations in which foliar applications MAY be useful instead of utilizing them as a rule or standard practice.
2. Be clear about the challenges associated with foliar feeding as a routine practice and experiment with it carefully. Select the key crop and crop stage and use the right material, at the right rate, and at the right time (under the required conditions), being sure to check solution chemistry and monitor crop condition.
For Additional Reading:
https://ipm.missouri.edu/mpg/2019/4/foliarFeeding/
https://s3.wp.wsu.edu/uploads/sites/403/2015/03/foliar-feeding.pdf
https://crops.extension.iastate.edu/blog/aaron-saeugling/foliar-feed-or-not