Senna (Cassia angustifolia) an erect shrub is one of important medicinal plant. The leaves and pods of senna contain sennosides A, B, C, D, which are well known for the preparation of laxatives and purgative. The crop is grown in about 10,000 ha, mainly in Southern districts of Tamil Nadu viz. Tirunelveli, Ramanathapuram and Madurai districts.
It is very sensitive to waterlogged conditions, heavy rainfall and low temperature. An average rainfall of 25-40cm distributed from June to October is sufficient to produce good harvests.
It grows well on sandy-loam with a pH ranging from 7-8.5. Once established, the crop withstands moderate saline conditions. The land should be ploughed and exposed to sun for 2-3 weeks.
Seed treatment with protective fungicides (thiram, captan or agrasan @ 2.5g/kg of seeds to protect against damping off and sowing at the optimum time and proper depth are the three most important factors which ensure a good and uniform plant population in the field. The seeds are sown in line at 30-40cm apart at 1.5-2.0cm depth. The crop is thinned at 30 days to maintain a plant to plant distance of 30cm in the rows. Seed rate is 5kg/ha.
At sowing, 4-5 cartloads of well rotten farmyard manure pet ha and 80kg of nitrogen (N) and 40kg of phosphorus (P2O5) may be applied to this crop. Of this 40kg of nitrogen and the entire dose of P2O5 may be given at sowing and is placed at 4-5cm deeper below the seed. The remaining quantity of 40kg of nitrogen is given 35-40 days (just after thinning), 80-85 days, and 105-110 days age (i.e. after first and second picking of the leaf crops) in equal doses.
Senna could be grown under rainfed conditions. Irrigation, whenever easily available, it is given at 40 days, 75 days and 100 days age when plants bear new growth of foliage and flowers.
Fields are drenched with any Organo fungicides.
Leaf spot and leaf blight
Usually occurring at later stage of growth
Spraying with 0.15% Diathane M.45 at fortnightly interval for 3 times in a period of 5-6 weeks is recommended.
Harvesting and yield
First picking starts at 50-70 days age, depending upon that plant growth. Second picking at 90-100 days and the third picking between 130-150 days when the entire plants are removed so that the harvested material includes both leaves and pods together. The harvested crop should be spread in a thin layer in open area to reduce the moisture. It takes 3-5 days to dry the produce in the sheds. The dried produce usually possesses 8% moisture. The properly dried leaves and pods should have light-green to greenish-yellow colour. A good average crop of senna can give 1500kg/ha of dry leaves and 700kg/ha of pods under irrigated and good management conditions. The yield under rainfed condition is about 1000kg of leaves and 400kg of pods.