# Allelopathic Trade-Offs of Rye and Wheat Residues Versus 2-Benzoxazolinone: Impacts on Cotton Growth

## TL;DR

This study shows that while rye and wheat residues can help the soil, too much can harm cotton growth, with the residues themselves being more harmful than the chemicals they release.

## Contribution

The study quantifies the dose-dependent allelopathic effects of rye and wheat residues on cotton and compares them to the effects of a purified chemical.

## Key findings

- High levels of rye residue significantly reduced cotton germination and biomass.
- Wheat residue had weaker effects on cotton compared to rye.
- The natural chemical 2-benzoxazolinone caused only short-term effects on cotton.

## Abstract

Cover crops such as rye and wheat are widely used to protect the soil, save water, and reduce weeds in farming systems. While these benefits are clear, the remains of these plants left in the soil can also release natural chemicals that may slow down the growth of the next crop. Cotton is an important crop grown after cover crops in many regions, and farmers are often concerned that too much residue could reduce cotton yield. In this study, we grew cotton in greenhouse conditions and compared the effects of rye and wheat residues with those of a purified natural chemical produced by these plants. We found that moderate amounts of rye sometimes improved cotton germination, but high levels of residue greatly reduced germination and growth. Wheat had weaker effects, and the purified chemical alone caused only short-term changes. Our results show that the main risk comes from the residues themselves rather than from the chemical alone. These findings are important for farmers because they provide practical advice on how much residue can be left in the soil and how long to wait before planting cotton. By managing residue levels and timing, farmers can enjoy the benefits of cover crops while avoiding risks to cotton production.

Cover crops provide soil cover benefits but can impose allelopathic risks on cotton. We evaluated the functional trade-offs of rye and wheat residues versus purified 2-benzoxazolinone (BOA) under greenhouse conditions. Four experiments applied graded residue or BOA inputs in Pullman clay loam; cotton germination, height, chlorophyll (SPAD), and biomass were measured, and soil BOA, DIBOA, and DIMBOA were quantified by HPLC at designated sampling dates. Responses were dose dependent: BOA reduced germination linearly (−16.5% at 1000 nmol g−1 versus control) and shortened plants, and biomass and SPAD were directionally lower, most evident at 500 nmol g−1, but not statistically significant. Rye showed hormesis at 6400 kg ha−1 (+7.3% germination) and strong inhibition at 12,800 kg ha−1 (−31% germination; biomass up to −45%). Wheat produced intermediate inhibition (biomass −23.7%) and did not affect germination. In soil, benzoxazinoids exhibited significant rate effects at specific sampling dates followed by rapid decline. After storage, BOA showed no residual effects, whereas prior rye still reduced height, SPAD, and biomass. Framed at the agroecosystem scale, maintaining residue biomass below inhibitory thresholds and adjusting termination-to-planting intervals to avoid the early post-termination period, together with species or cultivar choice, can reconcile soil cover services with reliable cotton establishment.