EFFECTS OF CaCO3 AND INOCULUM LEVEL ON NODULATION AND GROWTH OF ALFALFA IN AN ACID SOIL

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Abstract
The effects of CaCO3 and inoculum level on nodulation and growth of alfalfa (Medicago sativa L.) in an acid soil were studied by measuring alfalfa yield, nodule numbers and nodule weights in relation to various levels of CaCO3 amendment and to the number of Rhizobium meliloti applied per seed. When sufficient CaCO3 was applied to the soil (4 mg CaCO3/g soil) to reduce soluble Al to sub-toxic levels, the relative yield (yield without N/yield with N) of alfalfa increased from 0.7 with no inoculum to 1.0 with 3 × 107 rhizobia per seed. Increasing the inoculum level from no inoculum to 3 × 107 rhizobia per seed decreased the amount of ineffective nodule tissue from 0.65 to 0.27 mg/pot without CaCO3 added, and from 0.60 to 0.06 mg/pot with the addition of 4.0 mg CaCO3/g soil. When no inoculum was applied, the amount of effective nodule tissue was increased from 0 to 0.91 mg/pot by adding 4.0 mg CaCO3/g soil. Application of inoculum increased the amount of effective nodule tissue at all levels of CaCO3. The results demonstrate the importance of liming to decrease the soluble Al content of acid soils for alfalfa production, and show that high inoculum levels can be used to improve alfalfa yields on acid soils.

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