Common bean (Phaseolus vulgaris) is known under different names (French bean, kidney bean, snap bean, runner bean, string bean). It can be grown as a vegetable crop for fresh pods or as- a pulse crop for dry seed. World production of dry beans is about 16.7 million tons from about 23 million ha and green beans 4.7 million tons from 0.7 million ha (FAOSTAT, 2001).
Common bean grows well in areas with medium rainfall, but the crop is not suited to the humid, wet tropics. Excessive rain and hot weather cause flower and pod drop and increase the incidence of diseases. Optimum mean daily temperatures range between 15 and 20°C. The minimum mean daily temperature for growth is l0°C, the maximum 27°C. High temperatures increase the fibre content in the pod. Germination requires a soil temperature of 15°C or more, and at 18°C germination takes about 12 days, and at 25°C about 7 days. Most bean varieties are not affected, by daylength. The length of the total growing period varies with the use of the product and is 60 to 90 days for green bean and 90 to 120 days for dry bean.
The crop does not have specific soil requirements but friable, deep soils with pH of 5.5 to 6.0 are preferred. Fertilizer requirements for high production are 20 to 40 kg/ha N, 40 to 60 kg/ha P and 50 to 120 kg/ha K. Bean is capable of fixing nitrogen which can meet its requirements for high yields. However, a starter dose of N is beneficial for good early growth. The crop is sensitive to soil-borne diseases and should be grown in a rotation; in the subtropics in the USA wheat, sorghum, onion and potato are common rotation crops, whereas in tropical Africa and Asia maize, sweet potato and cotton are common.
Normal sowing depth is about 5 to 7 cm. Spacing depends on variety. Bush types (erect) normally have a plant and row spacing of 5 to 10 x 50 to 75 cm, while pole-type (climbing) are 10 to 15 x 90 to 150 cm. Pole beans are also often grown on hills spaced 90 to 120 cm apart. Other spacings are possible, and these depend on the method of harvest.
Common bean is sensitive to soil salinity. The yield decrease at different levels of ECe is:0% at ECe 1.0, 10% at 1.5, 25% at 2.3, 50% at 3.6 and 100% at ECe 6.5 mmhos/cm.
The graph below depicts the crop stages of bean, and the table summarises the main crop coefficients used for water management.