Background

Dry bean (Phaseolus vulgaris L.) is a food crop of high economic importance with high protein content and grown in all habitable continents (Beninger and Hosfield 2003). It has probably been domesticated from a wild form having a long slender vine which is found in Mexico and Central America (Beninger and Hosfield 2003). Dry bean is an annual crop which thrives in warm climates. It grows optimally at temperatures of 18^oC to 24^oC and requires a minimum of 400 to 500 mm of rain during the growing season. It prefers an optimum soil pH of 5.8 to 6.5, is very sensitive to acidic soils (pH<5) and will not grow well in soils that are compacted, too alkaline or poorly drained (Dry bean Production in South Africa 2002).

The choice of cultivars to be grown in a particular area is also important to be sure that the cultivar produces beans of an appropriate size and colour, which can be both genetic and associated with growth and yield performance (Dry Bean Production in South Africa 2002). For successful production, high-quality (certified) seed with a high germination percentage (80% or higher) must be used. Low quality seed can cause a poor and an uneven field stand, resulting in uneven maturity and loss in yield. The growth habit of a dry bean cultivar also needs to be well understood. Some cultivars are determinate (i.e. they produce flowers once) or indeterminate (i.e. they flower continuously over a period of time).

The probability of fully effective inoculation and high rates of nitrogen fixation is rather low. Accordingly, many growers apply nitrogen to reduce the risk of inoculation failure. Soil tests are recommended to determine whether other nutrients are at appropriate levels. Preliminary research was conducted by the Department of Plant Sciences at the University of Saskatchewan on nitrogen fertilisation. Results from their research in 1999 indicated that inoculation had little effect. However, addition of fertiliser nitrogen increased dry bean yield.