Plant Biostimulants: A Categorical Review, Their Implications for Row Crop Production, and Relation to Soil Health Indicators

Abstract

Plant biostimulants are specialty products used to increase crop production and are quickly becoming common in the agricultural seed and chemical marketplace. Unlike traditional crop inputs, such as fertilizers or pesticides, biostimulants are unique in that a single product may have multiple avenues for influencing crop growth and development based on both the timing and the placement of application. This review presents a summary of the current status and descriptions of plant biostimulants with available literature on their uses in the row crop production of maize (Zea mays L.), soybean (Glycine max (L.) Merr.), wheat (Triticum aestivum), and other major crop species. Biostimulants have much potential to improve crop production through enhanced yields, grain quality, and increased sustainability of agronomic production systems, particularly in relation to nutrient management. However, there is great variability in the efficacy of biostimulants and a limited understanding of the mechanisms responsible in field-tested scenarios where differences are observed. These unknown mechanisms may align with the recognized soil health indicators, providing opportunities for unrealized biostimulant potential beyond crop growth and development. This review aims to identify the predominant types of crop biostimulants, the known understandings of their modes of action, and examples of their current field efficacy with an outlook for their future.

Understanding the Role of Humic Acids on Crop Performance and Soil Health

“…Although HA and FA fractions are decomposable in nature, their break down is slow, resulting in a constant supply of C to the soil. In the review by Sible et al (2021), HA contain a high amount of C compared to FA. This indicates that the application of HA may provide additional C to soil microorganisms, essential for soil biological activities.…”

“…The rate of urea hydrolysis has also been linked to high concentrations of nickel (Tan et al, 2000). Due to the chelating properties of HA, it is able to form complex nickel, thus slowing down urea hydrolysis (Sible et al, 2021).…”

“…The ability of HA to withstand degradation for long periods and their amphiphilic properties enable them to form complex cations (Wood, 1996). HA fraction contains about 60% organic carbon (C), which plays an important role in the growth of soil microorganisms (Sible et al, 2021). In addition to C, HA also contain nitrogen (N), oxygen (O), hydrogen (H), and sulfur (S).…”

“…A recent review by Nardi et al (2021) showed that HA chemical and molecular structures, sources, and application rates are critical for determining their effects on crops and soil. Importantly, HA application can have inconsistent results on yield, possibly due to the different HA biological origins (Sible et al, 2021).…”

Microbiome engineering and plant biostimulants for sustainable crop improvement and mitigation of biotic and abiotic stresses

“…The application of seaweed extracts in agricultural farms has been reported during the first century [91]. Currently, seaweed extracts have been applied to plants to mitigate abiotic stress, enhance nutrition efficiency and improve root growth and microbial activity of the root zone [74]. Seaweeds can be categorized into three groups based on their pigmentation: (i) Phaeophyta (brown), (ii) Rhodophyta (red), and (iii) Chlorophyta (green) [92].…”