Incorporation of humic-derived active molecules into compound NPK granulated fertilizers: main technical difficulties and potential solutions

Abstract

Numerous studies carried out both in open field and laboratory scale have provided experimental evidence for a beneficial action of humic substances (HS) on plant growth and mineral nutrition. In fact, many products containing diverse concentrations of humic substances, mainly humic and fulvic acids, are marketed as plant growth enhancers all over the world. However, the incorporation of molecules containing humic substances into the granules of compound NPK fertilizers is not a common practice mainly due to technical difficulties and problems associated with the manufacture process of these mineral fertilizers. These problems are normally linked to the potential deleterious effects of granulation conditions (principally, heat and pH) on the structure and properties of molecules containing humic substances. In this review, we discuss several strategies for the incorporation of active molecules containing humic substances into granules of NPK compound fertilizers as well as the main constraints that have to be considered in this process, which normally depend on the agronomical results intended with the preparation of special humic-containing NPK compound fertilizers. We also discuss why, in our opinion, the beneficial action of HS in NPK compound fertilizers is more related to the "so called" indirect effects of HS on plant growth than to the "so called" direct effects.

Concepts and Misconceptions of Humic Substances as the Stable Part of Soil Organic Matter: A Review

“…They obviously avoided including humic substances as reference material. Remember that humic substances also contain fused aromatic rings [1,37,63], which may be measured as BC, e.g., by the BPCA marker method. The possible interference of soil humic substances in the determination of BC was not evaluated by Hammes et al [50].…”

“…A Spanish group of soil scientists, plant nutritionists, and production managers are working on the use of humic substances in fertilizer production [63,89], emphasizing the effect of humic substances on P and micronutrient availability.…”

Biochar association with phosphate fertilizer and its influence on phosphorus use efficiency by maize

“…Acidulated PR are the most used sources for fertilizer production, which release P very fast (Chien;Prochnow;Cantarella, 2009), causing sorption on soil particles and, consequently, reducing P uptake and the effectiveness of P fertilizer application (Kang et al, 2011). Recently, new technologies of phosphate fertilizer have been developed in order to enhance P use efficiency in soils, such as the incorporation of humic substances (Erro et al, 2016), coating with polymers (Sanders et al, 2012;Guelfi et al, 2018), pelletization or granulation with biochar (Kim;Hensley;Labbé, 2014), and pretreating or post-treating the biochar to produce enhanced biochar-based fertilizers (Yao et al, 2015;Lustosa Filho et al, 2017).…”

Black (pyrogenic) carbon in soils and waters: a fragile data basis extensively interpreted

“…Aromatic C NMR signals are assigned to BC or lignin, and humic substances have been ignored for the quantitative interpretation of the NMR spectra [42][43][44][45][46]. However, aromatic C and PAC are present in soil humic substances [7,25,28,[47][48][49][50][51][52]. Some of the humic substances C will be determined as BC.…”