Studies of bioactive natural chemicals (also called "natural defense chemicals") in soil are scarce, in spite of the fact that soil forms the basis for agricultural production. The interaction between two successive crops, between crops and weeds, and between crops and soil-borne diseases, happens in the soil.

“We have combined modern chemical analytical methods for quantification of natural defense chemicals with biochemical methods for quantifying microorganisms.”

Research into the microbial transformation of naturally occurring small molecules from agricultural plants is thus highly needed to improve the understanding of these interactions—often called allelopathic interactions.

2-Benzoxazolinone (BOA) is a natural chemical that often is present in rye and wheat. Also BOA is the first metabolite that appears in soil after release of 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) from the plant.

This paper describes the transformation kinetics of BOA to 2-amino-3H-phenoxazin-3-one (APO) and further on to 2-acetylamino-3H-phenoxazin-3-one (AAPO) together with the quantitative relationships between the compounds. The paper shows that the presence of the compounds in soil did not have any measurable effect on the soil microorganisms. The paper also concludes that high concentrations of the water-soluble compound BOA in soil will not leach to ground water due to the fast transformation of BOA. This is important basic knowledge for future investigations on the exploitation of the biological activity of these compounds as suppressants of weeds and soil-borne diseases.

   Does it describe a new discovery or a new methodology that’s useful to others?

In this podcast audio commentary, Inge Fomsgaard, Professor of Agricultural Sciences at the University of Aarhus, discusses the possible exploitation of natural defense chemicals for protecting agricultural plants against weeds, insects, pathogens, and other pests.  Podcast formats: mp3 (3.4 MB) wma (928 KB)

We have combined modern chemical analytical methods for quantification of natural defense chemicals with biochemical methods for quantifying microorganisms. This approach is new and can help in improving the knowledge of the environmental effects of natural defense chemicals.

Recent recommendations for the use of kinetic models on the transformation of chemical compounds in soil were reported in a FOCUS report¹. 

(FOCUS: Forum for the Co-ordination of Pesticide Fate Models and their Use).

We applied these models to natural chemicals, which had not been done before. Future evaluations of the fate of natural chemicals in soil can benefit from our results.

Alternative methods for controlling weeds, insects, pathogens, and other pests have come into focus during the last several decades. The possible exploitation of natural defense chemicals for protecting agricultural plants against weeds, insects, pathogens, and other pests is one of several alternatives to the use of synthetic pesticides. The term "allelopathy" denotes the production of specific biomolecules by one plant that can induce suffering in, or give benefit to, another plant.

When rye plants that contain amounts of BOA and DIBOA sufficient for the formation of APO are used as green manure, the timing of formation and disappearance of the most biologically active metabolite APO is crucial both for the sowing of the subsequent crop and also for the evaluation of the impact on the soil environment.

During the last decade the European Commission has given high priority to research into sustainable agriculture where, for instance, the use of synthetic pesticides is replaced or supported by the use of alternative and more naturally oriented methods for controlling weeds, insects, and diseases. Such methods are expected to be more environmentally sustainable.

I therefore brought together a group of experts and obtained funding from the European Commission’s 5th Framework Program for the project FATEALLCHEM ("Fate and Toxicity of Allelochemicals in Relation to Environment and Consumer").

In this project, we realized that the pattern of biologically active secondary metabolites that can be formed in soil is very complex.

BOA, APO, and AAPO, for which the kinetics of formation and disappearance is determined in this highly cited paper, are important soil metabolites related to the use of rye as green mulch. We did not obtain the exact chemical structure for the high number of additional metabolites that can be formed in soil. However, this is not to be considered a failure—it is, rather, an ongoing scientific challenge.