Open Access

REVIEW

Biostimulants in Modern Agriculture: A Comprehensive Review with Emphasis on Protein Hydrolysates

Matthew Starr¹, Lori Unruh-Snyder^1,*, Luke Gatiboni¹, Koralalage Jayaratne²

1 Crop and Soil Science Department, College of Agriculture and Life Sciences, North Carolina State University, Raleigh, NC, USA
2 Agricultural and Human Sciences Department, College of Agriculture and Life Sciences, North Carolina State University, Raleigh, NC, USA

* Corresponding Author: Lori Unruh-Snyder. Email:

Phyton-International Journal of Experimental Botany 2026, 95(4), 2 https://doi.org/10.32604/phyton.2026.072898

Received 05 September 2025; Accepted 26 March 2026; Issue published 28 April 2026

Abstract

Biostimulants, categorized as microbial or non-microbial, including humic substances, seaweed extracts, chitosan, or protein hydrolysates (PHs), have gained significant attention in modern agriculture for their ability to enhance crop productivity, improve nutrient use efficiency, and increase resilience to abiotic and biotic stresses, while reducing dependence on conventional agrochemicals. This review synthesizes the historical development, classification, mechanisms of action, and agronomic benefits of biostimulants, with a particular emphasis on PHs, which are mixtures of amino acids, peptides, and polypeptides derived from plant or animal proteins through enzymatic, chemical, or thermal hydrolysis. The concept of biostimulants has evolved considerably over the past century, transitioning from vague notions of biogenic stimulants to clear definitions guided by international councils and regulatory bodies. Among these, PHs demonstrated the ability to promote plant growth, improve soil microbial activity, and mitigate environmental stresses. Evidence across the literature shows that PHs can deliver measurable agronomic benefits: a meta-analysis of 47 field trials reported an average yield increase of 16.5%, while greenhouse studies documented 21%–35% increases in root and shoot biomass, together with improved chlorophyll content and enhanced uptake of nutrients such as N, Fe, and Zn. These responses are associated with stimulation of root development, nutrient assimilation, osmotic adjustment, antioxidant activity, and beneficial soil microbial processes. The effectiveness of PHs, however, varies with source material, hydrolysis method, crop species, environmental conditions, and application strategy. Plant-derived enzymatic PHs often contain more bioactive peptides, whereas animal-derived PHs may provide higher concentrations of free amino acids and nitrogen. These properties have been reported to reduce reliance on synthetic inputs and contribute to more resilient cropping systems. Despite their promise, inconsistent product composition, incomplete mechanistic understanding, and fragmented regulatory frameworks continue to limit reproducibility and wider adoption. Future research should focus on standardized product characterization, multi-omics approaches, and long-term multi-environment field studies to improve the reliability and practical integration of PHs into sustainable cropping systems.

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Keywords

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