EFFECT OF LIME-PELLETING ON THE NODULATION OF LUCERNE (MEDICAGO-SATIVA L) IN AN ACID SOIL - A COMPARATIVE-STUDY CARRIED OUT IN THE FIELD, IN POTS AND IN RHIZOTRONS

The nodulation of lucerne was studied in soil (pH-H2O 5.2) with seeds either inoculated with Rhizobium meliloti (R), or inoculated and pelleted with lime (RP). For comparison, experiments were done in the field and in two types of micro-cosmos: pots and rhizotrons. In the field experiments, lime-pelleting improved the establishment of seedlings and augmented the nitrogen yield of the first harvest. These positive responses in plant growth were the consequence of a better nodulation on the upper 10 mm of the seedling tap root. The number of seedlings carrying crown nodules increased from 18% (R) to 56% (RP) at 26 days after sowing. In both, pots and rhizotrons, lime-pelleting also increased crown nodulation: in pots from 32% (R) to 60% (RP), and in rhizotrons from 5% (R) to 90% (RP). Rhizotrons, made of plastic petri dishes, allowed for continuously following of early root developments and nodule formation. Crown nodulation could already be measured after 14 days. Based on these experiments, it was concluded (i) that crown nodulation is an adequate parameter to quantify the benefit of lime-pelleting, and (ii) that rhizotrons, because of the more pronounced effects and shorter incubation time, are more suitable to study the nodulation responses in the soil caused by the addition of rhizobia and lime. © 1990 Kluwer Academic Publishers.