Balancing Soil Health and Crop Performance: Winter Cover Crops in Sunflower Farming

Abstract

Sunflower (Helianthus annuus L.) is a globally significant crop for vegetable oil production, with its cultivation methods playing a pivotal role in agricultural sustainability. Our aim was to explore the potential of winter cover crops (WCC) to preserve soil health between crops, fostering diverse rhizospheric microbial populations after two years under field conditions. Specifically, this study investigates how WCC inclusion in the rotation and the suppression methods (chemical suppression or rolling) used prior to cash crop impact sunflower growth and its rhizosphere bacterial and fungal communities, determined through Illumina sequencing of bacterial 16S rRNA genes and fungal internal transcribed spacer (ITS) amplicons. Our results showed a significant increase in plant height, stem diameter, head diameter, and head dry weight in plots where WCC was suppressed with glyphosate when compared to those under standard chemical fallow. In addition, we observed that the bacterial community of sunflower plants cultivated in plots where WCC underwent chemical suppression had greater Pielou’s evenness index than those maintained as fallow. The fungal Chao1 index increased in the sunflower rhizosphere in plots that included WCC in the rotation and received phosphorus fertilization. The choice of suppression method—mechanical or chemical—showed a differential impact. While rolling adversely affects sunflower growth, certain reproductive stage variables perform better in chemically-suppressed WCC plots. However, chemical suppression was associated with a decline in rhizospheric bacteria with beneficial potential for plant growth, while mechanical methods, such as rolling, enhance their presence. Additionally, our results evidenced a significant and positive correlation between fungal diversity and sunflower growth parameters (height and number of leaves, stem diameter, head diameter, and head dry weight). Transitioning from chemical fallow to WCC offers soil and crop health benefits but requires exploring herbicide reduction strategies, including mechanical control methods and compatible WCC species, for a balanced and sustainable approach that maintain soil health.

Keywords: winter cover crop, sunflower rhizosphere, rolling, glyphosate