Abstract
Crop residues and mulches release phytotoxic substances into the soil that affect plant growth. An experiment was conducted at the Uganda National Crop Resources Research Institute, Namulonge during 2016, to identify compounds in the stover of potted Cymbopogon nardus, Desmodium uncinatum, Oryza sativa, (NERICA 1), Mucuna pruriens and Zea mays (LONGE 6H) at fourty five days after germination. This marked near the average stationary phase for test crops’ growth when secondary metabolites are maximum. Organic compounds in the stover were extracted using solid phase micro-extraction. Samples were subjected to analysis using a 7890A Gas Chromatography system. Data files were transferred into a distinct folder and data was uploaded onto XCMS online platform for pair wise comparison and other related statistical analysis in the National institute of Science and Technology library. Ten terpenoids and one ester were identified in cymbopogon stover. Desmodium stover released six terpenoids and three phenols. Rice stover produced six terpenoids, three phenolic compounds and one ester. Mucuna stover released two terpenoids and four phenols. The maize stover produced five terpenoids and four phenolic compounds. Profiled compounds from cymbopogon, desmodium, rice, mucuna and maize could be responsible for the reported negative allelopathic effects such as auto-toxicity and suppression of companion crops expressed in agricultural ecosystems. Allelopathic activity of the profiled compounds should be confirmed through bioassays extracts and residues studies. The development and incorporation of the profiled metabolites into agricultural management system may lead to the production of bio-herbicides that reduce environmental degradation and increase crop productivity.
Highlights
Crop residues left in the soil release phytotoxic substances that are sometimes harmful to plant growth
3.1 Bioactive Compounds Identified in the Stover of Rice, Cymbopogon, Desmodium, Mucuna and Maize
Ten terpenoids namely Citronellal, β-Citral, cis-Geraniol, trans-Carane, Eugenol, Geraniol acetate, β-Elemen, Caryophyllene, α-Gurjunene and γ-Cadinene and one ester named Citronellyl butyrate were identified in Cymbopogon nardus stover (Table 1)
Summary
Crop residues left in the soil release phytotoxic substances that are sometimes harmful to plant growth. The substances are produced by bacteria, fungi or plants as secondary metabolites that are organic in nature and not directly involved in the normal growth, development or reproduction of the organism. In eastern Uganda, upland rice ecosystems are basically mixed cropping or in companion with some plants that improve soil nutrient status, provide livestock feed or raw materials to farmers. The stovers from these crops are often being used as mulching materials. The metabolites in the crop stover are not well known and could be allelopathic in nature, releasing phytotoxins into cultivated agricultural ecosystems
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