Sorghum crop rotation systems

Rizvi SJH, Mishra GP, Rizvi V (1989) AUelopathic effects of nicotine on maize I. Its possible importance in crop rotation. Plant Soil 116 289-291 Roshchina VV (2001) Molecular-cellular mechanisms in pollen allelopathy. Allelopathy J 8 11-28 Roth CM, Shroyer JP, Paulsen GM (2000) Allelopathy of sorghum on wheat under several tillage systems. Agron J 92 855-860... 

Atrazine remains the standard herbicide for making the transition from wheat to sorghum or corn in Great Plains cropping systems. Even where more intensified crop rotations have been developed, they are built around winter wheat followed by ecofallow sorghum or com. The success of atrazine is due to its persistence as a soil-applied herbicide, to the broad spectrum of weeds controlled, to its low cost per acre, and to its safety on sorghum and com. In the Great Plains, repeated burndown of weeds in fallow with nonresidual herbicides is not a viable alternative to the role that atrazine plays. 

Another approach is the utilization of allelopathic rotational crops or companion plants in annual or perennial cropping systems (19). Living rye (Secale cereale L.) and its residues have been shown to provide nearly complete suppression of a variety of agroecosystem weeds (33). Similarly, residues of sorghums, barley, wheat and oats can provide exceptional suppression of certain weed species Q ). Although some progress has been made on identifying the allelochmicals from these plants, much remains to be accomplished. 

Triazine herbicides are particularly well suited for conservation tillage because they provide foliar and residual control of a broad spectrum of weeds. Atrazine, simazine, and metribuzin are used in com, atrazine and propazine in sorghum, metribuzin in soybean, and simazine reduces tillage required for weed control in many perennial and tree crops. Atrazine is also used extensively in chemical fallow cropping systems in rotations involving corn, sorghum, and wheat. Cyanazine was also used extensively in corn and cotton until 2002. 

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