Dolichos or Lablab bean (Lablab purpureus) an important vegetable grown in India, is popularly known as sem. It is a very nutritive vegetable grown for the consumption of green pods, green seeds, and dry seeds as pulse also. Regional preferences are predominant, playing an important role in its cultivation. The green pods are mostly consumed in south India, whereas white ones are preferred in eastern India and green, fleshy pods in north India. Uttar Pradesh, Madhya Pradesh, Maharashtra, Andhra Pradesh, Tamil Nadu, Haryana, West Bengal, and northeastern states are the major sem growing states.
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Climate and soil
Lablab beans can be grown in a wide range of soils of average fertility having a pH up to 9.0. This can also grow well in alkaline and saline soils. For obtaining good yield loam soil is preferred. Lablab bean responds to photoperiods, there being some short day and some long day types. It is well-adapted to tropical and subtropical regions. High temperature and humidity favor plant growth, whereas fruiting starts when the temperature and humidity are low generally with the onset of winters and continues throughout spring. There are strains that are drought resistant and are being grown as a dryland crop in regions with 630-890 mm rainfall. It is a relatively cool-season crop.
On the basis of growth habits, varieties can be classified into two groups bushy field varieties and twining pole garden varieties. Many dwarf varieties have also been recommended.
Arka Amogh: Plants are medium tall, 50% flowering in 40 days, and pods are ready for harvest in 55 days. Pods have wavy surfaces and are similar to Arka Jay and Konkan Bhushan. Pod yield 20 t/ha in 90 days.
Arka Jay: Plants dwarf, bushy, erect, and photo insensitive. Pods long, light green slightly curved. Tolerant to low moisture stress. Pod yield 12 t/ha in 80 days.
Arka Sambhram: Plants are of medium height, 50% flowering in 40 days, and pods are ready for harvest in 55 days. Pods are flat, light green, medium-long (13-15 cm), medium width (1.5 cm). Pod yield 20 t/ha in 90 days.
Arka Soumya: Plants are medium tall, 50% flowering in 45 days, and pods are ready for harvest in 55 days. Pods are slender (1.0 cm width), medium-long (13-15 cm) oval. Pod yield 20 t/ha in 90 days.
Arka Vijay: Dwarf, bushy, erect, and photo insensitive. The pods are short dark green. Seeds are bold in size. Pods with a characteristic aroma. Tolerant to low moisture stress. Pod yield is 12 t/ha in 80 days.
Arka Swagath (IIHR): As it is photo insensitive it can be grown around the year. Pods mature in 65 days. Pods are flat, green, and medium-long vegetable types with 4- 5 seeds. Pod yield 26 t/ha in 120-130 days.
Co 11 (TNAU, Coimbatore): Compact plant type. Pods flat and light green with purple margin. Yield 9-10 t/ha.
Deepaliwal (PDKV, Akola): Pole type. Pods extra long (18.4 cm), white, not smooth due to bulging at each seed. Pod width 2.7 cm, weight 1.5 g. Yield 6-8 t/ ha in 200-210 days.
JDL 79: Pole type. Pods flat, broad, whitish-green with parrot green broader along the line of seed attachment. Pod length 11.8 cm, width 3.6 cm, weight 1.5 g. Yield 5.6 t/ha in 200 days.
KDB 403 (CSAUA&T, Kanpur): Pole type. Pods long, narrow, shining green. Pod length 12.9 cm, width 1.2 cm, weight 2.0 g. Yield 5-6 t/ha in 180-210 days.
KDB 405 (CSAUA&T, Kanpur):Pole type. Pods medium-long, the narrow, dark green band in the middle, and boarder light green. Pod length 9.6 cm, width 1.3 cm, weight 1.1 g. Yield 3-4 t/ha in 180-200 days.
Konkan Bhushan: Bush type, light green medium long, tender pods 8-10 t/ha 100-105 days.
Pusa Early Prolific: It bears early, medium-sized, thin, stringless pods in bunches. It is suitable for sowing both in the summer and rainy seasons.
Pusa Sem 2: Its pods are long, dark, green, stringless, and semi-round in shape. It is high yielding, tolerant to viruses and insect pests, pod-borer, etc. June July is a suitable time for its sowing in north India. Flowers appear on separate spikes, above the plant canopy.
Pusa Sem 3: The pods are green, meaty, very tender, stringless, and flat in shape. It is high-yielding, flowers appear on nodes in bunches under the plant canopy. It is tolerant of viruses. It can be sown in June-July.
