Indigofera crops are suitable for growing in light (sandy) and medium (loamy) soils and prefers well-drained soil. So far as suitable pH is concerned it can grow in wide range of soils, acid, neutral and basic (alkaline) soils and can grow in very alkaline soils also. It cannot grow in the shade. It prefers moist soil. The plant can fix Nitrogen in soil. 

Complements to Suresh K Malhotra Sir for the answer. Very few works have been reported on Indigofera species. The following links may also be seen (especially the review part):

http://khartoumspace.uofk.edu/bitstream/handle/123456789/11165/Potentialities%20of%20Indigo%20plant%20%28Indigofera%20tinctoria%29%20Production%20in%20the%20Sudan%20for%20Domestic%20Use%2C%20and%20Exportation.pdf?sequence=1&isAllowed=y

http://repository.up.ac.za/bitstream/handle/2263/23566/00thesis.pdf?sequence=1&isAllowed=y

http://www.pcaarrd.dost.gov.ph/home/momentum/nonwood/index.php?option=com_content&view=article&id=1317:effects-of-planting-distance-and-stages-of-harvesting-on-the-growth-and-dyeyield-of-malatayum-indigofera-tinctoria-l&catid=96

thank you very much special for Dr. Suresh K. Malholtra and Dr. Nilai Borahof your answer...