Allelopathic Effects of Sorghum and Sudan Grass on Some Following Winter Field Crops

Allelopathic compounds are secreted into the environment by living plants or released from dead plant tissues. The basic release routes of allelopathic substances by donor plants are secretion from the roots, washing out of compounds by water, emission of volatile substances and destruction of tissues during the decomposition of plant material. These observations led to the principles of crop sequence. A two-year study was carried out at Sids Agric. Exp. & Res. St., ARC, Beni – Sweif governorate, Egypt, during 2011/2012 and 2012/2013 seasons to study the allelopathic effects of sorghum and Sudan grass on berseem, faba bean, fodder beet, onion, sugar beet and wheat crops. This experiment included 18 treatments which were the combinations of fallow, sorghum and Sudan grass as preceding crops and six winter field crops (berseem 'Trifolium alexandrinum', faba bean 'Vicia faba', fodder beet 'Beta vulgaris', onion 'Allium cepa', sugar beet 'Beta vulgaris' and wheat 'Triticum aestivum') as following crops. A split plot distribution in randomized complete block design replicated thrice was used. The results indicated that roots of sorghum or Sudan grass secreted biologically active chemical compounds which have a positive effect on the growth and development of berseem, faba bean and onion which led to increase in their yields as compared with the fallow treatment. The preceding crops tested appear to be promising for berseem, faba bean and onion production, some benefits included releasing compounds that activate growth of Rhizobia sp. in berseem field, accelerate growth of Bacillus sp. that inhibit Orobanche plant emergence in faba bean field, produce nematicidal compounds that reduce nematodes in onion field. On the contrary, fodder beet, sugar beet and wheat yields were depressed when the crops are grown after sorghum or Sudan grass as compared with the fallow treatment.