Foliar Fertilizers Promote Root Exudation

Tuesday, May 16, 2017

When I first starting advocating for the use of foliar fertilizers around 2005, many growers did not share my perspective that building better soils coupled with the use of foliar fertilizers was the most expeditious way to get crop production moving in the right direction. I remember having a meeting with a number of managers for a very large grower and when I mentioned that foliar fertilizers trigger greater root exudation which contributes to feeding soil microbes leading to increased nutrient uptake, you would have thought that I had just announced that I was from Mars. Fortunately, I had a mentor, early in my career, who had lifelong experience in agriculture and loved to share his viewpoint with me in regard to why foliar fertilization was so important and crucial to good agricultural practices. I’m still amazed that a plant relocates these carbohydrates, including sugars and proteins, to the rhizosphere versus consuming it all for fruit or seed production or overall plant development (above ground).

Well, what a difference a few years make, as now a number of research reports find that a significant proportion of plant photosynthates are transported below ground shortly after photo assimilation and subsequently released to soil microbes (Dilkes et al., 2004; Bahn et al., 2009; Mencuccini & Holtta,, 2010). This release can be through direct exudation from the surface of fine roots or by transfer to the extraradical mycelium of mycorrhizal fungi (Jones et al., 2004, 2009; Drigo et al., 2010). Both root exudation and transfer to mycorrhizal fungi occur rapidly after photosynthesis, ranging from a few hours in grasses to a few days in trees (Johnson et al., 2002; Dilkes et al., 2004; Kuzyakov & Gavrichkova, 2010). Root exudation stimulates microbial decomposition of soil organic matter, which in turn improves nutrient availability along the rhizosphere (Kuzyakov, 2010; Bird et al., 2011; Philippot et al., 2013). Carbon (C) transfer to mycorrhizal fungi benefits the plant through direct nutrient transfer from the fungal hyphal network (Bever et al., 2009; Fellbaum et al., 2011; Kiers et al., 2011). In both cases, the plant’s investment in below ground C allocation is rewarded with increased nutrient availability, in particular nitrogen (N) and phosphorus (P) (Hodge & Storer, 2014).

Now we’re finding out that this root exudation process not only improves nutrient uptake but also supports the growth of mycorrhizal fungi to help the plant’s access to nutrients and water by extending its range into soil areas that are not accessible by roots or into nutrient rich soil “hot spots.” In addition, the extraradical hyphae which enlarge root areas, facilitate the distribution of recently assimilated plant carbon to the soil microbial community. This process, along with the sugar and protein responses through root exudation, may help the plant stimulate specific microbial responses, including enzyme production to consume the nutrients that the plant needs. Imagine, the plant is communicating with the microbial community, letting it know what it needs at any given time!

Andaman Ag sells an array of innovative foliar fertilizers and biostimulants. We’ve been a leader in introducing products that make a significant difference to our growers’ crops and finances. We look forward to working with you.