Allelopathic effects of cotton in continuous cropping

Pot experiments were conducted to explore the autotoxic effects of cotton under long-term continuous cropping. Aqueous extracts of cotton significantly inhibited the seed germination and seedling growth of wheat (Triticum aestivum L.), tomato (Lycopersicon esculentum L.), rape (Brassica napus L.) and alfalfa (Medicago sativa L.). Cotton was grown in soil continuously under cotton cropping for 5 and 10 years. At 45 days growth, plant height, leaf area, shoot and root fresh weights were determined. These parameters were lower in soil under continuous monocropping than in 1 year cropping. The inhibitory effects became stronger with the increase in duration of continuous cropping. Meanwhile monocropping of cotton decreased activity of both e root Tripheyl Tetrazolium Chloride (TTC) and superoxide dismutase (SOD), but guaiacol peroxidase (POD) activity was increased. The addition of activated charcoal decreased the harmful effects on TTC and SOD. Our results suggest that cotton plant release allelochemicals which get accumulated during the monocropping. The addition of activated charcoal to the soil greatly improved the growth of plants.