Rajani (CSAUA&T, Kanpur):Pole type. Pods narrow oval in cross-section, shining green. Pod length 10.4 cm, width 1.2 cm, weight 1.78 g. Yield 7-8 t/ha in 200-210 days.
Swarna Utkrisht: The Swarna Utkrisht suitable for Jharkhand, Bihar, and Uttar Pradesh. Fresh pods are ready for harvest in 118-120 days. Pods, straight, flat, and fleshy. The pods are 11- 12 cm long. The green pod yield potential of the variety is 35-40 t/ha.
Apart from these, many climbing types varieties has been released. They are Rajni, Deepali, KDB 403, KDB 405, and T I, JDL series; Co. series of Coimbatore and HD 18, Arka Swagath and Swarna Utkrisht. Many varieties having green, white, and purple pods have been recommended from different sources in India.
Lablab beans can be grown in flatbeds as well as on trellis. It is an ideal crop for growing in kitchen garden and terrace as its vines can be trained on roof-tops and walls.
Two to three deep ploughings are needed to make the soil friable. Channels are prepared 90 cm wide and 2.5 m apart so that weeding can be done by tractor till the vines start spreading. Sowing in channels saves irrigation water. Channel cultivation can also minimize the quantity of fertilizers, which are mixed in pits rather than the whole fields. On one side of the channel pits of 45 cm x 30 cm x 30 cm size should be dug at a distance of 1.5m between two pits. Each pit may be filled with a mixture of an equal quantity of soil and farmyard manure with 50 g of single superphosphate. After filling the pits channel should be irrigated to ensure proper moisture for quicker and proper germination.
In north India, the sowing time is June-July, while in south India it is July-August. Three to four seeds are sown on each hill at 2.0-2.5 cm depth. After germination one or two plants are kept on each hill. This method is adopted both for flatbed sowing as also for growing on a trellis.
In the north and central India, it is usually grown as a mixed crop with ragi or sorghum. Seeds are drilled 1 m apart in between ragi or sorghum. Ear heads of these crops are harvested first leaving the stalk for giving support to the vines. The vines grow on them profusely and flower during November-December giving green pods as well as dry seeds throughout winter and spring. The vines when cut with sorghum straw give mixed fodder for animals. It is also grown as a pure crop in these regions. For climbing type 10-12 kg seed is enough for one-hectare crop, whereas for bushy type 30-40 kg/ha of seed is required. In the kitchen garden, plants can be retained for 2-3 years.
Being a legume crop, lablab bean requires lesser nitrogenous fertilizers. When the crop is grown in channels, 5-6 tonnes of farmyard manure, 10 kg N, and 20 kg P are required for a hectare of land at the time of sowing. If it is grown as a mixed crop with ragi or sorghum, it requires 10-12 tonnes of farmyard manure, 15-20 kg N, and 20 kg P/ha. After one month of germination, a dose of 10 kg N is applied as a top dressing.
Light irrigation is given when required. In summers, it should be watered at weekly intervals in winters at 15 days intervals, and in the rainy season as and when needed. Weeds may be controlled mechanically and by using weedicides. Between two channels weeding can be done by tractor till the vine’s start spreading and after that with the help of spade. Within the channels, weeds should be removed with the khurpee. Weeds can be controlled by soil application of Stomp or Basalin @2 ml/liter of water. Weedicides may be sprayed before and after the sowing of seeds but sufficient moisture in the field ensures the effectiveness of weedicides. Many insect pests and diseases attack the crop from early-stage to harvesting green pods and dry seed. To save the crop from these insects pests and diseases proper and timely spraying of insecticides and pesticides is recommended.
Harvesting and post-harvest management
Green pods are harvested and packed in baskets, card-board boxes, and in gunny bags for sending to the nearby markets. The picking may be done either early in the morning or late in the afternoon so that quality may not go down due to more water evaporation from the surface of pods because of heat during day time. Owing to more heat the pods start shrivelling/shrinking. In climbing types, pods are harvested in 9-10 pickings at 7-day intervals but in dwarf types, only 2-3 pickings are obtained. Improved varieties such as Pusa Sem 2 and Pusa Sem 3 give 150 170 q/ha of green pods when grown in flat beds. If these are grown on trellis then green pod yield may be doubled. In other varieties, the average yield of green pod varies from 50 to 80 q/ha.