ABSTRACT

Retardations in plant development and fiber maturity of field-grown cotton were correlated with the presence of decomposing residues of winter fallow weeds, e.g., pigweeds, and cover crops, e.g., crimson clover, Berseem clover, hairy vetch. The pigweeds are common in winter fallow across much of the Cotton Belt, and the legumes are recommended for use in low input cotton production. The presence of these residues in soil planted to cotton resulted in significant reductions of stand establishment and lint yield in a field experiment [cover X planting date] in which fallow weed and crimson clover residues were incorporated before early and late plantings of cotton. Stand establishment and lint yield were better in the fallow than in the clover treatment in the early planting. Both fallow and clover treatment soils, compared to a sterile potting soil, inhibited cotton seedling growth. Soils containing clover and weed residues sampled within two weeks of residue incorporation inhibited root elongation [>50% inhibition], and root and shoot fresh and dry weight accumulation [>40%] at both 30 and 20EC. The initial soil sample also inhibited shoot elongation [>25%] and cotyledon expansion [>20%]. Soil collected from fields containing these residues also significantly retarded cotton seedling growth in greenhouse environments. Residues of Crimson clover and pigweed emit mixtures of volatile compounds that inhibit both seed germination and seedling growth of crops, including cotton.

These species-specific mixtures of volatile biologically-active compounds include C₄ and C₉ ketones. The C₇ through C₉ ketones are potent inhibitors of seed germination AND seedling growth in a number of crops. Growth of cotton seedlings transplanted into sterile and non-sterile soil injected with micromolar amounts of these ketones was retarded to a degree comparable to that of seedlings grown in soil containing the residues. The results of this study demonstrate a need for improved cover crop residue management and indicate possibilities for effecting those improvements.