Can i plan a crop rotation experiment using six crops (sesame, cotton, sorghum, soyabean, sunflower ,sorghum) ?

1. First of all, thank you very much for your nice question and inquiry. Herein I have suggested the most recommended intercropping/multiple/mixed cropping systems in Ethiopia as well as in some parts of the World being practised as follows:
 Cereal/cereal e.g. Sorghum/F. millet, Barley/wheat, Sorghum/maize, etc.  Cereal/legume e.g. Sorghum/pigeon pea, Sorghum/cowpea, Maize/bean  Cereal/cereal/legume e.g. Sorghum/maize/bean  Legume/legume e.g. Faba bean/field pea  Cereal/root crop e.g. Sorghum/sweet potato  Cereal/vegetables e.g. Maize/cabbage  Legume/tree crop e.g. Bean/coffee  Cereal/tree crop e.g. Sorghum/Chat  Cereal/oil crop e.g. Teff/sunflower  Multi-crop mixture e.g. Ensete/coffee/maize/bean
Regarding plot size please use each crop recommended spacing and the plot size may be you can use 4-meter width with the 5-meter length (4m*5). Most probably you can use component/major crop standard design in accordance with intercropping one. The methodology also depends on your treatment numbers and the nature of your experimental site.
2. The length of the cropping systems depends on the nature of the crop that you have selected, so in terms of the durability or the maturity period of your crop and your given environment have to be used, therefore you can refer your selected crops nature, then you can determine.
3. My last suggestion please avoid too many cropping systems because you will be troubled to practice properly, your experimental precision will be declined, experimental and management cost also high, high growth-limiting factor competition (moisture, light, nutrient, etc…), due to the above reasons selecting too many crops are not recommended and practical, so please prioritize your crops based on your objectives.
Thank you!