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2.Effect of Organic Materials on the Growth, Nodule Formation and Nitrogen Fixation of Legume Crops Cultured under Acid and Saline Conditions

Ichio Nioh(Institute for Agro-Microbiology)

To examine the effect of two composts on the growth and nitrogen fixation of leguminous crops cultured on acid-stressed soil, a greenhouse experiment was conducted to examine the effect of two commercially prepared organic materials, bark compost (abbr. BC) and calcium-amended peat moss (abbr. TP), on the growth, nodulation and root colonization of bacteria in kidney bean, soybean and alfalfa in an acid soil. Both organic materials improved shoot and root growth of these legumes. Number of nodules and root colonizing bacteria were increased by application of BC. On the other hand, increase induced by TP was only found in soybean. The application of these materials also improved nutrient uptake. The increase in plant growth was mainly due to improvement of nutrient uptake. Nodule number increased concomitantly with the improvement of root colonization and availability of Ca and P.

A field experiment was conducted to ascertain the beneficial effect of above two organic materials on the growth, nodulation and acetylene reducing activity of soybean (Glycine max L.) under acid and saline conditions. The organic materials were incorporated into the acid and saline (induced by irrigating the soil with NaCl solution) soils at 4% rate of application. These materials tended to improve nodule formation of soybean under acid and saline conditions, especially of the plant treated with BC. These materials also tended to improve shoot growth under acid and saline conditions, presumably due to the improvement of the soil moisture status of the soils and nutrient uptake. These results suggested that the growth of soybean could be improved by the application of organic matter under acid and saline conditions without modifying soil pH and concentration of salts.

Survival rate of rhizobia in acid soil was higher in the organic particles, which suggested that the effect of organic materials was in part due to supplying beneficial habitat to the rhizobia under stressed conditions.


Keywords: acid soil, saline soil, rhizobia, nitrogen fixation, application of organic materials