Use of sorghum allelopathic properties to control weeds in irrigated wheat in a semi arid region of Punjab

Conventional methods of weed control are weather dependent, costly and labour intensive. Indiscriminate use of chemicals for controlling weeds may pose environmental problems. Sorghum allelopathy is a new technique, which has been tested for controlling weeds of wheat (Triticum aestivum L.) as a substitute for chemical herbicides to reduce environmental pollution. Mature sorghum herbage contains a number of water-soluble secondary chemical substances (allelochemicals). Sorghum allelopathy can be used as sorgaab (water extract of mature Sorghum bicolor L. Moench plants obtained after soaking in water for 24 h and sprayed as a natural herbicide), sorghum mulch, sorghum soil incorporation and in crop rotation. Two experiments were conducted. In Experiment 1, allelopathic effects of sorghum stalk incorporation into soil and sorgaab foliar spray along with chemical and cultural weed control methods on the growth of different rabi (winter) weeds and on the growth and yield of wheat were studied. In Experiment 2, the effects of concentration (5 and 10%) and frequency of sprays of sorgaab on the growth of weeds and wheat were compared with hand weeding and chemical herbicides. Sorgaab controlled up to 35-49% weeds and increased wheat yield by 10-21%. Mature sorghum chopped herbage (2-6 Mg ha(-1)) incorporated in the soil at sowing controlled up to 40-50% weeds and increased wheat yield by 15%. Two foliar sprays of 10% sorgaab at 30 and 60 days after sowing was the most economical method for controlling weeds in wheat with maximum net benefits and 535% marginal rate of return. Weed control through hand weeding and/or chemical herbicides was found to be uneconomical due to higher costs involved in both the cases. Sorgaab can be used as a natural weed inhibitor in wheat. (C) 2000 Elsevier Science B.V. All rights reserved.