Commercial Humates in Agriculture: Real Substance or Smoke and Mirrors?

Abstract

Soil humic substances (HS) are known to be beneficial for soils and plants, and most published studies of HS and humates, usually conducted under controlled conditions, show benefits. However, the value of commercial humate application in the field is less certain. This review attempts to answer the question: How effective are commercial humates in the field? Commercial humates, especially K humate, are used widely in agriculture today as "soil conditioners". A wide range of benefits is claimed, including growth of beneficial soil microbes; deactivation of toxic metals; improvements in soil structure including water retention capacity, enhanced nutrient and micronutrient uptake and photosynthesis; resistance to abiotic stress, including salinity; and increased growth, yield and product quality. Despite this, there is a surprising lack of solid evidence for their on-farm effectiveness and findings are often inconsistent. The industry relies largely on anecdotal case studies to promote humates, which are often applied at unrealistically low levels. It is recommended that products should be well characterised, physically and chemically, and that careful field studies be conducted on foliar humate application and pelletised humates at realistic rates, targeted to the seedling rhizosphere, for a variety of crops in a range of soils, including low C sandy and saline soils.

Nutrient acquisition and eucalyptus growth affected by humic acid sources and concentrations

“…The effect of HA application on plants has recently been researched and has shown high potential for use (BALDOTTO et al, 2016;ROSE et al, 2014). Humic acid action occurs through direct action on plants, or indirectly, due to HA changes in the growth media, affecting nutrient acquisition and plant growth (LYONS;GENC, 2016). HA direct action on plants includes an effect similar to the role played by auxins on plants (DOBBSS et al, 2010;NARDI et al, 2016).…”

“…In addition, HA can stimulate nutrient transporter activity (JINDO et al, 2016;TAVARES et al, 2017;TOMASI et al, 2014). Indirect effects are those associated with the ability of HA to change the growth medium pH and electrical conductivity (EC) and nutrient complexation, changing macro and micro nutrients availability (LYONS; GENC, 2016;PINHEIRO et al, 2010). These effects on nutrient acquisition are controlled by HA source and concentration (ROSE et al, 2014).…”

“…All these HA sources include materials that are differentiated in regard their chemical composition, fractions molecular weight, and bioactivity of humic fragments contained in HA matrix, which makes it difficult to foresee the agronomic efficiency as well as comparisons of the action mechanisms of different HA sources (GARCÍA et al, 2016;LYONS;GENC, 2016;ROSE et al, 2014). The structure, chemical composition, and quantity and types of functional groupings in the HA structure are key factors to establish the relationship between the chemical and physicochemical nature of the HA and its effects on plants (GARCÍA et al, 2016).…”

Evaluation of the possibilities of using humic acids obtained from lignite in the production of commercial fertilizers

“…Today, the value of application of commercial products containing humic substances in agriculture is less certain. There is currently not enough research to explain possible mechanisms and accurately predict when humic materials might prove beneficial (Lamar et al 2014;Lyons and Genc, 2016;Yakimenko et al 2016). It is recommended that such products should be well characterized physically and chemically.…”

“…For this purpose, it is necessary to determine the quality standard requirements for such material. This approach could not only contribute to understanding the chemical nature of commercial humic products, but might also be useful for the development of theoretical considerations on their application in agriculture or environmental technologies (Lyons and Genc, 2016;Yakimenko et al 2016). For this purpose, UV-Vis, 13 C NMR, fluorescence spectroscopy, and thermal analysis can be used as diagnostic criteria.…”