Effects of interactions of moisture regime and nutrient addition on nodulation and carbon partitioning in two cultivars of bean (Phaseolus vulgaris L)

Major limitations of bean (Phaseolus vulgaris L.) production in and and sem iarid regions are lack of moisture and low soil fertility. An experiment wa s conducted to determine the effects of soil moisture and N : P : K (20 : 1 0 : 10) fertilizer on root and shoot growth of two cultivars of bean: cv. C arioca, an indeterminate Brazilian landrace, and cv. Prince, a determinate cultivar grown in Europe. Carioca appears generally stress-tolerant while P rince is intolerant. Seedlings were grown in pots of nonsterile soil at 30, 60 or 90 % field capacity (FC), and given 0, 0.1 or 1 g (kg soil)(-1) of c ompound fertilizer. The soil contained a population of effective Rhizobium. Growth of both cultivars was greatest in the high moisture and high nutrie nt treatments. Root fractions were highest at low nutrient supply; the effe ct of water was not significant. Leaf fraction decreased as root fraction i ncreased. Numbers of nodules were highest at high and intermediate moisture when no fertilizer was applied. Numbers were lowest at 30 % FC and at the highest fertilizer rate. Masses of nodules and fractions followed the same pattern. Decreasing water regime reduced the relative growth rate (RGR) of Prince, while Carioca maintained high RGR at unfavourable conditions of wat er and nutrients. Net assimilation rates (NAR) were unaffected by nutrient addition, and reduced by low moisture regime. Water use efficiencies (WUEs) were reduced by water stress but increased by nutrient deficiency. The wat er utilization for dry matter production was optimal at 60 % FC.