MOISTURE STRESS IMPACT ON N PARTITIONING, N-REMOBILIZATION AND N-USE EFFICIENCY IN BEANS (PHASEOLUS-VULGARIS)

Field and glasshouse studies were conducted in Durango, Mexico in 1987 and in East Lansing, Michigan, USA in 1989, respectively, to determin e the effects of moisture deficits upon N-use efficiency (NUE), N part itioning and remobilization, and N harvest index (NHI) in edible beans (Phaseolus vulgaris L.). Four indeterminate, semi-prostrate genotypes adapted to the semi-arid high plains of Mexico, Pinto Nacional-1, Dur ango 222, L1213-2 and Bayo Madero, were used in the field study and Pi nto Nacional-1 and Bayo Madero were used in the glasshouse study. A Xe rosol Haplic soil was used in the field study and a Spinks loamy sand in the glasshouse study. A moisture deficit was induced by use of temp orary rainshelters in the field and curtailment of water in the glassh ouse. Plants were sampled periodically and subdivided into leaves, ste ms, pods and flowers, and roots (in the glasshouse study only) for det ermination of dry weight and total N content. Water-use efficiency was determined in the glasshouse study. A moderate moisture deficit (drou ght intensity index 0.41) reduced yield by 41% in comparison with non- stressed yield (from 134.3 down to 79.2 g/m2) and resulted in a greate r percentage of seed-N derived from N that had been redistributed from the leaf, indicating that N partitioning was not impaired by this deg ree of stress. In contrast, N remobilization was greatly reduced by a more severe moisture deficit (drought intensity index 0.92), which res ulted in yield losses of 92% (from 2.19 down to 0.17 g/pot). These res ults suggest that N remobilization may be an important drought adaptat ion strategy under moderate or intermittent moisture deficits. Severe moisture deficits reduced NHI, harvest index (HI), NUE and water-use e fficiency (WUE) when WUE was expressed as seed dry weight per litre wa ter used. Genotypic variability was observed for NHI, HI and NUE.