The growth and nitrogen fixation of Trifolium repens have been investigated during the imposition of and recovery from different levels of water stress. Growth (measured as fresh and dry weight of roots and shoots, shoot length and nitrogen content) and nitrogen fixation (per plant and per unit weight of nodule) were depressed by application of water stress. The ability of plants to recover and the time taken for recovery were both related to the duration of the stress period. Meristematic activity in nodules was resumed after watering, making clover nodules more resistant to stress than plants, such as soybean, with spherical nodules.
Nitrogen fixation, estimated by the acetylene reduction technique, was compared with the total nitrogen content of plants. Differences between the estimated and actual nitrogen content varied with age and degree of water stress.