Rhizobia1 Inoculation and Phosphorus and Zinc Nutrition for Annual Medics Adapted to Mediterranean Environments

Cereal production in the Mediterranean region (where rainfall averages 200 to 600 mm yr−1) has traditionally used fallowing in alternate years to conserve crop‐limiting soil moisture. Self‐regenerating pasture medics (Medicago spp.) were introduced to provide forage for livestock in the alternate year and to reduce the cereal's need for fertilizer N; their adaptation depends on compatible Rhizobium meliloti bacteria for N2 fixation and on climatic conditions. In addition, nutrients such as P and Zn are potentially limiting factors. Therefore, in a greenhouse experiment (60 d) using a P‐deficient, air‐dried, nonsterilized clay soil (Calcixerollic Xerochrept) treated with P (0, 15, 45, and 135 mg kg−1) and Zn (0 and 5 mg kg−1, we assessed growth of four annual medic species with and without rhizobial inoculation and fertilizer N: Medicago polymorpha L., M. rotata Boiss., M. rigidula (L.) All., and M. noeana Boiss. Except for M. noeana, growth of all species responded significantly to applied P and to Zn only with adequate P and N levels (or rhizobial inoculation). Pod number and root biomass were also increased by P application, with differences occurring between species. Thus, when a medic species is newly introduced, inoculation has a role to play where no compatible rhizobia exist. Phosphorus fertilization and medic seed inoculation can easily be done, while the use of adapted biotypes in low‐Zn soils is more problematic