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

J Erro,M Fuentes,R Baigorri,J M Garcia-Mina,A M Zamarreño,O Urrutia

doi:10.1186/s40538-016-0071-7

J Erro, M Fuentes + Show 4 more

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https://doi.org/10.1186/s40538-016-0071-7

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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.

Highlights

It has been well established that soil fertility, and crop yields and fruit quality, is principally related to three main complementary components of soil ecosystems: natural organic matter (NOM), soil microbiota and the pool of bioavailable mineral nutrients [1, 2].As for the relevant role of NOM in plant development, many studies indicated that it is associated with the activity of specific organic fractions present in soil solutions and soil matrix, which have been operativelyThe beneficial action of humic substances (HS) in crop production has been ascribed to two main complementary HS actions on plant–soil systems [4, 5]:(i) HS effects expressed as a consequence of their previous action on soil properties and fertility
The beneficial action of HS in crop production has been ascribed to two main complementary HS actions on plant–soil systems [4, 5]: (i) HS effects expressed as a consequence of their previous action on soil properties and fertility
This type of factory involves many steps, but we focus our interest on four main steps that might affect the efficiency of compound NPK fertilizers containing humic acids when incorporated during the granulation process [44]: Step I Pre-granulation reactions (PGR)

Summary

Background

It has been well established that soil fertility, and crop yields and fruit quality, is principally related to three main complementary components of soil ecosystems: natural organic matter (NOM), soil microbiota and the pool of bioavailable mineral nutrients [1, 2]. The electronic features of the cation complexed by HA play an important role in the stability of phosphate complexation in metal–humic binding sites, with transition metals showing the highest stability [43] Summarizing, all these results taken together indicate that the metal complexing ability of HS can be a very useful tool to produce two types of special NPK compound fertilizers with beneficial effects on mineral plant nutrition:. This type of factory involves many steps, but we focus our interest on four main steps that might affect the efficiency of compound NPK fertilizers containing humic acids when incorporated during the granulation process [44]: Step I Pre-granulation reactions (PGR) This technical operation consists of pre-mixing specific raw materials to produce a liquid-slurry phase mass that is further added to the granulator drum in order to favor the granulation process. This step may include several complementary reactors [44]

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