French bean also known as rajma (Hindi) or haricot
bean or kidney bean or common bean or snap bean, navy bean. It is valued for its protein rich (23%) seeds. Seeds are also rich in calcium, phosphorus and iron. The fresh pods and green leaves are used as vegetable. The antimetabolites of dry beans needs removal by cooking
and soaking in water.
French beans have evolved in the highlands of middle America and Ander from a wild vine over a period of 7000-8000 years.The primary and Peruvian-Ecquadrion-Bolvian region of South America as the secondary center of French bean.
Globally French bean is cultivated on about 28 m ha with a production of 19 million tonnes. Brazil is the leading producer of French beans. Columbia, USA, Canada, Ethiopia, China and Turkey are other leading countries producing French bean.
In India, it is grown on an area of about 1 lakh ha mainly in the states of Maharashtra , Jammu and Kashmir, Himachal Pradesh and Uttar Pradesh Hills, Nilgiri (Tamil Nadu) and Palni (Kerala) hills,Chickmagalur (Karnataka) and Darjeeling hills (West Bengal).
The genus Phaseolus has over 50 species and Rajma (Phaseolus vulgaris L) is one of them accounting for 90% of cultivated species worldwide. In India, both bushy and trailing types rajmash are found.
Major rajma producing areas are located in tropical and temperate regions with a temperature around 21oC. The optimum temperature for better growth is 16-24oC. Growth of plant ceases if temperature falls below 10oC. Temperatures above 35oC cause dropping of buds and flowers resulting in poor yield. It is highly susceptible to frost. The crop is generally raised in areas receiving 50-150 cm annual rainfall. Water logging at any stage adversely affects its yield. Rains cause flower drop and spread of leaf spot diseases.
Soil and its Preparation
Rajma grows on a variety of soils ranging from light sand to heavy clay, but well drained loams are the best. The crop is sensitive to salinity. Soil pH around 5.2-5.8 is optimum. An electrical conductivity of 1 dS/m is threshold limit for frenchbean. Soil having high amount of organic matter promote more vegetative growth.
Crop requires fine seedbed and adequate soil moisture for good germination. A deep ploughing followed by 2-3 harrowings and planking is adequate to obtain required tilth.
Time of Sowing
Rajma is grown in kharif and rabi seasons in different parts of the country. The optimum time of sowing in rabi season varies from state to state. It is first and second fortnight of November for central Uttar Pradesh and north Bihar. However, mid October is optimum for Vidarbha region (Maharashtra). For early varieties, October end is the optimum, while late varieties can be sown up to mid November. In kharif, mid May – mid June is ideal. The spring crop can be sown from February – early March.
Seed Rate and Spacing
Seed rate varies with seed size. Bold seeded varieties with a test weight of 350-450 g need 120-140 kg seed/ha, while in small seeded varieties, it varies from 80-100 kg/ha. The seed rate in intercropping may vary with row proportions.
Rajma is generally sown in rows 30 cm apart. In northern plain, rabi rajma is sown in rows of 45 cm. The plant-to-plant spacing is 10-12 cm. For obtaining good yield, its plant population should be 2.5-3.0 lakh plants/ha. 8-10 cm is the optimum depth of sowing.
Manures and Fertilizers
French bean lacks biological N fixation because of poor or no nodulation. Hence, it needs liberal N fertilization (100-120 kg/ha). The crop requires 60 kg P2O5/ha and response to potassium and other micronutrients are rarely observed.
Rajma has shallow root system and hence moisture stress at any stage is detrimental to its performance. As a rainy season crop, it does not require irrigation, when rainfall distribution is even throughout crop cycle. However, rabi crop requires irrigation. Irrigation at 25 days after sowing (DAS) is critical. In north-east plains zone, 3 irrigations at 25, 75 and 100 DAS and in central zone 4 irrigations at 25, 50, 75 and 100 DAS are necessary for optimum crop performance.
Rajma suffers severe competition from weeds in initial stages. First 30-40 days after planting is the critical period for crop weed competition. One hand weeding at 30-35 days after sowing is found beneficial. Pre-emergence application of pendimethalin @ 1.0 kg/ha or pre-plant incorporation of 1.0 kg/ha of fluchloralin have been found effective in controlling weeds.
In north India it is grown in spring season after potato or mustard. In the hills, it is intercropped between maize and soybean. In rabi, intercropping of potato + rajma (3:2 ratio) is being practiced in central and eastern Uttar Pradesh and northern Bihar. Rajma + linseed (2:1) is also found to be an efficient cropping system.
Pests and Diseases
Bihar hairy caterpillar, blister beetle, bean bug and aphids are important insect pests of the crop. Rot (collar, stem and pod) and bean golden mosaic virus are important diseases limiting rajmash productivity.
Harvesting and Threshing
At maturity, leaves and pods turn yellowish brown and majority of leaves drop. Delay in harvesting may cause shattering. Selection of shattering resistant varieties like HUR 137 is necessary to overcome this problem. The harvested crop is kept for sun drying for 5-7 days, and thereafter threshed.
Under optimum conditions, 2.0-2.5 t/ha of grain and 3.0-3.5 t/ha straw yield can be obtained.
(Compiled by Harsh saxena)