Phenotypic traits of sunflower varieties depend on the composition of cover crops

Abstract

Context

Introducing cover crop (CC) mixtures is a promising approach to enhance the multifunctionality of ecosystem services provided by CCs. However, CC mixtures have contrasting effects on subsequent crop yield, depending on multiple factors such as the type of subsequent crop and the mixture composition. In the context of climate change, sunflower (Helianthus annuus L.), which is adapted to environments with low nitrogen (N) and water requirements, has multiple varieties with different drought-tolerance strategies. However, little is known about how drought-tolerant sunflower varieties differ in their response to CCs in low-input systems.

Objective

This study aimed to characterize CC ecosystem services related mainly to N and water and to investigate how CC ecosystem services influence the responses of sunflower varieties that differ in drought sensitivity.

Methods

CCs and sunflower varieties were organized in a randomized non-complete block design with a split-plot arrangement in 2021–2022 and 2022–2023. CC treatments consisted of a pure grass CC (rye), a mixture of legume CCs (purple vetch/fodder pea), three mixtures of legume and non-legume CCs (faba bean/Indian mustard/phacelia; fodder pea/rye/purple vetch and fodder radish/hairy vetch/white mustard) and a relay CC treatment (fodder sorghum then faba bean). Sunflower varieties exhibited different drought-tolerance strategies for leaf expansion and transpiration. Establishment, development, growth, N status and productivity were evaluated for the sunflower varieties preceded by CCs through low- and high-throughput phenotyping. Multiple variables of growth and development were assessed by applying image-processing tools to unmanned aerial vehicle (UAV) RGB images.

Results

The results indicate that CCs influenced early and late N-release uptake by sunflower, thereby extending the seed-filling period. Optimizing the CC chosen allows for yields equivalent to those of intensively tilled bare soil, while increasing the amount of carbon returned to the soil and weed control in low-input cropping systems. Furthermore, in addition to the CC chosen, optimizing the sunflower varieties chosen can improve sunflower growth during dry years.

Implications

These results can inform decisions about CCs, sunflower variety and management in low-input systems to better match the nitrogen released from CC residues to subsequent cash crop responses during vegetative and post-flowering phases.