The responses of burr medic (Medicago polymorpha) to phosphorus (P) and calcium (Ca) were studied in both glasshouse and field experiments. The responses of other two species (M. arabica and M. truncatula cv. Jemalong) were evaluated only in glasshouse conditions. Changes in the available P-Olsen and Ca in a granitic soil (Serie Maule) ofthe interiordryland ofthe mediterranean zone of Chile, after the application of increasing amounts of P and Ca, were also evaluated. In the laboratory, the available P-Olsen increased Iinearly afier the applícation of increasing amounts of P, at the rate of 0.28 mg kg-1 P per unit P applied. In the field, approximatly 7.2 kg ha-1 of P were needed to change the available Pin 1mg kg-1. The available Ca increased exponentially with increasing amounts of Ca supply. The pH also increased rapidly up to 615 mg kg-1 of Ca supplied. In the glasshouse, shoot, root and nodule dry Weight increased but, the rootlshoot ratio decreased with increasing P supply, in the three species of Medicago. In the field, the percentage of P in shoots of M. polymorpha increased with increasing P supply, and ranged from 0.18 to 0.25%. Phytomass reached 2,682 kg ha-1 in 1987, and 3,050 kg ha-1 in 1988, both at the highest P application rate. Seed yield ranged from 305 to 681 kg ha-1 in 1987, and from 300 to 387 kg ha-1 in 1988. Phosphorus utilization efficiency, measured as phytomass per unit of P content, ranged from 391 and 566 kg dry matter/kg of P. Phosphorus use efficiency, measured as phytomass per unit P applíed, was 73, 36 and 27 kg dry matter/kg P, with the application of 24,62 and 97 kg P ha", respectively. Both phytomass and seed production increased curvilinearly with available P in the 5 cm top soil. The P-Olsen requirement in t |
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