GROWTH-RESPONSE OF MEDITERRANEAN HERBACEOUS SWARDS TO INOCULATION WITH AZOSPIRILLUM-BRASILENSE

A study was conducted on the effect of the rhizobacterium Azospirillum brasilense strain Cd on the production of herbaceous swards growing a t 2 rangeland habitats in Israel. One habitat was the semiarid zone (< 300 mm annual rainfall, calcareous soil on rocky slopes) while the oth er was a typical Mediterranean zone (approximately 600 mm annual rainf all, karstic rock covered with terra rossa soil). The inoculum was app lied in water suspension at a concentration of 10(8) colony forming un its (CFU) ml-1. The effect of inoculation was compared with P-fertiliz er application at a rate of 5 g/m2. The same treatments were also appl ied on potted soil from the 2 sites. The semiarid ecosystem showed a s trong response to Azospirillum inoculation, to P-fertilizer and to the combination of these 2 treatments, with aerial biomass production inc reasing by approximately fourfold in the treatments as compared with t he control. The response to inoculation or P-fertilization was similar , with no interaction or additive effect noted for the combined treatm ent. At the Mediterranean site, the response to inoculation or P-ferti lization alone was variable, with only a moderate effect on biomass pr oduction as compared with the control; however, the inoculation-fertil ization interaction was highly significant and doubled biomass product ion. In the greenhouse experiment, the response to inoculation or fert ilization was significant and the biomass production at the end of the growing season was approximately 50% higher than in the control. At b oth sites, standing biomass was greater in the treated plots already a t early stages of growth, thereby potentially lengthening the effectiv e grazing season. It is suggested that inoculation with Azospirillum b rasilense on a commercial scale may offer a means of increasing rangel and production without resorting to costly and ecologically unfavorabl e fertilizer application.