Impact of biological seed treatments on maize (Zea mays L.) and soil: Crop growth and yield

Seed treatments have been used since the 17th century, but interest has accelerated in the last 20 years due to our increased understanding and importance of the plant microbiome. Particularly, biological seed treatments (BST) have rapidly gained popularity because soil biota is critical to plant health. Despite growing interest and an expanding market, we still lack understanding of what conditions BST are most effective for plant health. The objective of this study was to understand if seed treatments (including BST) will increase maize (Zea mays L.) growth and grain yield. Here, we tested (1) four maize hybrids and (2) five seed treatments (untreated control [UTC], base fungicide control [BFC], BFC + Poncho [P5] [Clothianidin], BFC + Poncho Votivo [P5V] [Bacillus firmus I-1582], BFC + Poncho Votivo + TWO.O [P5V2] [Bacillus firmus I-1582 plus Bacillus thuringiensis EX297512]) across four site-years. Both BFC and BST had little effect on normalized difference vegetation index (NDVI), plant height, and lodging. We did find a variable effect of BST on maize yield, with a significant site-year x hybrid interaction (p = 0.06). For instance, in 2019 in Northwest Iowa, both BST treatments (P5V and P5V2) increased yield by an average of 1.5 Mg ha(-1) compared to the control (+12%, p < 0.032). BST can improve maize yields, but complex hybrid-BST interactions warrant further understanding in order to maximize the benefit of BST.