Decomposing residues of many plant species (1), including those of weed and cover crops recommended for use in low input, sustainable agriculture [LISA] emit mixtures of volatile organic compounds (2) that inhibit seedling growth (3,4) of crops, including cotton (Gossypium spp). Previously, the activities of the individual components of these plant-residue volatile emission have been determined, using seed germination laboratory condition (3,4). This year, a field experiment [cover X planting date] in which winter weeds were incorporated before early [7 date after incorporation] and late [14 days after incorporation] and late[14 days after incorporation]plantings of cotton (var. Coker 315) was undertaken. Stand counts and lint yields were determined. Soil samples were collected immediately after residue incorporation [t = 0 days], at after residue incorporation. The 30 C vs 20 C root-zone temperature seedling-growth system used to determine the activities of the emission mixture components was the temperature X cover] of the effects of these soil samples on Coker 315 root and shoot elongation, fresh and dry weight accumulation, relative water contents [RWC], and cotyledon expansion.

Clover dry weight was 3.3 times that of the winter weeds in the fallow treatment. Cotton stand establishment was better in the fallow than the clover treatment, but the difference was significant only in the early planting. Lint yield was also reduced in the first picking of the clover X early planting treatment. in the seedling growth assays, soils from the first two samplings of both the fallow and clover treatments inhibited root elongation [ >50% inhibition], and root and shoot fresh and dry weight accumulation [>40%] at booth and 30 and 20 C. The [t = 0 days] soil sample also inhibited shoot elongation [ >25%] and cotyledon expansion [ >20%]. There were no clear effects of either cover or temperature on root or shoot RWC.

The inhibitory effects of both the fallow and clover treatments disappeared with time after residue incorporation and with time elapsed since sampling. The second soil samples from the fallow treatment were less inhibitory than the corresponding samples from the clover treatment when root and shoot elongation cotyledon expansion were considered, but both fallow and clover treatment soils were inhibitory when compared to the sterile potting soil used in the earlier determination of volatile emission activities. Root-zone temperature was generally less important than was the presence of decomposing plant residues, and no consistent temperature x residue interactions were apparent. there was no evidence of cotton seedling-disease complex. The presence of inhibitory effects observed in the laboratory.