Concentrations and allelopathic effects of benzoxazinoid compounds in soil treated with rye (Secale cereale) cover crop

Authors: Rice, Clifford; CAI, GUIMEI - University Of Maryland; Teasdale, John

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2012
Publication Date: 4/15/2012
Citation: Rice, C., Cai, G., Teasdale, J.R. 2012. Concentrations and allelopathic effects of benzoxazinoid compounds in soil treated with rye (Secale cereale) cover crop. Journal of Agricultural and Food Chemistry. 60:4471-4479.

Interpretive Summary: Bioactive chemicals in rye, a popularly-used cover crop, are claimed to enhance the beneficial aspects of their use by actively participating in weed suppression, and warding of disease and insect attacks. Indentifying the causative chemical agents in the benzoxazinoid (BX) family that imparts this bioactivity under actual field conditions has so far eluded scientists. To attempt to clarify the role of the benzoxazinoid group, the more abundant chemical forms were measured in rye cover crop applied under field conditions and also those arising in the soil for about two weeks after treatment. The observed maximum concentrations in the soils were much lower than expected, ranging from 11 to 27% of expected concentrations and the spectrum of BX compounds arising in the soil was dominated by methoxy containing BX compounds which were only minor components in the rye foliage. Evidence was provided to suggest that these methoxy forms were coming from the roots of the rye plants. Laboratory spiking with pure compounds of BX materials showed that soil binding, limited aqueous mobility and rapid degradation of these compounds may cause reduced availability and explain our inability to account for more of the material in our soil analyses.

Technical Abstract: Benzoxazinoids (Bx), a commonly investigated allelopathic chemical group, was measured in rye cover crop at the time of application and in soils at time-spaced intervals after treatment. The rye cover crop was applied under field conditions and at recommended doses as surface and incorporated treatments to two soil types, silt loam and fine sandy loam. The observed maximum concentrations in the soils were much lower than expected, estimated recoveries ranging from 11 to 27% of expected. The spectrum of compounds arising in the soil from the applied plant material was dominated by methoxy containing BX compounds which were only minor components of the rye foliage. Evidence was provided to suggest that these methoxy forms were coming from the roots of the rye plants. Solution applications of two pure BX compounds (BOA and MBOA) to the surface of soils revealed that movement into the soil column was minimal with greater than 70% BOA and 97% MBOA remaining in the top 1-cm of 3-cm deep soil profiles. The time course for dissipation of these pure materials supported rapid and complete losses in less than 24 hours. Thus it appears that in the cover crop experiments there was gradual release of the BX materials as the rye decomposed accompanied by rapid degradation which caused low levels to occur over the approximate 2 week intervals where BX compounds were observed in the collected soils.